U.S. patent application number 12/961027 was filed with the patent office on 2012-09-27 for semiconductor device and method of forming high routing density interconnect sites on substrate.
This patent application is currently assigned to STATS CHIPPAC, LTD.. Invention is credited to Rajendra D. Pendse.
Application Number | 20120241946 12/961027 |
Document ID | / |
Family ID | 44760338 |
Filed Date | 2012-09-27 |
United States Patent
Application |
20120241946 |
Kind Code |
A9 |
Pendse; Rajendra D. |
September 27, 2012 |
Semiconductor Device and Method of Forming High Routing Density
Interconnect Sites on Substrate
Abstract
A semiconductor device has a semiconductor die with a plurality
of bumps formed over contact pads on a surface of the semiconductor
die. The bumps can have a fusible portion and non-fusible portion.
A plurality of conductive traces is formed over a substrate with
interconnect sites having a width greater than 20% and less than
80% of a width of a contact interface between the bumps and contact
pads. The bumps are bonded to the interconnect sites so that the
bumps cover a top surface and side surface of the interconnect
sites. An encapsulant is deposited around the bumps between the
semiconductor die and substrate. The conductive traces have a pitch
as determined by minimum spacing between adjacent conductive traces
that can be placed on the substrate and the width of the
interconnect site provides a routing density equal to the pitch of
the conductive traces.
Inventors: |
Pendse; Rajendra D.;
(Fremont, CA) |
Assignee: |
STATS CHIPPAC, LTD.
Singapore
SG
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Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20110248399 A1 |
October 13, 2011 |
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Family ID: |
44760338 |
Appl. No.: |
12/961027 |
Filed: |
December 6, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12757889 |
Apr 9, 2010 |
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12961027 |
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11388755 |
Mar 24, 2006 |
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12757889 |
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60665208 |
Mar 25, 2005 |
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Current U.S.
Class: |
257/737 ;
257/E21.295; 257/E21.502; 257/E23.175; 438/124 |
Current CPC
Class: |
H01L 2224/13144
20130101; H01L 2924/01046 20130101; H01L 2924/0105 20130101; Y02P
70/611 20151101; H01L 24/73 20130101; H01L 2924/01049 20130101;
H05K 2201/09727 20130101; H01L 2924/01075 20130101; H01L 2924/13091
20130101; H01L 24/09 20130101; H01L 2224/1308 20130101; H01L
2224/16235 20130101; H01L 2224/16238 20130101; H01L 2224/73203
20130101; H01L 2224/97 20130101; H01L 2224/17104 20130101; H01L
2224/32145 20130101; H01L 2224/16237 20130101; H01L 2224/48091
20130101; H05K 2201/09427 20130101; H01L 2924/01074 20130101; H01L
2224/13019 20130101; H01L 2224/13023 20130101; H01L 23/49811
20130101; H01L 24/81 20130101; H01L 2224/81211 20130101; H01L
2224/81204 20130101; H01L 2924/01006 20130101; H01L 2924/01047
20130101; H01L 2924/12041 20130101; H05K 3/3452 20130101; H01L
2224/83192 20130101; H01L 2924/00013 20130101; H01L 2924/01322
20130101; H01L 24/97 20130101; H01L 2224/05557 20130101; H01L
2224/92125 20130101; H01L 21/563 20130101; H01L 2224/13082
20130101; H01L 23/49838 20130101; H01L 24/48 20130101; H01L
2224/0401 20130101; H01L 24/16 20130101; H01L 2924/01079 20130101;
H01L 2924/3011 20130101; H01L 2224/81815 20130101; H01L 2924/181
20130101; H01L 24/13 20130101; H01L 2224/16225 20130101; H01L
2924/12042 20130101; H01L 25/0657 20130101; H01L 2924/1306
20130101; H01L 2924/19041 20130101; H01L 2224/13116 20130101; H01L
2224/13155 20130101; H01L 2924/01013 20130101; H01L 2924/014
20130101; H01L 2924/01005 20130101; H01L 2224/13111 20130101; H01L
2924/1433 20130101; H01L 2924/15787 20130101; H05K 2201/10674
20130101; H01L 2924/00014 20130101; H05K 1/111 20130101; H01L 24/17
20130101; H01L 2224/1134 20130101; H01L 2224/73204 20130101; H01L
2224/8121 20130101; H01L 2924/14 20130101; Y02P 70/50 20151101;
H01L 24/11 20130101; H01L 2224/81801 20130101; H01L 2924/01078
20130101; H01L 2224/48227 20130101; H01L 2224/81136 20130101; H01L
2224/73265 20130101; H01L 2224/131 20130101; H01L 2224/16227
20130101; H01L 2224/83856 20130101; H01L 2224/0901 20130101; H01L
2224/13147 20130101; H01L 2924/01029 20130101; H01L 2924/01082
20130101; H01L 2224/32225 20130101; H01L 2224/83102 20130101; H05K
2201/0989 20130101; H01L 2924/01033 20130101; H01L 2224/48091
20130101; H01L 2924/00014 20130101; H01L 2224/13144 20130101; H01L
2924/00014 20130101; H01L 2224/13147 20130101; H01L 2924/00014
20130101; H01L 2224/13111 20130101; H01L 2924/00014 20130101; H01L
2224/13155 20130101; H01L 2924/00014 20130101; H01L 2224/13116
20130101; H01L 2924/00014 20130101; H01L 2224/13111 20130101; H01L
2924/01047 20130101; H01L 2224/13111 20130101; H01L 2924/01047
20130101; H01L 2924/01029 20130101; H01L 2224/13111 20130101; H01L
2924/01047 20130101; H01L 2924/01049 20130101; H01L 2224/13111
20130101; H01L 2924/01029 20130101; H01L 2224/13111 20130101; H01L
2924/01082 20130101; H01L 2224/13116 20130101; H01L 2924/0105
20130101; H01L 2224/131 20130101; H01L 2924/014 20130101; H01L
2224/1308 20130101; H01L 2224/13111 20130101; H01L 2224/1308
20130101; H01L 2224/13111 20130101; H01L 2924/01047 20130101; H01L
2224/1308 20130101; H01L 2224/13111 20130101; H01L 2924/01082
20130101; H01L 2224/1308 20130101; H01L 2224/13111 20130101; H01L
2924/01029 20130101; H01L 2224/1308 20130101; H01L 2224/13111
20130101; H01L 2924/01047 20130101; H01L 2924/01029 20130101; H01L
2224/1308 20130101; H01L 2224/13111 20130101; H01L 2924/01047
20130101; H01L 2924/01049 20130101; H01L 2924/00013 20130101; H01L
2224/13099 20130101; H01L 2224/16225 20130101; H01L 2924/13091
20130101; H01L 2224/16225 20130101; H01L 2224/13144 20130101; H01L
2924/00 20130101; H01L 2224/16225 20130101; H01L 2224/13147
20130101; H01L 2924/00 20130101; H01L 2224/16225 20130101; H01L
2224/13111 20130101; H01L 2924/00 20130101; H01L 2224/16225
20130101; H01L 2224/13116 20130101; H01L 2924/00 20130101; H01L
2224/16225 20130101; H01L 2224/13155 20130101; H01L 2924/00
20130101; H01L 2924/00012 20130101; H01L 2224/73265 20130101; H01L
2224/32145 20130101; H01L 2224/48227 20130101; H01L 2924/00012
20130101; H01L 2224/73265 20130101; H01L 2224/32225 20130101; H01L
2224/48227 20130101; H01L 2924/00 20130101; H01L 2224/73204
20130101; H01L 2224/16225 20130101; H01L 2224/32225 20130101; H01L
2924/00 20130101; H01L 2924/12041 20130101; H01L 2924/00 20130101;
H01L 2224/83192 20130101; H01L 2224/32225 20130101; H01L 2924/00
20130101; H01L 2224/97 20130101; H01L 2224/73265 20130101; H01L
2224/32225 20130101; H01L 2224/48227 20130101; H01L 2924/00
20130101; H01L 2924/1306 20130101; H01L 2924/00 20130101; H01L
2224/92125 20130101; H01L 2224/73204 20130101; H01L 2224/16225
20130101; H01L 2224/32225 20130101; H01L 2924/00 20130101; H01L
2224/83192 20130101; H01L 2224/73204 20130101; H01L 2224/16225
20130101; H01L 2224/32225 20130101; H01L 2924/00 20130101; H01L
2924/15787 20130101; H01L 2924/00 20130101; H01L 2924/12042
20130101; H01L 2924/00 20130101; H01L 2224/1134 20130101; H01L
2924/00014 20130101; H01L 2224/97 20130101; H01L 2224/73265
20130101; H01L 2224/32145 20130101; H01L 2224/48227 20130101; H01L
2924/00 20130101; H01L 2924/181 20130101; H01L 2924/00012 20130101;
H01L 2924/00014 20130101; H01L 2224/45099 20130101; H01L 2924/00014
20130101; H01L 2224/45015 20130101; H01L 2924/207 20130101 |
Class at
Publication: |
257/737 ;
438/124; 257/E23.175; 257/E21.295; 257/E21.502 |
International
Class: |
H01L 23/538 20060101
H01L023/538; H01L 21/56 20060101 H01L021/56; H01L 21/3205 20060101
H01L021/3205 |
Claims
1. A method of making a semiconductor device, comprising: providing
a semiconductor die having a plurality of bumps formed over contact
pads on a surface of the semiconductor die; providing a substrate;
forming a plurality of conductive traces over the substrate with
interconnect sites having a width greater than 20% and less than
80% of a width of a contact interface between the bumps and contact
pads; bonding the bumps to the interconnect sites so that the bumps
cover a top surface and side surface of the interconnect sites; and
depositing an encapsulant around the bumps between the
semiconductor die and substrate.
2. The method of claim 1, wherein the conductive traces have a
pitch as determined by minimum spacing between adjacent conductive
traces that can be placed on the substrate and the width of the
interconnect site provides a routing density equal to the pitch of
the conductive traces.
3. The method of claim 1, wherein the width of the interconnect
site is 120% of a width of the conductive traces.
4. The method of claim 1, wherein the interconnect sites have
generally rectangular, elongated, or rounded shape.
5. The method of claim 1, further including forming a masking layer
over the substrate.
6. The method of claim 1, wherein the bumps include a fusible
portion and non-fusible portion.
7. A method of making a semiconductor device, comprising: providing
a semiconductor having a plurality of contact pads; providing a
substrate; forming a plurality of conductive traces over the
substrate with interconnect sites; forming a plurality of
interconnect structures between the contact pads on the
semiconductor die and the interconnect sites on the substrate so
that the interconnect structures cover a top surface and side
surface of the interconnect sites; and depositing an encapsulant
between the semiconductor die and substrate.
8. The method of claim 7, wherein the conductive traces have a
pitch as determined by minimum spacing between adjacent conductive
traces that can be placed on the substrate and a width of the
interconnect site provides a routing density equal to the pitch of
the conductive traces.
9. The method of claim 7, wherein the width of the interconnect
site is greater than 20% and less than 80% of a width of a contact
interface between the interconnect structure and contact pad.
10. The method of claim 7, wherein the width of the interconnect
site is substantially equal to a width of the conductive
traces.
11. The method of claim 7, wherein the interconnect sites have
generally rectangular, elongated, or rounded shape.
12. The method of claim 7, wherein the interconnect structures
include a fusible portion and non-fusible portion.
13. The method of claim 7, wherein the interconnect structures
include a conductive pillar and bump formed over the conductive
pillar.
14. A method of making a semiconductor device, comprising:
providing a semiconductor die; providing a substrate; forming a
plurality of conductive traces over the substrate with interconnect
sites; and forming a plurality of interconnect structures to bond
the semiconductor die to the interconnect sites on the substrate,
wherein the conductive traces have a pitch as determined by minimum
spacing between adjacent conductive traces that can be placed on
the substrate and a width of the interconnect site provides a
routing density equal to the pitch of the conductive traces.
15. The method of claim 14, further including depositing an
encapsulant between the semiconductor die and substrate.
16. The method of claim 14, wherein the width of the interconnect
site is greater than 20% and less than 80% of a width of a contact
interface between the interconnect structure and contact pad.
17. The method of claim 14, wherein the interconnect sites have
generally rectangular, elongated, or rounded shape.
18. The method of claim 14, wherein the interconnect structures
cover a top surface and side surface of the interconnect sites.
19. The method of claim 14, wherein the interconnect structures
include a fusible portion and non-fusible portion.
20. The method of claim 14, wherein the interconnect structures
include a conductive pillar and bump formed over the conductive
pillar.
21. A semiconductor device, comprising: a semiconductor die having
a plurality of contact pads; a substrate; a plurality of conductive
traces formed over the substrate with interconnect sites; a
plurality of interconnect structures formed between the contact
pads on the semiconductor die and the interconnect sites on the
substrate, wherein the interconnect structures cover a top surface
and side surface of the interconnect sites and a width of the
interconnect site is greater than 20% and less than 80% of a width
of a contact interface between the interconnect structure and
contact pad; and an encapsulant deposited between the semiconductor
die and substrate.
22. The semiconductor device of claim 21, wherein the width of the
interconnect site is 120% of a width of the conductive traces.
23. The semiconductor device of claim 21, wherein the interconnect
sites have generally rectangular, elongated, or rounded shape.
24. The semiconductor device of claim 21, wherein the interconnect
structures include a fusible portion and non-fusible portion.
25. The semiconductor device of claim 21, wherein the interconnect
structures include a conductive pillar and bump formed over the
conductive pillar.
Description
CLAIM TO DOMESTIC PRIORITY
[0001] The present application is a continuation-in-part of U.S.
patent application Ser. No. 12/757,889, filed Apr. 9, 2010, and
claims priority to the foregoing parent application pursuant to 35
U.S.C. .sctn.120.
FIELD OF THE INVENTION
[0002] The present invention relates to semiconductor devices and,
particularly, to a semiconductor device and method of forming high
routing density interconnect sites on a substrate.
BACKGROUND OF THE INVENTION
[0003] Semiconductor devices are commonly found in modern
electronic products. Semiconductor devices vary in the number and
density of electrical components. Discrete semiconductor devices
generally contain one type of electrical component, e.g., light
emitting diode (LED), small signal transistor, resistor, capacitor,
inductor, and power metal oxide semiconductor field effect
transistor (MOSFET). Integrated semiconductor devices typically
contain hundreds to millions of electrical components. Examples of
integrated semiconductor devices include microcontrollers,
microprocessors, charged-coupled devices (CCDs), solar cells, and
digital micro-mirror devices (DMDs).
[0004] Semiconductor devices perform a wide range of functions such
as signal processing, high-speed calculations, transmitting and
receiving electromagnetic signals, controlling electronic devices,
transforming sunlight to electricity, and creating visual
projections for television displays. Semiconductor devices are
found in the fields of entertainment, communications, power
conversion, networks, computers, and consumer products.
Semiconductor devices are also found in military applications,
aviation, automotive, industrial controllers, and office
equipment.
[0005] Semiconductor devices exploit the electrical properties of
semiconductor materials. The atomic structure of semiconductor
material allows its electrical conductivity to be manipulated by
the application of an electric field or base current or through the
process of doping. Doping introduces impurities into the
semiconductor material to manipulate and control the conductivity
of the semiconductor device.
[0006] A semiconductor device contains active and passive
electrical structures. Active structures, including bipolar and
field effect transistors, control the flow of electrical current.
By varying levels of doping and application of an electric field or
base current, the transistor either promotes or restricts the flow
of electrical current. Passive structures, including resistors,
capacitors, and inductors, create a relationship between voltage
and current necessary to perform a variety of electrical functions.
The passive and active structures are electrically connected to
form circuits, which enable the semiconductor device to perform
high-speed calculations and other useful functions.
[0007] Semiconductor devices are generally manufactured using two
complex manufacturing processes, i.e., front-end manufacturing, and
back-end manufacturing, each involving potentially hundreds of
steps. Front-end manufacturing involves the formation of a
plurality of die on the surface of a semiconductor wafer. Each die
is typically identical and contains circuits formed by electrically
connecting active and passive components. Back-end manufacturing
involves singulating individual die from the finished wafer and
packaging the die to provide structural support and environmental
isolation.
[0008] One goal of semiconductor manufacturing is to produce
smaller semiconductor devices. Smaller devices typically consume
less power, have higher performance, and can be produced more
efficiently. In addition, smaller semiconductor devices have a
smaller footprint, which is desirable for smaller end products. A
smaller die size can be achieved by improvements in the front-end
process resulting in die with smaller, higher density active and
passive components. Back-end processes may result in semiconductor
device packages with a smaller footprint by improvements in
electrical interconnection and packaging materials.
[0009] In conventional flipchip type packages, a semiconductor die
is mounted to a package substrate with the active side of the die
facing the substrate. Conventionally, the interconnection of the
circuitry in the semiconductor die with circuitry in the substrate
is made by way of bumps which are attached to an array of
interconnect pads on the die and bonded to a corresponding
complementary array of interconnect pads, often referred to as
capture pads on the substrate.
[0010] The areal density of electronic features on integrated
circuits has increased enormously, and semiconductor die having a
greater density of circuit features also may have a greater density
of sites for interconnection with the package substrate.
[0011] The package is connected to underlying circuitry, such as a
printed circuit board or motherboard, by way of second level
interconnects between the package and underlying circuit. The
second level interconnects have a greater pitch than the flipchip
interconnects, and so the routing on the substrate conventionally
fans out. Significant technological advances have enabled
construction of fine lines and spaces. In the conventional
arrangement, space between adjacent pads limits the number of
traces that can escape from the more inward capture pads in the
array. The fan-out routing between the capture pads beneath the
semiconductor die and external pins of the package is
conventionally formed on multiple metal layers within the package
substrate. For a complex interconnect array, substrates having
multiple layers can be required to achieve routing between the die
pads and second level interconnects on the package.
[0012] Multiple layer substrates are expensive and, in conventional
flipchip constructs, the substrate alone typically accounts for
more than half the package cost. The high cost of multilayer
substrates has been a factor in limiting proliferation of flipchip
technology in mainstream products. In conventional flipchip
constructs, the escape routing pattern typically introduces
additional electrical parasitics because the routing includes short
runs of unshielded wiring and vias between wiring layers in the
signal transmission path. Electrical parasitics can significantly
limit package performance.
[0013] The flipchip interconnection can be made by using a melting
process to join the bumps, e.g., solder bumps, onto the mating
surfaces of the corresponding capture pads, referred to as
bump-on-capture pad (BOC) interconnect. Two features are evident in
the BOC design: first, a comparatively large capture pad is
required to mate with the bump on the semiconductor die, and
second, an insulating material, typically a solder mask, is
required to confine the flow of solder during the interconnection
process. The solder mask opening defines the contour of the melted
solder at the capture pad, i.e., solder mask defined, or the solder
contour may not be defined by the mask opening, i.e., non-solder
mask defined. In the latter case, the solder mask opening is
significantly larger than the capture pad. Since the techniques for
defining solder mask openings have wide tolerance ranges for a
solder mask defined bump configuration, the capture pad must be
large, typically considerably larger than the design size for the
mask opening, to ensure that the mask opening will be located on
the mating surface of the pad. The width of capture pads or
diameter can be as much as two to four times wider than the trace
width. The larger width of the capture pads results in considerable
loss of routing space on the top substrate layer. In particular,
the escape routing pitch is much larger than the finest trace pitch
that the substrate technology can offer. A significant number of
pads must be routed on lower substrate layers by means of short
stubs and vias, often beneath the footprint of the die, emanating
from the pads in question.
[0014] In a typical example of a conventional solder mask defined
BOC interconnection, the capture pad has a diameter about 140
.mu.m, and the solder mask opening has a diameter about 90 .mu.m,
and the routing traces are about 25-30 .mu.m wide. The diameter of
the mating surface for attachment of the bump to the die pad, that
is, the place of interface between the bump and the die pad, is
defined by the solder mask opening as having a diameter about 90
.mu.m.
[0015] Some examples of conventional BOC interconnect layouts are
shown in FIGS. 1 and 2 in portions 10 and 20 of a flipchip package.
The partial sectional view in FIG. 1 is taken in a plane parallel
to the package substrate surface, along the line 1-1' in FIG. 2.
The partial sectional view in FIG. 2 is taken in a plane
perpendicular to the package substrate surface, along the line 2-2'
in FIG. 1. Certain features are shown as if transparent, but many
of the features in FIG. 1 are shown partly obscured by overlying
features.
[0016] A die attach surface of the package substrate includes a
metal or layer formed on a dielectric layer over substrate 12. The
metal layer is patterned to form traces or leads 13 and capture
pads 14. An insulating layer or solder mask 16 covers the die
attach surface of substrate 12. The solder mask 16 is usually made
with a photo-definable material patterned by photoresist to leave
the mating surfaces of capture pads 14 exposed. The interconnect
bumps 15 attached to pads on the active side of semiconductor die
18 are joined to corresponding capture pads 14 on substrate 12 to
form appropriate electrical interconnection between the circuitry
on the die and the leads on the substrate. After the reflowed
solder is cooled to establish the electrical connection, an
underfill material 17 is introduced into the space between
semiconductor die 18 and substrate 12 to mechanically stabilize the
interconnects and protect the features between the die and
substrate.
[0017] FIG. 1 shows signal escape traces 13 in the upper metal
layer of substrate 12 routed from their respective capture pads 14
across the die edge location, indicated by broken line 11, and away
from the die footprint. The signal traces 13 can have an escape
pitch P.sub.E about 112 micrometers (.mu.m). A 30 .mu.m/30 .mu.m
design rule is typical for traces 13 in a configuration such as
shown in FIG. 1. Traces 13 are nominally 30 .mu.m wide and can be
spaced as close together as 30 .mu.m. The capture pads 14 are
typically three times greater than the trace width, and the capture
pads have a width or diameter nominally 90 .mu.m. The openings in
the solder mask are larger than the pads, having a nominal width or
diameter of 135 .mu.m.
[0018] FIGS. 1 and 2 show a non-solder mask defined solder contour.
As the fusible material of the bumps on the die melt, the molten
solder tends to wet the metal of the leads and capture pads, and
the solder tends to run out over any contiguous metal surfaces that
are not masked. The solder tends to flow along the contiguous lead
13, and here the solder flow is limited by the solder mask at
location 19 in FIG. 1. A non-solder mask defined solder contour at
the pad is apparent in FIG. 2, in which portion 29 of bumps 15 is
shown as having flowed over the sides of capture pads 14 and down
to the surface of the dielectric layer of substrate 12. The
non-solder mask defined contour does not limit the flow of solder
over the surface and down over the sides of the capture pads and,
unless there is a substantial excess of solder at the pad, the flow
of solder is limited by the fact that the dielectric surface of
substrate 12 is typically not wettable by the molten solder. A
lower limit on the density of the capture pads in the arrangement
shown in FIG. 1 is determined by, among other factors, the capacity
of the mask forming technology to make reliable narrow mask
structures, and the need to provide mask structures between
adjacent mask openings. A lower limit on the escape density is
additionally determined by, among other factors, the need for
escape lines from more centrally located capture pads to be routed
between more peripherally located capture pads.
[0019] FIG. 3 shows a solder mask defined solder contour, in a
sectional view similar to FIG. 2. Semiconductor die 38 is shown
affixed by way of bumps 35 onto the mating surfaces of capture pads
34 formed along with traces or leads 33 by patterning a metal layer
on the die attach side of a dielectric layer of substrate 32. After
the reflowed solder is cooled to establish the electrical
connection, an underfill material 37 is introduced into the space
between die 38 and substrate 32 to mechanically stabilize the
interconnects and protect the features between the die and
substrate. Capture pads 34 are wider than in the examples of FIGS.
1 and 2, and the solder mask openings are smaller than the capture
pads so that the solder mask material covers the sides and part of
the mating surface of each capture pad, as shown at location 39, as
well as leads 33. When bumps 35 are brought into contact with the
mating surfaces of the respective capture pads 34, and then melted
with solder mask material 36 restricting the flow of the molten
solder so that the shapes of the solder contours are defined by the
shapes and dimensions of the mask openings over capture pads
34.
SUMMARY OF THE INVENTION
[0020] A need exists to minimize the interconnect sites on a
substrate to increase routing density without impacting electrical
functionality or manufacturing reliability. Accordingly, in one
embodiment, the present invention is a method of making a
semiconductor device comprising the steps of providing a
semiconductor die having a plurality of bumps formed over contact
pads on a surface of the semiconductor die, providing a substrate,
forming a plurality of conductive traces over the substrate with
interconnect sites having a width greater than 20% and less than
80% of a width of a contact interface between the bumps and contact
pads, bonding the bumps to the interconnect sites so that the bumps
cover a top surface and side surface of the interconnect sites, and
depositing an encapsulant around the bumps between the
semiconductor die and substrate.
[0021] In another embodiment, the present invention is a method of
making a semiconductor device comprising the steps of providing a
semiconductor having a plurality of contact pads, providing a
substrate, forming a plurality of conductive traces over the
substrate with interconnect sites, forming a plurality of
interconnect structures between the contact pads on the
semiconductor die and the interconnect sites on the substrate so
that the interconnect structures cover a top surface and side
surface of the interconnect sites, and depositing an encapsulant
between the semiconductor die and substrate.
[0022] In another embodiment, the present invention is a method of
making a semiconductor device comprising the steps of providing a
semiconductor die, providing a substrate, forming a plurality of
conductive traces over the substrate with interconnect sites, and
forming a plurality of interconnect structures to bond the
semiconductor die to the interconnect sites on the substrate. The
conductive traces have a pitch as determined by minimum spacing
between adjacent conductive traces that can be placed on the
substrate and a width of the interconnect site provides a routing
density equal to the pitch of the conductive traces.
[0023] In another embodiment, the present invention is a
semiconductor device comprising a semiconductor die having a
plurality of contact pads. A plurality of conductive traces is
formed over a substrate with interconnect sites. A plurality of
interconnect structures is formed between the contact pads on the
semiconductor die and the interconnect sites on the substrate. The
interconnect structures cover a top surface and side surface of the
interconnect sites and a width of the interconnect site is greater
than 20% and less than 80% of a width of a contact interface
between the interconnect structure and contact pad. An encapsulant
is deposited between the semiconductor die and substrate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 illustrates a conventional bump-on-capture pad
flipchip interconnection parallel to the plane of the package
substrate surface;
[0025] FIG. 2 illustrates a conventional bump-on-capture pad
flipchip interconnection perpendicular to the plane of the package
substrate surface;
[0026] FIG. 3 illustrates another conventional bump-on-capture pad
flipchip interconnection perpendicular to the plane of the package
substrate surface;
[0027] FIG. 4 illustrates a PCB with different types of packages
mounted to its surface;
[0028] FIGS. 5a-5c illustrate further detail of the representative
semiconductor packages mounted to the PCB;
[0029] FIG. 6 illustrates a BONP flipchip interconnection parallel
to the plane of the package substrate surface;
[0030] FIG. 7 illustrates the BONP flipchip interconnection of FIG.
6 perpendicular to the plane of the package substrate surface;
[0031] FIG. 8 illustrates a second BONP flipchip interconnection
parallel to the plane of the package substrate surface;
[0032] FIG. 9 illustrates the BONP flipchip interconnection of FIG.
8 perpendicular to the plane of the package substrate surface;
[0033] FIG. 10 illustrates a third BONP flipchip interconnection
parallel to the plane of the package substrate surface;
[0034] FIG. 11 illustrates a third BONP flipchip interconnection
parallel to the plane of the package substrate surface;
[0035] FIGS. 12a-12c illustrate a process for making a flipchip
interconnection;
[0036] FIGS. 13a-13d illustrate further detail of the process for
making a flipchip interconnection;
[0037] FIG. 14 illustrates a force and temperature schedule for a
process for making a flipchip interconnection;
[0038] FIG. 15 illustrates a bump-on-narrow-pad flipchip
interconnection;
[0039] FIGS. 16a-16e illustrate various interconnect pad
shapes;
[0040] FIGS. 17a-17c illustrate various interconnect pad
configurations;
[0041] FIGS. 18a-18b illustrate various solder mask openings;
[0042] FIG. 19 illustrates various interconnect pad configurations
in relation to a solder mask opening;
[0043] FIG. 20 illustrates various solder mask configurations in
relation to an interconnect pad;
[0044] FIGS. 21a-21h illustrate various interconnect structures
formed over a semiconductor die for bonding to conductive traces on
a substrate;
[0045] FIGS. 22a-22g illustrate the semiconductor die and
interconnect structure bonded to the conductive traces;
[0046] FIGS. 23a-23d illustrate the semiconductor die with a
wedge-shaped interconnect structure bonded to the conductive
traces;
[0047] FIGS. 24a-24d illustrate another embodiment of the
semiconductor die and interconnect structure bonded to the
conductive traces;
[0048] FIGS. 25a-25c illustrate stepped bump and stud bump
interconnect structures bonded to the conductive traces;
[0049] FIGS. 26a-26b illustrate conductive traces with conductive
vias;
[0050] FIGS. 27a-27c illustrate mold underfill between the
semiconductor die and substrate;
[0051] FIG. 28 illustrates another mold underfill between the
semiconductor die and substrate;
[0052] FIG. 29 illustrates the semiconductor die and substrate
after mold underfill;
[0053] FIGS. 30a-30g illustrate various arrangements of the
conductive traces with open solder registration;
[0054] FIGS. 31a-31b illustrate the open solder registration with
patches between the conductive traces; and
[0055] FIG. 32 illustrates a POP with masking layer dam to restrain
the encapsulant during mold underfill.
DETAILED DESCRIPTION OF THE DRAWINGS
[0056] The present invention is described in one or more
embodiments in the following description with reference to the
figures, in which like numerals represent the same or similar
elements. While the invention is described in terms of the best
mode for achieving the invention's objectives, it will be
appreciated by those skilled in the art that it is intended to
cover alternatives, modifications, and equivalents as can be
included within the spirit and scope of the invention as defined by
the appended claims and their equivalents as supported by the
following disclosure and drawings.
[0057] Semiconductor devices are generally manufactured using two
complex manufacturing processes: front-end manufacturing and
back-end manufacturing. Front-end manufacturing involves the
formation of a plurality of die on the surface of a semiconductor
wafer. Each die on the wafer contains active and passive electrical
components, which are electrically connected to form functional
electrical circuits. Active electrical components, such as
transistors and diodes, have the ability to control the flow of
electrical current. Passive electrical components, such as
capacitors, inductors, resistors, and transformers, create a
relationship between voltage and current necessary to perform
electrical circuit functions.
[0058] Passive and active components are formed over the surface of
the semiconductor wafer by a series of process steps including
doping, deposition, photolithography, etching, and planarization.
Doping introduces impurities into the semiconductor material by
techniques such as ion implantation or thermal diffusion. The
doping process modifies the electrical conductivity of
semiconductor material in active devices, transforming the
semiconductor material into an insulator, conductor, or dynamically
changing the semiconductor material conductivity in response to an
electric field or base current. Transistors contain regions of
varying types and degrees of doping arranged as necessary to enable
the transistor to promote or restrict the flow of electrical
current upon the application of the electric field or base
current.
[0059] Active and passive components are formed by layers of
materials with different electrical properties. The layers can be
formed by a variety of deposition techniques determined in part by
the type of material being deposited. For example, thin film
deposition may involve chemical vapor deposition (CVD), physical
vapor deposition (PVD), electrolytic plating, and electroless
plating processes. Each layer is generally patterned to form
portions of active components, passive components, or electrical
connections between components.
[0060] The layers can be patterned using photolithography, which
involves the deposition of light sensitive material, e.g.,
photoresist, over the layer to be patterned. A pattern is
transferred from a photomask to the photoresist using light. The
portion of the photoresist pattern subjected to light is removed
using a solvent, exposing portions of the underlying layer to be
patterned. The remainder of the photoresist is removed, leaving
behind a patterned layer. Alternatively, some types of materials
are patterned by directly depositing the material into the areas or
voids formed by a previous deposition/etch process using techniques
such as electroless and electrolytic plating.
[0061] Depositing a thin film of material over an existing pattern
can exaggerate the underlying pattern and create a non-uniformly
flat surface. A uniformly flat surface is required to produce
smaller and more densely packed active and passive components.
Planarization can be used to remove material from the surface of
the wafer and produce a uniformly flat surface. Planarization
involves polishing the surface of the wafer with a polishing pad.
An abrasive material and corrosive chemical are added to the
surface of the wafer during polishing. The combined mechanical
action of the abrasive and corrosive action of the chemical removes
any irregular topography, resulting in a uniformly flat
surface.
[0062] Back-end manufacturing refers to cutting or singulating the
finished wafer into the individual die and then packaging the die
for structural support and environmental isolation. To singulate
the die, the wafer is scored and broken along non-functional
regions of the wafer called saw streets or scribes. The wafer is
singulated using a laser cutting tool or saw blade. After
singulation, the individual die are mounted to a package substrate
that includes pins or contact pads for interconnection with other
system components. Contact pads formed over the semiconductor die
are then connected to contact pads within the package. The
electrical connections can be made with solder bumps, stud bumps,
conductive paste, or wirebonds. An encapsulant or other molding
material is deposited over the package to provide physical support
and electrical isolation. The finished package is then inserted
into an electrical system and the functionality of the
semiconductor device is made available to the other system
components.
[0063] FIG. 4 illustrates electronic device 50 having a chip
carrier substrate or printed circuit board (PCB) 52 with a
plurality of semiconductor packages mounted on its surface.
Electronic device 50 can have one type of semiconductor package, or
multiple types of semiconductor packages, depending on the
application. The different types of semiconductor packages are
shown in FIG. 4 for purposes of illustration.
[0064] Electronic device 50 can be a stand-alone system that uses
the semiconductor packages to perform one or more electrical
functions. Alternatively, electronic device 50 can be a
subcomponent of a larger system. For example, electronic device 50
can be part of a cellular phone, personal digital assistant (PDA),
digital video camera (DVC), or other electronic communication
device. Alternatively, electronic device 50 can be a graphics card,
network interface card, or other signal processing card that can be
inserted into a computer. The semiconductor package can include
microprocessors, memories, application specific integrated circuits
(ASIC), logic circuits, analog circuits, RF circuits, discrete
devices, or other semiconductor die or electrical components. The
miniaturization and the weight reduction are essential for these
products to be accepted by the market. The distance between
semiconductor devices must be decreased to achieve higher
density.
[0065] In FIG. 4, PCB 52 provides a general substrate for
structural support and electrical interconnect of the semiconductor
packages mounted on the PCB. Conductive signal traces 54 are formed
over a surface or within layers of PCB 52 using evaporation,
electrolytic plating, electroless plating, screen printing, or
other suitable metal deposition process. Signal traces 54 provide
for electrical communication between each of the semiconductor
packages, mounted components, and other external system components.
Traces 54 also provide power and ground connections to each of the
semiconductor packages.
[0066] In some embodiments, a semiconductor device has two
packaging levels. First level packaging is a technique for
mechanically and electrically attaching the semiconductor die to an
intermediate carrier. Second level packaging involves mechanically
and electrically attaching the intermediate carrier to the PCB. In
other embodiments, a semiconductor device may only have the first
level packaging where the die is mechanically and electrically
mounted directly to the PCB.
[0067] For the purpose of illustration, several types of first
level packaging, including wire bond package 56 and flipchip 58,
are shown on PCB 52. Additionally, several types of second level
packaging, including ball grid array (BGA) 60, bump chip carrier
(BCC) 62, dual in-line package (DIP) 64, land grid array (LGA) 66,
multi-chip module (MCM) 68, quad flat non-leaded package (QFN) 70,
and quad flat package 72, are shown mounted on PCB 52. Depending
upon the system requirements, any combination of semiconductor
packages, configured with any combination of first and second level
packaging styles, as well as other electronic components, can be
connected to PCB 52. In some embodiments, electronic device 50
includes a single attached semiconductor package, while other
embodiments call for multiple interconnected packages. By combining
one or more semiconductor packages over a single substrate,
manufacturers can incorporate pre-made components into electronic
devices and systems. Because the semiconductor packages include
sophisticated functionality, electronic devices can be manufactured
using cheaper components and a streamlined manufacturing process.
The resulting devices are less likely to fail and less expensive to
manufacture resulting in a lower cost for consumers.
[0068] FIGS. 5a-5c show exemplary semiconductor packages. FIG. 5a
illustrates further detail of DIP 64 mounted on PCB 52.
Semiconductor die 74 includes an active region containing analog or
digital circuits implemented as active devices, passive devices,
conductive layers, and dielectric layers formed within the die and
are electrically interconnected according to the electrical design
of the die. For example, the circuit may include one or more
transistors, diodes, inductors, capacitors, resistors, and other
circuit elements formed within the active region of semiconductor
die 74. Contact pads 76 are one or more layers of conductive
material, such as aluminum (Al), copper (Cu), tin (Sn), nickel
(Ni), gold (Au), or silver (Ag), and are electrically connected to
the circuit elements formed within semiconductor die 74. During
assembly of DIP 64, semiconductor die 74 is mounted to an
intermediate carrier 78 using a gold-silicon eutectic layer or
adhesive material such as thermal epoxy or epoxy resin. The package
body includes an insulative packaging material such as polymer or
ceramic. Conductor leads 80 and wire bonds 82 provide electrical
interconnect between semiconductor die 74 and PCB 52. Encapsulant
84 is deposited over the package for environmental protection by
preventing moisture and particles from entering the package and
contaminating die 74 or wire bonds 82.
[0069] FIG. 5b illustrates further detail of BCC 62 mounted on PCB
52. Semiconductor die 88 is mounted over carrier 90 using an
underfill or epoxy-resin adhesive material 92. Wire bonds 94
provide first level packaging interconnect between contact pads 96
and 98. Molding compound or encapsulant 100 is deposited over
semiconductor die 88 and wire bonds 94 to provide physical support
and electrical isolation for the device. Contact pads 102 are
formed over a surface of PCB 52 using a suitable metal deposition
process such as electrolytic plating or electroless plating to
prevent oxidation. Contact pads 102 are electrically connected to
one or more conductive signal traces 54 in PCB 52. Bumps 104 are
formed between contact pads 98 of BCC 62 and contact pads 102 of
PCB 52.
[0070] In FIG. 5c, semiconductor die 58 is mounted face down to
intermediate carrier 106 with a flipchip style first level
packaging. Active region 108 of semiconductor die 58 contains
analog or digital circuits implemented as active devices, passive
devices, conductive layers, and dielectric layers formed according
to the electrical design of the die. For example, the circuit can
include one or more transistors, diodes, inductors, capacitors,
resistors, and other circuit elements within active region 108.
Semiconductor die 58 is electrically and mechanically connected to
carrier 106 through bumps 110.
[0071] BGA 60 is electrically and mechanically connected to PCB 52
with a BGA style second level packaging using bumps 112.
Semiconductor die 58 is electrically connected to conductive signal
traces 54 in PCB 52 through bumps 110, signal lines 114, and bumps
112. A molding compound or encapsulant 116 is deposited over
semiconductor die 58 and carrier 106 to provide physical support
and electrical isolation for the device. The flipchip semiconductor
device provides a short electrical conduction path from the active
devices on semiconductor die 58 to conduction tracks on PCB 52 in
order to reduce signal propagation distance, lower capacitance, and
improve overall circuit performance. In another embodiment, the
semiconductor die 58 can be mechanically and electrically connected
directly to PCB 52 using flipchip style first level packaging
without intermediate carrier 106.
[0072] In a flipchip type semiconductor die, the interconnect is
accomplished by connecting the interconnect bump directly onto a
narrow interconnection pad, rather than onto a conventional capture
pad. The width of the narrow pad is selected according to the base
diameter of the interconnect bump that is to be connected onto the
narrow pad. Particularly, the width of the narrow pad is less than
the base diameter of the interconnect bump, e.g., in a range about
20% to about 80%. The present flipchip interconnect provides more
efficient routing of traces on the substrate. The signal routing
can be formed entirely in a single metal layer of the substrate to
reduce the number of layers in the substrate. Forming the signal
traces in a single layer permits relaxation of some of the via,
line, and space design rules that the substrate must meet. The
simplification of the substrate greatly reduces the overall cost of
the flipchip package. The bump-on-narrow-pad (BONP) architecture
also helps eliminate such features as vias and stubs from the
substrate design and enables a microstrip controlled impedance
electrical environment for signal transmission, thereby improving
performance.
[0073] The flipchip interconnection has bumps attached to
interconnect pads on a semiconductor die and mated onto
corresponding narrow interconnection pads on a substrate. A
flipchip package includes a semiconductor die having bumps attached
to interconnect pads in an active surface, and a substrate having
narrow interconnection pads in a die attach surface, in which the
bumps are mated onto the narrow pads. The BONP interconnection can
be formed without use of a solder mask to confine the molten solder
during a re-melt stage in the process which allows for finer
interconnection geometry.
[0074] FIGS. 6 and 8 each show a portion of a BONP flipchip
interconnection, in a diagrammatic partial sectional view taken in
a plane parallel to the substrate surface, along the lines 6-6' and
8-8' in FIGS. 7 and 9, respectively. Certain features are shown as
if transparent. The interconnection is achieved by mating the bumps
onto respective narrow interconnection pads on the substrate. In
this embodiment, the function of confining molten flow is
accomplished without a solder mask in the course of the assembly
process, as described below. FIG. 7 shows a partial sectional view
of a package as in FIG. 6, taken in a plane perpendicular to the
plane of the package substrate surface, along the line 7-7' in FIG.
6. FIG. 9 shows a partial sectional view of a package as in FIG. 8,
taken in a plane perpendicular to the plane of the package
substrate surface, along the line 9-9' in FIG. 8.
[0075] The escape routing patterns for BONP substrates are shown in
FIGS. 6 and 8. In FIG. 6, the routing patterns are arranged for a
semiconductor die on which the die attach pads for the interconnect
balls are formed in a row near the die perimeter. Bumps 120 are
mated onto corresponding narrow interconnection pads on escape
traces 122 in a row near the edge of the die footprint, indicated
by broken line 124. In FIG. 8, the routing patterns are arranged
for a semiconductor die on which the die attach pads are in an
array of parallel rows near the die perimeter. Bumps 126 are mated
onto corresponding narrow interconnection pads on escape traces 128
in a complementary array near the edge of the die footprint,
indicated by broken line 130.
[0076] In FIGS. 6 and 8, the routing density achievable using a
BONP interconnect can equal the finest trace pitch offered by the
substrate technology. In one embodiment, a width of the
interconnect site on the trace can be up to 1.2 times a width of
the trace. The conductive traces have a pitch as determined by
minimum spacing between adjacent conductive traces that can be
placed on the substrate and the width of the interconnect site
provides a routing density equal to the pitch of the conductive
traces. The routing density is significantly higher than is
achieved in a conventional BOC arrangement, as described in FIGS.
1-3. Conventional capture pads are typically two to four times as
wide as the trace or lead width.
[0077] As FIGS. 6 and 8 illustrate, the BONP interconnect can
provide a significantly higher signal trace escape routing density.
In FIG. 6, bumps 120 are placed at a fine pitch, which can equal
the finest trace pitch of the substrate. The arrangement poses a
challenge for the assembly process because the bumping and bonding
pitch must be very fine. In FIG. 8, bumps 126 are arranged on an
area array providing greater space for a larger bumping and bonding
pitch and relieving the technological challenges for the assembly
process. Even in the array embodiments, the routing traces on the
substrate have the same effective pitch as in the perimeter row
arrangement, which relieves the burden of fine pitch bumping and
bonding without sacrificing the fine escape routing pitch
advantage.
[0078] FIGS. 6 and 7 show traces or leads 122 and narrow
interconnection pads 131 are formed by patterning a metal layer on
a die attach surface of substrate dielectric layer 132. The narrow
pads 131 can be formed as a widening of traces 122 at the
interconnection sites. The width of an interconnection pad W.sub.p
is the nominal or design dimension across the widened part of the
trace at the interconnection site. The width of the narrow
interconnection pad on the substrate is established according to
the bump base width or base diameter of the bumps on the
semiconductor die that is to be connected to the substrate. The
bump base width W.sub.b is the nominal or design diameter of the
generally round or circular contact interface between bump 120 and
die pad 133. The diameter of the bump, taken in a plane parallel to
the bump-pad interface, can be greater than W.sub.b, as illustrated
in FIGS. 7 and 9. The interconnection pad width W.sub.p is smaller
than the bump base width W.sub.b, e.g., W.sub.p can be as small as
20% of W.sub.b. In other embodiments, W.sub.p is in a range about
20% to about 80% of W.sub.b, or W.sub.p is less than W.sub.b and
greater than about 25% of W.sub.b, or W.sub.p is less than about
60% of W.sub.b.
[0079] The electrical interconnection of semiconductor die 134 is
made by joining bumps 120 onto the narrow interconnection pads 131
on leads 122. A narrow interconnection pad has a nominal or design
width about 120% of the nominal or trace design rule width, and
bump-on-narrow-lead (BONL) interconnection includes bumps connected
to widened parts of traces that are greater than about 120% of the
nominal or trace design rule width and less than the bump base
diameter. The interconnection made with bumps bonded to portions of
leads that are less than about 120% of the nominal or trace design
rule width is referred to as a bump-on-lead (BOL)
interconnection.
[0080] FIGS. 8 and 9 show signal escape traces or leads 128 and
narrow interconnection pads 136 formed by patterning a metal layer
on a die attach surface of substrate dielectric layer 137. The
signal escape traces 128 are routed across the die edge location,
indicated by broken line 130, and away from the die footprint. The
narrow pads 136 can be formed as a widening of traces 128 at the
interconnection sites. The width of an interconnection pad W.sub.p
is the nominal or design dimension across the widened part of the
trace at the interconnection site. The width of the narrow
interconnection pad on a substrate is established according to the
bump base width of the bumps on the die that is to be connected to
the substrate. The bump base width W.sub.b is the nominal or design
diameter of the generally round or circular contact interface
between bump 126 and die pad 138. The interconnection pad width
W.sub.p is smaller than the bump base width W.sub.b, and W.sub.p
can be as small as 20% of W.sub.b. In other embodiments, W.sub.p is
in a range about 20% to about 80% of W.sub.b, or W.sub.p is less
than W.sub.b and greater than about 25% of W.sub.b, W.sub.p is less
than about 60% of W.sub.b.
[0081] The electrical interconnection of semiconductor die 140 is
made by joining bumps 126 on the narrow interconnection pads 126 on
leads 128. Certain of the escape traces 142 leading across the die
edge location from interconnect sites in rows toward the interior
of the die footprint pass between bumps 126 on more peripheral rows
of interconnect sites. In embodiments as in FIGS. 6-9, no capture
pads and no solder mask is required.
[0082] FIGS. 10 and 11 show two examples of a BOL flipchip
interconnection, in a diagrammatic sectional view taken in a plane
parallel to the substrate surface. Certain features are shown as if
transparent. In this embodiment, a solder mask is provided, which
can have a nominal mask opening diameter in the range about 80
.mu.m to 90 .mu.m. Solder mask materials can be resolved at such
pitches and, particularly, substrates can be made comparatively
inexpensively with solder masks having 90 .mu.m openings and having
alignment tolerances plus or minus 25 .mu.m. In some embodiments
laminate substrates made according to standard design rules, such
as 4-metal layer laminates, are used. The traces can be about 90
.mu.m pitch and the narrow pads are arranged in a 270 .mu.m area
array providing an effective escape pitch about 90 .mu.m across the
edge of the die footprint, indicated by broken line 146.
[0083] In FIG. 10, the interconnection is achieved by mating the
bumps directly onto an narrow interconnect pad 147 on a narrow lead
or trace 148 patterned on a dielectric layer on the die attach
surface of substrate 149. Solder mask 150 serves to limit flow of
solder within the bounds of mask openings 151, preventing solder
flow away from the interconnect site along the solder-wettable
lead. The solder mask can additionally confine flow of molten
solder between leads, which can be accomplished in the course of
the assembly process.
[0084] In FIG. 11, narrow pads 154 on traces 152 are patterned on a
dielectric layer on the die attach surface of substrate 153. Solder
paste is provided at interconnect sites 154 on leads 152 to provide
a fusible medium for the interconnect. The openings 155 in solder
mask 156 serve to define the paste. The paste is dispensed,
reflowed, and coined if necessary to provide uniform surfaces to
meet the bumps. The solder paste can be applied in the course of
assembly using a substrate as described above with reference to
FIG. 10. Alternatively, a substrate can be provided with paste
suitably patterned prior to assembly. Other approaches to applying
solder selectively to the interconnect sites can be employed in the
solder-on-narrow-pad, including electroless plating and
electroplating techniques. The solder-on-narrow-pad configuration
provides additional solder volume for the interconnect, and can
accordingly provide higher product yield, and can also provide a
higher die standoff. A capillary underfill can be employed.
[0085] Accordingly, in some embodiments the solder-on-narrow-pad
configuration is employed for interconnection of a semiconductor
die having high-melting temperature bumps, such as a high lead
solder used for interconnection with ceramic substrates, onto an
organic substrate. The solder paste can be selected to have a
melting temperature low enough that the organic substrate is not
damaged during reflow. To form the interconnect in such
embodiments, the high-melting interconnect bumps are contacted with
the solder-on-narrow-pad sites, and the remelt fuses the
solder-on-narrow-pad to the bumps. Where a noncollapsible bump is
used, together with a solder-on-narrow-pad process, no preapplied
adhesive is required, as the displacement or flow of the solder is
limited by the fact that only a small quantity of solder is present
at each interconnect. The non-collapsible bump prevents collapse of
the assembly. In other embodiments, the solder-on-narrow-pad
configuration is employed for interconnection of a semiconductor
die having eutectic solder bumps.
[0086] The flipchip interconnection can be formed by providing a
substrate having narrow interconnection pads formed in a die attach
surface and a semiconductor die having bumps attached to
interconnect pads in an active surface, supporting the substrate
and the die, dispensing a quantity of a curable adhesive on the
substrate covering the narrow interconnection pads or on the active
side of the die, positioning the die with the active side of the
die toward the die attach surface of the substrate, aligning the
die and substrate and moving one toward the other so that the bumps
contact the corresponding narrow interconnection pads on the
substrate, applying a force to press the bumps onto the mating
narrow pads, sufficient to displace the adhesive from between the
bump and the mating narrow pad. The adhesive is partially cured.
The solder is melted and then re-solidified to form a metallurgical
interconnection between the bump and the narrow pad.
[0087] One embodiment of making a BONP interconnection is shown in
FIGS. 12a-12c. In FIG. 12a, substrate 112 has at least one
dielectric layer and having a metal layer on a die attach surface
159. The metal layer is patterned to provide circuitry,
particularly narrow interconnection pads 160 on traces or leads, on
the die attach surface. Substrate 158 is supported on a carrier or
stage 162, with a substrate surface opposite die attach surface 159
facing the support. A quantity of an encapsulating resin 163 is
dispensed over die attach surface 159 of substrate 158, covering
the narrow interconnection pads 160 on the leads. Semiconductor 164
has bumps 166 attached to die pads on active side 167. Bumps 166
include a fusible material which contacts the mating surfaces of
the narrow pads. A pick-and-place tool 168 including a chuck 169
picks up semiconductor die 164 by contact of the chuck with
backside 170 of the die. Using pick-and-place tool 168,
semiconductor die 164 is positioned facing substrate 158 with
active side 167 of the die toward the die attach surface of
substrate 158. Semiconductor die 164 and substrate 158 are aligned
and moved one toward the other, as shown by arrow M, so that bumps
166 contact the corresponding narrow interconnection pads 160 on
the traces or leads on the substrate. A force F is applied to press
bumps 166 onto mating surfaces 171 at narrow pads 160 on the leads,
as shown in FIG. 12b. The force F must be sufficient to displace
adhesive 163 from between bumps 166 and mating surfaces 171 at the
narrow interconnection pads 160. Bumps 166 can be deformed by the
force F, breaking the oxide film on the contacting surface of the
bumps and/or on mating surface 171 of narrow pads 160. The
deformation of bumps 166 can result in the fusible material of the
bumps being pressed onto the top and over the edges of the narrow
pads 160. Adhesive 163 is cured partially by heating to a selected
temperature. At this stage, adhesive 163 need only be partially
cured, that is, only to an extent sufficient subsequently to
prevent flow of molten solder along an interface between the
adhesive and the conductive traces. The fusible material of bumps
166 is melted and re-solidified forming a metallurgical
interconnection between bump 166 and narrow pad 160. Adhesive 163
is completely cured to finish the die mount and secure the
electrical interconnection at mating surface 171, as shown
generally at 172 in FIG. 12c. An electrical interconnect is thus
formed between bumps 166 and corresponding narrow interconnection
pads 160 on the leads, in a configuration as in FIG. 8. Other leads
173 are interconnected on narrow interconnection pads at other
localities, which would be visible in other sectional views. The
curing of adhesive 163 can be completed prior to, or concurrently
with, or following melting the solder. Typically, adhesive 163 is a
thermally curable adhesive, and the extent of curing at any phase
in the process is controlled by regulating the temperature. The
components can be heated and cured by raising the temperature of
chuck 169 on pick and place tool 168, or by raising the temperature
of the substrate support.
[0088] The process is shown in further detail in FIGS. 13a-13d. In
FIG. 13a, substrate 176 is provided on a die attach surface with
conductive traces and narrow interconnection pads 178 at
interconnect sites on the traces covered with an adhesive 179.
Semiconductor die 180 is positioned in relation to substrate 176
such that the active side of the die faces the die attach side of
the substrate and aligned by arrows A so that bumps 182 on the die
coincide with corresponding mating surfaces on narrow pads 178.
Semiconductor die 180 and substrate 176 are moved toward one
another so that bumps 182 contact the respective mating surfaces on
narrow pads 178. In FIG. 13b, a force is applied to move bumps 182
and narrow pads 178 against one another, displacing adhesive 179
and deforming the bumps onto mating surfaces 183 and over the edges
of the narrow pads. The deformation of bumps 182 on narrow pads 178
breaks the oxide film on the contact surfaces of the bumps and
mating surfaces 183 of the narrow pads establishing a good
electrical connection. The deformation of the bumps over the edges
of the narrow pads helps establish a good temporary mechanical
connection. The narrow interconnection pads of traces 184 are out
of the plane of FIG. 13b. Heat is applied to partially cure
adhesive 179, as shown in FIG. 13c. Additional heat is applied to
raise the temperature of bumps 182 sufficiently to cause the
fusible material of the bumps to melt and complete the cure of
adhesive 179, as shown in FIG. 13d. A metallurgical interconnection
is thus formed between bumps 182 and narrow interconnection pads
178 at mating surfaces 183. The cured adhesive 179 stabilizes the
die mount.
[0089] In an alternative embodiment, the adhesive can be
pre-applied to the die surface, or at least to the bumps on the die
surface, rather than to the substrate. The adhesive can be pooled
in a reservoir, and the active side of the die can be dipped in the
pool and removed so that a quantity of the adhesive is carried on
the bumps. Using a pick-and-place tool, the die is positioned
facing a supported substrate with the active side of the die toward
the die attach surface of the substrate. The die and substrate are
aligned and moved one toward the other so that the bumps contact
the corresponding traces or leads on the substrate. Such a method
is described in U.S. Pat. No. 6,780,682, which is hereby
incorporated by reference. The forcing, curing, and melting steps
are carried out as described above.
[0090] Alternatively, the flipchip interconnection is formed by
providing a substrate having narrow interconnection pads formed in
a die attach surface, providing a solder mask having openings over
the narrow pads and a semiconductor die having bumps attached to
interconnect pads in an active surface, supporting the substrate
and the die, positioning the die with the active side of the die
toward the die attach surface of the substrate, aligning the die
and substrate and moving one toward the other so that the bumps
contact the corresponding narrow pads on the substrate, and melting
and then re-solidifying to form the interconnection between the
bump and the narrow pad.
[0091] In another embodiment, the flipchip interconnection is
formed by providing a substrate having narrow interconnection pads
formed in a die attach surface, providing a solder mask having
openings over the narrow pads, depositing solder paste on the
narrow pads, attaching a semiconductor die having bumps to
interconnect pads in an active surface, supporting the substrate
and the die, positioning the die with the active side of the die
toward the die attach surface of the substrate, aligning the die
and substrate and moving one toward the other so that the bumps
contact the solder paste on the corresponding narrow pads on the
substrate, and melting and then re-solidifying the solder paste to
form a metallurgical interconnection between the bump and the
narrow pad.
[0092] A force and temperature schedule for the above processes is
shown in FIG. 14. Time runs from left to right on the horizontal
axis. A force profile 200 is shown as a thick solid line, and a
temperature profile 210 is shown as a dotted line. The temperature
profile begins at a temperature in the range about 80.degree. C. to
90.degree. C. The force profile begins at essentially zero force.
Beginning at an initial time t.sub.i, the force is rapidly raised
202 from F.sub.i to a displacement/deformation force F.sub.d and
held 204 at that force for a time, as discussed below. The force
F.sub.d is sufficient to displace the adhesive away from between
the bumps and mating surfaces of the narrow interconnection pads.
The force F.sub.d is sufficient to deform the fusible portion of
the bumps onto the mating surface, breaking the oxide films and
forming a good metal-to-metal metallurgical contact. In some
embodiments, the bumps flow over the edges of the narrow pads to
establish a mechanical interlock of the bumps and the narrow pads,
referred to as creep deformation. The total amount of force
required depends upon the bump material and dimensions and upon the
number of bumps, and can be determined without undue
experimentation.
[0093] As the force is raised, the temperature is also rapidly
raised 212 from an initial temperature T.sub.i to a gel temperature
T.sub.g. The gel temperature T.sub.g is a temperature sufficient to
partially cure the adhesive to a gel state. The force and
temperature ramps are set so that there is a short lag time
t.sub.def, following the moment when F.sub.d is reached and before
T.sub.g is reached, at least long enough to permit the elevated
force to displace the adhesive and deform the bumps before the
partial cure of the adhesive commences. The assembly is held 204
and 214 at the displacement/deformation pressure F.sub.d and at the
gel temperature T.sub.g for a time t.sub.gel sufficient to effect
the partial cure of the adhesive. The adhesive should become
sufficiently firm that it can subsequently maintain a good bump
profile during the solder remelt phase, that is, sufficiently firm
to prevent undesirable displacement of the molten fusible material
of the bump, or flow of the molten fusible material along the
narrow pads and leads.
[0094] Once the adhesive has partially cured to a sufficient
extent, the pressure can be ramped down rapidly 206 to
substantially no force, i.e., only the weight of the components.
The temperature is then rapidly raised further 216 to a temperature
T.sub.m sufficient to remelt the fusible portions of the bumps. The
assembly is held 218 at the remelt temperature T.sub.m for a time
t.sub.melt/cure at least sufficient to fully form the solder remelt
on the narrow pads, and sufficient to substantially though not
necessarily fully cure the adhesive. The temperature is ramped down
220 to the initial temperature T.sub.i, and eventually to ambient.
The process outlined in FIG. 14 can run its course over a time
period of 5-10 seconds.
[0095] The adhesive in FIG. 14 can be a no-flow underfill material.
In some approaches to flipchip interconnection, the metallurgical
interconnection is formed first, and then an underfill material is
flowed into the space between the die and substrate. The no-flow
underfill material is applied before the semiconductor die and
substrate are brought together, and the no-flow underfill material
is displaced by the approach of the bumps onto the narrow pads, and
by the opposed surfaces of the die and substrate. The adhesive for
the no-flow underfill material is a fast-gelling adhesive, that is,
a material that gels sufficiently at the gel temperature in a time
period in the order of 1-2 seconds. Typical materials for the
no-flow underfill adhesive include non-conductive pastes.
[0096] Alternative bump structures can be employed in the BONP
interconnects, such as composite bumps. Composite bumps have at
least two bump portions, made of different bump materials,
including one which is collapsible under reflow conditions, and one
which is substantially non-collapsible under reflow conditions. The
non-collapsible portion is attached to the interconnect site on the
die. Typical materials for the non-collapsible portion include
various solders having a high Pd content or Au. The collapsible
portion is joined to the non-collapsible portion, and the
collapsible portion makes the connection with the narrow
interconnect pad. Typical materials for the collapsible portion of
the composite bump include eutectic solders.
[0097] FIG. 15 shows a BONP interconnect employing a composite
bump. Semiconductor die 222 is provided with die pads on the active
side of the die with composite bumps 224 that include a
non-collapsible portion 226 and collapsible portion 228. The
collapsible portion 228 can be eutectic solder or a relatively low
temperature melt solder. The collapsible portion 228 contacts the
mating surface of narrow pad 230 formed on substrate 232 and, where
deformation of the fusible portion of the bump over the narrow pad
is desired, the collapsible portion of the bump is deformable under
the conditions of force employed. The non-collapsible portion 226
does not deform when the die is moved under pressure against the
substrate during processing, and does not melt during the reflow
phase of the process. Accordingly the non-collapsible portion 226
can be dimensioned to provide a standoff distance between the
active surface of semiconductor die 222 and the die attach surface
of substrate 232.
[0098] An interconnect in FIG. 15 can also be formed by bringing a
non-composite non-collapsible bump with high-Pb or Au into contact
with a narrow interconnect pad provided on the mating surface with
a fusible material, such as, a eutectic solder or a relatively low
temperature melt solder or solder paste. Alternatively, the narrow
interconnect pad can be provided on the mating surface with a
fusible material and the bumps can be composite bumps, also
provided with a collapsible or fusible portion. Where the narrow
interconnect pads are provided on the mating surface with a fusible
material, a solder mask can be employed, followed by a capillary
underfill, in the process.
[0099] The bumps in embodiments as shown in FIGS. 6-11 can be
composite bumps, as described in FIG. 15, or using non-collapsible
bumps with high-Pb or Au in a solder-on-narrow-pad method, as
described above.
[0100] As the techniques for forming the traces improve, it is
possible to reliably form traces having nominal or design rule
widths less than about 25 .mu.m. The reduced trace widths can
provide for increased routing density. A reliable mechanical
connection and good electrical interconnection can be made by
forming a narrow interconnect pad by widening the lead to an extent
dimensionally related to the bump base diameter, and limited to
less than the bump base diameter.
[0101] The narrow interconnect pad can be formed with a variety of
shapes. Some such shapes can be more readily manufacturable, and
some may provide other process advantages. The narrow pad can be
generally rectangular, either square or elongated, as shown with
narrow pad 240 on the end of trace 242 in FIG. 16a and narrow pad
244 on the end of trace 246 in FIG. 16b, or generally round, either
circular or elliptical, as shown with narrow pad 248 on the end of
trace 250 in FIG. 16c and narrow pad 252 on the end of trace 254 in
FIG. 16d. Other shapes can be used such as shown in FIG. 16e with
semicircular end portions 256 separated lengthwise by a square or
rectangular portion 257 on the end of trace 258. The narrow pad can
be formed as a symmetrical or asymmetrical widening in the lead or
trace shown as a generally rectangular pad 260 on the end of trace
262 in FIG. 17a and narrow pad 264 on the end of trace 266 in FIG.
17b. Also, the narrow pad need not be situated at, or near, the end
of the lead or trace, but can be formed at any point where
interconnection is specified, as shown in FIG. 17c with generally
rectangular pad 268 formed along trace 270. Forming the pad longer
than wide increases the wettable mating surface of the narrow pad
by nature of the planar surface plus the exposed parts of the
sides, and can improve the mechanical strength of the
interconnection. Where the pad is longer than wide, the tolerance
for misalignment of solder mask openings or bump is increased,
particularly where the pad is at the end of the trace, an elongated
pad can reduce the likelihood that a solder mask opening or bump
will be situated off the end of the pad.
[0102] FIGS. 18a-18b show an embodiment with a generally
rectangular solder mask opening, either square or elongated. A
square or rectangle of a given width has a greater area than a
circle or ellipse having the same width or diameter along short
axis. In FIG. 18a, square mask opening 272 has a capacity to hold a
greater quantity of solder paste or other fusible material, and can
provide an advantage where a fusible material such as a solder
paste is to be applied to the mating surfaces on narrow pads 273,
as formed on trace 274, prior to mating with the bumps. FIG. 18b
shows a rectangular mask opening 275 over narrow pad 276 formed on
trace 278 with similar capacity to hold a greater quantity of
solder paste or other fusible material. Also, it can be easier to
print a fusible material into a square or rectangular mask opening
than into a circular or elliptical mask opening, because there is
greater tolerance for misalignment in the printing process. Given a
width limitation for the mask opening, a square or rectangular mask
opening provides a greater open area for mounting a large bump on
pad 273 or 276 during the interconnection process.
[0103] Various narrow pad configurations are shown in FIG. 19 in
relation to a circular mask opening 280 in solder mask 282. The
mask opening in each example has a width or diameter W.sub.m of
about 90 .mu.m. A BOL configuration is shown at 284 with lead or
trace 286 having a nominal design width W.sub.L of about 30 .mu.m.
A narrow pad having a rectangular shape is shown at 288 with lead
or trace 290 having a nominal design width W.sub.L' of about 30
.mu.m. The rectangular narrow pad 288 has a width W.sub.P of about
45 .mu.m. A narrow pad having an oval shape is shown at 292 formed
at a wider lead or trace 294, having a nominal design width
W.sub.L'' of about 50 .mu.m. The oval portion of narrow pad 292 has
a width W.sub.P' of about 55 .mu.m. A narrow pad having a
rectangular shape expanded with an oval shape is shown at 296. The
narrower lead or trace 298 at which narrow pad 296 is formed has a
nominal design width W.sub.L''' of about 30 .mu.m. The rectangular
portion of narrow pad 296 has a width W.sub.P'' of about 45 .mu.m,
and the oval expanded portion has a width WPE of about 50
.mu.m.
[0104] Various solder mask opening configurations are shown in FIG.
20 in relation to a lead or trace 300 or narrow pad 304. In these
examples the lead or narrow pad at the interconnect site has a
width W.sub.L of about 40 .mu.m. In a first example, a circular
solder mask opening 302 having a width or diameter W.sub.m of about
90 .mu.m, exposes an interconnect site portion 304. In a second
example, a rectangular solder mask opening 306 having a width
across the lead or narrow pad W.sub.m' of about 80 .mu.m, and a
length L.sub.m' of about 120 .mu.m, exposes an interconnect site
portion 308. In a third example, an elliptical solder mask opening
310 having a width across the lead or narrow pad W.sub.m'' of about
80 .mu.m, and a length L.sub.m'' of about 120 .mu.m exposes an
interconnect site portion 312. Both the rectangular opening 306 and
oval opening 310 expose a greater length or area of the lead or pad
312 than does the circular solder mask opening 302, even though the
circular opening has a greater diameter, which provides a greater
area for solder reflow during the interconnect process, and can
result in a more robust interconnection. The area exposed by the
rectangular opening 306 is slightly greater than that provided by
the elliptical opening 310 having the same width and length.
Moreover, the area would be reduced if there were a slight
misalignment of the elliptical opening, but not by a slight
misalignment of the rectangular opening. As a practical matter,
however, a design rectangular opening can have more or less rounded
corners because of resolution limitations in processes for
patterning openings in the solder mask dielectric.
[0105] The diameter of the bump base on the die can be about 90
.mu.m, and the narrow interconnect pad is formed on the substrate
to a width in a range about 25 .mu.m, where the trace width is less
than about 25 .mu.m, to about 50 .mu.m. The narrow interconnect pad
provides a significant improvement in routing density, as compared
with a substrate having a conventional capture pad having a much
larger diameter, typically two to four times as great as the trace
width.
[0106] The BOL, BONL, and BONP interconnection structures shown in
FIGS. 6-20 can be produced by any of several methods, with or
without a solder mask. In general, interconnect bumps are affixed
onto interconnect pads on the active side of the die. An upper die
attach surface of the substrate has an upper metal layer patterned
to provide the traces and narrow pads at interconnect sites as
appropriate for interconnection with the arrangement of bumps on
the particular die. An encapsulating resin adhesive is employed to
confine the solder flow during a melt phase of the interconnection
process. The BOL, BONL, and BONP interconnects can provide a
significantly higher signal trace escape routing density. The
conductive traces have a pitch as determined by minimum spacing
between adjacent conductive traces that can be placed on the
substrate and the width of the interconnect site provides a routing
density equal to the pitch of the conductive traces.
[0107] FIGS. 21-26 describe other embodiments with various
interconnect structures which can be used with the BOL, BONL, or
BONP interconnect, as described in FIGS. 6-20. FIG. 21a shows a
semiconductor wafer 320 with a base substrate material 322, such as
silicon, germanium, gallium arsenide, indium phosphide, or silicon
carbide, for structural support. A plurality of semiconductor die
or components 324 is formed on wafer 320 separated by saw streets
326 as described above.
[0108] FIG. 21b shows a cross-sectional view of a portion of
semiconductor wafer 320. Each semiconductor die 324 has a back
surface 328 and active surface 330 containing analog or digital
circuits implemented as active devices, passive devices, conductive
layers, and dielectric layers formed within the die and
electrically interconnected according to the electrical design and
function of the die. The circuit can include one or more
transistors, diodes, and other circuit elements formed within
active surface 330 to implement analog circuits or digital
circuits, such as digital signal processor (DSP), ASIC, memory, or
other signal processing circuit. Semiconductor die 324 may also
contain integrated passive devices (IPDs), such as inductors,
capacitors, and resistors, for RF signal processing. In one
embodiment, semiconductor die 324 is a flipchip type semiconductor
die.
[0109] An electrically conductive layer 332 is formed over active
surface 330 using PVD, CVD, electrolytic plating, electroless
plating process, or other suitable metal deposition process.
Conductive layer 332 can be one or more layers of Al, Cu, Sn, Ni,
Au, Ag, or other suitable electrically conductive material.
Conductive layer 332 operates as contact pads electrically
connected to the circuits on active surface 330.
[0110] FIG. 21c shows a portion of semiconductor wafer 320 with an
interconnect structure formed over contact pads 332. An
electrically conductive bump material 334 is deposited over contact
pads 332 using an evaporation, electrolytic plating, electroless
plating, ball drop, or screen printing process. Bump material 334
can be Al, Sn, Ni, Au, Ag, Pb, Bi, Cu, solder, and combinations
thereof, with an optional flux solution. Bump material 334 can be
eutectic Sn/Pb, high-lead solder, or lead-free solder. Bump
material 334 is generally compliant and undergoes plastic
deformation greater than about 25 .mu.m under a force equivalent to
a vertical load of about 200 grams. Bump material 334 is bonded to
contact pad 332 using a suitable attachment or bonding process.
Bump material 334 can be compression bonded to contact pad 332.
Bump material 334 can also be reflowed by heating the material
above its melting point to form spherical balls or bumps 336, as
shown in FIG. 21d. In some applications, bumps 336 are reflowed a
second time to improve electrical connection to contact pad 332.
Bumps 336 represent one type of interconnect structure that can be
formed over contact pad 332. The interconnect structure can also
use stud bump, micro bump, or other electrical interconnect.
[0111] FIG. 21e shows another embodiment of the interconnect
structure formed over contact pads 332 as composite bumps 338
including a non-fusible or non-collapsible portion 340 and fusible
or collapsible portion 342. The fusible or collapsible and
non-fusible or non-collapsible attributes are defined for bumps 338
with respect to reflow conditions. The non-fusible portion 340 can
be Au, Cu, Ni, high-lead solder, or lead-tin alloy. The fusible
portion 342 can be Sn, lead-free alloy, Sn--Ag alloy, Sn--Ag--Cu
alloy, Sn--Ag-indium (In) alloy, eutectic solder, tin alloys with
Ag, Cu, or Pb, or other relatively low temperature melt solder. In
one embodiment, given a contact pad 332 width or diameter of 100
.mu.m, the non-fusible portion 340 is about 45 .mu.m in height and
fusible portion 342 is about 35 .mu.m in height.
[0112] FIG. 21f shows another embodiment of the interconnect
structure formed over contact pads 332 as bump 344 over conductive
pillar 346. Bump 344 is fusible or collapsible and conductive
pillar 346 is non-fusible or non-collapsible. The fusible or
collapsible and non-fusible or non-collapsible attributes are
defined with respect to reflow conditions. Bump 344 can be Sn,
lead-free alloy, Sn--Ag alloy, Sn--Ag--Cu alloy, Sn--Ag--In alloy,
eutectic solder, tin alloys with Ag, Cu, or Pb, or other relatively
low temperature melt solder. Conductive pillar 346 can be Au, Cu,
Ni, high-lead solder, or lead-tin alloy. In one embodiment,
conductive pillar 346 is a Cu pillar and bump 344 is a solder cap.
Given a contact pad 332 width or diameter of 100 .mu.m, conductive
pillar 346 is about 45 .mu.m in height and bump 344 is about 35
.mu.m in height.
[0113] FIG. 21g shows another embodiment of the interconnect
structure formed over contact pads 332 as bump material 348 with
asperities 350. Bump material 348 is soft and deformable under
reflow conditions with a low yield strength and high elongation to
failure, similar to bump material 334. Asperities 350 are formed
with a plated surface finish and are shown exaggerated in the
figures for purposes of illustration. The scale of asperities 350
is generally in the order about 1-25 .mu.m. The asperities can also
be formed on bump 336, composite bump 338, and bump 344.
[0114] In FIG. 21h, semiconductor wafer 320 is singulated through
saw street 326 using a saw blade or laser cutting tool 352 into
individual semiconductor die 324.
[0115] FIG. 22a shows a substrate or PCB 354 with conductive trace
356. Substrate 354 can be a single-sided FR5 laminate or 2-sided
BT-resin laminate. Semiconductor die 324 is positioned so that bump
material 334 is aligned with an interconnect site on conductive
trace 356, see FIGS. 30a-30g. Alternatively, bump material 334 can
be aligned with a conductive pad or other interconnect site formed
on substrate 354. Bump material 334 is wider than conductive trace
356. In one embodiment, bump material 334 has a width of less than
100 .mu.m and conductive trace or pad 356 has a width of 35 .mu.m
for a bump pitch of 150 .mu.m. Conductive trace 356 could be part
of the BOL, BONL, or BONP interconnect of FIGS. 6-20.
[0116] A pressure or force F is applied to back surface 328 of
semiconductor die 324 to press bump material 334 onto conductive
trace 356. The force F can be applied with an elevated temperature.
Due to the compliant nature of bump material 334, the bump material
deforms or extrudes around the top surface and side surfaces of
conductive trace 356, referred to as BOL. In particular, the
application of pressure causes bump material 334 to undergo a
plastic deformation greater than about 25 .mu.m under force F
equivalent to a vertical load of about 200 grams and cover the top
surface and side surfaces of the conductive trace, as shown in FIG.
22b. Bump material 334 can also be metallurgically connected to
conductive trace 356 by bringing the bump material in physical
contact with the conductive trace and then reflowing the bump
material under a reflow temperature.
[0117] By making conductive trace 356 narrower than bump material
334, the conductive trace pitch can be reduced to increase routing
density and I/O count. The narrower conductive trace 356 reduces
the force F needed to deform bump material 334 around the
conductive trace. For example, the requisite force F may be 30-50%
of the force needed to deform bump material against a conductive
trace or pad that is wider than the bump material. The lower
compressive force F is useful for fine pitch interconnect and small
die to maintain coplanarity with a specified tolerance and achieve
uniform z-direction deformation and high reliability interconnect
union. In addition, deforming bump material 334 around conductive
trace 356 mechanically locks the bump to the trace to prevent die
shifting or die floating during reflow.
[0118] FIG. 22c shows bump 336 formed over contact pad 332 of
semiconductor die 324. Semiconductor die 324 is positioned so that
bump 336 is aligned with an interconnect site on conductive trace
356. Alternatively, bump 336 can be aligned with a conductive pad
or other interconnect site formed on substrate 354. Bump 336 is
wider than conductive trace 356. Conductive trace 356 could be part
of the BOL, BONL, or BONP interconnect of FIGS. 6-20.
[0119] A pressure or force F is applied to back surface 328 of
semiconductor die 324 to press bump 336 onto conductive trace 356.
The force F can be applied with an elevated temperature. Due to the
compliant nature of bump 336, the bump deforms or extrudes around
the top surface and side surfaces of conductive trace 356. In
particular, the application of pressure causes bump material 336 to
undergo a plastic deformation and cover the top surface and side
surfaces of conductive trace 356. Bump 336 can also be
metallurgically connected to conductive trace 356 by bringing the
bump in physical contact with the conductive trace under reflow
temperature.
[0120] By making conductive trace 356 narrower than bump 336, the
conductive trace pitch can be reduced to increase routing density
and I/O count. The narrower conductive trace 356 reduces the force
F needed to deform bump 336 around the conductive trace. For
example, the requisite force F may be 30-50% of the force needed to
deform a bump against a conductive trace or pad that is wider than
the bump. The lower compressive force F is useful for fine pitch
interconnect and small die to maintain coplanarity within a
specified tolerance and achieve uniform z-direction deformation and
high reliability interconnect union. In addition, deforming bump
336 around conductive trace 356 mechanically locks the bump to the
trace to prevent die shifting or die floating during reflow.
[0121] FIG. 22d shows composite bump 338 formed over contact pad
332 of semiconductor die 324. Semiconductor die 324 is positioned
so that composite bump 338 is aligned with an interconnect site on
conductive trace 356. Alternatively, composite bump 338 can be
aligned with a conductive pad or other interconnect site formed on
substrate 354. Composite bump 338 is wider than conductive trace
356. Conductive trace 356 could be part of the BOL, BONL, or BONP
interconnect of FIGS. 6-20.
[0122] A pressure or force F is applied to back surface 328 of
semiconductor die 324 to press fusible portion 342 onto conductive
trace 356. The force F can be applied with an elevated temperature.
Due to the compliant nature of fusible portion 342, the fusible
portion deforms or extrudes around the top surface and side
surfaces of conductive trace 356. In particular, the application of
pressure causes fusible portion 342 to undergo a plastic
deformation and cover the top surface and side surfaces of
conductive trace 356. Composite bump 338 can also be
metallurgically connected to conductive trace 356 by bringing
fusible portion 342 in physical contact with the conductive trace
under reflow temperature. The non-fusible portion 340 does not melt
or deform during the application of pressure or temperature and
retains its height and shape as a vertical standoff between
semiconductor die 324 and substrate 354. The additional
displacement between semiconductor die 324 and substrate 354
provides greater coplanarity tolerance between the mating
surfaces.
[0123] During a reflow process, a large number (e.g., thousands) of
composite bumps 338 on semiconductor die 324 are attached to
interconnect sites on conductive trace 356 of substrate 354. Some
of the bumps 338 may fail to properly connect to conductive trace
356, particularly if die 324 is warped. Recall that composite bump
338 is wider than conductive trace 356. With a proper force
applied, the fusible portion 342 deforms or extrudes around the top
surface and side surfaces of conductive trace 356 and mechanically
locks composite bump 338 to the conductive trace. The mechanical
interlock is formed by nature of the fusible portion 342 being
softer and more compliant than conductive trace 356 and therefore
deforming over the top surface and around the side surfaces of the
conductive trace for greater contact surface area. The mechanical
interlock between composite bump 338 and conductive trace 356 holds
the bump to the conductive trace during reflow, i.e., the bump and
conductive trace do not lose contact. Accordingly, composite bump
338 mating to conductive trace 356 reduces bump interconnect
failures.
[0124] FIG. 22e shows conductive pillar 346 and bump 344 formed
over contact pad 332 of semiconductor die 324. Semiconductor die
324 is positioned so that bump 344 is aligned with an interconnect
site on conductive trace 356. Alternatively, bump 344 can be
aligned with a conductive pad or other interconnect site formed on
substrate 354. Bump 344 is wider than conductive trace 356.
Conductive trace 356 could be part of the BOL, BONL, or BONP
interconnect of FIGS. 6-20.
[0125] A pressure or force F is applied to back surface 328 of
semiconductor die 324 to press bump 344 onto conductive trace 356.
The force F can be applied with an elevated temperature. Due to the
compliant nature of bump 344, the bump deforms or extrudes around
the top surface and side surfaces of conductive trace 356. In
particular, the application of pressure causes bump 344 to undergo
a plastic deformation and cover the top surface and side surfaces
of conductive trace 356. Conductive pillar 346 and bump 344 can
also be metallurgically connected to conductive trace 356 by
bringing the bump in physical contact with the conductive trace
under reflow temperature. Conductive pillar 346 does not melt or
deform during the application of pressure or temperature and
retains its height and shape as a vertical standoff between
semiconductor die 324 and substrate 354. The additional
displacement between semiconductor die 324 and substrate 354
provides greater coplanarity tolerance between the mating surfaces.
The wider bump 344 and narrower conductive trace 356 have similar
low requisite compressive force and mechanical locking features and
advantages described above for bump material 334 and bump 336.
[0126] FIG. 22f shows bump material 348 with asperities 350 formed
over contact pad 332 of semiconductor die 324. Semiconductor die
324 is positioned so that bump material 348 is aligned with an
interconnect site on conductive trace 356. Alternatively, bump
material 348 can be aligned with a conductive pad or other
interconnect site formed on substrate 354. Bump material 348 is
wider than conductive trace 356. A pressure or force F is applied
to back surface 328 of semiconductor die 324 to press bump material
348 onto conductive trace 356. The force F can be applied with an
elevated temperature. Due to the compliant nature of bump material
348, the bump deforms or extrudes around the top surface and side
surfaces of conductive trace 356. In particular, the application of
pressure causes bump material 348 to undergo a plastic deformation
and cover the top surface and side surfaces of conductive trace
356. In addition, asperities 350 are metallurgically connected to
conductive trace 356. Asperities 350 are sized on the order about
1-25 .mu.m.
[0127] FIG. 22g shows a substrate or PCB 358 with trapezoidal
conductive trace 360 having angled or sloped sides. Bump material
361 is formed over contact pad 332 of semiconductor die 324.
Semiconductor die 324 is positioned so that bump material 361 is
aligned with an interconnect site on conductive trace 360.
Alternatively, bump material 361 can be aligned with a conductive
pad or other interconnect site formed on substrate 358. Bump
material 361 is wider than conductive trace 360. Conductive trace
360 could be part of the BOL, BONL, or BONP interconnect of FIGS.
6-20.
[0128] A pressure or force F is applied to back surface 328 of
semiconductor die 324 to press bump material 361 onto conductive
trace 360. The force F can be applied with an elevated temperature.
Due to the compliant nature of bump material 361, the bump material
deforms or extrudes around the top surface and side surfaces of
conductive trace 360. In particular, the application of pressure
causes bump material 361 to undergo a plastic deformation under
force F to cover the top surface and the angled side surfaces of
conductive trace 360. Bump material 361 can also be metallurgically
connected to conductive trace 360 by bringing the bump material in
physical contact with the conductive trace and then reflowing the
bump material under a reflow temperature.
[0129] FIGS. 23a-23d show a BOL embodiment of semiconductor die 324
and elongated composite bump 362 having a non-fusible or
non-collapsible portion 364 and fusible or collapsible portion 366.
The non-fusible portion 364 can be Au, Cu, Ni, high-lead solder, or
lead-tin alloy. The fusible portion 366 can be Sn, lead-free alloy,
Sn--Ag alloy, Sn--Ag--Cu alloy, Sn--Ag--In alloy, eutectic solder,
tin alloys with Ag, Cu, or Pb, or other relatively low temperature
melt solder. The non-fusible portion 364 makes up a larger part of
composite bump 362 than the fusible portion 366. The non-fusible
portion 364 is fixed to contact pad 332 of semiconductor die
324.
[0130] Semiconductor die 324 is positioned so that composite bump
362 is aligned with an interconnect site on conductive trace 368
formed on substrate 370, as shown in FIG. 23a. Composite bump 362
is tapered along conductive trace 368, i.e., the composite bump has
a wedge shape, longer along a length of conductive trace 368 and
narrower across the conductive trace. The tapered aspect of
composite bump 362 occurs along the length of conductive trace 368.
The view in FIG. 23a shows the shorter aspect or narrowing taper
co-linear with conductive trace 368. The view in FIG. 23b, normal
to FIG. 23a, shows the longer aspect of the wedge-shaped composite
bump 362. The shorter aspect of composite bump 362 is wider than
conductive trace 368. The fusible portion 366 collapses around
conductive trace 368 upon application of pressure and/or reflow
with heat, as shown in FIGS. 23c and 23d. The non-fusible portion
364 does not melt or deform during reflow and retains its form and
shape. The non-fusible portion 364 can be dimensioned to provide a
standoff distance between semiconductor die 324 and substrate 370.
A finish such as Cu OSP can be applied to substrate 370. Conductive
trace 368 could be part of the BOL, BONL, or BONP interconnect of
FIGS. 6-20.
[0131] During a reflow process, a large number (e.g., thousands) of
composite bumps 362 on semiconductor die 324 are attached to
interconnect sites on conductive trace 368 of substrate 370. Some
of the bumps 362 may fail to properly connect to conductive trace
368, particularly if semiconductor die 324 is warped. Recall that
composite bump 362 is wider than conductive trace 368. With a
proper force applied, the fusible portion 366 deforms or extrudes
around the top surface and side surfaces of conductive trace 368
and mechanically locks composite bump 362 to the conductive trace.
The mechanical interlock is formed by nature of the fusible portion
366 being softer and more compliant than conductive trace 368 and
therefore deforming around the top surface and side surfaces of the
conductive trace for greater contact area. The wedge-shape of
composite bump 362 increases contact area between the bump and
conductive trace, e.g., along the longer aspect of FIGS. 23b and
23d, without sacrificing pitch along the shorter aspect of FIGS.
23a and 23c. The mechanical interlock between composite bump 362
and conductive trace 368 holds the bump to the conductive trace
during reflow, i.e., the bump and conductive trace do not lose
contact. Accordingly, composite bump 362 mating to conductive trace
368 reduces bump interconnect failures.
[0132] FIGS. 24a-24d show a BOL embodiment of semiconductor die 324
with bump material 374 formed over contact pads 332, similar to
FIG. 21c. In FIG. 24a, bump material 374 is generally compliant and
undergoes plastic deformation greater than about 25 .mu.m under a
force equivalent to a vertical load of about 200 grams. Bump
material 374 is wider than conductive trace 376 on substrate 378. A
plurality of asperities 380 is formed on conductive trace 376 with
a height on the order about 1-25 .mu.m.
[0133] Semiconductor die 324 is positioned so that bump material
374 is aligned with an interconnect site on conductive trace 376.
Alternatively, bump material 374 can be aligned with a conductive
pad or other interconnect site formed on substrate 378. A pressure
or force F is applied to back surface 328 of semiconductor die 324
to press bump material 374 onto conductive trace 376 and asperities
380, as shown in FIG. 24b. The force F can be applied with an
elevated temperature. Due to the compliant nature of bump material
374, the bump material deforms or extrudes around the top surface
and side surfaces of conductive trace 376 and asperities 380. In
particular, the application of pressure causes bump material 374 to
undergo a plastic deformation and cover the top surface and side
surfaces of conductive trace 376 and asperities 380. The plastic
flow of bump material 374 creates macroscopic mechanical
interlocking points between the bump material and the top surface
and side surfaces of conductive trace 376 and asperities 380. The
plastic flow of bump material 374 occurs around the top surface and
side surfaces of conductive trace 376 and asperities 380, but does
not extend excessively onto substrate 378, which could cause
electrical shorting and other defects. The mechanical interlock
between the bump material and the top surface and side surfaces of
conductive trace 376 and asperities 380 provides a robust
connection with greater contact area between the respective
surfaces, without significantly increasing the bonding force. The
mechanical interlock between the bump material and the top surface
and side surfaces of conductive trace 376 and asperities 380 also
reduces lateral die shifting during subsequent manufacturing
processes, such as encapsulation.
[0134] FIG. 24c shows another BOL embodiment with bump material 374
narrower than conductive trace 376. A pressure or force F is
applied to back surface 328 of semiconductor die 324 to press bump
material 374 onto conductive trace 376 and asperities 380. The
force F can be applied with an elevated temperature. Due to the
compliant nature of bump material 374, the bump material deforms or
extrudes over the top surface of conductive trace 376 and
asperities 380. In particular, the application of pressure causes
bump material 374 to undergo a plastic deformation and cover the
top surface of conductive trace 376 and asperities 380. The plastic
flow of bump material 374 creates macroscopic mechanical
interlocking points between the bump material and the top surface
of conductive trace 376 and asperities 380. The mechanical
interlock between the bump material and the top surface of
conductive trace 376 and asperities 380 provides a robust
connection with greater contact area between the respective
surfaces, without significantly increasing the bonding force. The
mechanical interlock between the bump material and the top surface
of conductive trace 376 and asperities 380 also reduces lateral die
shifting during subsequent manufacturing processes, such as
encapsulation.
[0135] FIG. 24d shows another BOL embodiment with bump material 374
formed over an edge of conductive trace 376, i.e., part of the bump
material is over the conductive trace and part of the bump material
is not over the conductive trace. A pressure or force F is applied
to back surface 328 of semiconductor die 324 to press bump material
374 onto conductive trace 376 and asperities 380. The force F can
be applied with an elevated temperature. Due to the compliant
nature of bump material 374, the bump material deforms or extrudes
over the top surface and side surfaces of conductive trace 376 and
asperities 380. In particular, the application of pressure causes
bump material 374 to undergo a plastic deformation and cover the
top surface and side surfaces of conductive trace 376 and
asperities 380. The plastic flow of bump material 374 creates
macroscopic mechanical interlocking between the bump material and
the top surface and side surfaces of conductive trace 376 and
asperities 380. The mechanical interlock between the bump material
and the top surface and side surfaces of conductive trace 376 and
asperities 380 provides a robust connection with greater contact
area between the respective surfaces, without significantly
increasing the bonding force. The mechanical interlock between the
bump material and the top surface and side surfaces of conductive
trace 376 and asperities 380 also reduces lateral die shifting
during subsequent manufacturing processes, such as
encapsulation.
[0136] FIGS. 25a-25c show a BOL embodiment of semiconductor die 324
with bump material 384 formed over contact pads 332, similar to
FIG. 21c. A tip 386 extends from the body of bump material 384 as a
stepped bump with tip 386 narrower than the body of bump material
384, as shown in FIG. 25a. Semiconductor die 324 is positioned so
that bump material 384 is aligned with an interconnect site on
conductive trace 388 on substrate 390. More specifically, tip 386
is centered over an interconnect site on conductive trace 388.
Alternatively, bump material 384 and tip 386 can be aligned with a
conductive pad or other interconnect site formed on substrate 390.
Bump material 384 is wider than conductive trace 388 on substrate
390.
[0137] Conductive trace 388 is generally compliant and undergoes
plastic deformation greater than about 25 .mu.m under a force
equivalent to a vertical load of about 200 grams. A pressure or
force F is applied to back surface 328 of semiconductor die 324 to
press tip 384 onto conductive trace 388. The force F can be applied
with an elevated temperature. Due to the compliant nature of
conductive trace 388, the conductive trace deforms around tip 386,
as shown in FIG. 25b. In particular, the application of pressure
causes conductive trace 388 to undergo a plastic deformation and
cover the top surface and side surfaces of tip 386.
[0138] FIG. 25c shows another BOL embodiment with rounded bump
material 394 formed over contact pads 332. A tip 396 extends from
the body of bump material 394 to form a stud bump with the tip
narrower than the body of bump material 394. Semiconductor die 324
is positioned so that bump material 394 is aligned with an
interconnect site on conductive trace 398 on substrate 400. More
specifically, tip 396 is centered over an interconnect site on
conductive trace 398. Alternatively, bump material 394 and tip 396
can be aligned with a conductive pad or other interconnect site
formed on substrate 400. Bump material 394 is wider than conductive
trace 398 on substrate 400.
[0139] Conductive trace 398 is generally compliant and undergoes
plastic deformation greater than about 25 .mu.m under a force
equivalent to a vertical load of about 200 grams. A pressure or
force F is applied to back surface 328 of semiconductor die 324 to
press tip 396 onto conductive trace 398. The force F can be applied
with an elevated temperature. Due to the compliant nature of
conductive trace 398, the conductive trace deforms around tip 396.
In particular, the application of pressure causes conductive trace
398 to undergo a plastic deformation and cover the top surface and
side surfaces of tip 396.
[0140] The conductive traces described in FIGS. 22a-22g, 23a-23d,
and 24a-24d can also be compliant material as described in FIGS.
25a-25c.
[0141] FIGS. 26a-26b show a BOL embodiment of semiconductor die 324
with bump material 404 formed over contact pads 332, similar to
FIG. 21c. Bump material 404 is generally compliant and undergoes
plastic deformation greater than about 25 .mu.m under a force
equivalent to a vertical load of about 200 grams. Bump material 404
is wider than conductive trace 406 on substrate 408. A conductive
via 410 is formed through conductive trace 406 with an opening 412
and conductive sidewalls 414, as shown in FIG. 26a. Conductive
trace 406 could be part of the BOL, BONL, or BONP interconnect of
FIGS. 6-20.
[0142] Semiconductor die 324 is positioned so that bump material
404 is aligned with an interconnect site on conductive trace 406,
see FIGS. 30-30g. Alternatively, bump material 404 can be aligned
with a conductive pad or other interconnect site formed on
substrate 408. A pressure or force F is applied to back surface 328
of semiconductor die 324 to press bump material 404 onto conductive
trace 406 and into opening 413 of conductive via 410. The force F
can be applied with an elevated temperature. Due to the compliant
nature of bump material 404, the bump material deforms or extrudes
around the top surface and side surfaces of conductive trace 406
and into opening 412 of conductive vias 410, as shown in FIG. 26b.
In particular, the application of pressure causes bump material 404
to undergo a plastic deformation and cover the top surface and side
surfaces of conductive trace 406 and into opening 412 of conductive
via 410. Bump material 404 is thus electrically connected to
conductive trace 406 and conductive sidewalls 414 for z-direction
vertical interconnect through substrate 408. The plastic flow of
bump material 404 creates a mechanical interlock between the bump
material and the top surface and side surfaces of conductive trace
406 and opening 412 of conductive via 410. The mechanical interlock
between the bump material and the top surface and side surfaces of
conductive trace 406 and opening 412 of conductive via 410 provides
a robust connection with greater contact area between the
respective surfaces, without significantly increasing the bonding
force. The mechanical interlock between the bump material and the
top surface and side surfaces of conductive trace 406 and opening
412 of conductive via 410 also reduces lateral die shifting during
subsequent manufacturing processes, such as encapsulation. Since
conductive via 410 is formed within the interconnect site with bump
material 404, the total substrate interconnect area is reduced.
[0143] In the BOL embodiments of FIGS. 22a-22g, 23a-23d, 24a-24d,
25a-25c, and 26a-26b, by making the conductive trace narrower than
the interconnect structure, the conductive trace pitch can be
reduced to increase routing density and I/O count. The narrower
conductive trace reduces the force F needed to deform the
interconnect structure around the conductive trace. For example,
the requisite force F may be 30-50% of the force needed to deform a
bump against a conductive trace or pad that is wider than the bump.
The lower compressive force F is useful for fine pitch interconnect
and small die to maintain coplanarity within a specified tolerance
and achieve uniform z-direction deformation and high reliability
interconnect union. In addition, deforming the interconnect
structure around the conductive trace mechanically locks the bump
to the trace to prevent die shifting or die floating during
reflow.
[0144] FIGS. 27a-27c show a mold underfill (MUF) process to deposit
encapsulant around the bumps between the semiconductor die and
substrate. FIG. 27a shows semiconductor die 324 mounted to
substrate 354 using bump material 334 from FIG. 22b and placed
between upper mold support 416 and lower mold support 418 of chase
mold 420. The other semiconductor die and substrate combinations
from FIGS. 22a-22g, 23a-23d, 24a-24d, 25a-25c, and 26a-26b can be
placed between upper mold support 416 and lower mold support 418 of
chase mold 420. The upper mold support 416 includes compressible
releasing film 422.
[0145] In FIG. 27b, upper mold support 416 and lower mold support
418 are brought together to enclose semiconductor die 324 and
substrate 354 with an open space over the substrate and between the
semiconductor die and substrate. Compressible releasing film 422
conforms to back surface 328 and side surfaces of semiconductor die
324 to block formation of encapsulant on these surfaces. An
encapsulant 424 in a liquid state is injected into one side of
chase mold 420 with nozzle 426 while an optional vacuum assist 428
draws pressure from the opposite side to uniformly fill the open
space over substrate 354 and the open space between semiconductor
die 324 and substrate 354 with the encapsulant. Encapsulant 424 can
be polymer composite material, such as epoxy resin with filler,
epoxy acrylate with filler, or polymer with proper filler.
Encapsulant 424 is non-conductive and environmentally protects the
semiconductor device from external elements and contaminants.
Compressible material 422 prevents encapsulant 424 from flowing
over back surface 328 and around the side surfaces of semiconductor
die 324. Encapsulant 424 is cured. The back surface 328 and side
surfaces of semiconductor die 324 remain exposed from encapsulant
424.
[0146] FIG. 27c shows an embodiment of MUF and mold overfill (MOF),
i.e., without compressible material 422. Semiconductor die 324 and
substrate 354 are placed between upper mold support 416 and lower
mold support 418 of chase mold 420. The upper mold support 416 and
lower mold support 418 are brought together to enclose
semiconductor die 324 and substrate 354 with an open space over the
substrate, around the semiconductor die, and between the
semiconductor die and substrate. Encapsulant 424 in a liquid state
is injected into one side of chase mold 420 with nozzle 426 while
an optional vacuum assist 428 draws pressure from the opposite side
to uniformly fill the open space around semiconductor die 324 and
over substrate 354 and the open space between semiconductor die 324
and substrate 354 with the encapsulant. Encapsulant 424 is
cured.
[0147] FIG. 28 shows another embodiment of depositing encapsulant
around semiconductor die 324 and in the gap between semiconductor
die 324 and substrate 354. Semiconductor die 324 and substrate 354
are enclosed by dam 430. Encapsulant 432 is dispensed from nozzles
434 in a liquid state into dam 430 to fill the open space over
substrate 354 and the open space between semiconductor die 324 and
substrate 354. The volume of encapsulant 432 dispensed from nozzles
434 is controlled to fill dam 430 without covering back surface 328
or the side surfaces of semiconductor die 324. Encapsulant 432 is
cured.
[0148] FIG. 29 shows semiconductor die 324 and substrate 354 after
the MUF process from FIGS. 27a, 27c, and 28. Encapsulant 424 is
uniformly distributed over substrate 354 and around bump material
334 between semiconductor die 324 and substrate 354.
[0149] FIGS. 30a-30g show top views of various conductive trace
layouts on substrate or PCB 440. In FIG. 30a, conductive trace 442
is a straight conductor with integrated bump pad or interconnect
site 444 formed on substrate 440. The sides of substrate bump pad
444 can be co-linear with conductive trace 442. In the prior art, a
solder registration opening (SRO) is typically formed over the
interconnect site to contain the bump material during reflow. The
SRO increases interconnect pitch and reduces I/O count. In
contrast, masking layer 446 can be formed over a portion of
substrate 440; however, the masking layer is not formed around
substrate bump pad 444 of conductive trace 442. That is, the
portion of conductive trace 442 designed to mate with the bump
material is devoid of any SRO of masking layer 446 that would have
been used for bump containment during reflow.
[0150] Semiconductor die 324 is placed over substrate 440 and the
bump material is aligned with substrate bump pads 444. The bump
material is electrically and metallurgically connected to substrate
bump pads 444 by bringing the bump material in physical contact
with the bump pad and then reflowing the bump material under a
reflow temperature.
[0151] In another embodiment, an electrically conductive bump
material is deposited over substrate bump pad 444 using an
evaporation, electrolytic plating, electroless plating, ball drop,
or screen printing process. The bump material can be Al, Sn, Ni,
Au, Ag, Pb, Bi, Cu, solder, and combinations thereof, with an
optional flux solution. For example, the bump material can be
eutectic Sn/Pb, high-lead solder, or lead-free solder. The bump
material is bonded to substrate bump pad 444 using a suitable
attachment or bonding process. In one embodiment, the bump material
is reflowed by heating the material above its melting point to form
bump or interconnect 448, as shown in FIG. 30b. In some
applications, bump 448 is reflowed a second time to improve
electrical contact to substrate bump pad 444. The bump material
around the narrow substrate bump pad 444 maintains die placement
during reflow.
[0152] In high routing density applications, it is desirable to
minimize escape pitch of conductive traces 442. The escape pitch
between conductive traces 442 can be reduced by eliminating the
masking layer for the purpose of reflow containment, i.e., by
reflowing the bump material without a masking layer. Since no SRO
is formed around die bump pad 332 or substrate bump pad 444,
conductive traces 442 can be formed with a finer pitch, i.e.,
conductive trace 442 can be disposed closer together or to nearby
structures. With no SRO around substrate bump pad 444, the pitch
between conductive traces 442 is given as P=D+PLT+W/2, wherein D is
the base diameter of bump 448, PLT is die placement tolerance, and
W is the width of conductive trace 442. In one embodiment, given a
bump base diameter of 100 .mu.m, PLT of 10 .mu.m, and trace line
width of 30 .mu.m, the minimum escape pitch of conductive trace 442
is 125 .mu.m. The mask-less bump formation eliminates the need to
account for the ligament spacing of masking material between
adjacent openings, solder mask registration tolerance (SRT), and
minimum resolvable SRO, as found in the prior art.
[0153] When the bump material is reflowed without a masking layer
to metallurgically and electrically connect die bump pad 332 to
substrate bump pad 444, the wetting and surface tension causes the
bump material to maintain self-confinement and be retained within
the space between die bump pad 332 and substrate bump pad 444 and
portion of substrate 440 immediately adjacent to conductive trace
442 substantially within the footprint of the bump pads.
[0154] To achieve the desired self-confinement property, the bump
material can be immersed in a flux solution prior to placement on
die bump pad 332 or substrate bump pad 444 to selectively render
the region contacted by the bump material more wettable than the
surrounding area of conductive traces 442. The molten bump material
remains confined substantially within the area defined by the bump
pads due to the wettable properties of the flux solution. The bump
material does not run-out to the less wettable areas. A thin oxide
layer or other insulating layer can be formed over areas where bump
material is not intended to make the area less wettable. Hence,
masking layer 440 is not needed around die bump pad 332 or
substrate bump pad 444.
[0155] FIG. 30c shows another embodiment of parallel conductive
traces 452 as a straight conductor with integrated rectangular bump
pad or interconnect site 454 formed on substrate 450. In this case,
substrate bump pad 454 is wider than conductive trace 452, but less
than the width of the mating bump. The sides of substrate bump pad
454 can be parallel to conductive trace 452. Masking layer 456 can
be formed over a portion of substrate 450; however, the masking
layer is not formed around substrate bump pad 454 of conductive
trace 452. That is, the portion of conductive trace 452 designed to
mate with the bump material is devoid of any SRO of masking layer
456 that would have been used for bump containment during
reflow.
[0156] FIG. 30d shows another embodiment of conductive traces 460
and 462 arranged in an array of multiple rows with offset
integrated bump pad or interconnect site 464 formed on substrate
466 for maximum interconnect density and capacity. Alternate
conductive traces 460 and 462 include an elbow for routing to bump
pads 464. The sides of each substrate bump pad 464 is co-linear
with conductive traces 460 and 462. Masking layer 468 can be formed
over a portion of substrate 466; however, masking layer 468 is not
formed around substrate bump pad 464 of conductive traces 460 and
462. That is, the portion of conductive trace 460 and 462 designed
to mate with the bump material is devoid of any SRO of masking
layer 468 that would have been used for bump containment during
reflow.
[0157] FIG. 30e shows another embodiment of conductive traces 470
and 472 arranged in an array of multiple rows with offset
integrated bump pad or interconnect site 474 formed on substrate
476 for maximum interconnect density and capacity. Alternate
conductive traces 470 and 472 include an elbow for routing to bump
pads 474. In this case, substrate bump pad 474 is rounded and wider
than conductive traces 470 and 472, but less than the width of the
mating interconnect bump material. Masking layer 478 can be formed
over a portion of substrate 476; however, masking layer 478 is not
formed around substrate bump pad 474 of conductive traces 470 and
472. That is, the portion of conductive trace 470 and 472 designed
to mate with the bump material is devoid of any SRO of masking
layer 478 that would have been used for bump containment during
reflow.
[0158] FIG. 30f shows another embodiment of conductive traces 480
and 482 arranged in an array of multiple rows with offset
integrated bump pad or interconnect site 484 formed on substrate
486 for maximum interconnect density and capacity. Alternate
conductive traces 480 and 482 include an elbow for routing to bump
pads 484. In this case, substrate bump pad 484 is rectangular and
wider than conductive traces 480 and 482, but less than the width
of the mating interconnect bump material. Masking layer 488 can be
formed over a portion of substrate 486; however, masking layer 488
is not formed around substrate bump pad 484 of conductive traces
480 and 482. That is, the portion of conductive trace 480 and 482
designed to mate with the bump material is devoid of any SRO of
masking layer 488 that would have been used for bump containment
during reflow.
[0159] As one example of the interconnect process, semiconductor
die 324 is placed over substrate 466 and bump material 334 is
aligned with substrate bump pads 464 from FIG. 30d. Bump material
334 is electrically and metallurgically connected to substrate bump
pad 464 by pressing the bump material or by bringing the bump
material in physical contact with the bump pad and then reflowing
the bump material under a reflow temperature, as described for
FIGS. 22a-22g, 23a-23d, 24a-24d, 25a-25c, and 26a-26b.
[0160] In another embodiment, an electrically conductive bump
material is deposited over substrate bump pad 464 using an
evaporation, electrolytic plating, electroless plating, ball drop,
or screen printing process. The bump material can be Al, Sn, Ni,
Au, Ag, Pb, Bi, Cu, solder, and combinations thereof, with an
optional flux solution. For example, the bump material can be
eutectic Sn/Pb, high-lead solder, or lead-free solder. The bump
material is bonded to substrate bump pad 464 using a suitable
attachment or bonding process. In one embodiment, the bump material
is reflowed by heating the material above its melting point to form
bump or interconnect 490, as shown in FIG. 30g. In some
applications, bump 490 is reflowed a second time to improve
electrical contact to substrate bump pad 464. The bump material
around the narrow substrate bump pad 464 maintains die placement
during reflow. Bump material 334 or bumps 490 can also be formed on
substrate bump pad configurations of FIGS. 30a-30g.
[0161] In high routing density applications, it is desirable to
minimize escape pitch of conductive traces 460 and 462 or other
conductive trace configurations of FIGS. 30a-30g. The escape pitch
between conductive traces 460 and 462 can be reduced by eliminating
the masking layer for the purpose of reflow containment, i.e., by
reflowing the bump material without a masking layer. Since no SRO
is formed around die bump pad 332 or substrate bump pad 464,
conductive traces 460 and 462 can be formed with a finer pitch,
i.e., conductive traces 460 and 462 can be disposed closer together
or to nearby structures. With no SRO around substrate bump pad 464,
the pitch between conductive traces 460 and 462 is given as
P=D/2+PLT+W/2, wherein D is the base diameter of bump 490, PLT is
die placement tolerance, and W is the width of conductive traces
460 and 462. In one embodiment, given a bump base diameter of 100
.mu.m, PLT of 10 .mu.m, and trace line width of 30 .mu.m, the
minimum escape pitch of conductive traces 460 and 462 is 125 .mu.m.
The mask-less bump formation eliminates the need to account for the
ligament spacing of masking material between adjacent openings,
SRT, and minimum resolvable SRO, as found in the prior art.
[0162] When the bump material is reflowed without a masking layer
to metallurgically and electrically connect die bump pad 332 to
substrate bump pad 464, the wetting and surface tension causes the
bump material to maintain self-confinement and be retained within
the space between die bump pad 332 and substrate bump pad 464 and
portion of substrate 466 immediately adjacent to conductive traces
460 and 462 substantially within the footprint of the bump
pads.
[0163] To achieve the desired self-confinement property, the bump
material can be immersed in a flux solution prior to placement on
die bump pad 332 or substrate bump pad 464 to selectively render
the region contacted by the bump material more wettable than the
surrounding area of conductive traces 460 and 462. The molten bump
material remains confined substantially within the area defined by
the bump pads due to the wettable properties of the flux solution.
The bump material does not run-out to the less wettable areas. A
thin oxide layer or other insulating layer can be formed over areas
where bump material is not intended to make the area less wettable.
Hence, masking layer 468 is not needed around die bump pad 332 or
substrate bump pad 464.
[0164] In FIG. 31a, masking layer 492 is deposited over a portion
of conductive traces 494 and 496. However, masking layer 492 is not
formed over integrated bump pads 498. Consequently, there is no SRO
for each bump pad 498 on substrate 500. A non-wettable masking
patch 502 is formed on substrate 500 interstitially within the
array of integrated bump pads 498, i.e., between adjacent bump
pads. The masking patch 502 can also be formed on semiconductor die
324 interstitially within the array of die bump pads 498. More
generally, the masking patch is formed in close proximity to the
integrated bump pads in any arrangement to prevent run-out to less
wettable areas.
[0165] Semiconductor die 324 is placed over substrate 500 and the
bump material is aligned with substrate bump pads 498. The bump
material is electrically and metallurgically connected to substrate
bump pad 498 by pressing the bump material or by bringing the bump
material in physical contact with the bump pad and then reflowing
the bump material under a reflow temperature, as described for
FIGS. 22a-22g, 23a-23d, 24a-24d, 25a-25c, and 26a-26b.
[0166] In another embodiment, an electrically conductive bump
material is deposited over die integrated bump pads 498 using an
evaporation, electrolytic plating, electroless plating, ball drop,
or screen printing process. The bump material can be Al, Sn, Ni,
Au, Ag, Pb, Bi, Cu, solder, and combinations thereof, with an
optional flux solution. For example, the bump material can be
eutectic Sn/Pb, high-lead solder, or lead-free solder. The bump
material is bonded to integrated bump pads 498 using a suitable
attachment or bonding process. In one embodiment, the bump material
is reflowed by heating the material above its melting point to form
spherical balls or bumps 504. In some applications, bumps 504 are
reflowed a second time to improve electrical contact to integrated
bump pads 498. The bumps can also be compression bonded to
integrated bump pads 498. Bumps 504 represent one type of
interconnect structure that can be formed over integrated bump pads
498. The interconnect structure can also use stud bump, micro bump,
or other electrical interconnect.
[0167] In high routing density applications, it is desirable to
minimize escape pitch. In order to reduce the pitch between
conductive traces 494 and 496, the bump material is reflowed
without a masking layer around integrated bump pads 498. The escape
pitch between conductive traces 494 and 496 can be reduced by
eliminating the masking layer and associated SROs around the
integrated bump pads for the purpose of reflow containment, i.e.,
by reflowing the bump material without a masking layer. Masking
layer 492 can be formed over a portion of conductive traces 494 and
496 and substrate 400 away from integrated bump pads 498; however,
masking layer 492 is not formed around integrated bump pads 498.
That is, the portion of conductive trace 494 and 496 designed to
mate with the bump material is devoid of any SRO of masking layer
392 that would have been used for bump containment during
reflow.
[0168] In addition, masking patch 502 is formed on substrate 500
interstitially within the array of integrated bump pads 498.
Masking patch 502 is non-wettable material. Masking patch 502 can
be the same material as masking layer 492 and applied during the
same processing step, or a different material during a different
processing step. Masking patch 502 can be formed by selective
oxidation, plating, or other treatment of the portion of the trace
or pad within the array of integrated bump pads 498. Masking patch
502 confines bump material flow to integrated bump pads 498 and
prevents leaching of conductive bump material to adjacent
structures.
[0169] When the bump material is reflowed with masking patch 502
interstitially disposed within the array of integrated bump pads
498, the wetting and surface tension causes the bump material to be
confined and retained within the space between die bump pads 332
and integrated bump pads 498 and portion of substrate 500
immediately adjacent to conductive traces 494 and 496 and
substantially within the footprint of the integrated bump pads
498.
[0170] To achieve the desired confinement property, the bump
material can be immersed in a flux solution prior to placement on
die bump pads 332 or integrated bump pads 498 to selectively render
the region contacted by the bump material more wettable than the
surrounding area of conductive traces 494 and 496. The molten bump
material remains confined substantially within the area defined by
the bump pads due to the wettable properties of the flux solution.
The bump material does not run-out to the less wettable areas. A
thin oxide layer or other insulating layer can be formed over areas
where bump material is not intended to make the area less wettable.
Hence, masking layer 492 is not needed around die bump pads 332 or
integrated bump pads 498.
[0171] Since no SRO is formed around die bump pads 332 or
integrated bump pads 498, conductive traces 494 and 496 can be
formed with a finer pitch, i.e., the conductive traces can be
disposed closer to adjacent structures without making contact and
forming electrical shorts. Assuming the same solder registration
design rule, the pitch between conductive traces 494 and 496 is
given as P=(1.1D+W)/2, where D is the base diameter of bump 404 and
W is the width of conductive traces 494 and 496. In one embodiment,
given a bump diameter of 100 .mu.m and trace line width of 20
.mu.m, the minimum escape pitch of conductive traces 494 and 496 is
65 .mu.m. The bump formation eliminates the need to account for the
ligament spacing of masking material between adjacent openings and
minimum resolvable SRO, as found in the prior art.
[0172] FIG. 32 shows package-on-package (PoP) 505 with
semiconductor die 506 stacked over semiconductor die 508 using die
attach adhesive 510. Semiconductor die 506 and 508 each have an
active surface containing analog or digital circuits implemented as
active devices, passive devices, conductive layers, and dielectric
layers formed within the die and electrically interconnected
according to the electrical design and function of the die. For
example, the circuit may include one or more transistors, diodes,
and other circuit elements formed within the active surface to
implement analog circuits or digital circuits, such as DSP, ASIC,
memory, or other signal processing circuit. Semiconductor die 506
and 508 may also contain IPDs, such as inductors, capacitors, and
resistors, for RF signal processing.
[0173] Semiconductor die 506 is mounted to conductive traces 512
formed on substrate 514 using bump material 516 formed on contact
pads 518, using any of the embodiments from FIGS. 22a-22g, 23a-23d,
24a-24d, 25a-25c, and 26a-26b. Conductive trace 512 could be part
of the BOL or BONP interconnect of FIGS. 6-20. Semiconductor die
508 is electrically connected to contact pads 520 formed on
substrate 514 using bond wires 522. The opposite end of bond wire
522 is bonded to contact pads 524 on semiconductor die 506.
[0174] Masking layer 526 is formed over substrate 514 and opened
beyond the footprint of semiconductor die 506. While masking layer
526 does not confine bump material 516 to conductive traces 512
during reflow, the open mask can operate as a dam to prevent
encapsulant 528 from migrating to contact pads 520 or bond wires
522 during MUF. Encapsulant 528 is deposited between semiconductor
die 508 and substrate 514, similar to FIGS. 27a-27c. Masking layer
526 blocks MUF encapsulant 528 from reaching contact pads 520 and
bond wires 522, which could cause a defect. Masking layer 526
allows a larger semiconductor die to be placed on a given substrate
without risk of encapsulant 528 bleeding onto contact pads 520.
[0175] While one or more embodiments of the present invention have
been illustrated in detail, the skilled artisan will appreciate
that modifications and adaptations to those embodiments may be made
without departing from the scope of the present invention as set
forth in the following claims.
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