U.S. patent application number 11/641152 was filed with the patent office on 2007-05-03 for structure and method of making capped chips having vertical interconnects.
This patent application is currently assigned to Tessera, Inc.. Invention is credited to Belgacem Haba, Giles Humpston, Bruce M. McWilliams, Craig S. Mitchell, David B. Tuckerman.
Application Number | 20070096311 11/641152 |
Document ID | / |
Family ID | 34382320 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070096311 |
Kind Code |
A1 |
Humpston; Giles ; et
al. |
May 3, 2007 |
Structure and method of making capped chips having vertical
interconnects
Abstract
Capped chips and methods of forming a capped chip are provided
in which electrical interconnects are made by conductive elements
which extend from bond pads of a chip at least partially through a
plurality of through holes of a cap. The electrical interconnects
may be solid, so as to form seals extending across the through
holes. In some cases, stud bumps extend from the bond pads, forming
parts of the electrical interconnects. In some cases, a fusible
conductive medium forms a part of the electrical interconnects.
Inventors: |
Humpston; Giles; (Aylesbury,
GB) ; Tuckerman; David B.; (Lafayette, CA) ;
McWilliams; Bruce M.; (San Jose, CA) ; Haba;
Belgacem; (Saratoga, CA) ; Mitchell; Craig S.;
(San Jose, CA) |
Correspondence
Address: |
TESSERA;LERNER DAVID et al.
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
Tessera, Inc.
San Jose
CA
95134
|
Family ID: |
34382320 |
Appl. No.: |
11/641152 |
Filed: |
December 19, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10949674 |
Sep 24, 2004 |
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11641152 |
Dec 19, 2006 |
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10928839 |
Aug 27, 2004 |
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11641152 |
Dec 19, 2006 |
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60568041 |
May 4, 2004 |
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60568041 |
May 4, 2004 |
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60532341 |
Dec 23, 2003 |
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60515615 |
Oct 29, 2003 |
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60506500 |
Sep 26, 2003 |
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60574523 |
May 26, 2004 |
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60532341 |
Dec 23, 2003 |
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60515615 |
Oct 29, 2003 |
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60506500 |
Sep 26, 2003 |
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Current U.S.
Class: |
257/734 ;
257/E23.021; 257/E23.181 |
Current CPC
Class: |
B81C 2203/019 20130101;
H01L 2924/01042 20130101; H01L 2924/16151 20130101; H01L 2924/3025
20130101; H01L 24/48 20130101; H01L 2924/014 20130101; H01L
2224/484 20130101; H01L 2924/16235 20130101; H03H 3/007 20130101;
H01L 2224/13099 20130101; H01L 2924/01077 20130101; H03H 9/1057
20130101; H01L 24/13 20130101; H01L 2224/13169 20130101; H01L
2924/0105 20130101; H01L 24/82 20130101; H01L 2224/0401 20130101;
H01L 2224/131 20130101; H01L 2924/09701 20130101; B81C 1/00293
20130101; H01L 2224/48091 20130101; H01L 2924/01029 20130101; H01L
2924/15165 20130101; B81C 2203/0118 20130101; H01L 2224/13139
20130101; H01L 2924/01028 20130101; H01L 2924/01082 20130101; H01L
2924/12044 20130101; H03H 9/1064 20130101; H01L 2224/13144
20130101; H01L 2924/0103 20130101; H01L 2924/01058 20130101; H01L
2924/15311 20130101; H01L 2924/01014 20130101; H01L 27/14618
20130101; H01L 27/14627 20130101; H01L 2224/48228 20130101; H01L
2224/82101 20130101; H01L 2924/01322 20130101; H01L 2924/07811
20130101; B81B 2207/095 20130101; H01L 2924/01023 20130101; H01L
23/04 20130101; H01L 2224/13124 20130101; H01L 2924/1461 20130101;
H01L 23/3114 20130101; H01L 2224/16 20130101; H01L 2224/48247
20130101; H01L 2924/12042 20130101; H01L 2924/16195 20130101; H01L
2924/3011 20130101; H03H 9/1071 20130101; B81C 1/00301 20130101;
H01L 2224/05644 20130101; H03H 9/059 20130101; H01L 33/62 20130101;
H01L 2224/48227 20130101; H01L 2924/01005 20130101; H01L 24/11
20130101; H01L 2224/4824 20130101; B81C 2203/0145 20130101; H01L
2924/01006 20130101; H01L 2924/00014 20130101; H03H 9/0585
20130101; H01L 2924/01022 20130101; H01L 2924/01061 20130101; H01L
2924/15153 20130101; H01L 27/14636 20130101; H01L 2224/11334
20130101; H01L 2924/01024 20130101; H01L 2924/04941 20130101; H01L
2924/01013 20130101; H01L 2224/06135 20130101; H01L 2224/05624
20130101; H01L 2224/81801 20130101; H01L 2924/01047 20130101; H01L
2924/10253 20130101; H01L 2224/9202 20130101; H01L 21/76898
20130101; H01L 24/24 20130101; H01L 2224/1401 20130101; H01L
2924/01078 20130101; H01L 2924/01079 20130101; H03H 9/0547
20130101; H01L 2924/15787 20130101; H01L 2224/13147 20130101; H01L
2924/01018 20130101; H01L 2924/01033 20130101; H01L 2924/01046
20130101; H01L 2224/13 20130101; H01L 2924/14 20130101; H01L
2224/11 20130101; H01L 2924/01027 20130101; H01L 2224/484 20130101;
H01L 2924/00014 20130101; H01L 2224/48091 20130101; H01L 2924/00014
20130101; H01L 2224/131 20130101; H01L 2924/014 20130101; H01L
2924/00014 20130101; H01L 2924/10253 20130101; H01L 2924/00
20130101; H01L 2224/1401 20130101; H01L 2924/00012 20130101; H01L
2924/07811 20130101; H01L 2924/00 20130101; H01L 2924/1461
20130101; H01L 2924/00 20130101; H01L 2924/15787 20130101; H01L
2924/00 20130101; H01L 2224/13 20130101; H01L 2924/00 20130101;
H01L 2224/11 20130101; H01L 2924/00 20130101; H01L 2924/00014
20130101; H01L 2224/45099 20130101; H01L 2924/12042 20130101; H01L
2924/00 20130101 |
Class at
Publication: |
257/734 |
International
Class: |
H01L 23/48 20060101
H01L023/48 |
Claims
1. A capped chip, comprising: a chip having an upwardly facing
front surface and a plurality of bond pads exposed in a bond pad
region at said front surface; a cap member having a bottom surface
confronting said front surface of said chip, a top surface opposite
said bottom surface, and a plurality of through holes extending
between said top and bottom surfaces, said cap member being mounted
to said chip with at least a portion of said bottom surface spaced
from said front surface to define a void; and a plurality of solid
electrically conductive interconnects extending at least partially
through said through holes to form seals extending across said
through holes.
2. A capped chip as claimed in claim 1, further comprising a seal
disposed between said bottom surface of said cap member and a
portion of said front surface of said chip, said seal at least
substantially enclosing said void.
3. A capped chip as claimed in claim 2, wherein said chip includes
an active area and said through holes are disposed between said
seal and said active area such that said seal and said
interconnects seal said active area within said void.
4. A capped chip as claimed in claim 2, wherein said interconnects
include a fusible material and an attach temperature of a sealing
material of said seal coincides with a reflowing temperature for
said fusible material.
5. A capped chip as claimed in claim 2, wherein said bottom surface
of said cap member includes a stop, said stop being engaged with
said front surface of said active chip to control a spacing between
said cap member and said chip.
6. A capped chip as claimed in claim 5, wherein a sealing material
of said seal is disposed in contact with said stop and with said
front surface of said chip such that said cap member is sealed to
said chip at said stop.
7. A capped chip as claimed in claim 5, wherein said stop includes
a knife-edge.
8. A capped chip as claimed in claim 2, wherein said seal includes
a polymer.
9. A capped chip as claimed in claim 2, wherein said polymer
includes at least one of a thermoplastic, a self-fluxing underfill
and an adhesive.
10. A capped chip as claimed in claim 2, wherein said seal includes
a low melting point glass.
11. A capped chip as claimed in claim 2, wherein said seal includes
solder.
12. A capped chip as claimed in claim 2, wherein said seal includes
a eutectic composition.
13. A capped chip as claimed in claim 2, wherein said seal is
diffusion bonded to at least one of said chip and said cap
member.
14. A capped chip as claimed in claim 2, wherein said seal includes
spacing elements, such that said front surface of said chip and
said bottom surface of said cap member are spaced by no less than a
width of said spacing elements.
15. A capped chip as claimed in claim 2, wherein said chip includes
a rear surface opposite said front surface and peripheral edges
extending between said front and rear surfaces, and said cap member
includes peripheral edges disposed between said bottom surface and
said top surface, wherein said chip further comprises an additional
seal sealing at least said peripheral edges of said cap member to
said peripheral edges of said chip.
16. A capped chip as claimed in claim 1, wherein said cap member
includes at least one material selected from the group consisting
of ceramics, metals, glasses, and semiconductor materials.
17. A capped chip as claimed in claim 16, wherein said cap member
consists essentially of a material having a coefficient of thermal
expansion (CTE) closely matched to a CTE of said chip.
18. A capped chip as claimed in claim 17, wherein said chip
includes a surface acoustic wave (SAW) device exposed at said front
surface and said cap member includes a material having a CTE which
is closely matched to a CTE of said SAW device.
19. A capped chip as claimed in claim 18, wherein said SAW device
includes a component consisting essentially of lithium tantalate,
and said cap member includes a layer of aluminum and a layer of an
oxide overlying said layer of aluminum.
20. A capped chip as claimed in claim 17, wherein said cap member
includes a metal layer and an oxide layer overlying said metal
layer, said oxide layer including an oxide of a metal of said metal
layer, wherein said oxide layer lines said through holes.
21. A capped chip as claimed in claim 17, wherein said material of
said cap member includes at least one material selected from the
group consisting of nickel alloys.
22. A capped chip as claimed in claim 16, wherein said through
holes are metallized with two or more layers of metal disposed on
sidewalls thereof.
23. A capped chip as claimed in claim 22, wherein said layers of
metal include a layer consisting essentially of titanium contacting
said sidewall of said through hole, a layer consisting essentially
of platinum contacting said titanium layer, and an exposed layer
consisting essentially of gold contacting said platinum layer.
Description
[0001] This application is a division of U.S. application Ser. No.
10/949,674 filed Sep. 24, 2004. Said application Ser. No.
10/949,674 claims the benefit of the filing dates of U.S.
Provisional Patent Application Nos. 60/506,500 filed Sep. 26, 2003,
60/515,615 filed Oct. 29, 2003, 60/532,341 filed Dec. 23, 2003,
60/568,041 filed May 4, 2004, 60/574,523 filed May 26, 2004, and is
a continuation-in-part of U.S. patent application Ser. No.
10/928,839, filed Aug. 27, 2004, the disclosures of all such
applications being hereby incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to microelectronic packaging.
Microelectronic chips typically are thin, flat bodies with
oppositely facing, generally planar front and rear surfaces and
with edges extending between these surfaces. Chips generally have
contacts on the front surface, which are electrically connected to
the circuits within the chip. Certain chips require a protective
element, referred to herein as a cap or lid, over all or part of
the front surface. For example, chips referred to as surface
acoustic wave or "SAW" chips incorporate acoustically-active
regions on their front surfaces, which must be protected from
physical and chemical damage by a cap. Microelectromechanical or
"MEMS" chips include microscopic electromechanical devices, e.g.,
acoustic transducers such as microphones, which must be covered by
a cap. The caps used for MEMS and SAW chips must be spaced from the
front surface of the chip to an open gas-filled or vacuum void
beneath the cap in the active area, so that the cap does not touch
the acoustical or mechanical elements. Certain electro-optical
chips such as optical sensing chips and light-emitting chips have
photosensitive elements which also must be protected by a lid.
Voltage controlled oscillators (VCOs) sometimes also require a cap
to be placed over the active area.
[0003] Miniature SAW devices can be made in the form of a wafer
formed from or incorporating an acoustically active material such
as lithium niobate or lithium tantalate material. The wafer is
treated to form a large number of SAW devices, and typically also
is provided with electrically conductive contacts used to make
electrical connections between the SAW device and other circuit
elements. After such treatment, the wafer is severed to provide
individual devices. SAW devices fabricated in wafer form can be
provided with caps while still in wafer form, prior to severing.
For example, as disclosed in U.S. Pat. No. 6,429,511 a cover wafer
formed from a material such as silicon can be treated to form a
large number of hollow projections and then bonded to the top
surface of the active material wafer, with the hollow projections
facing toward the active wafer. After bonding, the cover wafer is
polished to remove the material of the cover wafer down to the
projections. This leaves the projections in place as caps on the
active material wafer, and thus forms a composite wafer with the
active region of each SAW device covered by a cap.
[0004] Such a composite wafer can be severed to form individual
units. The units obtained by severing such a wafer can be mounted
on a substrate such as a chip carrier or circuit panel and
electrically connected to conductors on the substrate by
wire-bonding to the contacts on the active wafer after mounting,
but this requires that the caps have holes of a size sufficient to
accommodate the wire bonding process. This increases the area of
the active wafer required to form each unit, requires additional
operations and results in an assembly considerably larger than the
unit itself.
[0005] In another alternative disclosed by the '511 patent,
terminals can be formed on the top surfaces of the caps and
electrically connected to the contacts on the active wafer prior to
severance as, for example, by metallic vias formed in the cover
wafer prior to assembly. However, formation of terminals on the
caps and vias for connecting the terminals to the contacts on the
active wafer requires a relatively complex series of steps.
[0006] Similar problems occur in providing terminals for MEMS
devices. For these and other reasons, further improvements in
processes and structures for packaging SAW, MEMS, electro-optical
and other capped devices would be desirable.
SUMMARY OF THE INVENTION
[0007] As used herein in relation to a cap and cap wafer and a lid
and lid wafer, the term "top surface" refers to an outer surface of
the cap, and the term "bottom surface" refers to an inner surface
of the cap, the inner and outer surfaces of the cap relating to the
form in which the cap is joined to the chip. Stated another way,
the outer surface of the cap faces away from the front, i.e., the
contact-bearing surface of the chip, while the inner surface of the
cap faces towards the front or contact-bearing surface of the chip.
The outer surface of the cap is referred to as the top surface, and
the inner surface of the cap is referred to as the bottom surface,
even if the capped chip structure including both chip and cap is
turned over and mounted, such that the top surface faces downwardly
and is joined to another article, such as a printed circuit
panel.
[0008] According to an aspect of the invention, a capped chip is
provided which includes a chip having an upwardly facing front
surface and a plurality of bond pads exposed in a bond pad region
at the front surface. A cap member having a top surface, a bottom
surface opposite the top surface, and a plurality of through holes
extending between the top and bottom surfaces, is mounted to the
chip such that the bottom surface faces the front surface of the
chip and is spaced therefrom to define a void. A plurality of solid
electrically conductive interconnects extend from the bond pads at
least partially through the through holes to form seals extending
across the through holes.
[0009] An assembly including a capped chip according to a preferred
aspect of the invention further includes a circuit panel having a
plurality of terminals, wherein the interconnects are joined to the
terminals of the circuit panel.
[0010] According to a particular preferred aspect of the invention,
the interconnects may include a fusible conductive material joined
to the bond pads. Wettable regions are desirably provided on
sidewalls of the through holes, the fusible material contacting the
wettable regions. The fusible conductive material may include at
least one of a solder, tin, or eutectic composition, and the
through holes have a substantially frusto-conical shape.
[0011] According to a particular preferred aspect of the invention,
a seal disposed between the bottom surface of the cap member and a
portion of the front surface of the chip, the seal at least
substantially enclosing the bond pad region and the void. The chip
preferably includes an active area and the through holes are
disposed between the seal and the active area such that the seal
and the interconnects seal the active area within the void. In one
embodiment, the interconnects include a fusible material and an
attach temperature of a sealing material of the seal coincides with
a reflowing temperature for the fusible material.
[0012] In an embodiment, the bottom surface of the cap member
includes a stop, the stop being engaged with the front surface of
the active chip to control a spacing between the cap member and the
chip. A sealing material of the seal is preferably disposed in
contact with the stop and with the front surface of the chip such
that the cap member is sealed to the chip at the stop.
Illustratively, the stop includes a knife-edge and the seal
includes a material such as a thermoplastic, adhesive, low melting
point glass, solder or eutectic composition. In one embodiment, the
seal is diffusion bonded to at least one of the chip and the cap
member.
[0013] In a particular embodiment, the seal includes spacing
elements, such that the front surface of the chip and the bottom
surface of the cap member are spaced by no less than a width of the
spacing elements. The cap member preferably includes at least one
material selected from the group consisting of ceramics, metals,
glasses, and semiconductor materials. In a highly preferred
embodiment, the cap member consists essentially of a material
having a coefficient of thermal expansion (CTE) closely matched to
a CTE of the chip. Such chip may include a surface acoustic wave
(SAW) device exposed at the front surface and the cap member
includes a material having a CTE, which is closely matched to a CTE
of the SAW device. In a specific embodiment, the SAW device
includes a component consisting essentially of lithium tantalate,
and the cap member includes a layer of aluminum and a layer of
aluminum oxide overlying the layer of aluminum. In such embodiment,
the cap member may include a metal layer and an oxide layer
overlying the metal layer, the oxide layer including an oxide of a
metal of the metal layer, wherein the oxide layer lines the through
holes. The material of the cap member may further include one or
more nickel alloys.
[0014] Preferably, through holes of the cap are metallized with two
or more layers of metal disposed on sidewalls thereof. The layers
of metal desirably include a layer consisting essentially of
titanium contacting the sidewall of the through hole, a layer
consisting essentially of platinum contacting the titanium layer,
and an exposed layer consisting essentially of gold contacting the
platinum layer. Such metallization is a preferred example of a
broader class of metallization schemes colloquially referred to as
"under bump metallizations" ("UBMs"), a UBM typically being applied
to form a bondable surface on a larger surface, prior to applying a
molten fusible conductive material thereto, such as a solder
mass.
[0015] According to another preferred aspect of the invention, the
chip includes a rear surface opposite the front surface and
peripheral edges extending between the front and rear surfaces, and
the cap member includes peripheral edges disposed between the
bottom surface and the top surface, wherein the chip further
comprises an additional seal sealing at least the peripheral edges
of the cap member to the peripheral edges of the chip.
[0016] According to yet another preferred aspect, the cap member
includes a dielectric layer having an inner surface and an outer
surface, a ground layer disposed on at least the inner outer
surface and at least one trace extending along the outer surface
from the interconnect.
[0017] In a particular embodiment, the interconnects of the capped
chip include stud bumps in conductive communication with the bond
pads, and the stud bumps extend at least partially through the
through holes. Contacts at the top surface of the cap member are
disposed in conductive communication with the stud bumps.
[0018] In one embodiment, some of the stud bumps have shoulders
abutting the bottom surface of the cap member, whereby the spacing
between the bottom surface and the cap member is determined by the
shoulders.
[0019] In another particular embodiment of the invention, the
through holes are tapered, becoming smaller in a direction from the
top surface towards the bottom surface.
[0020] In a preferred embodiment, the interconnects include at
least one conductive trace extending horizontally along the top
surface of the cap member. The interconnects may further include
one or more contacts in conductive communication with the at least
one conductive trace.
[0021] According to another aspect of the invention, a capped chip
is provided which includes a chip having a front surface, and a
plurality of bond pads exposed at the front surface. The cap member
has a top surface, a bottom surface opposite the top surface, and a
plurality of through holes which extend between the top and bottom
surfaces. The cap member is mounted to the chip such that the
bottom surface faces the chip and is spaced therefrom to define a
void. In such capped chip, a plurality of electrically conductive
interconnects extend from the bond pads at least partially through
the through holes. The interconnects including a flowable
conductive material that extends at least partially through the
through holes.
[0022] Preferably, the flowable conductive material extends from
the bond pads through the holes. As in the above aspect of the
invention, a seal preferably extends between the chip and the cap
member, the seal surrounding at least some or all of the
interconnects, and the flowable conductive material sealing the
through holes. In one embodiment, the seal includes a flowable
conductive material of the same composition as the
interconnects.
[0023] According to a preferred aspect of the invention, the
flowable conductive material wets portions of the cap member
surrounding the through holes. In a particular embodiment, the cap
member defines walls extending from the top surface to the bottom
surface, the walls surrounding each of the through holes and the
flowable conductive material wets the walls. When the cap member
includes a structural material not wettable by the flowable
conductive material, the cap may include liners formed from a
material wettable by the flowable conductive material covering the
walls. In a preferred embodiment, the flowable conductive material
is a solder.
[0024] According to yet another aspect of the invention, a method
of forming capped chips is provided which includes assembling a lid
member to a chip member so that a bottom surface of the lid member
faces downwardly toward a front surface of the chip member and a
top surface of the lid member faces upwardly away from the chip
member. Through-holes extending between the top and bottom surfaces
of the lid member are aligned with electrically conductive features
of the chip member and so that the bottom surface of the lid member
is spaced apart from the front surface of the chip member in at
least some regions including the aligned through holes and
conductive features. Electrical connections are formed which extend
from the conductive features at least partially through the through
holes. This is performed by providing a flowable conductive
material at the through holes and causing the flowable conductive
material to flow in the through holes.
[0025] According to particular aspect of the invention, the step of
providing a flowable conductive material includes introducing the
flowable conductive material into the through holes from the top
surface of the lid member. The step of causing the flowable
conductive material to flow may include causing the flowable
conductive material to flow downwardly in the through holes into
contact with the electrically conductive features of the chip
member. The electrically conductive features include features
projecting upwardly from the front surface of the chip member into
the through holes. The electrically conductive features can be
spaced, for example, below the bottom surface of the lid member and
the step of causing the flowable conductive material to flow
includes forming menisci projecting downwardly from the bottom
surfaces at the through holes so that the menisci contact the
conductive features. In one embodiment, the step of causing the
flowable material to flow includes causing the flowable material to
wet walls bounding the through holes.
[0026] According to another aspect of the invention, a method of
forming a capped chip having a plurality of metallic interconnects
at least partially extending through a cap member is provided which
includes aligning (i) a chip having a front surface and a plurality
of bond pads exposed at the front surface; with (ii) a cap member
having a horizontally extending top surface, a horizontally
extending bottom surface, and a plurality of through holes
extending between the top surface and the bottom surface, so that
the through holes are aligned to the bond pads. The method further
includes forming solder-wettable metallizations are formed on the
cap member at least where the through holes meet the top surface
and simultaneously forming solder-wettable metallizations overlying
the bond pads of the chip, the solder-wettable metallizations
overlying the bond pads being formed in the self-aligned manner to
the through holes. The solder-wettable metallizations of the
through holes are bonded to the solder-wettable metallizations on
the chip to form metallic interconnects extending from the bond
pads at least partially through the through holes.
[0027] Preferably, the solder-wettable metallizations are formed by
deposition, the aligned cap member functioning as an in situ mask
during the deposition of the solder-wettable metallizations on the
chip. Specifically, the chip may include a surface acoustic wave
(SAW) device, wherein the bond pads are not wettable by solder
prior to the solder-wettable metallizations being formed, e.g.,
such as when the bond pads of the chip have at least a surface film
of aluminum. In one embodiment, the bonding step includes disposing
solder balls on the solder-wettable metallizations of the cap
member and heating the aligned cap member and the chip to cause
solder of the solder balls to bond the solder-wettable
metallizations of the cap member to the solder-wettable
metallizations of the chip. In a particular embodiment, the bonding
step is performed fluxlessly, i.e., without using a flux, such as
may be performed in a nitrogen atmosphere.
[0028] According to an aspect of the invention, a method of making
a chip assembly includes the steps of assembling (i) a capped chip
including a chip, a cap overlying a front surface of the chip and a
sacrificial layer overlying the cap with (ii) one or more further
components. After the assembling step, the sacrificial layer is
removed from the capped chip. Preferably, the assembling step
includes bonding electrically-conductive features of the capped
chip to at least one of the further components using an
electrically-conductive bonding material.
[0029] Preferably, the electrically-conductive features of the
capped chip include interconnections extending through the lid
element. When that is the case, the method preferably further
includes the steps of patterning the sacrificial layer and forming
at least portions of the interconnections using the patterned
sacrificial layer as a mask.
[0030] In another preferred embodiment, the method further includes
a step of forming the capped chip by assembling a lid member and a
chip member including a plurality of chips and then severing the
lid member and chip member, the sacrificial layer being present on
the cap member during the severing step.
[0031] According to another preferred aspect of the invention, a
method is provided for making a plurality of capped chip
assemblies. The method includes the steps of: (a) assembling a lid
member and a chip member including a plurality of chips to one
another so that the lid member overlies the chip member and a top
surface of the lid member faces away from the chip member; (b)
severing the lid member and chip member to form a plurality of
individual units each including one or more of the chips and a
portion of the lid member; (c) providing a sacrificial layer
overlying the top surface of the lid member prior to the severing
step; and (d) removing the sacrificial layer after the severing
step.
[0032] In a preferred aspect of the invention, the cap includes a
region which is at least partially optically transmissive. The
sacrificial layer desirably includes a developed photoresist layer.
The chip preferably includes at least one first bonding area, and
the cap includes at least one second bonding area including a
wettable region. Preferably, in such case, the assembling step
includes bonding the first bonding area of the chip member to the
second bonding area of the cap by a fusible material.
[0033] According to another aspect of the invention, a capped chip
is provided which includes a chip having a front surface and a
plurality of bond pads exposed at the front surface. A cap member
having a bottom surface faces the front surface of the chip and has
a top surface opposite the front surface. The cap member further
has a plurality of through holes extending from the bottom surface
to the top surface. In this aspect of the invention, at least
portions of the through holes are tapered, becoming smaller in a
direction from the bottom surface toward the top surface. A
plurality of electrically conductive interconnects extend from the
bond pads at least partially through the through holes.
[0034] According to a preferred aspect of the invention, the
interconnects include fusible material joined to the bond pads. The
fusible material may includes solder, tin and/or a eutectic
composition, for example, or such other suitable fusible material.
In a preferred embodiment, the through holes have substantially
frusto-conical shapes. A sealing material is desirably disposed
between the bottom surface of the cap member and a portion of the
front surface of the chip. Preferably, an attach temperature of the
sealing material coincides with a temperature for bonding the
fusible material.
[0035] In one preferred aspect of the invention, a bottom surface
of the cap member includes a downwardly protruding feature such as
a knife edge. The sealing material is preferably disposed in
contact with the protruding feature and with the front surface of
the chip to seal the cap member to the chip. In particular
embodiments, the sealing material includes a thermoplastic, an
adhesive, a low melting point glass, a solder, and a eutectic
composition. In a preferred embodiment, the sealing material is
diffusion bonded to at least one of the chip and the cap
member.
[0036] Preferably, the sealing material includes spacing elements,
such that the front surface of the chip and the cap member are
spaced by no less than a width of the spacing elements. In one
embodiment, the bond pads are exposed at a bond pad region of the
front surface, and the capped chip further includes a sealing
material sealing the front surface to the bottom surface of the cap
member, such that the sealing material at least substantially
encloses the bond pad region.
[0037] In a particular embodiment, the cap member consists
essentially of at least one material selected from the group
consisting of ceramics, metals, glasses, and semiconductor
materials. Preferably, the through holes of the cap are lined with
two or more layers of metal disposed on the sidewalls. The layers
of metal include, for example, a layer consisting essentially of
titanium contacting the sidewalls of the through holes, a layer
consisting essentially of platinum contacting the titanium layer,
and an exposed layer consisting essentially of gold contacting the
platinum layer.
[0038] In one embodiment, the chip has a rear surface opposite the
front surface and peripheral edges extending between the front and
rear surfaces. The cap member has peripheral edges disposed between
the bottom surface and the top surface. In such embodiment, the
chip preferably includes an additional seal sealing at least the
peripheral edges of the cap member to the peripheral edges of the
chip.
[0039] According to a particular aspect of the invention, an
assembly is provided which further includes a circuit panel having
a plurality of terminals, wherein the interconnects are joined to
the terminals of the circuit panel.
[0040] According to another aspect of the invention, a capped chip
is provided which includes a chip having a front surface, a cap
member having a bottom surface facing the front surface of the chip
and having a top surface opposite the front surface. The cap member
further includes a plurality of through holes extending from the
bottom surface to the top surface. A plurality of metallic
interconnects including stud bumps are electrically connected to
the chip and project upwardly from the front surface at least
partially through the through holes.
[0041] According to such preferred aspect, the chip has bond pads
exposed at the front surface and the stud bumps are joined to the
bond pads and electrically connected to the chip through the bond
pads. The stud bumps preferably extend at least to the top surface.
The metallic interconnects may include annular solderable
metallizations which surround the through holes on the top surface
of the cap member and the capped chip preferably includes solder
masses joining the solderable metallizations to the stud bumps.
[0042] In a preferred embodiment, the stud bumps are sealed to the
cap member.
[0043] In one embodiment, the through holes do not have solderable
metallizations. In such case, in a particular embodiment, the stud
bumps may be sealed by a conductive organic material. For instance,
the stud bumps may be sealed by a nonconductive material and the
stud bumps protrude through the nonconductive material, which is
preferably an organic material. In a highly preferred aspect of
such embodiment, masses of an electrically conductive bonding
material can be joined to the stud bumps at positions external to
the top surface.
[0044] In a particular embodiment, an assembly is provided
including a capped chip and further including an interconnection
element. The interconnection element includes pressure contacts
pressed against the stud bumps to electrically interconnect the
interconnection element to the capped chip.
[0045] In a particular embodiment, the metallic interconnects are
coplanar with the top surface.
[0046] In one embodiment, the stud bumps are sealed to the through
holes of the capped chip by the nonconductive material. The
sidewalls of the through holes may be oriented at an angle of about
90 degrees to the top surface.
[0047] Alternatively, the through holes can be tapered, becoming
smaller in a direction from the bottom surface towards a midpoint
of a thickness of the cap member and becoming smaller in a
direction from the top surface towards the midpoint of the
thickness.
[0048] In other embodiments, the through holes are tapered and
become smaller in a direction from the bottom surface towards the
top surface; or alternatively, become smaller in a direction from
the top surface towards the bottom surface.
[0049] Preferably, a sealing material is disposed between the
bottom surface of the cap member and a portion of the front surface
of the chip.
[0050] In one embodiment, an assembly is provided which includes a
capped chip and further includes a circuit panel having a plurality
of terminals, wherein the metallic interconnects are joined to the
terminals of the circuit panel.
[0051] In a particular embodiment, the stud bumps include at least
one metal selected from the group consisting of aluminum, gold,
silver, platinum, and copper.
[0052] According to another aspect of the invention, a method is
provided of making a capped chip assembly. Such method includes the
steps of: (a) aligning a cap member with a chip member including
one or more chips so that electrically conductive elements
projecting from a front surface of the chip member extend into
through-holes in the lid member and at least partially control
location of the lid member relative to the chip member in one or
more horizontal directions parallel to the front surface; and (b)
forming interconnections extending through the lid member so that
the interconnections include the conductive elements.
[0053] According to a particular aspect, the chip member includes
contact pads and the electrically conductive elements include stud
bumps projecting from the contact pads. The step of forming the
stud bumps may be performed by wire bonding to the contact pads
before the aligning step.
[0054] In another preferred embodiment, the chip member includes
contact pads and the electrically conductive elements include
balls. In such embodiment, the balls may be bonded to the contact
pads before the aligning step.
[0055] In one embodiment, the electrically conductive elements hold
the lid member above the chip member during the forming step so
that there is a space between the lid member and the chip member at
the conclusion of the forming step.
[0056] In a preferred embodiment, the chip member is a unitary
wafer member including a plurality of chips, and the method further
includes severing the lid member and the wafer member after the
forming step so as to provide a plurality of individual units, each
unit including one or more of the chips, a lid and one or more of
the interconnections. In such case, the method may further include
a step of forming a plurality of ring seals extending between the
wafer member and the lid member so that each the ring seal
surrounds one or more of the interconnections. In that case, the
severing step is performed so that each the unit includes one or
more of the ring seals.
[0057] According to another aspect of the invention, a method is
provided of forming a capped chip having a plurality of metallic
interconnects at least partially extending through a cap member,
comprising: providing a chip having a front surface and a plurality
of bond pads on the front surface; providing conductive balls on
the bond pads; providing a cap member having a horizontally
extending bottom surface, a horizontally extending top surface, and
a plurality of metallized through holes extending from the bottom
surface to the top surface; aligning the cap member and the chip
such that the bottom surface faces the chip and the metallized
through holes are aligned to the conductive balls; and bonding the
conductive balls to the metallized through holes to form the
metallic interconnects.
[0058] In a preferred embodiment, the conductive balls include a
low melting point material, such that the conductive balls are
reflowed when the conductive balls are bonded to the metallized
through holes.
[0059] In some embodiments, at least some of the through holes are
tapered, having a dimension which becomes smaller from the bottom
surface toward the top surface. In one embodiment, the metallized
through holes preferably have substantially frusto-conical shape
and the conductive balls have substantially spherical faces, such
that the aligning self-locates the substantially metallized through
holes onto the substantially spherical faces of the conductive
balls.
[0060] Preferably, the aligning self-locates the metallized through
holes onto the conductive balls for variations in position having
six degrees of freedom including first and second horizontal axes,
a vertical axis, and rotation, pitch, and roll.
[0061] In a preferred embodiment, the method further includes
sealing the bottom surface of the cap member to the front surface
of the chip. Preferably, such sealing is performed simultaneously
with the reflowing. In a preferred aspect, the sealing includes
depositing a sealing material onto at least one of the bottom
surface of the cap member and the front surface of the chip,
wherein the reflowing draws the cap member and the chip toward each
other to complete the sealing. Preferably, an attach temperature of
the sealing material coincides with a reflowing temperature of the
conductive balls.
[0062] In one embodiment, the sealing is performed after the step
of bonding.
[0063] In a preferred embodiment, the bottom surface of the cap
member includes a downwardly protruding feature such as a knife
edge, wherein a sealing material is disposed in contact with the
feature and with the front surface of the chip to seal the cap
member to the chip. In such case, a sealing material is preferably
disposed in contact with the feature and with the front surface of
the chip to seal the cap member to the chip.
[0064] In another preferred aspect of the invention, the conductive
balls are placed on the bond pads in a fluxless manner, and the
method further comprises joining the conductive balls to the bond
pads prior to the step of bonding the conductive balls. In such
case, the conductive balls preferably include solder balls.
[0065] In a preferred aspect, the chip includes a rear surface
opposite the front surface and peripheral edges extending between
the front and rear surfaces, and the cap member includes a top
surface opposite the bottom surface and peripheral edges disposed
between the bottom and top surfaces, the method further comprising
depositing an additional sealing material onto the peripheral edges
of the cap member and onto the sealing material.
[0066] In a preferred embodiment, the above method used for forming
a capped chip can be further augmented include steps of aligning
and joining the metallic interconnects to terminals disposed on a
circuit panel to form an assembly.
[0067] According to another aspect of the invention, a method is
provided of forming a plurality of capped chips each having a
plurality of chip interconnections at least partially extending
through a cap member of the capped chip. Such method includes:
providing an array of chips each having a front surface and a
plurality of bond pads on the front surface, and providing
conductive balls on the bond pads. A cap member is provided which
includes a horizontally extending bottom surface, a horizontally
extending top surface, and a plurality of metallized through holes
extending from the bottom surface to the top surface. At least some
of the through holes are tapered, becoming smaller in a direction
from the bottom surface towards the top surface. The cap member and
the array of chips are aligned such that the bottom surface faces
the front surfaces of the chips and the metallized through holes
are aligned to the conductive balls. The cap member is joined to
the chips by bonding the conductive balls to the metallized through
holes, wherein the bonded conductive balls form at least part of
the chip interconnections.
[0068] In a preferred embodiment, the conductive balls include a
low melting point material, and the bonding is performed by
reflowing the conductive balls. Preferably, each of the chips of
the array of chips is attached to at least one other of the chips,
and the method further includes severing the joined chips.
[0069] According to another aspect of the invention, a capped chip
is provided which includes: a chip having a front surface and a
plurality of bond pads exposed at the front surface; a cap member
having a bottom surface facing the front surface of the chip and
having a top surface opposite the front surface, the cap member
further having a plurality of through holes extending from the
bottom surface to the top surface; and a plurality of metallic
interconnects extending from the bond pads at least partially
through the through holes, the metallic interconnects including
stud bumps joined to the bond pads, the stud bumps contacting and
engaging at least one of (i) the top surface of the cap member
surrounding the through holes and (ii) inner surfaces of the
through holes.
[0070] According to such aspect, in one embodiment, the through
holes of the capped chip do not have solderable metallizations. In
such case, the stud bumps are preferably sealed to the cap member,
such as by a conductive organic material.
[0071] An assembly including a capped chip according to such aspect
of the invention may further include an interconnection element, in
which the interconnection element includes pressure contacts that
are pressed against the stud bumps to electrically interconnect the
interconnection element to the capped chip. Preferably, in such
embodiment, the metallic interconnects are coplanar with the top
surface.
[0072] In a particular embodiment, the sidewalls of the through
holes are oriented at an angle of about 90 degrees to the top
surface.
[0073] An assembly including a capped chip according to such
embodiment may further include a circuit panel having a plurality
of terminals, wherein the metallic interconnects are joined to the
terminals of the circuit panel.
[0074] In a particular embodiment, the stud bumps consist
essentially of at least one metal selected from the group
consisting of gold and copper.
[0075] According to yet another aspect of the invention, a method
of making a capped chip is provided which includes the steps of:
assembling at least one chip with at least one cap so that stud
bumps project from the chip at least partially through
through-holes in the cap; and (b) deforming the stud bumps into
engagement with at least one of (i) a top surface of the cap
surrounding the through-holes and (ii) walls of the through
holes.
[0076] According to a preferred aspect, the deforming step is
performed so that the stud bumps sealingly engage the through
holes. In a preferred aspect, the method further includes a step of
forming a metallurgical bond between the stud bumps and a metallic
layer on the top surface or the walls.
[0077] According to yet another embodiment of the invention, a
capped chip is provided, which includes: a chip having a front
surface, one or more devices at the front surface, and a first
annular solder-wettable metallization enclosing the one or more
devices. The capped chip further includes a cap member having a top
surface, a bottom surface opposite the top surface, one or more
through holes extending between the top and bottom surfaces and a
second annular solder-wettable metallization at the bottom surface
in registration with the one or more through holes and the first
annular solder-wettable metallization. A sealing medium including a
fusible material is bonded to the first and second solder-wettable
metallizations.
[0078] According to a preferred aspect of the invention, the
sealing medium includes at least one material selected from the
group consisting of solder, eutectic composition, and tin.
[0079] In one embodiment, the one or more through holes is sized to
permit a flow of the sealing medium from the through hole onto the
first and second annular solder-wettable metallizations. In such
case, the one or more through holes is preferably tapered to become
smaller in a direction from the top surface of the cap member
towards the bottom surface. In one embodiment, the chip may further
include a plurality of bond pads on the front surface enclosed by
the first annular solder-wettable metallization, and a plurality of
metallic interconnects extending from the bond pads at least
partially through the cap member.
[0080] According to another aspect of the invention, a chip
includes: (a) a body defining a front surface and one or more
circuit elements on or within the body; (b) one or more bond pads
exposed at the front surface in a bond pad region; and (c) a
metallic ring exposed at the front surface, the ring substantially
surrounding the bond pad region. In a preferred aspect of the
invention, a unitary wafer includes a plurality of such chips.
[0081] According to yet another aspect of the invention, a method
of making a plurality of sealed assemblies is provided. Such method
includes: (a) assembling a first element to a second element so
that a bottom surface of the first element faces downwardly toward
a front surface of the second element and a top surface of the
first element faces upwardly away from the second element; and (b)
forming ring seals surrounding regions of the front surface of the
second element by introducing flowable material between the first
element and the second element from the top surface of the first
element through openings in the first element.
[0082] According to yet another aspect of the invention, another
method of making a plurality of capped chips is provided. Such
method includes: (a) assembling a lid member to a chip member so
that a bottom surface of the lid member faces downwardly toward a
front surface of the chip member and a top surface of the lid
member faces upwardly away from the chip member; and (b) forming
ring seals surrounding regions of the front surface of the chip
member by introducing flowable material between the lid member and
the cap member from the top surface of the lid member through
openings in the lid member.
[0083] In a preferred aspect of such method, at least one of the
bottom surface of the lid member and the front surface of the chip
member has one or more wettable regions forming at least a portion
of one or more rings and one or more non-wettable regions enclosed
by the one or more rings, and the step of forming the ring seals
includes contacting the flowable material with the wettable
regions.
[0084] According to such aspect of the invention, preferably the
bottom surface of the lid member and the front surface of the chip
member have the wettable and non-wettable regions, and the
assembling step is performed so as to at least partially align the
wettable regions with one another.
[0085] The method preferably includes an additional step of forming
electrically conductive interconnections extending from the regions
of the chip member surrounded by the ring seals through the lid
member.
[0086] In a preferred embodiment, the flowable material is an
electrically conductive material and the step of forming conductive
interconnections includes forming the conductive interconnections
using the same electrically conductive material.
[0087] In a particular preferred aspect, the method includes
maintaining the lid member spaced above the chip member at least in
the regions during the step of forming the ring seals.
[0088] According to another aspect of the invention, a packaged
microelectronic device is provided, which includes: (a) a unit
having a chip with an upwardly-facing front surface and a
downwardly-facing rear surface, and a lid overlying at least a
portion of the front surface of the chip, the lid having a top
surface facing upwardly away from the chip and unit connections
exposed at the top surface of the lid. At least some of the unit
connections are electrically connected to the chip. The device
further includes (b) a package structure including structure
defining package terminals, of which at least some of the package
terminals are electrically connected to the chip, such that the
package structure, the unit or both define a downwardly-facing
bottom surface of the package, the terminals of the package
structure being exposed at the bottom surface.
[0089] According to a preferred aspect of the invention, the rear
surface of the chip defines a bottom plane and the package
terminals have exposed surfaces disposed at or below the bottom
plane.
[0090] Preferably, in one embodiment, at least some of the package
terminals are disposed beneath the unit. In a particular
embodiment, all of the package terminals are disposed beneath the
unit.
[0091] According to a particular aspect, the unit connections have
a unit connection pitch and the package terminals have a package
terminal pitch greater than the unit connection pitch.
[0092] In a particular embodiment, the unit connections have a
first layout in plan and the package terminals have a second layout
in plan different from the first layout.
[0093] In one embodiment, the unit includes vertical interconnect
structures extending from the chip to the unit connections, at
least some of the package terminals being electrically connected to
at least some of the vertical interconnect structures.
[0094] In a particular embodiment, at least some of the package
terminals are electrically connected to at least some of the unit
connections.
[0095] In one embodiment, the package structure includes an
interposer extending outwardly beyond the unit, and having a
downwardly-facing bottom surface, the terminals being exposed at
the bottom surface of the interposer.
[0096] According to a particular preferred aspect, the device may
further include traces on the interposer electrically connected to
the unit connections and the terminals.
[0097] In a particular embodiment, the device includes masses
including an electrically conductive bonding material, such as
solder balls, connected to the terminals and projecting downwardly
from the terminals.
[0098] According to one embodiment of the invention, the terminals
of the device include posts projecting downwardly from the
interposer. Preferably, such posts are integral with the
traces.
[0099] In a preferred aspect of the invention, the structure
includes a bottom dielectric element extending at or below the
bottom plane, and the package terminals are carried on the bottom
dielectric element.
[0100] In one embodiment, the structure further includes lead
portions connected to the unit connections and extending downwardly
from the unit connections to the bottom dielectric element.
[0101] In a particular embodiment, the structure includes a
dielectric element having a bottom run extending at or below the
bottom plane and having at least some of the package terminals
thereon. Such dielectric element has a fold portion extending
upwardly from the bottom run. Electrically conductive traces are
connected to at least some of the package terminals and extend
along the bottom run and the fold portion.
[0102] In one preferred aspect of the invention, the dielectric
element includes a top run extending from the fold portion over the
top face of the unit, and the traces extending along the top
run.
[0103] In a particular embodiment of the invention, the package
structure includes a lead frame, and the lead frame includes leads
which extend to or below the bottom plane and define the package
terminals. In such embodiment, the lead frame is preferably
resiliently engaged with the unit.
[0104] In a particular embodiment, the package structure includes a
vertically-extensive spacer and one or more conductive vias
extending through the spacer. In such embodiment, the spacer can be
such as to define a cavity and the unit is disposed within the
cavity. The spacer preferably includes a plurality of dielectric
layers superposed on one another, wherein the conductive vias
extend through the dielectric layers so as to form
vertically-extensive interconnects extending through the
spacer.
[0105] An assembly including a packaged device according to a
preferred aspect of the invention includes a mounting element
having contact pads thereon, and an electrically conductive bonding
material connecting the package terminals to the contact pads. In
such assembly, at least one of the package structure and the
bonding material provide mechanical compliance between the contact
pads and the unit.
[0106] According to another aspect of the invention, a
microelectronic unit is provided which includes: (a) a chip with an
upwardly-facing front surface and a downwardly-facing rear surface.
The chip has contacts exposed at the front surface and has bottom
unit connections exposed at the rear surface. The microelectronic
unit further includes (b) a lid overlying at least a portion of the
front surface of the chip. The lid has a top surface facing
upwardly away from the chip and top unit connections exposed at the
top surface of the lid. At least some of the bottom unit
connections of the chip are electrically connected to at least some
of the top unit connections.
[0107] According to a preferred aspect of the invention, the chip
includes vertically-extensive conductive elements which extend
through the chip and interconnect at least some of the bottom unit
connections with at least some of the contacts. The unit preferably
further includes vertical interconnect structures which extend
through the lid and connect at least some of the contacts with at
least some of the top unit connections. In such manner, at least
some of the bottom unit connections are electrically connected to
at least some of the top unit connections by the conductive
elements and the vertical interconnect structures.
[0108] In one embodiment according to this aspect of the invention,
the chip and the lid each define vertically-extensive edges, and
the unit includes traces which extend along at least one of the
edges. At least some of the top and bottom unit connections are
interconnected with one another by the traces.
[0109] In a particular embodiment, at least some of the traces
include trace portions which extend between the chip and the lid.
Preferably, the lid is sealed to the chip.
[0110] In one embodiment, at least a part of the bottom surface of
the lid is spaced from the front surface of the chip so that the
lid and the chip cooperatively define an interior space within the
unit. In such case, the chip preferably includes one or more
elements selected from the group consisting of
microelectromechanical elements, acoustically active elements and
optoelectronic elements.
[0111] According to another aspect of the invention, a
microelectronic chip is provided which has front and rear surfaces,
and an active element selected from the group consisting of
microelectromechanical elements, electroacoustical elements and
optoelectronic elements. In such aspect, the active element is
exposed at the front surface, and bottom contacts are exposed at
the rear surface.
[0112] A particular microelectronic unit according to a preferred
aspect of the invention includes a chip and a lid covering the
active element.
[0113] According to a particular preferred aspect of the invention,
an assembly is provided which includes a microelectronic unit and a
circuit panel having contact pads thereon, the unit being mounted
on the circuit panel with the front surface facing upwardly away
from the circuit panel and with the bottom contacts electrically
connected to the contact pads.
[0114] According to yet another aspect of the invention, a
microelectronic unit is provided, which includes (a) a chip having
an upwardly-facing front surface, a downwardly-facing rear surface
and one or more edges extending between the front and rear
surfaces. Such chip further includes (b) a lid overlying at least a
portion of the front surface of the chip, the lid having a top
surface facing upwardly away from the chip, a bottom surface facing
toward the chip and edges extending between the top and bottom
surfaces. The unit also includes (c) edge unit connections exposed
at one or more of the edges.
[0115] The microelectronic unit preferably includes vertical
interconnect structures which are electrically connected to the
chip and extend upwardly through the lid, of which at least some of
the vertical interconnect structures are exposed at the one or more
of the edges of the lid so that the exposed vertical interconnect
structures define the edge unit connections.
[0116] In a preferred embodiment, the lid is sealed to the
chip.
[0117] In one embodiment, at least a part of the bottom surface of
the lid is spaced from the front surface of the chip so that the
lid and the chip cooperatively define an interior space within the
unit. In such case, the chip may include one or more elements
selected from the group consisting of microelectromechanical
elements, acoustically active elements and optoelectronic
elements.
[0118] According to another aspect of the invention, a method is
provided for making a microelectronic unit. Such method includes:
(a) assembling a lid element with a wafer element including a
plurality of chips so that a bottom surface of the lid element
faces toward a front surface of the wafer element bearing contacts
electrically connected to the chips. Such method further includes
(b) providing vertical interconnect structures extending from the
contacts upwardly through the lid element; and (c) severing the lid
element and the wafer element along lines of severance so as to
form individual units. At least some of the lines of severance
extend through at least some of the vertical interconnect
structures so that the at least some of the vertical interconnect
structures are exposed at edges of at least some of the units.
[0119] According to yet another aspect of the invention, a method
is provided for making a microelectronic unit. Such method
includes: assembling a lid element with a wafer element including a
plurality of chips so that a bottom surface of the lid element
faces toward a front surface of the wafer element bearing contacts
electrically connected to the chips. Vertical interconnect
structures are provided which extend from the contacts upwardly
through the lid element. Vertically-extensive vias are provided
which extend at least partially through the lid element.
Electrically conductive material in the vias is electrically
connected to the vertical interconnect structures. Such method
further includes severing the lid element and the wafer element
along lines of severance so as to form individual units, wherein at
least some of the lines of severance extend through at least some
of the vias so that the conductive material in at least some of the
vias is exposed at edges of at least some of the units.
[0120] According to another aspect of the invention, a method of
making sealed microelectronic units is provided which includes
providing a wafer element including a plurality of chips, wherein
the chips of the wafer element includes device areas at the front
surface. The method further includes aligning a lid element to the
wafer element so that a bottom surface of the cap member faces
toward a front surface of the wafer element. The lid element is
bonded to the wafer element to provide a lidded wafer element. The
lidded wafer element is then partially severed along lines of
severance to at least partially define edges of individual
microelectronic units. Thereafter, edges of the microelectronic
units are sealed with an impermeable medium. The lidded element can
thereafter be severed into the individual microelectronic
units.
[0121] According to a preferred aspect of the invention, the chips
of the wafer element include bond pads at the front surface and the
impermeable medium is electrically conductive. In such aspect, the
method further includes forming metallic interconnects extending
from the bond pads to the top surface of the lid element. Lands are
formed on the top surface in conductive communication with the
metallic interconnects, the lands having at least portions
including the impermeable medium, the portions being formed when
the edges are sealed.
[0122] According a highly preferred aspect of the invention, the
lands are preferably formed and the edges are sealed by forming a
patterned photoresist layer over the top surface and the partially
defined edges of the lidded wafer element. In such aspect, the
impermeable medium is deposited to overlie the lidded wafer element
and to overlie the patterned photoresist layer over the lidded
wafer element. The patterned photoresist layer is thereafter
removed, such that the deposited impermeable medium remains only
where the impermeable medium does not overlie the patterned
photoresist layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0123] FIGS. 1-3D are views illustrating a method of forming a
capped chip according to an embodiment of the invention.
[0124] FIGS. 3E-3F are a sectional view and a plan view
illustrating a capped chip according to another embodiment of the
invention.
[0125] FIGS. 3G-3H are sectional views illustrating a method of
forming a capped chip according to the embodiment shown in FIGS.
3E-3F.
[0126] FIGS. 3I-3N are sectional views illustrating a method of
forming capped chip according to a variation of the embodiment
shown in FIGS. 3G-3H.
[0127] FIGS. 3O-3R are sectional views illustrating capped chips
according to still other embodiments of the invention.
[0128] FIGS. 3S-3V are views illustrating a method of severing
capped chips according to another embodiment of the invention.
[0129] FIGS. 4A and 4B are a sectional view and a plan view
corresponding thereto, illustrating a particular embodiment of the
invention in which a redistribution wiring trace is provided.
[0130] FIGS. 4C and 4D are views illustrating a capped chip on
which redistribution traces are provided on an underside of the
cap, according to an embodiment of the invention.
[0131] FIG. 4E is a plan view illustrating a layout of a chip
having bond pads disposed along both vertical and horizontal edges
of the chip.
[0132] FIG. 4F is a plan view illustrating a layout of a chip which
is advantageously packaged according to an embodiment of the
invention, the chip having bond pads disposed along only vertical
edges or only horizontal edges.
[0133] FIG. 5 is a sectional view illustrating a particular
embodiment in which a bonding layer of a chip is formed through a
cap, after mounting the cap to the chip.
[0134] FIGS. 6A-6B are sectional views illustrating a method of
forming capped chips having electrical interconnects which include
stud bumps.
[0135] FIGS. 7A-7B are a sectional view and a plan view,
respectively, illustrating an embodiment of a capped chip having
redistribution wiring traces on the cap.
[0136] FIGS. 7C-7E are sectional views illustrating embodiments of
the invention in which conductive interconnects are provided in
form of wire-bonds.
[0137] FIGS. 8A-11B are sectional views illustrating various
methods of mounting a unit including a capped chip to a circuit
panel.
[0138] FIGS. 12-17 are sectional views illustrating stages in a
method of patterning and using a sacrificial coating on a cap
element to provide a capped chip.
[0139] FIGS. 18-23 are sectional views illustrating stages in a
method of making capped chips in which conductive features of the
chips assist in self-locating the cap element.
[0140] FIGS. 24-26 are sectional views illustrating a variation of
the embodiment shown in FIGS. 18-23 in which the conductive
features include conductive spheres having solid cores.
[0141] FIGS. 27-32 are sectional views illustrating embodiments of
capped chips in which electrical interconnects are formed which
include stud bumps extending from the chip into through holes in
the cap.
[0142] FIGS. 33 and 34A are plan views illustrating a plurality of
chips, and a cap, respectively, from which microelectronic units
are fabricated, according to an embodiment of the invention.
[0143] FIG. 34B is a sectional view of microelectronic units
fabricated from the chips and the cap illustrated in FIGS.
33-34A.
[0144] FIG. 35 is a plan view illustrating a plurality of caps of a
cap element from which microelectronic units are fabricated,
according to one embodiment of the invention.
[0145] FIGS. 36A-B are a plan view and a sectional view,
respectively, illustrating a plurality of caps of a cap element
from which microelectronic units are fabricated, according to one
embodiment of the invention.
[0146] FIG. 37-43 are sectional views illustrating various
embodiments of microelectronic units having lidded or capped chips,
and assemblies including such units, according to various
embodiments of the invention.
[0147] FIGS. 44-49B are sectional views illustrating methods of
fabricating microelectronic units having lidded or capped chips,
which have edge connections, and methods of mounting the units to
circuit panels or other elements.
[0148] FIGS. 50-56 include sectional and elevational views
illustrating various embodiments of microelectronic units having
bottom unit connections and methods of making such units.
[0149] FIGS. 57-60 are sectional views illustrating stages in
fabrication of microelectronic units in which an impermeable medium
is used to seal the units.
[0150] FIG. 61 is a sectional view illustrating an alternative
embodiment of that shown in FIG. 60, in which the impermeable
medium is conductive and is patterned to form conductive
traces.
DETAILED DESCRIPTION
[0151] FIGS. 1-3D illustrate a capped chip and stages in a method
for fabricating a capped chip according to an embodiment of the
invention. In particular, FIG. 3C is a sectional view illustrating
a capped chip 200 and FIG. 3D is a plan view illustrating the
interconnects and the seal provided on the surface of a chip
included in the capped chip.
[0152] Particular types of devices, such as SAW devices and MEMs
need to be sealed hermetically in order to function appropriately
over the life of the device. For many silicon semiconductor
devices, a package is considered to be hermitic if it has a leak
rate of helium below 1.times.10.sup.-8 Pa m.sup.3/sec. Other
devices such as electro-optical devices do not require hermeticity,
but nevertheless are best packaged under a protective lid, e.g.,
one that is optically transmissive, as a way of preventing
particles from reaching a surface of the electro-optic device.
[0153] In a method of forming the capped chips, a plurality of caps
102, e.g., as contained in a multiple cap-containing element 100 or
wafer, are simultaneously mounted to a plurality of chips, e.g., a
wafer containing the chips, and then the chips are severed to form
units 300, as best seen in FIG. 3C. In such method, as shown in
FIG. 1, the cap element 100 includes a plurality of caps 102,
joined at boundaries 101. The cap element 100 can be either rigid
or somewhat flexible, and a variety of materials are available for
its construction. In one embodiment, when the area of the cap
element 100 and the chips to be joined are fairly large, the cap
element 100 consists essentially of one or more materials or a
composition of materials which has a coefficient of thermal
expansion (hereinafter "CTE") similar to that of the chips that are
to be capped. For example, the cap element 100 may include or
consist of one or more materials such as ceramics, metals, glasses
and semiconductor materials. When the chips are provided on a
silicon wafer or other such semiconductor wafer having a relatively
low CTE, the cap element 100 can consist of a CTE-matched material
such as silicon or other semiconductor, aluminum, nickel alloys,
including those having especially low CTEs such as alloys of nickel
and iron and alloys of nickel and cobalt. Other CTE-matched metals
include molybdenum.
[0154] When the device region 208 includes a SAW device, the cap
element is desirably constructed of a material having a CTE which
is matched to that of the SAW device, When such SAW devices are
fabricated in lithium tantalate wafers, a preferred choice for the
cap element is aluminum, because aluminum has a CTE which is
similar to that of SAW devices, and a low modulus of elasticity,
and aluminum can be oxidized to form aluminum oxide, which is an
insulator, by processes such as "anodizing". In such manner,
insulating layers are formed on the top surface, bottom surface,
and through holes with which to isolate respective ones of the
subsequently formed electrical interconnects from each other.
[0155] As further shown in FIG. 1, the cap element 100 and each cap
102 thereof has a top surface 105 and a bottom surface 103. In one
embodiment as shown, the top and bottom surfaces define respective
planes. Through holes 104 are provided in the cap element 100, the
cap element 100 generally having one or more through holes per
chip. Through holes are provided by any technique suited for the
particular material or materials of which the cap element is made.
For example, when the cap element 100 is composed predominantly of
silicon, metal, ceramics and glasses, the through holes can be
provided by a subtractive process such as etching or drilling.
Alternatively, when the cap element 100 includes a polymer, the
through holes are more desirably provided through a molding
process. In the embodiment shown in FIG. 1, the cap element 100
consists predominantly of a dielectric or semiconductor material
such as a glass, ceramic or a silicon wafer. Typical etching
methods applied to wafers of such materials result in through holes
which are tapered as shown to grow smaller from one surface towards
the other surface, such that they have a substantially
frusto-conical shape. In this embodiment shown in FIG. 1, the
through holes are tapered to become smaller in a direction from the
top surface towards the bottom surface. In the embodiment shown in
FIG. 1, bonding layers, e.g., regions 106 which are wettable,
illustratively, by a fusible medium such as solder, tin, or a
eutectic composition, are provided on the sidewalls 107 of the
through holes 104. The tapered profile of the through holes
generally assists in permitting the wettable regions to be formed
on the sidewalls 107 of the through holes 104 by deposition.
Suitable bonding layers will vary with the material of the cap
element and the fusible material which is used to form the bond.
The particular fusible medium may affect the impedance
characteristics of the bond that is formed. For use with a fusible
medium such as a low-melting point tin-based solder and a
semiconductor, ceramic or glass cap element 100, one exemplary
bonding layer includes a 0.1 .mu.m thick layer of titanium
overlying the sidewalls of the through holes 104, an additional 0.1
.mu.m thick layer of platinum overlying the titanium layer, and a
0.1 .mu.m thick exposed layer of gold overlying the platinum
layer.
[0156] As shown in FIG. 2A, the cap element 100 is aligned to a
plurality of attached chips 202, such as contained in a wafer 201
or portion of a wafer and is sealed to the water by a sealing
medium 206. The sealing medium 206 includes, illustratively, an
adhesive, a glass, especially those which have a low-melting point,
a fusible material such as solder, or another material which forms
a diffusion bond to elements, e.g., the sealing medium may be such
as to form a bond to a bonding ring, as will be shown and described
below with reference to FIGS. 33-36B. The sealing material
preferably includes a material such as any one or more of the
following: a thermoplastic, an adhesive, and a low melting point
glass, which typically will bond the bottom surface 502 of the cap
directly to the front surface 601 of the chip, without requiring
intervening metallizations. Otherwise, bonding may be performed by
solder, eutectic composition or one or more metals capable of
forming a diffusion bond with a metallization provided on the front
surface 601 of the chip, e.g., a sealing ring 802, and a
corresponding metallization 804 provided therefor on the bottom
surface of the cap 500. When the sealing material has an attach
temperature that is coincident with the solder flow temperature,
the seal forms as the abutting bottom surface of the cap and the
front surface of the chip are drawn together by the decreasing
height of the solder.
[0157] The wafer 201 is also shown in plan view in FIG. 2B.
Illustratively, the wafer is one of many available types of wafers
which include at least a layer of semiconductor material, including
but not limited to silicon, alloys of silicon, other group IV
semiconductors, III-V semiconductors and II-VI semiconductors. Each
chip 202 includes a semiconductor device region 204 provided in the
semiconductor device layer, which contains, for example, one or
more active or passive devices formed integrally to the
semiconductor material of the chip. Examples of such device
include, but are not limited to a microelectronic or
micro-electromechanical device such as a SAW device, MEMS device,
VCO, etc., and an electro-optic device. When such device is
present, the bottom surface 103 is spaced from the front surface
216 of the chip 202 so as to define a gas-filled void or vacuum
void 214 between the cap element 100 and the chip 202. The device
region 204 of each chip 202 is conductively connected by wiring 210
to bond pads 208 disposed in a bond pad region at the front surface
216 of each chip. In some types of chips, the bond pads 208 include
solder-wettable regions which are exposed at the front surface. In
one embodiment, the device region 204 includes a SAW device, and
the sealing medium is disposed in an annular or ring-like pattern
in a way that surrounds the bond pads 208 and the device region 204
to hermetically seal each cap 102 to each chip 202.
[0158] FIGS. 3A-3C are further sectional views illustrating further
stages in which electrically conductive interconnects 303 are
formed which extend from the bond pads 208 of each chip 202 into
through holes 104. As shown in FIG. 3A, a mass, e.g. a ball of a
flowable conductive medium 302 is provided at the through hole 104
at the top surface 105 of the cap element 100. Illustratively, the
ball 302 includes a fusible conductive material such as, solder,
tin or a eutectic composition. The mass of fusible material 302 may
be placed on the cap element 100 so as to rest somewhat inside the
through hole 104, as shown. When the fusible material 302 is a
solder ball or ball of other fusible material, the balls can be
placed at or in the through holes of the cap element by placing and
aligning a screen containing holes over the cap element and
allowing the balls to drop through the holes of the screen into the
through holes 104 until one such ball rests in each through hole in
which a conductive interconnect is to be formed. Thereafter, as
shown in FIG. 3B, the fusible material of the balls is caused to
form bonds to the bond pads 208 of the chips 202 of the wafer. For
example, when the conductive material is a fusible material such as
solder, tin or eutectic composition, heat is applied to the balls
directly or by heating the cap element and the chip to a point that
causes the material to flow. As a result of this process, the
fusible material flows onto and wets the metallizations 106, and
flows onto and wets the bond pads 208 to form a bond to the bond
pads 208 of the chip 202. Another result of this process is that
the fusible conductive material 304 forms a unified solid
electrically conductive interconnect 303 which extends from the
bond pad 208 into the through hole to form a solid mass of the
fusible conductive material. The thus formed conductive mass
extends across the full width of the through hole to seal the
through hole and to thereby separate the void 214 underlying the
cap from the ambient medium which is present above the through
hole.
[0159] Thereafter, the assembly formed by the cap element 100 and
the wafer 201 is severed at dicing lanes defining their boundaries
101 into individual capped chips, one of which is shown in FIG.
3C.
[0160] The plan view of FIG. 3D illustrates features on the surface
of the chip 202 as completed, the features including the device
area 204 of the chip 202, the interconnects 303 which are joined to
bond pads of the chip, and the seal 206 which is disposed as an
annular or "ring" structure surrounding the bond pads and the
device area 204.
[0161] Note, with respect to the above processing, that various
stages of processing can optionally be performed in different
facilities, as the required cleanroom level, i.e., a level
specifying the maximum concentration of contaminating particles in
the air and on surfaces of the facility, varies during the stages
of processing. Moreover, some of the stages of processing are best
performed in facilities which are oriented to performing certain
steps of processing. In addition, in a preferred embodiment,
testing is performed as to intermediate results of processing to
eliminate product and materials from the process stream which are
determined to be defective at particular stages of processing.
[0162] Thus, with respect to the processes described in the
foregoing, a facility can fabricate cap elements, e.g. cap wafers
having dimensions sized to fit the chip-containing wafers to be
covered thereby. As an example, such cap elements are fabricated
from blank wafers, which can be either new or possibly wafers
recycled from previous processing. The cap elements are subjected
to processing to form the through holes, which are then tested to
assure conformance to standards of quality, e.g., placement,
location, alignment, pitch, depth, sidewall angle, etc., and any of
several other criteria for assuring quality. In either the same or
in another facility, when the through holes include wettable
regions, e.g., under bump metallizations ("UBM") on the sidewalls
thereof, processing is then performed to form the wettable regions.
Because of the techniques used, and the increased sizes of features
of the cap element, and tolerances therefor, these particular steps
can be performed in facilities which need not be geared to the
fabrication of semiconductor devices. However, such steps can be
performed in a semiconductor fabrication facility, if such is
desired. Again, at the conclusion of this processing, testing is
optionally performed to assure that the wettable regions of the cap
element meet quality standards.
[0163] Thereafter, the cap element and the chip-containing wafer
are joined together according to processing such as described above
with reference to FIG. 2A, such joining process preferably being
performed in a facility having a high cleanroom level. For example,
such process is desirably performed in a semiconductor fabrication
facility, such as the facility in which the chip wafer is made.
When the chips include optically active elements such as imaging
sensors, processing to complete the conductive interconnects 303
(FIG. 3B) of each cap element can be deferred until later
processing, if desired, since the primary concern is to mount the
cap element as a cover over the chip wafer to avoid dust
contamination. However, if the chip contains a SAW device, MEMs
device or other such device requiring hermetic packaging, it is
desirable to form the conductive interconnects 303 at this time as
well, to form a seal which protects the SAW device during
subsequent stages of processing. Again, some testing is then
desirably performed to assure that quality standards are met prior
to proceeding to subsequent stages of fabrication. Subsequent
processing to form the electrical interconnects, if not formed
already, and to provide any further sealing, if necessary, is then
performed. Such processing can be performed in another facility
other than the semiconductor fabrication facility, and at a
cleanroom level that is not required to be as high as that of a
semiconductor fabrication facility.
[0164] Similarly, subsequent processing to complete the packaging,
as by adding other elements, e.g., optical lenses, interposer
elements, thermally conductive elements and the like, and
processing to mount the packaged chip to a circuit panel, such as
the processes described below with reference to FIGS. 7C-11B, or
FIGS. 16-17, for example, need not be performed in the same
facility. Such subsequent processing can be performed in
environments which do not have the same cleanroom level as that in
which the cap element is mounted to the chip-containing wafer, that
step preferably being performed in the semiconductor fabrication
facility.
[0165] The mounting of a cap element to a chip wafer, as described
in the foregoing, is especially advantageous for the packaging of
certain types of chips, especially those including SAW devices,
MEMs devices, and optical devices, potentially resulting in
increased yields, due to the ability of such processing to be
performed efficiently in cleanroom environments of semiconductor
fabrication facilities, where sources of contamination are kept to
a minimum. In particular, it is especially desirable to protect
chips which include imaging sensors such as charge-coupled device
(CCD) arrays and the like from dust or other particle contamination
by attaching a cap or lid to the front surface of the chip, as
early in the packaging process as possible. Such imaging sensors
include an imaging device array of a chip, over which a layer
including an array of bubble-shaped microlenses is formed in
contact with the device array. The array of microlenses typically
includes one microlens per pixel unit of the device array, the
pixel unit having dimensions of a few microns on each side. In
addition, such microlenses are often made of a sticky material to
which dust tends to adhere after manufacture. Particles and dust,
if allowed to settle directly on an imaging sensor, can obscure a
portion of the pixel area of the imaging sensor, causing the image
captured by the sensor to exhibit a black spot or degraded
image.
[0166] However, owing to the shape of the microlenses and their
number, and the sticky nature of the material used to make them, it
is virtually impossible to remove dust or other particles that
settle on the surface of a typical imaging sensor having such
microlenses. Thus, any particles which settle on the imaging sensor
at any time after the microlens array is formed, such as during the
packaging process, render the imaging sensor defective, such that
it must be discarded. This provides an explanation why such imaging
sensor chips, when packaged according to conventional chip-on-board
techniques, exhibit a yield rate in the final packaged chips, which
is only 80% to 85% of the chips fabricated on each wafer.
[0167] On the other hand, particles and dust which settle on a
transparent cap or cover above the outer surface of the chip do not
obscure a portion of the image because the outer surface of the cap
lies outside of the focal plane of the device. At worst, particles
settling on the cover result in slightly decreased light intensity
striking a portion of the imaging sensor. The slightly decreased
light intensity rarely affects the quality of the image captured by
the imaging sensor. Moreover, as described herein, the caps or
covers can be mounted over the imaging sensors of the chips while
the chips remain attached in wafer form, i.e., before the wafer is
diced into individual chips. The mounting of the caps is preferably
performed in substantially the same level of cleanroom environment
as that used to fabricate the wafer, e.g., before the chip wafer
leaves the semiconductor fabrication facility. In such manner, dust
and particles are prevented from ever reaching the surface of
imaging sensors of the chips. Moreover, once the chips are
protected by such transparent caps, it becomes possible to clean
the top surfaces of the covers if particles such as dust reach
them. This is because the transparent caps can be made
substantially planar, unlike the topography of the bubble-shaped
microlenses of the imaging sensor, and are typically made of a
material such as glass, which is readily cleaned by a solvent.
Because the potential for direct dust contamination of the imaging
sensor is virtually eliminated once the transparent cap wafer is
mounted to the chip wafer, it is estimated that imaging sensor
chips which are provided with transparent covers early in the
packaging cycle have a yield rate of 97%-99%. In such case, the
defect rate becomes no longer primarily due to contamination of the
imaging sensors, but rather, for other reasons such as electrical
functionality.
[0168] Desirably, wafer-level testing is performed on the
chip-containing wafer 201 (FIG. 3B) prior to the cap element 100
being joined to the wafer 201 and the conductive interconnects 304
formed thereto. "Wafer-level testing" refers to such testing as is
generally performed on chips, prior to the chips being severed into
individual chips. More extensive testing, commonly referred to as
"chip-level testing," is typically performed only after the chip
has been severed from the wafer and packaged as an individual
chip.
[0169] Wafer-level testing typically tests for basic functionality,
such as for electrical continuity, and basic functional operation
of each chip. Such testing is desirably performed prior to
individually packaging each chip, in order to eliminate the costs
of packaging chips that are later determined to be defective. Thus,
it is desirable to perform steps to complete the packaging of chips
only with respect to chips which have passed initial wafer-level
testing, i.e., "known good dies." By completing the packaging only
as to "known good dies," unnecessary packaging operations and/or
rework of packaging operations are avoided.
[0170] Wafer-level testing generally takes much less time, perhaps
as much as 100 times smaller amount of time per chip tested than
chip-level testing. However, the cost per chip of wafer-level
testing performed by equipment capable of mechanically probing the
surface of the wafer can equal or exceed that of the cost of
chip-level testing, despite the greater amount of time per chip
needed to perform chip-level testing. The special equipment
required to precisely, mechanically probe the contacts on the wafer
surface is very expensive. For that reason, such special equipment
is typically also subject to resource constraints within the
manufacturing facility. Moreover, fewer contacts per chips are
capable of being simultaneously contacted by such equipment than is
generally the case for chip-level testing, for which chips are
generally placed in sockets for testing. Another factor that
affects the cost of wafer-level testing is that the special
equipment used to probe the contacts of the wafer is limited to
testing a single chip at a time, to at most a few chips at one
time.
[0171] On the other hand, chips that are processed into capped
chips in wafer form or lidded chips in wafer form, as described
herein, e.g., in FIGS. 1-3D, are capable of being tested at the
wafer level, with test equipment that is potentially less expensive
than the mechanical probing equipment described above, because
interconnects of the chips are disposed on the top surface of the
cap wafer and for that reason, are capable of being probed by
equipment similar to that used to perform chip-level testing. For
example, the top or outer surface of the cap wafer can be
mechanically contacted by a contact-bearing dielectric element of
test equipment, the contacts of the test equipment being held in
contact with the conductive interconnects of multiple chips of the
wafer, as by mechanical force. In such manner, testing is performed
through voltages and/or currents applied through the interconnects
303 of each capped chip 300 to a plurality of the chips which
remain attached in form of the wafer 201 (FIG. 3B). In that way, a
plurality of chips of each wafer are simultaneously tested and
determined to be good or defective, using equipment that can be
less expensive than the above-described test equipment, because the
need to mechanically probe the wafer surface directly is
eliminated. In a particular embodiment, a greater subset of tests
than is generally performed as "wafer-level testing" is performed
to the capped chips. This is possible because the wafer containing
the capped chips is able to be tested by test equipment that is
less expensive than the mechanical probing equipment discussed
above. In addition, the ability to test a greater number of the
chips at one time permits more testing to be performed per chip for
the same total amount of test time using the less expensive test
equipment. In a highly preferred embodiment, the capped chips are
tested in such equipment for all or nearly all of the same
functions ordinarily performed during chip-level testing, prior to
the chips being severed from the capped chip-containing wafer into
individual capped chips.
[0172] FIGS. 3E and 3F illustrate a variation of the
above-described embodiment, in which a sealing material is disposed
between the chip 202 and the cap 102 in such way that it separates
electrical interconnects 350 of the capped chip from adjacent
electrical interconnects.
[0173] FIGS. 3E and 3F are a sectional view of such capped chip and
a plan view corresponding thereto, through line 3F-3F. In this
embodiment, the capped chip 340 includes a sealing material 346
which surrounds the device area 204 of the chip 202, as in the
above embodiment, but also encompasses the area of the electrical
interconnects 250. Preferably, the sealing material is an
insulating material, for example, a nonconductive polymer, e.g.,
adhesive such as epoxy or other adhesive, a thermoplastic, a glass,
e.g., low-melting point glass, etc., such as described above, such
that the sealing material provides an isolating medium between
adjacent ones of the electrical interconnects.
[0174] As further shown in FIG. 3E, optionally, a seal ring layer
342 is disposed on the front surface of the chip 202, such that the
sealing material 346 adheres to the seal ring layer 342. The seal
ring layer presents a surface that is wettable by the sealing
material 346 such that the sealing material preferentially wets the
seal ring layer and forms a bond thereto. The capped chip
optionally includes a guard ring 348 which is used to prevent the
sealing material from flowing beyond the wettable seal ring layer
towards the device area 204 of the chip 202. The guard ring
presents a surface which is not wettable by the sealing material.
Certain materials present nonwettable surfaces to other materials.
For example, polytetrafluoroethylene (PTFE) presents a surface to
which most other materials will not adhere or wet. In one
embodiment, the guard ring 348 includes PTFE as a material at the
exposed surface thereof. A similar seal ring layer and guard ring
are optionally provided on the facing surface 103 of the cap.
[0175] Herein, while processes and accompanying figures are
generally described in relation to individual chips and individual
caps, unless otherwise noted, they shall also be understood to
apply to the simultaneous processing of multiple attached chips,
e.g., a wafer, and multiple attached caps of a cap element, e.g., a
cap wafer.
[0176] FIGS. 3G through 3H illustrate one option for fabricating
the capped chip shown in FIGS. 3E-3F. As in the above-described
embodiment, this embodiment is preferably practiced as a way of
simultaneously mounting a chip member including a plurality of
chips to a cap member including a plurality of caps, after which
the resulting joined article is severed to provide individual
capped chips. As shown in FIG. 3G, the insulative sealing material
346 is placed on the surface of the chip 202 or the cap 102. The
cap, having pre-formed through holes therein, is then juxtaposed
and aligned to the chip such that the sealing material 346 contacts
and wets respective areas of the cap 102 and the chip 202,
including the seal ring layer 342, but not wetting the guard ring
348. As a result, the sealing material flows onto and is disposed
on the contacts, e.g., the bond pads 208 of the chip 202.
[0177] Thereafter, as shown in FIG. 3H, a process is performed to
remove unwanted sealing material 346 which is disposed on the bond
pads 208. Such process is preferably tailored to the specific
sealing material that is used. For example, when the sealing
material is a glass, the process is preferably performed by
etching, which is preferably performed anisotropically, e.g., such
as by reactive ion etching, sputter etching, or other process which
includes removal of material primarily in the vertical direction.
However, in another embodiment, the etching process need not be
highly anisotropic. The etching process may even be a generally
isotropic process, if the relative thickness 352 of the sealing
material being removed is comparatively smaller than the dimensions
354 (FIG. 3F) between adjacent ones of the bond pads 208. In that
way, the removal of the sealing material 346 from on top of the
bond pads 208 does not result in areas wide enough for adjacent
electrical interconnects to contact each other. In a particular
embodiment, when the sealing material is an organic material, e.g.,
a polymer such as an adhesive or thermoplastic, the removal is
performed by a "plasma ashing" process, in which plasma etching
results in the polymer being converted to an ash-like substance,
leaving the surfaces of the bond pads 208 exposed. Thereafter, the
electrically conductive interconnects 350 are formed by a process
such as one of the above-described processes.
[0178] FIGS. 3I through 3N illustrate an alternative process for
making capped chips similar to those described above with reference
to FIGS. 3E through 3H. Referring to the completed capped chip as
shown in FIG. 3N, this embodiment differs from the embodiment
described therein, in that the sealing material 356 is a
self-fluxing underfill. A self-fluxing underfill is an insulative
material that is frequently used to fill a space between the front
surface of a chip and a packaging element to which it is mounted in
a flip-chip arrangement. Typically, a self-fluxing underfill
material is an epoxy-based material, which is viscous as applied at
a normal ambient temperature, or at a slightly elevated
temperature, but which hardens into a solid mass upon heating. The
self-fluxing aspect of the material relates to components of the
composition which cause it to function as a flux when articles are
soldered in its presence. Stated another way, the self-fluxing
underfill material carries away reaction products, e.g., oxidation
products from the soldering process that is performed in contact
with it. In a particular embodiment shown in FIG. 3N, the
self-fluxing underfill material is disposed in contact with a
sealing ring layer 342 and is prevented from contacting the device
area 204 of the chip by a guard ring. The sealing ring layer is
similar to the sealing ring layer and the guard ring described
above with reference to FIGS. 3E-3F. A Similar sealing ring layer
(not shown) and guard ring (not shown) may also be disposed on the
underside 103 (bottom side) of the cap member 100.
[0179] A process of forming capped chips using such self-fluxing
material will now be described, with reference to FIGS. 3I through
3N. An initial stage in fabricating a capped chip is illustrated in
FIG. 3I. In such stage, a cap member 100 including a plurality of
caps 102 is aligned to and disposed overlying a chip member 200
which includes a plurality of attached chips 202. For example, the
cap member 100 and the chip member 200 can be held together in a
fixture. Thereafter, as shown in FIG. 3K, the through vias of the
cap are loaded with a fusible conductive medium, e.g. solder, tin,
eutectic composition, or diffusion bondable medium, etc. In such
case, the fusible conductive medium may adhere to the walls 107 of
the through holes, the walls preferably presenting surfaces which
are wettable by the fusible conductive medium. Alternatively, the
walls are metallized to provide surfaces wettable by the fusible
medium, as described above. One method of applying the fusible
medium shown in FIG. 3J is by paste screening. Another method
includes application of molten solder to the cap 102 at the through
hole, for example. The result of this step is to provide a solder
mass held to the cap 102 at the through hole 358, such as through a
bond, adhesion, surface tension, etc. FIG. 3K illustrates an
alternative, in which the fusible medium is applied in form of a
ball such as a solder ball 304, in a manner such as that described
above with reference to FIG. 3A. Thereafter, the self-fluxing
underfill material is applied between the cap member 200 and the
chip member 100 to the space surrounding the device region 204 of
each chip, resulting in the structure as shown in FIGS. 3L and 3M.
The self-fluxing underfill material can be provided to the sealing
surfaces at the periphery of each chip of the chip member and each
cap of the cap member through capillary action. For example,
referring again to FIG. 2B, the filling process is conducted by
applying the sealing material onto the sealing surfaces of the
chips and the caps that are disposed along rectilinear dicing
channels, including the vertical dicing channels 211 of a chip
member such as a wafer, and also along horizontal dicing channels
213.
[0180] In a particular embodiment, if the above-described capillary
action is not sufficient to achieve adequate fill quality, the
process can be conducted as to a smaller number of attached chips
and caps, for which such filling method is adequate. For example,
in an embodiment, the cap member contains a one-cap wide strip of
chips and the chip member contains a one-chip wide strip of chips.
The underfill is applied to the interface between peripheral edges
of each chip and each cap on the strip, and the self-fluxing
material is then drawn onto the wettable sealing ring layers that
are disposed adjacent to the peripheral edges of each chip.
[0181] After the underfill is applied, the structure, as shown in
either of FIGS. 3L and 3M is heated, such that the fusible medium,
e.g., solder, flows down the walls of the through holes to wet,
contact and bond with the bond pads 208 of the chips 202, as shown
in FIG. 3N. During such heating step, the self-fluxing underfill
356 is displaced by the molten medium. The self-fluxing underfill
then preferably also provides flux to carry away oxides which may
occur due to the bonding process, such that a good conductive bond
is achieved between the resulting electrical interconnects 350, as
provided by the fusible medium 358, and the bond pads 208.
Thereafter, as in the embodiment described above with reference to
FIGS. 1-3D, the structure is severed into individual capped
chips.
[0182] In a variation of the above embodiment, the self-fluxing
underfill material is provided to at least one of the opposing
surfaces 103, 216 of the chip member and the cap member prior to
aligning and placing the cap member into a desired position
relative to the chip member.
[0183] In another embodiment as shown in FIG. 30, masses of fusible
conductive material are pre-bonded to wettable surfaces of the
through holes 104 of the cap 102, and the cap is then bonded by a
conductive adhesive 316 provided on bond pads 208 of the chip 202,
to form electrically conductive interconnects extending from the
bond pads 208 through the through holes to the top surface 105 of
the cap 102. Again, this process is preferably performed
simultaneously as to a plurality of attached chips, such as a
chip-containing wafer and a plurality of caps, such as a cap wafer,
and the joined structures then severed to form individual capped
chips. This process permits the cap wafer and the chip-containing
wafer to be joined at room temperature or at most, a minimally
elevated temperature, i.e., without requiring heating to a
temperature sufficient to cause the flowing of a fusible material
such as solder. Such process is advantageous, in order to avoid
problems of differential expansion between the chip-containing
wafer and the cap wafer, e.g., when the two wafers are not CTE
matched.
[0184] The masses of fusible material are provided, for example, by
screen printing a controlled amount of solder into each through
hole of the cap wafer. Alternatively, the masses of fusible
material can be provided by contacting a cap wafer having tapered
through holes wettable by solder with a bath of solder, such that
the solder is drawn onto the wettable surfaces of the through
holes, to fill the through holes with the solder. The through holes
are preferably tapered, either in the manner shown, i.e., growing
smaller from the top surface 105 towards the bottom surface 103, or
alternatively, growing smaller from the bottom surface towards the
top surface. In another alternative, the through holes are tapered
from both the top and bottom sides, growing smaller towards a
middle of the thickness of the through holes 104. The application
of the solder results in the mass 314 of solder having a protrusion
315 extending beyond the bottom surface 103 of the cap. The
protrusion 315 can be a natural consequence of applying the solder
in liquid, e.g., as a solder paste, or in a molten state. In either
case, due to surface tension, a sessile drop forms which causes the
protrusion 315 to appear. The protrusion 315 provides a surface
which displaces some amount of the conductive adhesive upon
bringing the cap together with the chip, such that the solder mass
314 fully contacts the conductive adhesive 316. The conductive
adhesive is preferably an anisotropically conductive adhesive,
which conducts in a vertical direction by way of conductive
elements in the adhesive that are pressed into contact with the
solder mass 314 and the bond pad 208. As also described and shown
below with reference to FIG. 10B, an anisotropically conductive
adhesive does not conduct in a lateral direction 317 due to lateral
spacing between the conductive elements of the adhesive.
[0185] In a variation of this embodiment, as shown in FIG. 3P, a
viscous, nonconductive adhesive 318 is applied to the vicinity of
the bond pad used. In this case, the protrusion 315 of the
pre-formed solder mass 314 displaces the nonconductive adhesive so
as to contact the upper surface of the bond pad. The nonconductive
adhesive functions to maintain the solder mass 314 in contact with
the bond pad 208. Application of a slightly elevated temperature
may be performed to cure and/or shrink the nonconductive adhesive
318, so as to better maintain the contact between the protrusion
315 and the bond pad 208.
[0186] FIGS. 3Q an 3R illustrate further variations of this
embodiment, in which additional protruding features are added to
the cap wafer in each case, in registration with the through holes
104, such protruding features provided to assure the quality of
contact between the pre-formed conductive interconnect structures
provided in the cap wafer 102 and the bond pads of the chips 102.
Specifically, in FIG. 3Q, the protruding feature includes a stud
bump 324 which is applied to the cap wafer 102 at the location of
the through hole 104. In a particular embodiment, the solder mass
314 is planarized, e.g., by polishing, after which the stud bump
324 is applied to make the structure shown. Embodiments including
stud bumps are described in greater detail below throughout the
present application. In FIG. 3R, the solder mass 314 does not
completely fill the through hole. In such case, the protruding
feature 326, e.g., a stud bump fills the remaining space within the
through hole to project beyond the bottom surface 103 of the cap
102. Although FIGS. 3Q and 3R illustrate structures in which a
conductive adhesive is used, i.e., a preferably anisotropic
conductive adhesive, a nonconductive adhesive can be used instead,
in the manner as described with reference to FIG. 3P.
[0187] FIGS. 3S through 3V illustrate a particular embodiment of a
method by which a structure 360 including capped chips, in wafer
form, are severed into individual capped chips.
[0188] As noted above, a cap wafer and a chip-containing wafer need
not consist of the same or similar materials. For example, a
chip-containing wafer consisting essentially of silicon may be
joined to a cap wafer which consists essentially of glass. In such
case, a difficulty arises in the manner in which the structure
including the cap wafer, as joined to the chip-containing wafer,
can be severed into individual capped chips. Conventionally, a
silicon wafer can be cut by sawing using a 25 .mu.m wide blade,
which saws through the thickness of the wafer at a rate of 70 mm
per minute. On the other hand, a glass wafer, having an exemplary
thickness of 325 .mu.m, must be cut using a blade having a
thickness of 75 .mu.m, which also cuts at a comparable rate. The
blade optimized for cutting a silicon wafer will cause chipping if
used on the glass wafer. Conversely, a blade optimized for cutting
a glass wafer produces unsatisfactory results when used to cut a
silicon wafer.
[0189] In order to cut through a structure including both the
silicon wafer and the glass wafer, a poor compromise is presented.
A sawing process capable of cutting both silicon wafer and glass
wafer together operates at a rate of only 5 mm per minute, which is
unacceptable, given the thickness of the combined structure, which
is in the hundreds of microns. In addition, typically, dozens of
cuts are required to sever all chips of such wafers into individual
units.
[0190] FIG. 3S illustrates an improved method of severing the
structure 360 into individual units according to an embodiment of
the invention. In this embodiment, a sealing material 206 is
disposed between the chip-containing wafer and the cap wafer, the
sealing material 206 being such as that described above with
reference to FIG. 2A or in other above-described embodiments. The
cap wafer 100 and the chip-containing wafer 200 are spaced from
each other by a distance. In one embodiment, the distance is
controlled, for example, by features of the cap wafer or the chip
wafer which protrude beyond the opposing surfaces 216, 103 of the
cap wafer or the chip wafer, respectively, as described in greater
detail below with reference to FIG. 23. Alternatively, the sealing
material can include spacing elements, e.g., spheres, for
maintaining a minimum distance between the chip and the cap
wafer.
[0191] The structure 360 is sawed, first by a saw optimized for
cutting one of the wafers, and thereafter by a saw which is
optimized for cutting the other one of the wafers. For example, a
saw having a thick blade is used to produce the wide cut 362 first,
cutting through the glass cap wafer 100, as shown in FIG. 3S. Such
cut 362 may touch the sealing material 206, but does not cut
through the sealing material. This sawing operation is preferably
then repeated to make all of the cuts through the glass across
throughout the cap wafer. As stated above, this sawing operation,
being optimized to the glass, proceeds quickly for that reason.
Thereafter, a saw having a relatively narrow blade is applied to
make the narrower cut 364, as shown in FIG. 3S. In this case, the
blade and the sawing operation are optimized to cutting the silicon
wafer, Preferably, this cut is performed to cut all of the way
through the silicon wafer and through the remaining sealing
material. In such case, given the greater width of the cut 362 in
the glass wafer 100, the narrower cut 364 meets the wide cut 362 to
complete the severing of the chip. Beneficial results are provided,
in that the rate of sawing through each wafer separately is at
about one order of magnitude or more greater than the rate of
sawing through a combined structure 360 using a single saw. Thus,
the rate of severing the chips is at least several times faster,
for example, about 5 to 10 times faster, when the method according
to this embodiment is utilized, as compared to using one blade
capable of cutting through both wafers.
[0192] FIG. 3T illustrates an individual capped chip 300, diced
using this embodiment of the invention. As shown therein, the edges
of the chip 366 and the cap 368 of the capped chip unit 300, are
not perfectly aligned. This is a consequence of the two separate
sawing operations that are performed. Perfect alignment and
orientation of the separately performed sawing operations is
difficult, if not impossible, to achieve. FIGS. 3U and 3V are plan
views illustrating the capped chips, after sawing them into
individual units. Some displacement in one or more axes of the
dicing lines 370, 372 produced by the two sawing operations is
likely to occur, as shown in FIG. 3U. Angular displacement of one
sawing operation relative to another sawing operation, may also
cause angular displacement of the dicing lines 370, 372, as shown
in FIG. 3V.
[0193] FIGS. 4A and 4B are a sectional view and a top-down view,
respectively, illustrating a particular embodiment of a capped chip
430 in which the electrical interconnects 303 are conductively
connected by a trace 434 formed on the top surface of the cap 102,
such as for the purpose of redistributing an electrical connection.
In such embodiment, the trace 434 extends from a bonding layer 106
provided on the sidewall through a through hole at one electrical
interconnect 303a to a bonding layer 106 provided at another
electrical interconnect 303a. The trace 434 can be formed at a
separate time as the bonding layer 106 or simultaneously with the
bonding layer 106. As shown in FIG. 4A, a sealing medium 432 is
provided between the cap and the chip 202 in an area underlying the
through hole 436. When a fusible conductive material is placed in
through hole 436, as well as through hole 438 and heated, the
material forms a solid bonded connection to the bonding layer 107
and forms an electrically conductive connection between the bond
pad 208 and the electrical interconnect 303b. Note that during such
process, the fusible material does not flow from the through hole
436 onto the chip because of the seal medium 432 which blocks the
material from flowing lower than the bottom surface of the cap 102.
Alternatively, if the arrangement permits two bond pads of the chip
to be at the same potential, e.g., such as for the distribution of
power or ground connections, the chip may include a bond pad
underlying the through hole 436, and the sealing medium 432 not be
disposed under through hole 436, such that the electrical
interconnect 303b is also bonded to that bond pad.
[0194] FIGS. 4C-4D are a sectional view, and a plan view,
respectively, illustrating a variation of the capped chip structure
100 discussed above with reference to FIGS. 4A-4B. With reference
to both figures, in this structure, a redistribution trace 440,
which may function as a "fan-out" trace, is provided on the side
103 of the cap 102 which faces the chip 202, that is, the underside
of the cap, also referred to herein as the "bottom side" of the
cap. The redistribution traces can function as a "fan-out" trace
for the purpose of providing contacts on the cap which are disposed
farther apart and at more convenient locations for higher level
packaging than the locations of the bond pads of the chip. Such
arrangement permits the size of the chip to be made smaller, which
allows more cost-effective chip processing, because more chips are
fabricated at a time on a single wafer. The cap 102 is provided of
a material such as that described above, and is preferably mounted
to the chip as a plurality of attached caps in wafer form to a
plurality of attached chips of a chip-containing wafer, after which
the joined structure is severed into individual units.
[0195] With specific reference to FIG. 4C, the redistribution
traces 440 extend along the underside 103 of the cap from the
locations of interconnecting masses 442 of conductive material
which extends from the bottom side 103 to the top side 105 of the
cap 102 by way of through holes 104. The conductive material
forming the masses 442 is a flowable conductive material such as a
conductively loaded polymer, one or more metals or a fusible
conductive medium. Most preferably, the masses 442 are formed of a
fusible conductive medium such as solder, tin or eutectic
composition, and are formed in contact with a bonding layer 107
disposed on walls of the through holes. At the other end of the
conductive traces, protrusions 444, such as stud bumps, are
preferably provided. The protrusions 44 provide surfaces to which a
bonding medium such as a conductive adhesive 446 adheres to form an
electrically conductive path from the bond pads 208 of the chip 202
to the traces 440. Preferably, the adhesive is an anisotropic
conductive adhesive, such as that described above with reference to
FIGS. 30-3R. Alternatively, a nonconductive adhesive can be used in
place of the conductive adhesive 446, in a manner such as that
described above with reference to FIG. 3P. Alternatively, a fusible
conductive medium such as solder is used in place of the conductive
adhesive. In such case, a mass of fusible material such as solder
is preferably applied as a bump to the protrusion 444 or the
corresponding location of the trace 440, if the protrusion is not
present, before the cap wafer is bonded to the chip wafer. The cap
wafer and the chip wafer are then heated to cause the solder to
reflow, thus forming a solder mass bonding the two wafers in the
place where the conductive adhesive 446 is shown.
[0196] In one embodiment, the cap wafer is formed by patterning a
layer of metal on the cap wafer to form the redistribution traces
440, after which the through holes are formed by an etching process
or other removal process which is endpointed upon reaching the
redistribution traces 440. Bonding layers 107 are then formed on
walls of the through holes, as needed, and the through holes are
then are then filled with the conductive material, that material
preferably being a fusible conductive material such as solder.
[0197] FIG. 4E is a plan view illustrating an example of a chip 202
which would benefit upon redesign, through use of the
redistribution scheme illustrated in FIGS. 4C-4D. As shown in FIG.
4E, the chip 202 is rectangular, such that the chip has a long edge
242, and a short edge 244. The rectangular shape is used because of
the rectangular shape of a device area 204 of the chip, which may
be, or may not be required to be rectangular. For example, a
charge-coupled device (CCD) array is required to be rectangular for
capturing images. In such chip 202, interconnection wiring 246
carries signals from points 248 connected to the device area 204 to
bond pads 208 of the chip 202. However, the rectangular shape of
the chip is not optimum, because a greater number of chips having
the same amount of area could be fabricated on a single wafer, and
thus, be fabricated more cost-effectively, if the chips had square
shape. Moreover, it is more difficult to form interconnections to a
package including the chip by way of wire-bonding when the contacts
of the package are provided at positions which may vary in two
degrees of freedom. For example, as shown in FIG. 4E, the positions
of the bond pads 208 of the chip vary vertically along the short
edge 244 of the chip 202. Other positions of the bond pads vary
horizontally along the long edge 242. These positions of the bond
pads 208 of the chip are reflected in corresponding positions of
the contacts of a package (not shown), e.g., a capped chip which
includes the chip, which are also disposed at different vertical
positions along a short edge of the package, and at different
horizontal positions along a long edge of the package.
[0198] Faster, more effective, and/or higher quality wire bonding
can be achieved if the contacts of the package, and thus, the bond
pads 208 of the chip are disposed in lines which extend in either
horizontal or vertical directions, but not both. In such way, when
the wire-bonder forms a bond wire to each location, it is only
required to move between respective horizontal locations along each
line.
[0199] Accordingly, as illustrated in FIG. 4F, in an embodiment of
the invention, wiring 252 extends from the connection points 248 to
bond pads 254 which are disposed at different horizontal locations
along one of the horizontal (long) edges 242 of the chip 256.
[0200] The above-described embodiment, showing caps having
redistribution traces disposed on the underside of the caps, is
desirably employed with chips having a design such as that shown in
FIG. 4F, the caps providing any redistribution of signal way that
is made necessary by the different layout of the bond pads on the
chip.
[0201] The flowing on and bonding of a fusible conductive material
such as solder in the manner discussed in the foregoing with
reference to FIGS. 1-3N and 4A-4B applies to chips which have bond
pads that include exposed regions which are wettable by solder or
other fusible material. In some types of chips, particularly those
having aluminum bond pads, and some types of SAW device chips, the
bond pads are not wettable by solder or other such fusible
material, in the form that the chips are available when packaged.
Aluminum bond pads oxidize under ordinary atmospheric conditions to
form a surface layer of alumina which is generally not wettable by
a molten mass of solder. On the other hand, some types of wafers,
especially III-V compound semiconductor wafers, include bond pads
which are formed of or include an outer layer of gold. Here, a
different problem exists in that the gold of the bond pad is
subject to being dissolved by solder and other fusible materials,
which potentially destroys the bond pad to cause an open circuit
between the bond pad and the connecting trace.
[0202] One way that these concerns is addressed is to specifically
form a bonding layer on the bond pads 208 of the wafer prior to
joining the cap element to the wafer, the bonding layer being
wettable by solder (or other fusible material to be used). Such
bonding layer can be formed by a process such as that used for
forming an "under bump metallization" ("UBM") on a chip. However,
some types of chips, particularly SAW devices, are very sensitive
to contamination and can be degraded by processing used to form
bonding layers.
[0203] Accordingly, in an embodiment of the invention illustrated
in FIG. 5A, such concern is addressed by forming bonding layers on
bond pads of a chip or wafer after the cap element has been joined
to the wafer. As shown in FIG. 5A, in such embodiment, the joined
assembly of the wafer containing the chip 202 and the cap 102 is
placed in a chamber in which it is subjected to deposition of one
or more materials to form a bonding layer 540, e.g., a UBM on the
surface of the bond pad 208. A mask, e.g., a contact mask, may also
be positioned over the cap 202 such that only the through holes 104
are exposed during the deposition. Otherwise, the deposited
material can be removed from the top surface of the cap 202 after
the chip has been joined to the cap and the electrical
interconnects 303 have been formed. During such deposition, the cap
202 also functions as a shadow mask to prevent the deposition of
the UBM on the device region 204 of the chip 202.
[0204] As a result of the deposition, a bonding layer 106 may also
be simultaneously formed on the sidewalls 107 of the through holes
104. During such process, dielectric oxide present on the surface
of the bond pad 208 is removed.
[0205] A limiting factor of the embodiments described above with
respect to FIGS. 1-3D is that it requires the solder ball 302 (FIG.
3A) to melt during the reflow process in such way that the meniscus
(not shown) of the molten solder ball hangs low enough to touch the
UBM coated bond pad 208, and thereby establish a solder bond with
the bond pad 208. Whether or not the solder bond is established
depends on several factors, including the volume of the molten
solder ball, the size of the opening of the through hole 104 which
faces the chip, and the height 125 of the spacing between the chip
102 and the cap 101, requiring tolerances on the process to be
relatively tight. In addition, such process allows little freedom
to choose the height 125 of the spacing between the cap 102 and the
chip 202. Desirably, such height is determined by the functionality
sought to be obtained by placing the cap over the device area of
the chip, such as when the device area includes a SAW device or
MEMS device which requires a cavity.
[0206] The embodiment, shown in FIGS. 6A-6B addresses this concern.
In this embodiment, conductive stud bumps 662 are applied to the
bond pads 208 of the chip, which is best performed while the chip
is in wafer form. Thereafter, the cap element is aligned to the
wafer and sealed thereto. During the alignment step, the stud
bumps, particularly if they contain relatively thick shafts, can
assist in the process of properly aligning the cap element to the
wafer, as the stud bumps 662, when aligned, stick up at least
partially through the through holes 106. Stud bumps containing
certain metals may be applied directly to bond pads without first
applying a bonding layer such as a UBM, thus providing a further
alternative way of forming conductive interconnects to bond pads
which are not directly wettable by solder. For example stud bumps
consisting essentially of one or more of copper, nickel, silver,
platinum and gold can be applied this way. When wettable bonding
layers are provided on bond pads, stud bumps of solder or other
fusible conductive materials can be used.
[0207] A process such as that described above relative to FIGS.
3A-3B is then used to form electrical interconnects 663 which
include stud bumps and the fusible material so as to extend from
the bond pads 208 through the through holes 665. As in the
embodiments described above, a sealing medium 664 is provided
between the chip 202 and the cap 102. One problem with some sealing
media is that it is difficult to control the thickness T of the
sealing medium, and thus the thickness of the void 214 between the
chip and the cap, simply by controlling the amount of the sealing
medium or the amount of pressure applied to locations of the chip
after the sealing medium is applied.
[0208] This concern is addressed in the embodiment shown in FIG.
6A, in which each conductive stud bump 662 has a shoulder 666, on
which the bottom surface 103 of the cap 102 rests, so as to space
the bottom surface 103 a distance T from the front surface 216 of
the chip. As apparent from FIG. 6A, that distance T includes any
thickness T2 of the bond pad 208 which extends above the front
surface 216 of the chip, as well as the thickness of the lower
`ball` portion of the stud bump from the bond pad 208 to the
shoulder 666.
[0209] FIG. 7C illustrates a capped chip 748 according to another
embodiment of the invention, in which conductive interconnects are
provided which include bonding wires 752 which extend from bond
pads 208 of the chip 202 through openings 754 in the cap 102 to
contacts 750 disposed on the top surface 105 of the cap. The
openings 754 can be such as the through holes 104 described above
with respect to FIGS. 1-3D, for example, which are sized to
accommodate one interconnect per through hole, and to permit the
bonding of bonding wires 752 to respective bond pads of the chip.
Alternatively, the openings 754 can be bonding windows which are
sized and shaped, e.g., extending primarily in one linear direction
along the cap, so as to overlie a linearly extending row of bond
pads 208 of the chip, and permitting the formation of wire-bonds to
each of the bond pads 208 of that row through the opening. While
the peripheral edges of the capped chip 748 are sealed by a sealing
material 206, in a manner such as that described above with
reference to FIGS. 1-3D, an additional sealing material 756 is
deposited in contact with the openings 754 of the cap to seal the
openings after the bonding wires have been formed. Such sealing
material can include, for example, a polymer which hardens to form
a nonconductive region for insulating respective bonding wires from
each other, while also mechanically supporting the bonding wires.
In a particular embodiment, the sealing material 756 is an
encapsulant which is disposed as an insulating medium over the top
surface 105 of the cap generally, except for the area in which the
contacts 750 are located. Alternatively, another insulator such as
a glass, e.g., preferably a low-melting point glass, is disposed in
each through hole to insulate and support the bonding wire. In a
particular embodiment, in which the wire bonds extend through
individual through holes 104 which are aligned to the bond pads, a
mass of a flowable conductive material such as a conductively
loaded polymer or a fusible conductive material is disposed in each
opening 754 to seal the opening in place of a polymer. In such
manner, enlarged conductive interconnects 758 are formed at the top
surface 105 of the cap 102, the interconnects 758 extending across
each opening to seal each opening including the area of the
contacts 750. In such case, higher level assemblies can be made by
forming appropriate electrically conductive bonds to the thus
formed interconnects 758.
[0210] FIG. 7D illustrates a variation of the embodiment described
in FIG. 7C in which bonding wires 762 that are joined to the bond
pads 208 of the chip are not bonded to contacts on the cap.
Instead, the chip is bonded by bonding wires in a face-up
orientation to contacts 764 of a packaging element 760, e.g., any
of many types of dielectric elements and substrates which have
conductive traces thereon. Advances in the capability of wire
bonding machines now permit bonding wires to be formed which have
relatively complex profiles, and to be formed reliably and
repetitively. Thus, FIG. 7D illustrates an example in which the
bonding wire 762 is formed to extend directly between a bond pad of
the chip and a secondary packaging element, e.g., a dielectric
panel, or circuit board, which is farther away from the bond pad
208 than that shown and described above in FIG. 7C. In this
embodiment, the cap 102 is preferably an at least partially
optically transmissive element, that term denoting an element which
is either somewhat translucent or transparent to light in a range
of wavelengths of interest. More preferably, the cap 102 is
transparent, consisting essentially of a material such as a glass
or a polymer, which can be molded. In a particular embodiment, the
cap 102 is molded to contain an optical element, e.g., a lens, such
as the caps and optical elements described in commonly assigned,
co-pending U.S. patent application Ser. No. 10/928,839, filed Aug.
27, 2004, of which this application is a continuation-in-part.
[0211] In this embodiment, the formation of the bonding wires to
bond the chip to the packaging element 760 is done after the cap
102 is affixed to the chip 202 by the sealing material 206, and the
chip is mounted to the packaging element, such as by an adhesive
766, e.g., an adhesive commonly known as a "die attach" adhesive.
Alternatively, a thermal conductor can be mounted between the chip
202 and the cap 102 for conducting heat away from the chip and onto
a thermal conductor mount provided in the packaging element, such
as described in commonly assigned, co-pending U.S. patent
application Ser. No. 10/783,314 filed Feb. 20, 2004, the contents
of which are hereby incorporated by reference herein. In a
particular embodiment, the chip is bonded, in a "chip-on-board"
configuration) to a circuit panel, e.g., a printed circuit board or
flexible circuit panel, in place of the packaging element 760.
[0212] The above-described embodiment shown in FIG. 7D can be
especially advantageous for the packaging of chips which include
optically active elements, for example, image sensors. Such sensors
are especially vulnerable to dust or other particle contamination
which is most likely to occur after the chip has been fabricated.
Dust or other particles which settle directly on the imaging are of
the chip can obscure a portion of the pixels of the active imaging
area, thus rendering the chip unusable. The method provided in this
embodiment reduces the risk of such contamination by providing a
protective optically transmissive cover over the chip prior to
performing subsequent higher-level packaging operations.
[0213] In another embodiment, as illustrated in FIG. 7E, bonding
wires 774 extend from bond pads 208 of the chip to bonding shelves
772 of a gull-wing package 770. This packaged chip preferably
includes an optically active chip and an optically transmissive
cover 202, such as that described above with respect to FIG. 7D. An
additional package lid 776 is mounted to vertical members 778 of
the package, the package lid 776 desirably also being at least
partially optically transmissive, and preferably being
transparent.
[0214] In a particular embodiment, as shown in FIG. 7A, a unit 700
includes a conductive interconnect 703 which include a stud bump
662 and a conductive material 704 that seals the stud bump to the
cap 102. In this embodiment, the conductive material 704 is a
conductive organic material such as a conductive adhesive or
conductive sealant. A conductive organic material which is curable
at room temperature or a slightly elevated temperature is
advantageously used when the material of which the cap is formed is
not CTE matched to the chip. In such manner, conductive
interconnects 703 can be made to the unit 700 without inducing
strains in the chip or cap due to CTE mismatch.
[0215] As further shown in FIG. 7A, and in the plan view in FIG.
7B, the unit 700 may further include a plurality of such conductive
interconnects 703, which are connected by redistribution or fan-out
traces 706, to respective conductive contacts 708. In such manner,
signals coming off of the chip 202 are redistributed through the
conductive interconnects 703 and the traces 706 to the contacts 708
which lie at a farther distance away from the device region 710 and
closer to the edges 712 of the capped chip 700.
[0216] As shown in FIGS. 8A and 8B, once a unit 300 including a
capped chip has been formed, it may then be aligned to and surface
mounted to a printed circuit board (PCB) or other type of circuit
panel 802 to form an assembly 800. FIG. 8A shows the unit 300
having the fusible material 304 of the interconnect aligned to a
terminal, e.g., a land 808 of the circuit panel 802. FIG. 8B
illustrates the resulting assembly 800 after heating to cause the
fusible material to be bonded to the terminal 808 of the circuit
panel 802. While flux is generally utilized for the purpose of
joining materials in an oxygen-containing environment, the joining
process can be performed fluxlessly, under conditions which inhibit
contamination, i.e., by joining the unit 300 to the circuit panel
802 in the presence of a non-oxygen containing environment such as
nitrogen, argon, or a vacuum, for example.
[0217] In accordance with some surface mounting practices, extra
solder can be applied to the circuit panel prior to mounting the
unit to increase the volume of solder available to make the
connection. Such pre-forms of solder can be applied to the
terminals of the circuit panel with flux, if needed, prior to
mounting the unit. FIGS. 9A and 9B illustrate such technique. As
illustrated in FIG. 9A, due to the process used to make the capped
chip unit 300, the fusible material 916 provided on the bonding
layer 917 of the through hole of the unit 300 does not completely
fill the through hole, but leaves a void 921 in a portion of the
through hole above the circuit panel 802. By providing a pre-form
922 of additional solder or other fusible material on the terminal
920 of the circuit panel 802, sufficient solder is provided to
provide a reliable connection between the unit 300 and the circuit
panel. FIG. 9B illustrates the assembly 900 formed by the unit and
the circuit after heating to cause the solder contained in the
pre-form and in the through hole to melt and join, being drawn into
the through hole to form connection 924 to terminal 920. As a
result of the added solder from the pre-form, a bulked up solder
connection 924 is provided which is sufficient to establish a
connection to the terminal.
[0218] As an alternative to that described above, the solder
pre-form can be provided for use in hierarchically soldering the
unit to the circuit panel. Stated another way, the conductive
interconnects of the unit 300 can be formed using a solder or other
fusible material which melts at a higher temperature than the
solder used to join the unit 300 to the circuit panel, such that
the original higher temperature material does not melt and reflow
during the subsequent joining operation.
[0219] FIGS. 10A and 10B illustrate another method for joining the
unit 300 to a circuit panel to form an assembly 1000, in which a
conductive adhesive 1022 is used to conductively join the unit 300
to a land 1020 of the circuit panel 1019. FIG. 10A illustrates a
stage after which the unit 300 has been placed in alignment with
the circuit panel 1019, such that the solder 1016 in the through
hole is positioned over the land 1020. FIG. 10B illustrates a
subsequent stage after the unit has been pressed into contact with
the land 1020, causing the conductive adhesive to at least
substantially fill the through hole to form a connection 1018.
However, as also shown in FIG. 10B, a certain amount of the
conductive adhesive 1024 flows off the land 1020 onto other areas
of the circuit panel. For this reason, in order to avoid the making
of electrical connections in places where they are not desired, the
conductive adhesive is desirably an anisotropic conductive adhesive
1024, as shown in FIG. 10B. Such anisotropic conductive adhesive
contains discrete conductive particles 1026, such as conductive
spheres that are normally spaced from each other by a fluid medium
used to carry them. When pressed between two objects at a spacing
equal to the width of the sphere, the conductive spheres provide an
electrical connection between the two objects. However, due to the
lateral spacing between the conductive spheres, no substantial
electrical connection is provided in a lateral direction which runs
between the surfaces of the two objects.
[0220] FIG. 11A illustrates a variation of the embodiment shown
above in which the unit 300 includes a bonding layer 1124 which
extends from inside the through hole 1104 to have an extension 1126
extending on the mounting face 1107 of the unit 300. The extension
1126 is preferably provided as an annular ring surrounding the
through hole 1104. The extension 1126 provides additional surface
area for retaining solder 1116, prior to and after the unit 300 is
bonded to the circuit panel 1119. The extension 1126 and a larger
amount of solder adhering thereto on the unit 300, can mitigate
against having to provide additional solder on the terminal 1120 of
the circuit panel, as discussed above with respect to FIG. 10A.
[0221] FIG. 11B illustrates yet another variation in which unit 300
includes an extension 1128 of the bonding layer 1126 on the surface
1105 of the cap 1106 which faces the chip 1102. During the joining
process of the cap to the chip, the extension 1128 draws solder
from inside the through hole 1104 onto itself to bring it closer to
the bond pad 1114 of the chip 1102. This, in turn, assists in
forming the bond between the cap 1106 and the chip 1102.
[0222] FIGS. 12-17 illustrate a particular variation of the process
described above with respect to FIGS. 1-3D and 8A-8B, or one of the
alternatives shown in FIGS. 9A-11B for making a unit and joining it
to a circuit panel. A "lid", like the "cap" described in the
foregoing, refers to an article that is mounted as a cover over the
front surface of a chip.
[0223] Some types of chips, particularly chips which include an
electro-optic device, need to be packaged with a cap which is at
least partially optically transmissive. The term "optically
transmissive" is used to refer to a material that is either
optically transparent or optically translucent in a range of
wavelengths of interest, whether such wavelengths of interest are
in a visible, infrared or ultraviolet range of the spectrum. For
example, electro-optic imaging chips including charge-coupled
device ("CCD") arrays require a lid which includes an optically
transmissive package window, in order to prevent dust or other
particles from landing on the CCD array, which would optically
impair and obscure pixels of the CCD array. Such lid can also be
used to protect against damage due to corrosion by atmospheric
contaminants, particularly water vapor. The lid can be of any
suitable optically transmissive material, including but not limited
to glass, polymer and semiconductors. After the chip is joined to
the lid, a turret or train assembly containing a lens, and
optionally infrared (IR) and/or ultraviolet (UV) filters is joined
to the lid, e.g., as by welding, adhesive bonding or use of a
fusible material such as solder.
[0224] In this variation, a sacrificial coating is applied to a
surface of a lid prior to joining the lid to a chip, in order to
protect the lid against contamination. The sacrificial coating is
then removed later, after steps are performed to join the lid to
the chip to form a unit to join that unit to a circuit panel. As
above, while the process is described here in terms of joining a
lid to a chip, it should also be understood, with appropriate
modifications, to apply to the joining of a lid element containing
multiple attached lids to a wafer or other substrate which includes
multiple attached chips, after which the joined lid element and
wafer are severed along dicing lanes to form individually lidded
chips.
[0225] When a lid is joined to a chip by one of the above-described
processes, steps to bond the lid to the chip can introduce
contaminating material. Thereafter, steps to join the lidded chip
to a circuit panel can introduce further contaminating material.
Contamination can result from the environment in which the chip is
packaged or, from the nature of the process itself that is used to
perform the joining processes. For example, a joining process that
involves solder with flux can produce residual material that is
undesirable to leave on the surface of the cap. Other methods of
bonding a lidded chips
[0226] Accordingly, as shown in FIG. 12, a sacrificial coating 1252
is applied to the surface of an optically transmissive lid 1250.
The sacrificial coating 1252 is a material which can be applied and
remain through the steps of bonding the lid to the chip, but then
be removed to leave the surface of the lid in a clean condition
without degrading the condition of the joints of the assembly. In
the embodiment shown in FIG. 12, the sacrificial coating includes a
photosensitive resist film, suitable for use in subsequent
photolithographic patterning of the lid. Such resist film is best
chosen with regard to the etchant which will be used to pattern the
material of the lid, which can vary between inorganic materials
such as glasses and organic materials such as polymers. For
example, an etchant such as fluorosilicic acid is suitable for
patterning a lid which is formed of glass, especially lids which
are formed of a glass which has been doped to facilitate chemical
etching such as borosilicate glass. In such case, a spin-on
photoresist or hot roll laminate photoresist is suitable for use in
etching of glass. Such photoresists are also not degraded by
temperatures at which solders melt, nor by fluxes used in soldering
processes. However, such photoresists are also readily dissolved
and cleared from a surface through organic solvents.
[0227] FIG. 13 illustrates the patterned photoresist film 1252,
after it has been exposed and developed to produce openings 1254 in
the photoresist layer 1254. Thereafter, as shown in FIG. 14, the
lid is etched, using the patterned photoresist film as a mask to
produce through holes 1256.
[0228] Thereafter, as shown in FIG. 15, further steps are performed
to deposit bonding layers 1258 on the sidewalls 1260 of the through
holes. The bonding layers 1258 are provided for the purpose of
permitting a fusible material such as solder, tin, etc. to be
bonded to the through holes of the lid 1256, in a manner as
described above with respect to FIGS. 1-3D. During the deposition,
a contact mask may be placed over the photoresist film 1252 as
needed, to prevent the photoresist film from being sealed within
the bonding material, which might interfere with its later removal
depending on the type of resist. Such bonding layer is provided,
for example, by deposition including electroless plating or
electroless plating followed by electroplating. Alternatively, the
bonding layer is provided through vapor phase deposition, i.e., any
one of many deposition processes such as physical vapor deposition
(PVD), chemical vapor deposition and the like.
[0229] A subsequent stage of fabrication is shown in FIG. 16, after
the lid 1250 has been joined to a chip 1264 by a set of
electrically conductive interconnects 1262, and after the
interconnects of the lidded chip have been joined to a circuit
panel 1264. The circuit panel 1264 includes an opening 1266 or,
alternatively, a window consisting of an optically transmissive
material, disposed in alignment with the electro-optic device 1268
of the chip 1264 to provide an optically transmissive path to and
from the electro-optic device 1268. The circuit panel 1264 can be
of any type, being either rigid, semi-rigid, or flexible. In one
embodiment, the circuit panel 1264 is flexible and has a flexible
dielectric element on which conductive traces are disposed.
[0230] As also shown in FIG. 16, one result of the prior joining
processes is unwanted residual matter 1270, e.g., particles, flux
or adhesive residue, etc., that remains on the surface of the
photoresist film 1252. As illustrated in FIG. 17, the residual
matter is then removed in steps used to remove the photoresist
film, such as through washing of the assembled circuit panel and
the lidded chip in an organic solvent in which the film is soluble.
This results in an assembly 1272 in which the contaminating
material has been removed, and which is now ready for steps to
provide a higher order assembly. Thereafter, a turret, train or
other optical element, may be mounted above the opening 1266 in the
circuit panel 1264.
[0231] The process shown and described above can be modified in
several alternative ways. In one alternative process, the lid is
patterned by laser drilling rather than chemical etching. The laser
drilling is performed after the sacrificial coating is applied, at
which time material ejected from the drilled openings collects on
the sacrificial coating. Thereafter, the ejected material is
prevented from contaminating the lid when the sacrificial coating
is removed from the surface of the lid.
[0232] In another embodiment, the sacrificial coating need not be a
photoresist film and the coating need not patterned to provide a
mask for etching through holes in the lid. Rather, in such
embodiment, the sacrificial coating is provided on a face of the
lid, and thereafter, the lid is mounted to the chip, such as
through a sealing medium or fusible conductive medium as described
above. The lidded chip is then mounted to an additional element
such as a circuit panel, or alternatively, a turret, or `train`, as
described above. Thereafter, the sacrificial coating is removed,
removing with it residual matter remaining from the prior steps
used to mount the lid to the chip and the lidded chip to the
additional element.
[0233] In a particular form of such embodiment, the sacrificial
coating is one that is mechanically releasable from the surface of
the lid, such as by peeling. For example, such film can be provided
of an adhesively backed plastic, polymeric film capable of
withstanding the processes used to join the lid to the chip and
that which joins the combined unit to another element. For example,
materials such as those used in the adhesive of removable
self-stick notepaper and in food-wrap film appear suited for this
purpose. Alternatively, the peelable film can be a metal such as
molybdenum or other metal or other rigid or semi-rigid polymer.
[0234] A limiting factor of the embodiments described above with
respect to FIGS. 1-3D, for example, is that the lateral spacing
between adjacent through holes might not be optimal. Increasing
integration density of chips and corresponding decreases in the
spacing between adjacent bond pads of a chip demand that a cap to
be mounted to the chip have correspondingly decreased spacing
between interconnects. Referring to FIG. 3C, the through holes 104
of the cap 102 are shown tapered only from the top surface 105 of
the cap, such that a sidewall 107 (FIG. 1) is oriented at an angle
typically ranging from about 5 degrees to 70 degrees from the
vertical (the vertical being the direction which is normal to the
top surface 105). More preferably, the angle of the sidewall (FIG.
1) to the vertical is between 20 degrees to 60 degrees and, most
preferably at an angle between 30 degrees and 60 degrees, such that
the diameter of the through holes 104 varies between a smaller
diameter 330 at the bottom surface 103 and a larger diameter 335 at
the top surface 105. Typically, a wet chemical etching process
applied to the cap wafer 100 which consists essentially of silicon
results in the sidewall 107 making an angle to the vertical of
between 20 and 60 degrees. However, laser drilling is another
process used to form through holes in a cap wafer which is
provided, for example, of silicon, glass, ceramic or other similar
material, typically results in an angle of 7 degrees relative to
the normal. The angle that the sidewall makes with the top surface
105 is desirably made small, in order to reduce the amount of area
occupied by each interconnect, due to the increased pitch of
through holes that have a larger angle, as is described in more
detail below with reference to FIG. 18. The variation in diameters
between the through hole at the top surface 105 with respect to the
bottom surface 103 assists the fabrication method as a way of
initially holding the solder ball 302 (FIG. 3A) (which is larger
than the smaller diameter 330) in place inside the through hole
104. Depending upon the thickness of the cap 102, which,
illustratively, ranges between 100 and 300 .mu.m, and the smaller
diameter 330 of the through holes, which is typically on the order
of 70 to 100 .mu.m, the larger diameter 335 of the through holes
may range from twice as large to many times larger than the smaller
diameter 330.
[0235] When considered in terms of forming interconnects to closely
spaced bond pads 208 of a chip 202, it is seen that the larger
diameters 335 of the through holes at the top surface 305 of the
cap may well limit the spacing at which such interconnects 303 can
be made. This concept is best illustrated with respect to FIG. 18.
FIG. 18 illustrates three individual caps 400, 402 and 404,
respectively, in which through holes 410, 412, and 414,
respectively, have been patterned differently, and in which the
pitch between adjacent through holes varies significantly according
to the method used to pattern the caps. Thus, cap 400, having
through holes 410 which are tapered from only one surface, i.e.,
the top surface 405, has the largest pitch 407, because of the
large diameter 403 of the through holes 410 that exist at the top
surface 405. Through holes are ordinarily tapered from one surface
of the cap by isotropic etching from that one surface. On the other
hand, cap 402 has smaller pitch 409 because its through holes are
tapered from both the top surface 415 and the bottom surface 417 of
the cap 402, such that the profile of the through holes includes an
internal edge 413. Such taper is typically achieved by etching the
through holes 412 simultaneously and isotropically from both the
top and bottom surfaces of the cap 402. In some cases, depending
upon the degree to which the through hole is etched in a lateral
direction (being the direction parallel to the diameter 409) the
internal edge 413 can acquire the appearance of a "knife edge". Cap
404 illustrates a case in which through holes 414 are patterned
without tapering, having straight, vertical sidewalls. The pitch
419 of through holes 414 of the cap 404 is the smallest of the
pitches 407, 409, 419, because of the straight, vertical profile of
the through holes 414.
[0236] However, the profiles of the through holes of cap 402 and
cap 404 are such that they do not permit the same techniques to be
used as described above relative to FIGS. 1 through 3D when joining
the cap 402 or 404 to a chip. Solderable metallizations cannot be
easily provided on sidewalls of the through holes 412 of cap 404 by
the patterning processes described above, which are conventionally
used in conjunction with vapor phase deposition and wet
electro-chemical processes to make the tapered through holes as
described above relative to FIGS. 1 through 3D. These patterning
processes cannot be performed from just the top surface 415 or the
bottom surface 417 of the cap, because patterning will be achieved
only on surfaces that face up, i.e. only the surface of the through
hole above the internal edge 413 and upward, including the top
surface 415 of the cap 402. This precludes the portion of the
through hole below the internal edge 413, i.e., facing towards the
bottom surface 417 from being properly metallized. In the case of
cap 404, the vertical, straight profile of the sidewall 418 of the
through hole 414 makes it difficult to achieve a suitable
metallization. However, in the case of cap 402, the knife-edge
through hole profile can still be used to form a capped chip having
electrical interconnects which include stud bumps extending from
the bond pads, similar to that described above in relation to FIG.
6A. In such case, only the portion of the through hole 412 that is
tapered towards the top surface 415 need be metallized. This
requires the stud bump (662 in FIG. 6A) to protrude upwardly
through the through hole 412 past the knife-edge 413 in the cap
402. On the other hand, the necessity for the through hole 412 to
have a bonding layer 106 (FIG. 6A) on the sidewall thereof is
diminished if another flowable conductive medium such as an organic
medium is used in place of the solder.
[0237] FIGS. 19 through 22 illustrate stages in a method of joining
a cap to a chip according to one embodiment of the invention. FIG.
19 shows a cap 500 in an inverted position during fabrication, the
cap 500 having a bottom or inner surface 502, a top or outer
surface 504, and through holes 510. These designations of the
bottom (inner) and top (outer) surfaces refer to the orientation in
which the cap will be mounted to the chip, when steps to complete
the bonding of the cap to the chip are performed, as shown in FIGS.
21-22. In this embodiment, the through holes are preferably tapered
so as to become progressively smaller from the bottom surface
toward the top surface. As such, the tapered through holes are
substantially frusto-conical in shape. The tapering of the through
holes 510 is not absolutely necessary. Tapered through holes assist
in achieving some of the potential benefits available by the
joining process, as will be apparent from the description
below.
[0238] In this inverted position, solderable metallizations 515 are
formed on the sidewalls 520 of the through holes 510, as by
conventional vapor-phase or wet electro-chemical processing
directed towards the bottom surface of the cap 500, as described
above. In one embodiment, the solderable metallizations optionally
extend onto a portion 525 of the bottom surface of the cap 500
surrounding each through hole.
[0239] FIG. 20 illustrates processing performed to a chip 600 to
which cap 500 is to be mounted, the chip having solder-wettable
bond pads 606, a device region 602 and wiring 604 interconnecting
the device region 602 to the bond pads. A conductive ball 610 is
placed on each metallized bond pad, preferably by a fluxless
process, in order to avoid flux vapor and residue therefrom from
potentially contaminating features at the surface of the chip 600,
e.g. the device area 602. A process is then conducted to bond the
conductive ball 610 to the chip 600. In a preferred embodiment, the
conductive ball is a solder ball, consisting essentially of a
solder or other fusible conductive material, e.g., one or more of
tin, lead, or eutectic composition or layered arrangement of such
metals or other metals, which is adapted to generally soften or
liquefy upon being heated to a reflowing temperature, which is
relatively low. FIG. 20 illustrates the chip after a solder ball
610 has been placed on each bond pad 606 and bonded thereto by a
process which is characterizable as "reflowing". After reflowing,
the solder balls typically retain a shape that is essentially
spherical. The temperature of the solder balls is then lowered
again for the performance of a subsequent step in which the cap 500
is aligned to the chip 600.
[0240] FIG. 21 illustrates such further stage in the process. In
this stage, the chip 600 is placed such that the front surface 601
faces up. The cap 500 is turned over, such that the bottom surface
502 of the cap now faces down, toward the front surface 601 of the
chip 600. At this stage, the metallized substantially
frusto-conical through holes 510 of the cap 500 assist in aligning
the cap 500 to the chip 600 in a self-locating manner. This occurs
as follows. Rough alignment is achieved between the cap 500 and the
chip 600, such that any misalignment is less than the spacing
between the centerlines of the through holes. If the cap 500 is
then allowed to rest on the chip 600, the through holes 510 will
align themselves to the solder balls 610, causing the through holes
of the cap 500 to drop down onto the solder balls 610, thus
self-locating the through holes 510 to the solder balls 610.
Misalignment between the cap 500 and the chip 600 is subject to
variation in two horizontal degrees of freedom (X) and (Y), in
three rotational degrees of freedom: turning in the horizontal
plane (yaw), forward or backward tilt (pitch) and side-to-side tilt
(roll), and in a vertical degree of freedom, i.e. vertical
displacement (Z). The self-locating mechanism described herein
aligns the cap to the chip with respect to all of these degrees of
freedom at the time that the cap 500 is placed on the chip 600.
[0241] In the stage shown in FIG. 22, a process is conducted to
bond the conductive balls 610 to the metallizations provided in the
cap 500. When the conductive balls are solder balls 610, this is
preferably conducted as a reflowing process, which causes the
material of the solder balls 610 to be drawn further into the
through holes 510. As a result of this reflowing process, the
solder balls 610 preferably extend somewhat above the top surface
504 of the cap 500. As also shown in FIG. 22, the cap 500 is
desirably sealed to the chip 600 by a sealing material 810 which
surrounds the device region and the region which includes the bond
pads of the chip 600. The sealing material preferably includes a
material such as that described above with reference to FIG.
2A.
[0242] During such reflowing process, due to the fluid nature of
the solder balls 610, means preferably are provided for maintaining
a desirable vertical spacing between the opposed surfaces 502, 601
of the cap and the chip. In one embodiment, one or more spacer
elements are incorporated into the sealing material. For example,
an adhesive sealing material can include spherical or fibrous
elements which deform little, thus maintaining a predetermined
spacing between the opposed surfaces. In a particular embodiment, a
spacer structure is incorporated into one or the other of the cap
and the chip. For example, as shown in FIG. 23, a spacer may take
the form of a ridge 900 formed as part of the cap 500, the ridge
900 having a knife-edge 902, which is allowed to rest on the front
surface 601 of the chip 600. A sealing material 910, such as an
adhesive, can be disposed in contact with the ridge 900, as shown
in FIG. 23. Otherwise, the sealing material can be displaced from
the location of the ridge 900. The ridge 900 allows the cap 500 to
be pressed to the chip, e.g., pressure clamped, during the joining
process for any of the above-listed sealing materials, while the
ridge maintains a desired spacing between the cap 500 and the chip
600. When the above processing is performed simultaneously on an
array of attached chips and attached caps, the packaged chips are
thereafter diced, i.e., severed into individual packaged chips.
[0243] FIG. 24 illustrates a variation of the embodiment described
above, in which the metallization of the cap to provide a bonding
layer extends as an annular structure 1004 disposed on the bottom
surface 1002 of a cap 1000. In one embodiment, an annular structure
1004 is formed by deposition through widened openings of a masking
layer (not shown) on the cap through which material is deposited in
an additive process to form the metallization, in comparison to
those used to form the metallizations shown in FIG. 1.
Alternatively, the annular structure 1004 can be formed by
decreasing the size of mask patterns disposed between the annular
structures, when metallization patterns are formed by a subtractive
process following the formation of a metallization layer over the
cap. FIG. 25 illustrates a packaged chip 1150 showing a further
variation in which the conductive balls 1144 are of a type which
remain substantially rigid upon heating to a bonding temperature,
or have a core which remains substantially rigid. In such
embodiment, the conductive balls 1144 are used to maintain a
desirable vertical spacing between the cap 1000 and the chip 1142.
A solder bond or diffusion bond can be provided between a metal
disposed at an exterior of the conductive ball and the
metallization layer 1001 of the cap 1000 and also between such
metal and the metallization 1141 of the chip, for example. Joining
at this location may also be accomplished using an electrically
conductive organic material.
[0244] As further shown in FIG. 25, solder or other conductive
material 1145 is provided to fill the space between the conductive
ball and the top surface 1006 of the cap 1000. In a particular
embodiment, an additional seal 1130 can be provided over the
peripheral edges 1042, 1140 of the cap and the chip, respectively,
by depositing an additional sealing material. The additional seal
1130, which desirably also covers the already provided sealing
material 910, may be provided for the purpose of achieving
hermeticity, electrical isolation, or other such purpose. The
additional seal also preferably extends onto the top surface 1006
of the cap and the rear surface 1146 of the chip.
[0245] FIG. 26 illustrates a further embodiment in which the
packaged chip 1150 shown in FIG. 25 is mounted to a circuit panel
1202 having one or more terminals 1204 and traces 1206 disposed
thereon. The mounting shown in FIG. 26 is through a solder bond
between the solder or other conductive material 1145 present at the
top surface 1006 of the cap 1000 and masses 1205 of solder disposed
on the terminals 1204 of the circuit panel 1202.
[0246] With reference to FIG. 27, another embodiment of a method of
making a capped chip having vertical interconnects is shown in
which the through holes 1310 of a cap 1300 are not required to have
solderable metallizations prior to the cap 1300 being joined to the
chip 1302. FIG. 27 illustrates a case in which the through holes
1310 of the cap 1300 are tapered from both the top surface 1303 and
the bottom surface 1305, as described above with respect to FIG.
18. In this embodiment, the chip 1302 has stud bumps 1320 disposed
on bond pads 1330. The stud bumps 1320 provide a surface for
bonding of solder or other conductive material to form a vertical
interconnect extending upwardly from a chip 1302. As described in
relation to other embodiments above, a "picture frame" ring-seal
1340 seals the gap between the chip and the cap.
[0247] The stud bumps 1320 are desirably tapered, as shown in FIG.
27, as can be provided according to several processes known to
those skilled in the art. In this embodiment, the stud bump
desirably has a shaft diameter 1315 which is close to the mashed
ball diameter obtained during the application of the stud bump, and
a length 1325 that exceeds the thickness of a sealing material 1340
that seals the cap 1300 to the chip 1302. For example, the stud
bumps can be such as those shown and made according to the process
described in U.S. Patent Publication No. US 2003/0159276 A1,
published Aug. 28, 2003, the disclosure of which is hereby
incorporated herein by reference. Tapered stud bumps are more
capable of retaining their upwardly extending shape when the cap
1300 is placed over the chip 1302, such that the stud bumps 1320
are more likely to maintain registration with the through holes
1310, than if the stud bumps had a narrow, much more deformable
profile. As such, the stud bumps assist the cap 1300 in becoming
aligned to the chip 1302 in a self-locating manner, at least on a
side-to-side basis, i.e., in at least the X and Y degrees of
freedom. However, as shown in FIG. 27, when a through hole 1310a is
not in perfect alignment with a stud bump 1320a, the taper of the
through hole 1310a allows the stud bump 1320a to deform somewhat,
thus allowing it to at least enter the through hole 1310a.
Desirably, stud bumps 1320 protrude through the through hole to
extend above the top surface 1303 of the cap.
[0248] FIG. 28A illustrates a variation of the embodiment shown in
FIG. 27, in which the through holes have a straight, vertical
profile, rather than being tapered from both sides, as described
above with respect to FIG. 27. As shown in FIG. 28A, the top
surface 1403 of the cap is optionally provided with a solderable
metallization 1410. The solderable metallization is preferably
provided as an annular structure surrounding each through hole.
FIGS. 28A and 28B illustrate two stages of processing. In an
earlier stage of processing, shown in FIG. 28A, a solder ball 1420
is disposed on the metallization 1410, as placed thereon by a prior
solder ball stenciling process. A subsequent stage of processing,
shown in FIG. 28B, illustrates the reflowed solder ball 1430 as
joined to the stud bump 1320 by a subsequent reflowing process.
During such reflowing process, the solder ball 1430 is drawn onto
the surface of the stud bump 1320 by a solder-wettable metal
present at the surface of the stud bump such as gold, tin or
platinum. As a result, the solder forms a continuous solid
electrically conductive mass connecting the stud bump to the
bonding layer 1410 of the cap and sealing the cap at the through
hole 1430.
[0249] In a variation of the above process, the solder ball 1420 is
placed on the metallization 1410 of the cap 1400 and bonded thereto
to form a solder bump, prior to the through holes 1405 of the cap
being aligned to the stud bumps 1420 provided on a chip 1402.
[0250] FIG. 29A illustrates a further embodiment; in which external
interconnects above the cap 1500 are not soldered to the top
surface 1502 of the cap. In this case, a sealing material 1505 such
as an organic material which can either be conductive, or
nonconductive, e.g. an adhesive material, is applied to the cap
1500 to cover the through holes 1506 at the top surface 1502. After
the cap 1500 is placed over the chip 1501 and aligned thereto, the
cap 1500 and the chip 1501 are pressed together, causing the peaks
1510 of the stud bumps 1516 to penetrate through the sealing
material. In yet another alternative embodiment, the sealing
material 1505 can be deposited onto the top surface 1502 of the cap
1500 after the through holes 1506 have been aligned to the stud
bumps 1516 and then the sealing material is etched back, leaving
the peaks 1510 of the stud bumps substantially free of the sealing
material. In still another alternative, the sealing material 1502
may be applied around the circumference of the stud bump 1516.
Thereafter, further steps are taken to complete the
interconnections. For example, a solder ball 1530 can be bonded to
the stud bump 1516 to provide a surface to form a further
interconnection, such as to a circuit panel, e.g., such as shown
and described above relative to FIGS. 8A through 11B.
Alternatively, the stud bump can be contacted by a sliding or
deformable mechanical contact 1540, such as shown in FIG. 29B.
[0251] FIG. 30 illustrates yet another variation, in which the stud
bumps 1516, which may further include a solder or other joining
material applied thereto, are planarized to the top surface 1502 of
the cap 1500, after the cap 1500 is aligned and joined thereto. The
planarized surfaces of the stud bumps 1516 thus form a land grid
array for interconnection of the cap 1500 to further elements such
as a circuit panel (not shown).
[0252] FIGS. 31 and 32 illustrate yet another alternative
embodiment in which a cap 1602, is aligned to and placed over a
chip 1600 having a stud bump provided on bond pad 1604, and
thereafter deformed under pressure until the stud bump engages the
sidewall 1607 of the through hole 1606. In such way, the stud bump
is `coined` into engagement with the through hole 1606 in a metal
forming operation similar to riveting. In this embodiment, the cap
1602 need not have a solder-wettable metallization in the through
hole 1606 or on the top surface 1605 of the cap 1602 surrounding
the through hole. The stud bump is desirably provided of a highly
malleable metal such as gold or alloy thereof, which tends to
retain the same shape after being worked in a cold-pressed manner.
When such malleable metal is used, the resulting coined stud bump
may provide a seal of sufficient integrity to the through hole of
the cap. Alternatively, an additional fusible material such as
solder or tin can thereafter be deposited and reflowed to seal top
surface 1605 of the cap at the through hole, such as when
hermeticity is needed. When the stud bump is formed of gold, a
fusible material such as solder or tin forms a permanent solid
bond.
[0253] FIGS. 33-34B illustrate a particular method of
simultaneously forming peripheral "picture frame" ring seals
between multiple caps of a cap element, e.g., cap wafer, and
multiple chips, such as are still attached in wafer form. In this
method, the ring seal is formed by aligning the multiple cap
element above a wafer containing the chips and providing a flowable
sealing material through an opening in a top surface of the cap
element. The sealing material is then allowed or caused to flow
down onto the surface of the chips below, at which time the sealing
material then seals the individual chips to the caps of the cap
element. Thereafter, the cap element and the wafer joined thereto
are separated into individually capped chips by severing chips
along dicing lanes between each chip.
[0254] FIG. 33 is a top-down view illustrating a plurality of chips
1700 each having a device region 1702 provided thereon. Chips
having sensitive device regions require caps such as those
described above in relation to FIGS. 1-3D. Picture frame ring seals
1704 are provided in order to seal the chips to the caps,
preferably when the chips are still in wafer form, as one way of
protecting against the possibility of degradation to the devices
thereon. A method of simultaneously forming seals surrounding a
device region of the chips will now be described with reference to
FIGS. 34A-B.
[0255] FIG. 34A is a top-down view and FIG. 34B is a sectional view
illustrating the structure of a cap 1710, such as may be provided
as part of a multiple cap element used in this embodiment. The cap
1710 includes ring-like troughs 1712 which are shown overlying a
bonding layer 1714 provided on a front surface of a chip which is
disposed below the cap 1710. As shown in FIG. 34B, the troughs 1712
extend all the way through the cap 1710 from the top surface 1716
to the bottom surface 1718 of the cap, and is tapered to become
smaller in the direction from the top surface towards the bottom
surface. A bonding layer 1726, e.g., a solder-wettable
metallization, is provided on sidewalls of the trough 1712 as a
surface to which a fusible material such as solder wets and fuses
to provide a solid bond.
[0256] Referring to FIG. 34A, the troughs 1712 extend to almost
completely surround a central portion 1720 of the cap which
overlies a device region of the chip, the trough being connected to
the central portion 1720 by bridges 1722. In a method similar to
that described above for making interconnects with reference to
FIGS. 1-3D, a fusible material is provided in the trough and then
caused to flow along the sidewalls of the trough down onto the
bonding layer 1714 of the chip 1700, as best seen in FIG. 34B.
[0257] In an alternative embodiment, a low-melting point glass or
other suitable material may be placed and flowed downward through
the trough to make the seal, in a manner similar to a fusible
conductive material. In yet another alternative embodiment, a fluid
organic adhesive may be utilized as the sealing material instead of
a fusible conductive material.
[0258] FIG. 35 illustrates a variation of the above-described
embodiment in which a set of discrete through holes 1812 are
provided in caps 1810 of a cap element 1800, rather than a trough
as described above. As shown therein, the cap 1810 is disposed
overlying a chip having a central device region 1802, bond pads
1806 and wiring 1806 connecting the device region 1802 to the bond
pads 1806, as shown in dotted outline form. The chip includes a
bonding layer 1814 disposed in an annular pattern surrounding the
bond pads 1806 and device region 1802 of the chip. In this
embodiment, the discrete through holes 1812 facilitate the delivery
of a more precisely controlled amount of solder to the bonding
layer 1814 of the chip, by way of solder balls which are sized to
be placed at or within the through holes, in a manner such as
described above in relation to FIG. 3B. To achieve a good ring seal
between the chip and the cap, neither too little solder nor too
much solder should be provided to the bonding layer. Too little
solder can cause the seal between the chip and the cap to have
voids and possible gaps which would permit air or other fluids,
e.g., water vapor to reach the device region 1802 of the chip. On
the other hand, too much solder could cause the solder to spread
beyond the boundaries of the bonding layer to cause a short
circuit.
[0259] Accordingly, in this embodiment, solder balls are placed in
the through holes and heated to cause the fusible material to flow
laterally along the bonding layer 1814 of the chip and a
corresponding bonding layer (not shown) of the cap to form a seal
which at least substantially surrounds the bond pads 1804 and the
device region 1802 of the chip. By judicious choice of the
dimensions of the bonding layer and the size of the solder balls, a
precisely metered amount of solder can be distributed to the
bonding surfaces. The steps used to form the seal are similar to
those described above in relation to FIGS. 1-3D or 6A-B for forming
electrical interconnects through holes in a chip. Thus, in one
embodiment, the solder balls used to form the ring seal are placed
in the through holes 1812 at or near the time that solder balls
used to form the interconnects are placed in the through holes
overlying the bond pads 1802, and then all of the solder balls are
melted together by one heating operation to form the ring seal at
the same time as conductive interconnects are formed.
[0260] FIGS. 36A-B illustrate yet another alternative in which
fewer through holes 1912 are provided in caps 1902 of a multiple
cap element 1900. The through holes 1912 are also provided at
boundaries between respective chips, thereby greatly decreasing the
number of through holes 1912 necessary to form the seal of each
chip covered by the cap element. The bonding ring layer 1914 of
each chip is provided on the front surface along the periphery of
the chip 1902 so as to permit the flow of solder from within a
given through hole 1912 onto the bonding layer 1914 to seal the
respective chip, thus forming a structure as shown in the sectional
view of FIG. 36B. Note, that as illustrated in FIG. 36B, a bonding
ring layer 1920 is disposed on the bottom surface 1922 of the cap,
as a corresponding wettable metallization onto which the molten
solder spreads during the process of reflowing the solder from the
solder balls to form the seal. The bond pads 1802 and the
conductive interconnects 1924 joined thereto are desirably formed
simultaneously with the formation of the ring seal by placing the
solder balls in the through holes 1912 at or near the same time
that solder balls are placed in through holes 1932 used to form the
interconnects. Thereafter, a simultaneous heating step can be used
to form the electrical interconnects and the ring seal.
[0261] With reference to FIG. 37, a packaged microelectronic device
according to another embodiment of the invention incorporates a
package structure including a dielectric interposer 30 having
electrically conductive traces 32 extending along the bottom
surface 31 of the dielectric element. In the embodiment depicted in
FIG. 37, the dielectric element incorporates an aperture or window
36. Terminals in the form of electrically conductive posts 38
project downwardly from the bottom surface 31 of the dielectric
element, and are electrically connected to traces 32. A dielectric
element with posts thereon can be formed, for example, by
assembling a metallic sheet or plate having projecting posts
thereon with a dielectric layer, and etching the sheet or plate to
form the traces. The traces may be disposed on either the bottom
surface 31 or the top surface 33 of the dielectric element, or
within the dielectric element.
[0262] A unit 10 as discussed above is assembled with the package
structure so that the top surface 24 of the cover faces upwardly
toward the bottom surface 31 of the interposer 30. The unit
connections 18 are electrically connected to the traces 31, and
hence to terminals or posts 38. The active area 21 of the chip is
aligned with the window 36 in the interposer. For example, where
active area 21 is an optical detector or emitter, the active area
can accept or send light through window 36. In other embodiments,
as, for example, where the active area is a MEMS structure, window
36 may be omitted. The bottom surface 13 of the chip incorporated
in unit 10 faces downwardly, and defines a theoretical horizontal
bottom plane 40 at the level of such bottom surface. The height of
posts 38 desirably is greater than the thickness or vertical extent
of unit 10, so that posts 38 project downwardly beyond bottom plane
40. Thus, the unit connections 18, and hence the electrical
connections to chip 11, are effectively routed to a plane below
unit 10.
[0263] The package can be mounted on a circuit panel 50 having
contact pads 52 thereon, as, for example, by soldering the tips of
the posts 38 to the contact pads using conventional
surface-mounting soldering techniques. In the completed assembly,
unit 10 is positioned with its top surface (the top surface 24 of
lid 12) facing upwardly away from circuit panel 50. Because the
interposer 30 is larger in plan area than the package, this affords
the possibility of the metal posts having a diameter and pitch that
is suited for attachment of the structure to a PCB (printed circuit
board). Preferably, the interposer 30 or the posts 38 have some
degree of mechanical compliance, so that the structure is able to
accommodate differences in the height of individual pins or
nonplanarity of the circuit panel during assembly and/or testing.
The mechanical compliance desirably accommodates thermal expansion
mismatch between the circuit panel and the unit 10.
[0264] A packaged device according to a further embodiment of the
invention (FIG. 38) includes a unit 10 as discussed above, together
with a package structure including a dielectric element having a
bottom run 102 extending beneath the rear surface 13 of the chip
incorporated in the unit and hence extending beneath the bottom
plane 40 defined by the unit. The dielectric element further
includes a fold region 104 projecting upwardly from the bottom run
and a top run 106 extending from the fold region. The dielectric
element preferably is a flexible dielectric film having one or more
layers of electrically conductive traces 105 extending along the
film. The traces extend from the bottom run, along the fold region
to the top run. Unit 10 is disposed between the top run 106 and
bottom run 102 of the folded dielectric element. Bottom run 102 has
terminals 108 connected to traces 105. Terminals 108 are exposed
through holes 109 at the bottom surface 110 of the bottom run,
which defines the bottom surface of the packaged device. The unit
connections 18 of the unit 10 are bonded to traces 105 on the top
run 106, and hence are electrically connected to terminals 108. The
bond between the unit connections and the traces mechanically
secures unit 10 to the top run. Additional elements such as an
adhesive between the top surface of the unit and top run 106 may be
provided for further securement. Alternatively or additionally, the
bottom surface of the unit may be secured to the bottom run. An
encapsulant (not shown) may be provided in the space between the
runs of the dielectric element, around the unit. Folded package
elements for conventional semiconductor chips are described in U.S.
Pat. No. 6,225,688 and in commonly assigned U.S. patent application
Ser. No. 10/077,388, filed Feb. 15, 2002; Ser. No. 10/640,177,
filed Aug. 13, 2003; 60/515,313, filed Oct. 29, 2003; and Ser. No.
10/654,375, filed Sep. 3, 2003 the disclosures of which are hereby
incorporated by reference herein. Similar structures and techniques
can be used in the folded package for a chip and lid unit. Here
again, package terminals 108 may have a different layout in plan
than the unit connections 18, and the package terminals may have a
larger pitch than the unit connections. The packaged device may be
secured to a printed circuit panel as, for example, by
solder-bonding the terminals 108 to the contact pads of the circuit
panel. The terminals 108 may be arranged in a layout which
facilitates surface mounting, with adequate terminal size and
pitch. A wide range of dimensions and pitches may be used to suit
any desired application as, for example, to fit a standard pad
layout. Furthermore the package structure desirably provides
mechanical compliance such that it is able to safely absorb the
differential strain mismatch between the circuit panel and the unit
arising from the differential thermal expansion during manufacture
and during service. Here again, the unit can be mounted readily
with the top surface 24 of the unit facing upwardly away from the
circuit panel. A window 116 optionally may be provided in the top
run 106 of the dielectric element to permit reception of light or
other energy through the top run and through the lid of the unit.
As described in the aforementioned incorporated applications, a
folded package structure may also define top package terminals (not
shown) exposed at the upwardly-facing surface of top run 106. Some
or all of the top package terminals are connected to some or all of
the traces 105 and, hence, to some or all of the unit connections
18, to some or all of the bottom package terminals 108, or both.
The top package terminals can be used for testing or for attaching
a further microelectronic element as further discussed below, as
for example, to stack several packaged devices. The packages of
FIG. 37, discussed above, and of FIGS. 39 and 40 can also be
provided with top package terminals.
[0265] The packaged device of FIG. 39 is generally similar to that
discussed above in connection with FIG. 37, except that the package
terminals 138 exposed at the bottom surface 132 of the interposer
130 are in the form of flat pads rather than downwardly-projecting
posts. Thus, the terminals themselves do not project downwardly
beyond the bottom plane 40 of unit 10. In the embodiment of FIG.
39, additional elements in the form of masses 150 of a bonding
material such as, for example, conventional solder balls are
provided in contact with the terminals. These additional elements
or masses 105 project downwardly beyond the bottom plane. The
additional elements or masses 150 can be provided as part of the
packaged device, or may be added during assembly to a circuit panel
as, for example, by providing the masses on the contact pads of the
circuit panel prior to mounting the packaged device. The additional
elements or masses desirably have a height or vertical extent
greater than the thickness of unit 10. The additional elements or
masses 150 desirably provide substantial mechanical compliance.
Elements other than solder conventional solder spheres may be used.
For example, elements commonly referred to as solid-core solder
balls, having a core formed from a high-melting metal such as
copper covered by a layer of solder may be used. In a further
variant, the core of such a ball may be hollow or may include a
polymeric or other non-metallic material covered by a thin layer of
metal, which in turn may be covered by a solder. In yet another
variant, the additional elements or masses 150 may be masses of a
polymer-based conductive material as, for example, a metal-filled
solder. In yet another variant, the additional elements may be
provided as pins (not shown) projecting upwardly from the circuit
panel or as contacts on a socket which, in turn, is surface-mounted
to the circuit panel.
[0266] The interposer 130 may be rigid, in the case of a
direct-bonded copper (DBC) ceramic substrate, semi flexible, for
example a PCB, or fully flexible, as typified by a dielectric film.
The choice of material for the planar interposer will depend on the
application. For example, a flexible dielectric film will help
absorb thermal expansion mismatch between the PCB and the wafer
scale package, while a DBC substrate will be mechanically robust
and facilitate the removal of heat from the package. The planar
interposer is larger in plan area than the unit 10, and hence trace
132 routes unit connections 18 to a layout which is different from,
and larger than, the layout of the unit connections. Traces 132 may
be provided on either or both sides of interposer 130, or within
the thickness of the interposer. Where the terminals are disposed
above plane of the interposer bottom surface 132, the terminals are
exposed at the bottom surface of the interposer through holes (not
shown) extending partially or fully through the interposer. Here
again, the interposer may have an aperture in the region of the
unit to facilitate assembly of the structure or provide a
passageway for radiation between the unit and the environment.
[0267] In the embodiment of FIG. 40, the package structure includes
a planar interposer 230 similar to those used in the embodiments of
FIGS. 37 and 39, discussed above, and also includes a spacer 202
disposed beneath a peripheral region of the interposer, outside of
the area occupied by unit 10. The spacer projects downwardly from
the interposer, and downwardly beyond the bottom plane 40 defined
by unit 10. The bottom surface 204 of the spacer defines a part of
the bottom surface of the packaged device. Spacer 202 is formed
from a dielectric material, and has package terminals 206 disposed
on spacer bottom surface 204. Package terminals 206 are
electrically connected by vertical conductors 208 carried on spacer
202 to traces 232 on the interposer. Thus, the package terminals
206 are electrically connected to unit connections 18. For example,
spacer 202 may include one or more layers of a dielectric material
such as a ceramic or polymeric circuit board having through vias
formed therein and partially or completely filled by a conductive
material forming the vertical conductors 208. In this arrangement,
the package structure including interposer 230 and spacer 202
defines a cavity to accommodate unit 10.
[0268] In another arrangement (FIG. 41), the package structure
incorporates a lead frame having generally `S`-shaped leads 302.
Leads 302 have portions 304 overlying the top surface 24 of the
unit, these portions being connected to unit connections 18. The
leads 302 also have downwardly-extending portions 306, and terminal
portions 308. The terminal portions have exposed surfaces 310
forming the package terminals. These package terminals are disposed
below the bottom plane 40 of unit 10, and are exposed at the bottom
surface of the package defined by the bottom surface of the unit.
In the embodiment illustrated, the terminal portions project
outwardly in horizontal directions. The downwardly-extending
portions 306 also may slope outwardly. The package structure
optionally may include an overmold or encapsulant 320 surrounding
the leads and unit and further securing the leads in place. The
overmold or encapsulant 320 should not cover the surfaces 310 of
the terminal portions, so that these surfaces remain exposed for
mounting. The overmold may terminate at or above the bottom plane
40 of the unit, or may extend below the unit. In a further variant,
the downwardly-extending portions 306 of the leads can be attached
to the sides of unit 10 as, for example, by a dielectric adhesive,
where additional mechanical support is required. In the embodiment
depicted in FIG. 41, the lead portions 304 are shown as directly
connected to unit connections 18 so that these connections
physically attach the lead frame to the unit. However, the lead
portions 304 may be connected to the unit connections by
intermediate elements as, for example, by wire bonds. The
techniques commonly employed to join a lead frame with a chip may
be used to join the lead frame with unit 10.
[0269] In the embodiment of FIG. 41, the leads route and fan out
the electrical connections to or below the bottom plane of the
unit, provided the lead frame height exceeds the package thickness.
The lead frame can be made to possess a certain degree of
compliancy and thereby accommodate thermal expansion mismatch
between the wafer scale package and the circuit panel. Also, it is
possible to extend the lead frame in plan area to provide fan out
and achieve connection to the circuit panel at a coarser pitch than
the interconnects to the wafer scale package.
[0270] The embodiment depicted in FIG. 42 is generally similar to
the embodiment of FIG. 41, except that the terminal portions 428 of
the leads constituting lead frame 422 extend inwardly from the
downwardly-extending portions 426, so that the terminal portions
428, and hence the exposed portions 421 constituting the package
terminals, are disposed within the area occupied by unit 10. Thus,
the packaged device as a whole may occupy an area which is
approximately the same as, or only slightly larger than, that
occupied by unit 10. The leads of lead frame 422 may be resilient,
and may be held in place on unit 10 in whole or in part by
resilient engagement with the unit. The unit is resiliently engaged
between the terminal portions 428 and the top portions 424 of the
leads. Alternatively or additionally, the leads can be affixed by
solder, glass or an organic adhesive on any or all of the faces of
the package that they touch. A similar structure can be made using
a flexible tape with traces thereon wrapped around the edges of the
unit. A structure with a flexible tape wrapped around edges of a
chip is disclosed in certain embodiments of U.S. Pat. No.
5,347,159, the disclosure of which is incorporated by reference
herein. For applications where fan-out is required, the metal leads
or tape can be provided with extensions than protrude outside of
the plan area of the package. In a further variant, an overmold or
encapsulant (not shown) may cover the leads and the unit, but
desirably does not cover the exposed surfaces 421 of terminal
portions 428 of the leads. In a further variant, the terminal
portions 428, at the innermost extremities 423, may be free of the
overmold or encapsulant, to increase flexibility and hence
mechanical compliance of the leads. In yet another variant, whether
or not an overmold is employed, upwardly facing surfaces 424 on the
upper portions 424 of the leads may remain exposed, so as to
provide exposed package terminals at the top of the packaged device
as well as at the bottom. As explained further below with reference
to FIGS. 50-52, the terminals at the top of the packaged device can
be used as test terminals, or for the mounting of additional
microelectronic devices. An additional microelectronic device
mounted on the top package terminals may be connected to the unit
10, to the circuit panel upon which the bottom package terminals
428 are mounted, or both by leads 422. Packages of this type may be
mounted in a stacked arrangement, with the top terminals of one
device connected to the bottom package terminals of the next higher
device in the stack.
[0271] In the structure depicted in FIG. 43, the bottom surface of
13 unit 10 (defined by the rear surface of chip 11) is mechanically
attached to a planar interposer 530 by a mounting structure 502
which may include a layer of a die attach material. As discussed
above, a wide variety of materials can be used for the interposer.
Preferably, the interposer 530 is flexible and the mounting
structure 502 has appreciable mechanical compliance. For example,
mounting structure 502 may include a layer of a compliant material.
In this embodiment, the bottom surface 531 of interposer 530
defines the bottom surface of the packaged device. Terminals 538
are exposed at this bottom surface. Electrical connection between
the terminals 538 and the unit connections 18 on the top surface of
unit 10 are made by leads 506 which may be wire bonds, metallic
ribbons or the like. The connections between the unit connections
18 and terminals 538 may include other conductive elements such as
traces (not shown) extending along the interposer and vias
extending through the interposer. The connections, such as wire
bonds 506, desirably are flexible, so that terminals 538 remain
movable with respect to unit 10 as permitted by the compliance of
mounting structure 502. Interposer 530 can carry a relatively
compact array of terminals 538, at any desired pitch. Some or all
of these terminals may be disposed in the region of interposer 530
disposed below unit 10. Arrangements of this type can provide a
high density and space efficient interconnect to the circuit
panel.
[0272] As shown in FIGS. 44 and 45, units can be provided with
additional unit connections. In a process according to one
embodiment of the invention, a lid element 611 is united with a
unitary wafer element 620, such as an entire wafer or a portion of
a wafer, incorporating a plurality of semiconductor chips 622, so
that a bottom surface 612 of the lid element faces toward a front
surface 624 of the wafer element. A top surface 614 of the lid
element faces upwardly away from the wafer element. Vertical
interconnect structures 626 are formed so that the vertical
interconnect structures extend upwardly through lid 611 from
contacts 628 on the chip so as to provide unit connections exposed
at the top surface 614 of the lid element 611. As described in the
aforementioned commonly owned incorporated applications 60/506,600;
60/515,615; 60/532,341; and 60/568,041, the lid element may have
through vias lined with a thin layer 630 of a metal. The metallic
via liners 630 can be provided, for example, by depositing the
metal on the lid element and selectively etching the metal prior to
assembly with the wafer element. A solder or other electrically
conductive bonding material is provided on the lid element, on the
wafer element or both and reflowed so that the bonding material
wets the metal lining in the vias and wets contacts 628 on the
wafer element to form the vertical interconnect structures. In the
process of FIG. 44, the lid element is provided with additional
rows of vias 632 at locations corresponding to the boundaries
between chips in the wafer element. These additional vias may
extend partially through the lid or entirely through the lid
element as depicted in FIG. 44. Additional vias 632 are lined with
metal or other conductive material 634, and electrically conductive
redistribution traces 636 are provided on a surface of the lid so
that the traces interconnect the liners in some or all of the
additional vias 632 with the via liners 630 in some or all of the
other vias used to form the vertical interconnect structures. The
additional liners 634 and traces 636 may be formed during the same
process steps used to make the via liners 630. Thus, the conductive
liners 634 in the additional vias will be electrically connected to
at least some of the vertical interconnect structures 626 when the
vertical interconnect structures are formed. As described in the
co-pending applications, a sealant 640 is provided between the lid
element and the wafer element at boundaries between adjacent chips,
so that the sealant extends around the periphery of each chip.
[0273] After assembly of the lid element, wafer element and
sealant, and desirably after formation of the vertical interconnect
structures, the lid element, wafer element and sealant are severed
along lines of severance 642, also referred to as dicing lanes, one
of which is visible in FIG. 44. The severing step forms individual
units, each including one or more chips and a lid with vertical
interconnect elements extending through it. As best seen in the
elevational view of FIG. 45, each such unit has
vertically-extensive edge surfaces 649 extending between the top
surface 614 of the lid and the bottom surface 625 of the chip. The
severing process cuts the additional vias 632, leaving partial vias
exposed at the edge surfaces of the units. As shown in FIG. 45, an
elevational view showing one such edge surface 649, the conductive
liners 634 within the severed vias form edge connections exposed at
the edge surfaces of the units. At least some of these edge
connections are electrically connected to at least some of the
vertical interconnect structures 626 and hence to at least some of
the contacts 628 on the chip. Edge connections can be provided in
this manner on one, some or all of the edge surfaces of the unit.
In a variant of this process, the redistribution traces 636 may be
formed of the bottom surface 612 of the lid element, rather than on
the top surface of such element.
[0274] As seen in FIG. 46, the edge connections 634 may be bonded
to contact pads 650 of a circuit panel 652 or other substrate so
that the unit can be mounted with the top surface 614 and bottom
surface 625 of the unit extending transverse to the plane of the
substrate, and with an edge surface 649 bearing the edge
connections facing downwardly toward the substrate. Alternatively,
the unit can be mounted in a socket 656 (FIG. 47) with elements of
the socket such as resilient fingers 658 engaging the edge
connections 634 on the edge surfaces 649. The unit also can be
mounted as discussed above, with connections made through top unit
connections made by vertical interconnect structures 626.
[0275] The embodiment of FIGS. 48A-48B is generally similar to the
embodiment discussed above with reference to FIGS. 44-47. However,
in the embodiment of FIGS. 48 and 49, the sealant 740 extends
inwardly from the boundaries of the chips beyond at least some of
the vertical interconnect structures 726. The severance operation
is conducted so as to cut through these interconnect structures and
thus form these vertical interconnect structures 726 into edge
contacts 734 at edge surfaces 749. The inwardly-extending sealant
740 remains as a continuous seal between the chip and lid in each
unit. The severing operation depicted in FIG. 48A uses two cuts,
along two parallel lines of severance, at each boundary between
adjacent chips. In a variant, some or all of the contacts 728 and
the associated vertical interconnect structures 726 may lie at the
boundary between adjacent chips, so that a single cut will form a
single row of vertical interconnect structures into edge contacts
on two units. Some or all of the vertical interconnect structures
in each unit may be converted to edge contacts. A unit formed in
this manner can be mounted as discussed above with reference to
FIGS. 46 and 47. In a further variant (not shown) a unit having
unit connections on the top surface of the lid can be provided with
edge connections by affixing the edge connections onto the unit as,
for example, by adhesively bonding a dielectric carrier with
conductive connections thereon to the edge surfaces of the unit, or
by affixing discrete edge connection elements to the edge surfaces
of the unit. The affixed edge connections can be electrically
connected to the unit connections on the top surface of the lid by
any suitable connection technique. For example, if the dielectric
carrier is a flexible dielectric element with traces thereon, the
same can be folded over the edge of the lid so that portions of the
traces extend along the lid top surface to the unit connections.
Alternatively, the edge connections can be connected to the unit
connections by wire bonding.
[0276] A variation of the capped chip structure described above is
illustrated in FIGS. 49A-49B. FIG. 49A is a sectional view of the
capped chip structure 730 shown in FIG. 49B through line 49A-49A.
In such structure 730, the vertical interconnect structures 726,
some of which are disposed along peripheral edges 731 of the chip,
are oriented in a first direction, as shown in FIG. 49B. Some
others of the interconnect structures are disposed along other
peripheral edges 733 of the chip, which are oriented in a second
direction which lies at an angle to the first direction. For
example, the edges 733 are oriented at a right angle to the edges
731. In a preferred embodiment, some of the interconnect structures
726 are also disposed at corners 732 between the two edges.
Providing the interconnect structures along the peripheral edges
731, 733 of the chip, and/or the corners 732 may permit further
improvements to reduce the area of the wafer occupied by the chip,
because fewer interconnect structures 726 are needed, which
consequently occupy less of the chip area. In some cases, the
interconnect structures 726 are placed as far apart or farther from
the device area 204 of the chip, as they are in the embodiments
described above with reference to FIGS. 1-3D, for example. This
assists in the manufacturability of the structure and the ability
to interconnect the structure 730 in the next higher level
assembly. Interconnects that are spaced at intervals farther apart
assist in manufacturability of the higher level assembly, because
the tolerances for making such connections of the assembly are not
as tight as they tend to be when fabricating the chip.
Interconnection of the structure 730 to the higher level assembly,
e.g., a circuit panel, is preferably by way of mechanical
attachment, e.g., socketing, or electrical connection, such as
shown and described above with reference to FIGS. 44-47.
[0277] A unit 812 (FIG. 50) according to a further embodiment of
the invention incorporates a chip 820 which, like the chips
discussed above, has a front face 822 and a rear face 824. Chip 820
has contacts 826 exposed at the front face 822. Here again, the
chip has an active element 827 such as a microelectromechanical
element, an electroacoustic element such as a SAW element, or an
optoelectronic element such as an array of sensing pixels, the
active element being disposed at or adjacent to the front face 822.
However, in this embodiment, the chip has rear contacts 830 exposed
at the rear face of the chip. Some or all of the rear-face contacts
830 are electrically connected to the front-face contacts 826 and
to the circuit elements of the chip, including the active element
827. The electrical connections to the rear-face contacts 830
include electrically conductive structures extending partially or
completely through the thickness of the chip. These conductive
structures should not compromise the physical integrity of the
unit, and thus should not provide leakage paths extending between
the front and rear surfaces of the chip. These connections
typically are formed while the chip is being processed as a part of
a wafer. One method of forming conductive structures through the
thickness of semiconductor wafers is by ion implantation, or other
techniques, to create a highly doped column 844 of semiconductor
material in the chip that is sufficiently low resistivity for the
application. Alternatively, a hollow via or "pipe" 846 may be
carved through the thickness of the semiconductor, so that the pipe
extends from the rear face 824 to the contact 826 on the front
face. The pipe is sealed at the front surface by the metallic
material of the front-face contact. The walls of the pipe may be
made conductive by coating with a metal film 847. In a variant, the
pipe can be completely filled with metal (not shown).
[0278] A wafer element incorporating numerous chips 820 as shown in
FIG. 50 is assembled with a lid element including lids 860, one of
which is shown in FIG. 50, and with a sealant 862 at the boundaries
between adjacent chips in the wafer element, and provided with
vertical interconnect structures 864 extending from at least some
of the top face contacts 826 on the chip through lid 860 to form
top unit connections 866 exposed at the top surface 868 of the lid.
The units are severed from the wafer element, leaving the
individual units in the configuration depicted in FIG. 50. In this
configuration, the rear face contacts 830 of the chip form bottom
unit connections exposed on the bottom surface 824 of the chip,
which constitutes the bottom surface of the unit, whereas top unit
connections 866 are exposed at the top surface 868 of the lid,
which constitutes the top surface of the unit. At least some of the
top unit connections 866 are electrically connected to at least
some of the bottom unit connections 830, to the internal circuitry
of the chip or both. The unit provides continuous electrical paths
between at least some, and preferably all, of the top unit
connections 866 and at least some, and preferably all, of the
bottom unit connections 830.
[0279] The completed unit 812 can be directly mounted on a circuit
panel by bonding the bottom unit connections 830 to contact pads on
the circuit panel using techniques similar to those used in
flip-chip direct chip mounting. This leaves the unit in a face-up
orientation, with the lid and unit top surface 868 facing upwardly
away from the circuit panel. Alternatively, the unit 802 can be
packaged on an intermediate substrate or interposer 870 (FIG. 51)
with the top surface 868 facing away from the interposer, and then
the interposer be bonded to a circuit panel 880. The interposer has
package terminals 872 exposed at its bottom surface, and traces 874
electrically connecting the bottom unit connections 830 to the
terminals. The interposer typically provides redistribution so that
the terminals 872 are disposed at a larger pitch than the bottom
terminals 830. The interposer may also provide mechanical
compliance between the unit and the circuit panel 880. The
interposer may be generally similar to those used in manufacture of
chip-scale packages.
[0280] The top unit connections 866 can be used as test connections
to allow engagement of a test probe either before or after mounting
the unit to a circuit panel. The top unit connections provide probe
points advantageously situated on the top surface of the unit.
Moreover, the probing process will not damage the bottom unit
connections that will be connected to the circuit panel. An
additional microelectronic element may be connected to the top unit
connections 866 to form part of the circuit in the completed
assembly. The additional microelectronic element may be another
unit 812 of similar configuration, so that the units are stacked
vertically as shown in FIG. 52. Top unit connections 866 of one
unit are connected to the bottom unit connections 830 of the next
higher unit in the stack. The units thus form common vertical
busses disposed inside of the plan area of the units.
[0281] In a further embodiment (FIGS. 53-55), bottom unit
connections are provided by forming conductive traces along the
edge surfaces of the chip, rather than by providing connections
through the chip. As shown in FIG. 53, the wafer element has top
surface traces 902 extending from at least some of the top surface
contacts 926 on the chips to the boundaries between chips. A lid
element 960 and vertical interconnect structures 964 forming top
unit connections 966 are provided, as discussed above. Here again,
the wafer element and lid element are severed by cutting along the
boundaries between chips to form individual units. Thus, after
severance, the top surface traces 902 extend to the edge surfaces
904 of the unit. The severing process may be conducted so as to
form a trench with sloping edges at the boundaries between units,
before severance of the lid element. The sloping trench surfaces
provide sloping edge surfaces 906 on the chips, as shown in FIG.
54. A further trace 910 is formed along this sloping edge surface,
typically before severance of the lid element. As shown in FIG. 55,
further conductive traces are formed along the bottom surface 924
of the chip, so as to provide bottom unit connections 930. Here
again, some or all of the bottom unit connections 930 are connected
to the circuitry of the chip and to the top unit connections 966. A
unit made in this manner can be used as discussed above with
reference to FIGS. 50 and 51.
[0282] In a further embodiment of the invention (FIG. 56), traces
1002 are provided on the bottom surface 1061 of the lid element
1060 prior to assembly of the lid element with the wafer element.
The traces extend from the vias used to form the vertical
interconnect structures 1064 to the areas corresponding to the
boundaries between chips. During formation of vertical interconnect
structures 1064, the solder used to form the vertical interconnect
structures makes contact with the interior ends of traces 1002.
After severance of the wafer element 1020 and lid element 1060, the
ends 1008 of traces 1002 are exposed at the edge surfaces 1049 of
the unit. Traces 1010 extending along the edge surfaces connect
traces 1002 with bottom unit contacts 1030 provided on the bottom
surface 1024 of the chip. This arrangement avoids the need for
special processing of the wafer element to form traces 902 as
discussed above with reference to FIGS. 53-55.
[0283] Numerous variations and combinations of the features
discussed above can be used. For example, units having bottom unit
connections in addition to top unit connections can be used with
package structures connected to the top unit connections as
discussed above, for example, those discussed with reference to
FIGS. 37 and 39. In such an arrangement, both the terminals of the
package structure and the bottom unit connections are exposed at
the bottom of the packaged device for connection to a circuit
panel. In a further variant, units can be provided with both edge
unit connections as discussed with reference to FIGS. 44-49 and
bottom unit connections as discussed above with reference to FIGS.
50-56.
[0284] FIGS. 57-60 illustrate an embodiment of the invention in
which an additional seal is formed to seal peripheral edges of
units, i.e., capped or lidded chips, that are produced by one or
the various embodiments of wafer-scale processes such as described
above with reference to FIGS. 1-6B, FIGS. 18-28B, and FIGS. 30-32.
FIG. 60 illustrates the structure of two such units 2030 that are
provided according to this embodiment of the invention.
[0285] Among many alternatives discussed in the foregoing, an
organic material is a preferred material for use in forming a
"picture frame" seal 2002 to enclose the active region of a chip,
due to the ability of at least some such materials to be applied
and form bonds at an ambient temperature to only slightly elevated
temperatures. Use of such materials helps to avoid the
above-described CTE mismatch problems, particularly when the
chip-containing wafer and the lid-containing wafer are of different
materials. The use of such organic sealing material is particularly
advantageous in conjunction with the low-temperature processes
described above for forming interconnects, such as those in which
stud bumps are mounted to the chips which remain in wafer form, and
a lid or cap-containing wafer is then aligned and sealed with a
conductive or nonconductive organic material to form interconnects
(e.g., as shown and described above relative to FIGS. 29A and 30).
Certain types of chips, particularly those containing SAW devices,
are especially sensitive to strain. SAW devices typically operate
to provide a narrow bandpass filter function in which the center
frequency of the passband is subject to change due to a strain in
the device. The low modulus of elasticity of organic materials
helps the organic material to mitigate the effects of differential
strain which occurs between the chip-containing wafer and the lid
wafer due to CTE mismatch.
[0286] However, despite the foregoing benefits, an organic material
may not provide a sufficiently hermetic seal for some devices. A
tighter seal is generally achieved through inorganic materials such
as a metal or glass rather than organic materials, but is subject
to the above-described difficulties.
[0287] Hence, in the embodiment illustrated in FIG. 60, an
additional layer 2004 is deposited and patterned to overlie
peripheral edges 2020 of the unit, as an impermeable medium to seal
edges 2006 of the chip 2001, the edges 2008 of the lid, as well as
the organic seal material 2002. As also shown in FIG. 60, the same
layer 2004, when provided of a conductive material, is also
desirably patterned to form metal contacts 2010 connected to
respective ones of the conductive interconnects 2012 on each chip
2001.
[0288] FIGS. 57-59 show stages in an illustrative method of
fabricating the units 2030 shown in FIG. 60. As shown in FIG. 57, a
pair of units 2030 are shown, each remaining attached at boundary
2034 as portions of a wafer. For ease of reference, only two such
units are shown. However, a substantial number of such units can be
simultaneously processed in wafer form according to the method
described herein. Each chip includes a device 2011, e.g.,
illustratively, a SAW or MEMs device, a void 2013 disposed above
the device and conductive interconnects 2012 extending upwardly
from the chips 2001.
[0289] A photosensitive resist film is patterned by
photolithography to form resist patterns 2032 on the surface 2022
of the lid portion of the units. Illustratively, the resist film is
a lift-off film, in that any material coating applied onto the
resist film will also be removed when the resist film is
subsequently removed. The resist patterns 2032 are formed as
islands surrounding each of the pre-existing interconnects 2012, so
as to maintain the interconnects isolated from each other upon the
subsequent removal of the resist patterns with metal coating
applied thereto.
[0290] Thereafter, as shown in FIG. 58, the individual units 2030
are partially severed along boundary 2034, which preferably
coincides with the dicing lane of the chips, to produce the
structure shown. In a further step illustrated in FIG. 59, one or
more metals is deposited to produce the structure shown in which
both the peripheral edges 2020 and the top surfaces 2022 of the
units are covered by metal. The metal is preferably chosen for its
qualities in functioning as a barrier to contaminants including
moisture, and its ability to conduct electricity. Metals which do
not corrode easily are preferred for this purpose. The metal layer
2004 should preferably be selected so as to form a coating which
adheres strongly to the surfaces of the unit, as well as adhering
to the sealing material 2002 and to provide good conductivity in
both a direction across the major surface of the layer and the
direction through its thickness. For these reasons, the metal layer
2004 is preferably formed of a stack of deposited metals, such as
are used in the semiconductor and MEMs fabrication industries.
Common examples of metals which may be used to form such stacks
include combinations of titanium, platinum and gold, as well as
combinations of chromium, copper and gold, combinations of zinc,
nickel and palladium, as well as various permutations and
combinations of the above-listed metals. Nickel can be included in
the metal layer stack to increase the ability of the patterned
metal to provide magnetic screening. The thickness of each
patterned metal layer of the stack is illustratively on the order
of about 0.1 .mu.m when the metal layer is applied by vapor phase
deposition and up to about 1 .mu.m when the metal layer is applied
by aqueous processing. A conductive non-metal, for example, a
conductive nitride such as titanium nitride or other nitride of a
metal, can be utilized as a portion or all of a coating in place of
a metal, provided that the material provides a requisite barrier
function to moisture or contamination and has sufficient
conductivity.
[0291] Thereafter, referring again to FIG. 60, steps are performed
to remove the resist patterns 2032 together with the unwanted
portions of the metal layer, to produce the structure shown as
described above. The units 2030 are also severed at this time into
individual units along dicing lanes at the boundary 2034 (FIG.
58).
[0292] In addition to the foregoing described embodiment shown in
FIG. 60, the above-described process can be modified to provide
several alternative structures. FIG. 61 illustrates one such
alternative structure. As shown therein, an electrical connection
can be established between respective ones of the interconnects
2012 and a peripheral metal sealing layer 2004, to maintain the
sealing layer and one interconnect of the chip at the same
potential, such as to provide a ground contact. Other ones 2014 of
the interconnects can connect to contacts 2010 patterned from the
metal layer as described above. In such embodiment, the peripheral
metal sealing layer 2004 preferably extends over most of the
exterior peripheral 2020 and top surfaces 2022 of the unit 2030. In
such case, the sealing layer 2004 can be used to provide an
electromagnetic shielding function for the unit 2030.
[0293] With continued reference to FIG. 61, in a variation of the
above embodiment, the metal layer 2004 is patterned to provide
conductive traces which extend laterally over the top surface 2022
of the lid. Such conductive trace can be used for redistribution of
contacts, e.g., in a manner similar to that described above with
reference to FIGS. 4A-B and 7B, to convert, for example, between
the pitch and lateral dimensions of the interconnects 2012 of the
unit and those of an industry standard land grid array.
[0294] In a particular embodiment, the patterned metal layer 2004
can be used for additional functions, such as the provision of
conductive elements on the surface 2022 of the unit for use as
resistive, inductive or capacitive devices, e.g., for the purpose
of providing impedance matching between the device of the chip 2001
and an external network to which the unit is attached in later
assembly steps. To form certain ones of such conductive elements,
prior to the final step of severing the chips, a dielectric layer
can be deposited and patterned to overlie the patterned metal layer
2004, followed by the deposition and patterning of one or more
additional patterned metal layers, as described above with
reference to FIGS. 57-59.
[0295] As these and other variations and combinations of the
features discussed above can be utilized without departing from the
present invention as defined by the claims, the foregoing
description of the preferred embodiments should be taken by way of
illustration rather than by way of limitation of the invention as
defined by the claims.
* * * * *