U.S. patent application number 11/724544 was filed with the patent office on 2007-07-26 for methods for fabricating fences on interposer substrates.
Invention is credited to Salman Akram, Warren M. Farnworth, Alan G. Wood.
Application Number | 20070170942 11/724544 |
Document ID | / |
Family ID | 24125820 |
Filed Date | 2007-07-26 |
United States Patent
Application |
20070170942 |
Kind Code |
A1 |
Akram; Salman ; et
al. |
July 26, 2007 |
Methods for fabricating fences on interposer substrates
Abstract
A method for modifying or fabricating one or more interposers
includes fabricating a fence on a substrate that includes the one
or more interposers. The fence may be fabricated on a single
surface of the interposer substrate. Alternatively, a fence and
associated features may be fabricated on both opposite surfaces of
the interposer substrate, for example, by fabricating features on
one surface of the substrate, inverting the substrate, and forming
features on the opposite surface of the substrate. The fence, a
portion thereof, or associated features or portions thereof may be
fabricated by selectively consolidating previously unconsolidated
material. Such selective consolidation may be effected under
control of a program. Additionally, the selective consolidation may
occur in conjunction with a machine vision system.
Inventors: |
Akram; Salman; (Boise,
ID) ; Wood; Alan G.; (Boise, ID) ; Farnworth;
Warren M.; (Nampa, ID) |
Correspondence
Address: |
TRASK BRITT, P.C./ MICRON TECHNOLOGY
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Family ID: |
24125820 |
Appl. No.: |
11/724544 |
Filed: |
March 15, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11507816 |
Aug 22, 2006 |
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11724544 |
Mar 15, 2007 |
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|
10648163 |
Aug 26, 2003 |
7093358 |
|
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11507816 |
Aug 22, 2006 |
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|
09843119 |
Apr 26, 2001 |
6634100 |
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10648163 |
Aug 26, 2003 |
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09533407 |
Mar 23, 2000 |
6529027 |
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09843119 |
Apr 26, 2001 |
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Current U.S.
Class: |
438/15 |
Current CPC
Class: |
H01L 2224/8114 20130101;
Y10T 29/49144 20150115; H01L 23/32 20130101; H01L 2924/00 20130101;
H01L 2924/00 20130101; H01L 2924/351 20130101; H01L 2924/00
20130101; G01R 1/0466 20130101; B33Y 30/00 20141201; G01R 1/0483
20130101; H05K 7/1061 20130101; H05K 2203/167 20130101; Y10T
29/49147 20150115; Y10T 29/49222 20150115; H01L 23/49827 20130101;
H01L 2924/12042 20130101; H05K 2201/09472 20130101; G01R 1/0433
20130101; B33Y 80/00 20141201; H01L 2924/12042 20130101; H05K
2201/10734 20130101; H05K 3/3436 20130101; H01L 2224/16111
20130101; H05K 2201/2018 20130101; H01L 2924/01082 20130101; H05K
2201/049 20130101; H01L 2924/351 20130101; H05K 1/112 20130101;
Y10T 29/4913 20150115; Y10T 29/49204 20150115; H01L 2924/01006
20130101; Y10T 29/49156 20150115; Y10T 29/49218 20150115; G01R 3/00
20130101; H01L 2924/01049 20130101; Y10T 29/49165 20150115; H05K
1/141 20130101; H01L 2924/12044 20130101; H01L 2924/15787 20130101;
G01R 1/0408 20130101; H01L 2924/01005 20130101; G01R 1/07378
20130101; H05K 2201/10378 20130101; H01L 2924/01033 20130101; B33Y
10/00 20141201; H01L 2224/16237 20130101; Y10T 29/49126 20150115;
H01L 2224/81385 20130101; H01L 2924/15787 20130101 |
Class at
Publication: |
324/758 |
International
Class: |
G01R 31/02 20060101
G01R031/02 |
Claims
1. A method for fabricating a plurality of interposers, comprising:
selectively consolidating material under control of a program to
fabricate at least a portion of at least one fence over at least
one interposer substrate of a plurality of interposer substrates,
each including a surface to which top contact pads are exposed, the
at least one fence including a receptacle through which the top
contact pads are exposed, the receptacle being configured to
receive a semiconductor device.
2. The method of claim 1, wherein selectively consolidating
comprises stereolithography.
3. The method of claim 1, wherein selectively consolidating
comprises selectively consolidating material in a plurality of
mutually adhered regions.
4. The method of claim 1, further comprising: recognizing a
location and orientation of each interposer substrate of the
plurality.
5. The method of claim 4, further comprising: storing in computer
memory data including at least one physical parameter of each of
the plurality of interposer substrates and of the at least one
fence; and using the stored data in conjunction with a machine
vision system to recognize a location and orientation of each
interposer substrate of the plurality of interposer substrates.
6. The method of claim 5, further comprising: using the stored
data, in conjunction with the machine vision system, to effect the
act of selectively consolidating at a desired location over the at
least one interposer substrate.
7. The method of claim 5, further comprising: using the stored
data, in conjunction with the machine vision system, to
sequentially form a plurality of mutually adhered regions of the
portion of the at least one fence.
8. The method of claim 1, further comprising: positioning each of
the plurality of interposer substrates in a common plane.
9. The method of claim 1, further comprising: inverting at least
one interposer substrate of the plurality; and fabricating a
further portion of the at least one fence.
10. The method of claim 9, wherein fabricating the further portion
includes selectively consolidating material under control of a
program.
11. The method of claim 10, wherein selectively consolidating
comprises stereolithography.
12. The method of claim 10, wherein selectively consolidating
comprises selectively consolidating unconsolidated material in a
plurality of mutually adhered regions.
13. The method of claim 10, further comprising: recognizing a
location and orientation of each interposer substrate of the
plurality.
14. The method of claim 13, further comprising: storing in computer
memory data including at least one physical parameter of each
interposer substrate of the plurality and the at least one fence;
and using the stored data in conjunction with a machine vision
system to recognize the location and orientation of each interposer
substrate.
15. The method of claim 14, further comprising: using the stored
data, in conjunction with the machine vision system, to effect the
act of selectively consolidating.
16. A method for fabricating an interposer, comprising: forming at
least a portion of a fence on a first surface of at least one
interposer substrate, the fence including a receptacle through
which contact pads of the at least one interposer substrate are
exposed; inverting the at least one interposer substrate; and
forming at least a portion of at least one feature on an opposite
surface of the interposer substrate.
17. The method of claim 16, wherein forming at least the portion of
at least one feature comprises forming at least a portion of a
feature comprising an extension of the fence.
18. The method of claim 16, wherein at least one of forming at
least the portion of the fence and forming at least the portion of
the at least one feature comprises selectively consolidating
material under control of a program.
19. The method of claim 18, wherein selectively consolidating is
effected in conjunction with a machine vision system configured to
recognize an orientation and location of at least one feature of
the at least one interposer substrate.
20. The method of claim 16, wherein forming at least a portion of a
fence comprises substantially concurrently forming at least
portions of a plurality of fences on a plurality of interposer
substrates of a common substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
11/507,816, filed Aug. 22, 2006, which is a continuation of
application Ser. No. 10/648,163, filed Aug. 26, 2003, now U.S. Pat.
No. 7,093,358, issued Aug. 22, 2006, which is a continuation of
application Ser. No. 09/843,119, filed Apr. 26, 2001, now U.S. Pat.
No. 6,634,100, issued Oct. 21, 2003, which is a divisional of
application Ser. No. 09/533,407, filed Mar. 23, 2000, which is now
U.S. Pat. No. 6,529,027, issued Mar. 4, 2003. The disclosure of
each of the previously referenced U.S. patent applications and
patents referenced is hereby incorporated by reference in its
entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to an interposer
configured to receive a semiconductor device for testing. More
specifically, the invention pertains to such a test interposer
having an alignment fence for receiving and aligning semiconductor
devices, such as flip-chip type semiconductor dice, ball grid array
(BGA) packages, and chip scale packages (CSPs), with test sockets
of the interposer. The present invention also relates to methods
for fabricating such a test interposer.
[0004] 2. Background of Related Art
[0005] The semiconductor industry produces extremely large numbers
of miniature electrical devices, or "chips" or dice, which are
referred to as semiconductor devices. Semiconductor devices are
installed in essentially every electronic device. Such devices are
typically fabricated in large numbers on a wafer of semiconductive
material (e.g., silicon, gallium arsenide, or indium phosphide).
The individual chips or dice are then singulated from the
wafer.
[0006] Tests are typically performed at several stages of
manufacture for the purposes of evaluating the electrical
characteristics of various circuits of the semiconductor devices
and for detecting electrical, structural, and other types of faults
in the semiconductor devices. These tests are sometimes performed
on representative semiconductor devices and sometimes on each
semiconductor device of a certain type, depending on the
criticality of use, manufacturing costs, and expectation of
flaws.
[0007] Conventionally, the semiconductor industry favored a "final"
electrical testing of semiconductor devices, which was effected
before semiconductor devices were packaged with electrical leads
extending therefrom and encapsulated in a protective material.
However, it is now recognized that conventional packaging processes
may cause significant numbers of semiconductor devices to fail. For
example, as a semiconductor device is being encapsulated, the
protective material may cause particulate die coat penetration,
"bond wire sweep," which may break electrical connections made by
the bond wires or cause electrical shorts between adjacent bond
wires, and other problems. Accordingly, it is desirable to test
semiconductor devices after they have been packaged.
[0008] Some state of the art semiconductor devices lack
conventional packages (e.g., leads and encapsulants) or are
minimally packaged. Flip-chip type semiconductor devices may be
left unpackaged and connected directly to a higher level substrate
by way of conductive structures, such as solder balls, disposed
between the bond pads of the flip-chip and corresponding contact
pads of the higher level substrate.
[0009] Ball grid array packages, a type of flip-chip semiconductor
device, may include a semiconductor die disposed on and
electrically connected to an interposer. The interposer has contact
pads on the opposite side thereof that are arranged in a pattern
complementary to that of contact pads on a higher level substrate
to which the ball grid array package is to be connected. The
interposer may also include electrical traces that lead to contact
pads arranged in a different pattern than the bond pads of the
semiconductor die and, therefore, reroute the bond pads of the
semiconductor die.
[0010] Another type of state of the art package is the so-called
"chip scale package," wherein the dimensions of the total package
are only slightly larger than the dimensions of the semiconductor
die thereof. A chip scale package typically includes a flip-chip
type semiconductor die with one or more thin layers of protective
material (e.g., plastic encapsulant) on the active surface thereof.
Conductive structures (e.g., solder bumps) protrude from bond pads
of the flip-chip type semiconductor die and extend above the layer
of protective material. Chip scale packages may also have one or
more thin layers of protective material on the edges or backsides
of the semiconductor dice thereof. Ball grid array packages may be
formed as chip scale packages.
[0011] When these types of semiconductor devices are tested, the
solder bumps or other conductive structures protruding therefrom
may not properly align with the corresponding test sockets of a
test substrate so as to establish adequate electrical contacts
between the tested semiconductor device and the test substrate.
Moreover, if misalignment occurs, the conductive structures may be
damaged.
[0012] In order to reduce potential damage to conductive
structures, such as solder bumps, during the testing of flip-chip
type semiconductor devices, interposers have been used between a
test substrate and a semiconductor device to be tested. These
interposers may comprise micromachined silicon or ceramic
structures that include metal-lined recesses for receiving
conductive structures of a semiconductor device to be tested,
metal-filled vias extending from the bottom of each recess to the
opposite, bottom side of the interposer, and conductive structures,
such as solder bumps, communicating with the metal-filled vias and
protruding from the bottom side of the interposer. The recesses of
the interposer are configured to receive the conductive structures
of a semiconductor device to be tested without stressing or
damaging the conductive structures. The metal lining of and
metal-filled via communicating with each recess facilitates
electrical communication between a conductive structure disposed in
each recess and the corresponding, underlying conductive structure
protruding from the bottom of the interposer. The conductive
structures of the interposer are precisely aligned with test pads
or sockets of a test substrate so as to establish an electrical
connection between a semiconductor device assembled with the
interposer and the test substrate. The test pads or sockets of the
test substrate communicate with known semiconductor device test
equipment.
[0013] Nonetheless, the conductive structures protruding from a
semiconductor device to be tested may be damaged when assembled
with such an interposer. Moreover, since the recesses of such
interposers are configured to receive the conductive structures of
a semiconductor device without stressing, deforming, or otherwise
damaging the conductive structures, the interposer may fail to make
adequate electrical connections between some of the conductive
structures and their corresponding test pads or sockets of the test
substrate. Moreover, test interposers typically lack any alignment
component other than the recesses thereof.
[0014] Accordingly, it appears that the art is lacking a structure
for aligning the conductive structures of a semiconductor device
with corresponding test pads or sockets of a test substrate without
stressing or damaging the conductive structures while facilitating
adequate electrical connections between the conductive structures
and the test pads or sockets.
[0015] In the past decade, a manufacturing technique termed
"stereolithography," also known as "layered manufacturing," has
evolved to a degree where it is employed in many industries.
[0016] Essentially, stereolithography as conventionally practiced
involves the use of a computer to generate a three-dimensional
(3-D) mathematical simulation or model of an object to be
fabricated, such generation usually effected with 3-D
computer-aided design (CAD) software. The model or simulation is
mathematically separated or "sliced" into a large number of
relatively thin, parallel, usually vertically superimposed layers,
each layer having defined boundaries and other features associated
with the model (and thus the actual object to be fabricated) at the
level of that layer within the exterior boundaries of the object. A
complete assembly or stack of all of the layers defines the entire
object, and surface resolution of the object is, in part, dependent
upon the thickness of the layers.
[0017] The mathematical simulation or model is then employed to
generate an actual object by building the object, layer by
superimposed layer. A wide variety of approaches to
stereolithography by different companies has resulted in techniques
for fabrication of objects from both metallic and nonmetallic
materials. Regardless of the material employed to fabricate an
object, stereolithographic techniques usually involve disposition
of a layer of unconsolidated or unfixed material corresponding to
each layer within the object boundaries, followed by selective
consolidation or fixation of the material to at least a semisolid
state in those areas of a given layer corresponding to portions of
the object, the at least partially consolidated or fixed material
also at that time being substantially concurrently bonded to a
lower layer. The unconsolidated material employed to build an
object may be supplied in particulate or liquid form, and the
material itself may be consolidated or fixed or a separate binder
material may be employed to bond material particles to one another
and to those of a previously formed layer. In some instances, thin
sheets of material may be superimposed to build an object, each
sheet being fixed to a next lower sheet and unwanted portions of
each sheet removed, a stack of such sheets defining the completed
object. When particulate materials are employed, resolution of
object surfaces is highly dependent upon particle size, whereas
when a liquid is employed, surface resolution is highly dependent
upon the minimum surface area of the liquid which may be fixed and
the minimum thickness of a layer which may be generated. Of course,
in either case, resolution and accuracy of object reproduction from
the CAD file is also dependent upon the ability of the apparatus
used to fix the material to precisely track the mathematical
instructions indicating solid areas and boundaries for each layer
of material. Toward that end, and depending upon the layer being
fixed, various fixation approaches have been employed, including
particle bombardment (electron beams), disposing a binder or other
fixative (such as by ink-jet printing techniques), or irradiation
using heat or specific wavelength ranges.
[0018] An early application of stereolithography was to enable
rapid fabrication of molds and prototypes of objects from CAD
files. Thus, either male or female forms on which mold material
might be disposed might be rapidly generated. Prototypes of objects
might be built to verify the accuracy of the CAD file defining the
object and to detect any design deficiencies and possible
fabrication problems before a design was committed to large-scale
production.
[0019] In more recent years, stereolithography has been employed to
develop and refine object designs in relatively inexpensive
materials, and has also been used to fabricate small quantities of
objects where the cost of conventional fabrication techniques is
prohibitive for same, such as in the case of plastic objects
conventionally formed by injection molding. It is also known to
employ stereolithography in the custom fabrication of products
generally built in small quantities or where a product design is
rendered only once. Finally, it has been appreciated in some
industries that stereolithography provides a capability to
fabricate products, such as those including closed interior
chambers or convoluted passageways, which may not be fabricated
satisfactorily using conventional manufacturing techniques. It has
also been recognized in some industries that a stereolithographic
object or component may be formed or built around another,
pre-existing object or component to create a larger product.
[0020] However, to the inventors' knowledge, stereolithography has
yet to be applied to mass production of articles in volumes of
thousands or millions, or employed to produce, augment or enhance
products including other pre-existing components in large
quantities, where minute component sizes are involved, and where
extremely high resolution and a high degree of reproducibility of
results are required. Furthermore, conventional stereolithography
apparatus and methods fail to address the difficulties of precisely
locating and orienting a number of pre-existing components for
stereolithographic application of material thereto without the use
of mechanical alignment techniques or to otherwise assure precise,
repeatable placement of components. In particular,
stereolithography has not been employed to fabricate interposers
for aligning and connecting a semiconductor device to a test
substrate.
SUMMARY OF THE INVENTION
[0021] The present invention includes an interposer for aligning
and connecting a semiconductor device to a test substrate, as well
as methods for making the interposer.
[0022] The interposer of the present invention includes a
semiconductor (e.g., silicon or ceramic) substrate having contact
pads on a top side thereof and arranged correspondingly to
conductive structures, such as solder bumps, protruding from a
semiconductor device to be tested. A conductive via connects each
contact pad on the top side of the interposer to a conductive
element, such as a contact pad on the bottom side thereof or an
electrically conductive pin, to facilitate connection with a
tester. Electrical traces may reroute the positions of one or more
of the contact pads from the top side to the bottom side of the
interposer. The contact pads on the bottom side of the interposer
are arranged correspondingly to test pads or test sockets of a test
substrate with which the interposer is to be used. Conductive
structures protrude from the contact pads on the bottom side of the
interposer to facilitate electrical communication between the
contact pads on the bottom of the interposer and their
corresponding test pads or sockets.
[0023] The interposer also includes a fence, or alignment
structure, disposed on the top thereof. The fence has a raised
periphery, which defines a receptacle configured to receive a
semiconductor device to be tested. The material of the fence may
also be extended to substantially cover the top surface of the
interposer and have apertures through which the contact pads on top
of the interposer are exposed. The raised periphery of the fence
and any apertures therethrough are configured to align a
semiconductor device to be tested and the conductive structures
protruding therefrom with the interposer.
[0024] According to another aspect of the present invention, the
contact pads exposed to the top surface of the interposer may be
recessed so as to receive conductive structures protruding from a
semiconductor device to be assembled therewith. The recesses
through which the contact pads are exposed may be shaped so as to
facilitate an adequate electrical connection between the conductive
structures of a semiconductor device to be tested and the contact
pads on the top of the interposer. In one embodiment, the recesses
have square shapes.
[0025] Such recesses may also have metallized, knife-edged spines
protruding thereinto. The metal layer on the spines is continuous
with and communicates with the contact pad exposed through the
recess. As a conductive structure is disposed into each of the
recesses, the spines pierce the surface of the conductive structure
to ensure that an adequate electrical connection is established
between the conductive structure and the corresponding contact pad
despite the pressure of oxides or contaminants on the exterior of
the conductive structure.
[0026] In another aspect, the raised periphery of the fence of the
present invention includes laterally recessed regions that are
facing, but spaced apart from, a semiconductor device when disposed
in the receptacle. These laterally recessed regions facilitate some
movement of a semiconductor device within the receptacle. Thus, a
fence including such lateral recesses may be said to roughly align
a semiconductor device disposed in the receptacle thereof, rather
than precisely aligning the semiconductor device. When a
semiconductor device is inserted into the receptacle of a fence
having lateral recesses in the raised periphery thereof, fine
alignment occurs as the conductive structures of the semiconductor
device are received within apertures of the fence or recesses
through which the contact pads on the top of the interposer are
exposed.
[0027] The fence of the present invention may also be extended
around one or more of the edges of the substrate of the interposer,
as well as over at least a portion of the bottom side thereof. If
the fence material covers all or a part of the bottom side of the
semiconductor substrate of the interposer, contact pads on the
bottom of the substrate and the conductive structures protruding
therefrom are exposed through the fence, with the conductive
structure preferably protruding from a bottom surface of the
fence.
[0028] A method for fabricating the fence of the present invention
is also within the scope of the present invention. The method may
employ computer-controlled, 3-D CAD initiated, stereolithographic
techniques to form the interposer fence and structures thereof
either directly on or separately from the substrate of the
interposer. At least the top portions of the fence may be
fabricated on an interposer substrate. Alternatively, a plurality
of fences may be substantially simultaneously fabricated over a
large number of interposer substrate locations on a semiconductor
wafer or other large-scale semiconductor substrate or on singulated
substrates that are grouped together.
[0029] In stereolithographic processes, precise mechanical
alignment of singulated interposers or larger substrates having
multiple interposer locations is not required to practice the
method of the present invention when machine vision is used to
locate single substrates and features or other components thereon
or associated therewith (such as bond pads, vias, solder bumps,
etc.) or features on a larger substrate for alignment and material
disposition purposes.
[0030] In a preferred embodiment of the invention, the interposer
structure is fabricated using precisely focused electromagnetic
radiation in the form of an ultraviolet (UV) wavelength laser under
control of a computer and responsive to input from a machine vision
system such as a pattern recognition system to fix or cure a liquid
material in the form of a photopolymer.
[0031] If it is desired that a portion of the fence cover all or
part of the bottom of the interposer substrate, the substrate may
be flipped over and the stereolithographic process used to
fabricate the bottom portion of the fence.
[0032] Alternatively, the fence may be fabricated by molding a
dielectric material (e.g., a thermoplastic material) onto the
substrate. Combinations of fabrication processes may also be used
to form different parts of the fence.
[0033] All or part of the fence may be fabricated separately from
the interposer substrate and assembled therewith, or all or part of
the fence may be fabricated directly on the interposer
substrate.
[0034] Other features and advantages of the present invention will
become apparent to those of skill in the art through consideration
of the ensuing description, the accompanying drawings, and the
appended claims.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0035] FIG. 1 is a perspective view assembly of a semiconductor
device and a first embodiment of an interposer having a fence
configured to receive the semiconductor device and align same with
an interposer substrate;
[0036] FIG. 1A is a top view of the fence and interposer of FIG.
1;
[0037] FIG. 1B is a bottom view of the fence and interposer of FIG.
1;
[0038] FIG. 2 is a cross-section taken along line 2-2 of FIG.
1;
[0039] FIG. 3 is a cross-section taken along line 2-2 of FIG. 1,
depicting a semiconductor device inserted in a receptacle formed by
the fence;
[0040] FIG. 4 is a top view of a portion of a wafer with a
plurality of unsingulated interposer substrates, depicting the
conductive structures thereof, including contact pads, metallized
recesses, and vias;
[0041] FIG. 5 is a cross-section taken along line 5-5 of FIG.
4;
[0042] FIG. 6 is a perspective view of a second embodiment of an
interposer configured to align and connect a semiconductor device
to a test substrate;
[0043] FIG. 6A is a close-up view of a recess of the interposer of
FIG. 6;
[0044] FIG. 7 is a cross-sectional view of a third embodiment of an
interposer incorporating teachings of the present invention;
[0045] FIG. 8 is a cross-sectional view of a fourth embodiment of
an interposer incorporating teachings of the present invention;
[0046] FIG. 9 is a schematic representation of an exemplary
stereolithography apparatus suitable for use in practicing the
method of the present invention;
[0047] FIGS. 10(A)-(F) are stepwise partial cross-sectional
depictions of the use of stereolithography to fabricate the fences
of the interposers of the present invention; and
[0048] FIG. 11 is a cross-sectional side view of a mold that may be
used to fabricate an interposer according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
The Interposer
[0049] FIGS. 1, 1A, 1B, and 2 depict an exemplary interposer 100 of
the present invention. Interposer 100 includes an interposer
substrate 110 with contact pads 102 on a top surface 104 thereof
and contact pads 106 on a bottom surface 108 thereof. Contact pads
102 may be recessed relative to top surface 104, as illustrated in
FIG. 2. Contact pads 102 on top surface 104 of interposer substrate
110 communicate with corresponding contact pads 106 on bottom
surface 108 by way of vias 118 filled or lined with metal 148 or
another conductive material. Conductive structures 142, such as
balls, bumps, or conductive pillars, of a conductive material, such
as a solder, a metal, a metal alloy, a conductor-filled epoxy, a
conductive epoxy, or a conductive (e.g., z-axis) elastomer, are
secured to and protrude from contact pads 106 and from interposer
100.
[0050] Interposer substrate 110 may be fabricated from any suitable
material for use in semiconductor device applications, such as a
semiconductor material (e.g., silicon, gallium arsenide, indium
phosphide), ceramics, polymers, or other materials that are used as
substrates in fabricating semiconductor devices and carrier
substrates.
[0051] Interposer 100 also includes a fence 120 disposed on top
surface 104 of interposer substrate 110. A periphery 126 of fence
120 is raised relative to top surface 104. Interior side walls 128
of raised periphery 126 form a receptacle 130, which is configured
to receive a semiconductor device 150 to be tested. Preferably,
receptacle 130 is also configured to align a semiconductor device
150 disposed face-down therein with interposer substrate 110,
conductive structures 152 protruding from semiconductor device 150
being aligned with corresponding contact pads 102 on top surface
104 of interposer substrate 110. Interior side walls 128 may taper
inward toward top surface 104 so as to facilitate the insertion of
an off-center semiconductor device 150 into receptacle 130 and the
alignment of such an off-center semiconductor device 150 with top
surface 104.
[0052] Referring now to FIGS. 1 and 3, a semiconductor device 150
is positioned face-down over interposer 100 and inserted into
receptacle 130. Upon insertion of semiconductor device 150 into
receptacle 130, conductive structures 152 (e.g., solder bumps)
protruding from semiconductor device 150 are received by recesses
136, which align and facilitate contact of conductive structures
152 with their corresponding contact pads 102 on top surface 104 of
interposer substrate 110. This accurate alignment, facilitated by
fence 120, reduces damage to conductive structures 152 during
testing, as well as contains and protects semiconductor device 150
from inadvertent damage during testing thereof.
[0053] As shown in FIG. 2, fence 120 may also cover one or more of
the peripheral edges 112 of interposer substrate 110, as well as
all or a portion of bottom surface 108 thereof. Portions of fence
120 that cover the peripheral edges 112 of interposer substrate 110
are referred to herein as side walls 132, while portions of fence
120 that cover bottom surface 108 are collectively referred to as
bottom protective layer 134.
[0054] Fence 120 may be fabricated from conventional semiconductor
device packaging materials, such as resins, thermoplastic
materials, or other polymers, but is preferably fabricated from a
photocurable polymer, which is also referred to herein as a
"photopolymer."
[0055] Referring now to FIG. 6, another embodiment of interposer
100' has a fence 120' with laterally recessed regions 129 in
sidewall 128' thereof. These laterally recessed regions 129 allow
for greater tolerances in the dimensions of a semiconductor device
150 to be inserted into receptacle 130' and, therefore, only
roughly align semiconductor device 150 relative to interposer
substrate 110'. Fence 120' of interposer 100' also lacks a
protective layer over interposer substrate 110'.
[0056] FIG. 6A also depicts interposer 100' as having contact pads
102' that are exposed to top surface 104' of interposer substrate
110' through recesses 136 ' in top surface 104'. Knife-edged spines
138 having metallization 140 thereon protrude toward the center of
each recess 136'. Spines 138 are configured to pierce a conductive
structure 152 of semiconductor device 150 as conductive structure
152 is aligned with and inserted into recess 136' to communicate
with contact pad 102' exposed therethrough. As metallization 140 on
spines 138 is continuous with and communicates with the contact pad
102' exposed through recess 136', when a conductive structure 152
is pierced by one or more spines 138, metallization 140 ensures
that conductive structure 152 will communicate with the
corresponding contact pad 102'.
[0057] FIG. 7 depicts an interposer 100'' having a fence 120'' that
lacks protective layers over both top surface 104 and bottom
surface 108 of interposer substrate 110.
[0058] Yet another embodiment of an interposer 100''' incorporating
teachings of the present invention is illustrated in FIG. 8.
Interposer 100''' includes a fence 120''' having an upper
protective layer 122 covering top surface 104 of interposer
substrate 110 and located at the bottom of receptacle 130. Contact
pads 102 of interposer substrate 110 are exposed through recesses
124 formed through layer 122. Fence 120''' also has a lower
protective layer 134 covering bottom surface 108 of interposer
substrate 110, through which conductive structures 142 secured to
contact pads 106 extend.
Method for Fabricating the Interposer Substrate
[0059] As noted previously, interposer substrate 110 can be a
silicon substrate. When silicon or another semiconductor, ceramic,
a polymer, or another appropriate electrically nonconductive
material is used as interposer substrate 110, several interposers
can be simultaneously fabricated on a larger substrate, such as a
silicon wafer 160 as depicted in FIGS. 4 and 5 or a large, thin
structure of another appropriate material. Once interposer
substrates 110 have been fabricated on wafer 160, individual
interposer substrates 110 can be singulated, or diced, from wafer
160 along scribe lines 146, which define the peripheral edges 112
of the individual interposer substrates 110. As illustrated, each
interposer substrate 110 is slightly larger than a semiconductor
device 150 (see, e.g., FIG. 1) to be assembled therewith for
testing.
[0060] With continued reference to FIGS. 4 and 5, top surface 104
of each interposer substrate 110 includes recesses 136. Recesses
136 are preferably arranged on top surface 104 in a mirror image to
the arrangement of conductive structures 152 (see, e.g., FIG. 1)
protruding from a semiconductor device 150 to be assembled with
interposer 100. Each recess 136 is continuous with a via 118 that
extends to bottom surface 108 of interposer substrate 110. Recesses
136 and vias 118 can be fabricated by any suitable semiconductor
device fabrication techniques, such as the use of a photomask and
etchants.
[0061] Known metallization techniques, such as chemical vapor
deposition (CVD), physical vapor deposition (PVD) (e.g.,
sputtering), or the use of solders or molten metals, can be
employed to fabricate electrically conductive structures in
recesses 136 and vias 118. Preferably, each recess 136 has a
contact pad 102 exposed therein. While contact pads 102 are
illustrated as being recessed relative to top surface 104, contact
pads 102 can be substantially flush with top surface 104 or raised
relative thereto.
[0062] Contact pads 102 exposed at top surface 104 communicate with
contact pads 106 at bottom surface 108 of interposer substrate 110
by way of metal or other conductive material 148 disposed in vias
118. Conductive structures 142 (FIGS. 2 and 3), such as solder
bumps, or bumps, balls, or pillars of any suitable conductive
material, are secured to and protrude from contact pads 106 so as
to facilitate communication between a semiconductor device 150 to
be assembled with interposer 110 adjacent to top surface 104 and a
test substrate to be assembled with interposer 110 adjacent to
bottom surface 108. Alternatively, conductive structures 142 may be
bonded to a test apparatus, such as a burn-in board. As another
alternative, interposer 100 could be used to electrically connect a
semiconductor device 150 to any type of substrate. Other techniques
may be employed to connect the interposer to test equipment, if
desired.
[0063] Although conductive structures 142 are illustrated in FIGS.
2 and 3 as solder bumps, various solders and solder combinations
(e.g., standard low temperature 63/37 lead/tin (Pb/Sn) solder 63%
lead, 37% tin, each by weight), metals, metal alloys, conductive
epoxies, and Z-axis elastomers, and other known conductive
materials could also be used to form conductive structures 142
configured as bumps, balls, pillars, or films with conductive
regions extending transverse to the plane of the film with
insulative regions laterally therebetween so that conductive paths
are established wherever the conductors are aligned with and
contact electrical traces or pads above and below without lateral
electrical shorting.
Methods for Fabricating the Fence
[0064] Once interposer substrate 110 has been fabricated, a fence
120 can be secured thereto. Exemplary methods that can be used to
fabricate fence 120 include transfer molding and stereolithography.
Fence 120 can be fabricated separately from interposer substrate
110 in one or more pieces, then secured thereto. Alternatively, all
or part of fence 120 can be fabricated directly on interposer
substrate 110. As another alternative, part of fence 120 can be
fabricated on interposer substrate 110 while another part of fence
120 is fabricated separately from interposer substrate 110 and
subsequently secured thereto.
Stereolithographic Method for Fabricating the Fence
[0065] FIG. 9 depicts schematically various components, and
operation, of an exemplary stereolithography apparatus 10 to
facilitate the reader's understanding of the technology employed in
implementation of the present invention, although those of ordinary
skill in the art will understand and appreciate that apparatus of
other designs and manufacture may be employed in practicing the
method of the present invention. The preferred, basic
stereolithography apparatus for implementation of the present
invention as well as operation of such apparatus are described in
great detail in United States Patents assigned to 3D Systems, Inc.
of Valencia, Calif., such patents including, without limitation,
U.S. Pat. Nos. 4,575,330; 4,929,402; 4,996,010; 4,999,143;
5,015,424; 5,058,988; 5,059,021; 5,059,359; 5,071,337; 5,076,974;
5,096,530; 5,104,592; 5,123,734; 5,130,064; 5,133,987; 5,141,680;
5,143,663; 5,164,128; 5,174,931; 5,174,943; 5,182,055; 5,182,056;
5,182,715; 5,184,307; 5,192,469; 5,192,559; 5,209,878; 5,234,636;
5,236,637; 5,238,639; 5,248,456; 5,256,340; 5,258,146; 5,267,013;
5,273,691; 5,321,622; 5,344,298; 5,345,391; 5,358,673; 5,447,822;
5,481,470; 5,495,328; 5,501,824; 5,554,336; 5,556,590; 5,569,349;
5,569,431; 5,571,471; 5,573,722; 5,609,812; 5,609,813; 5,610,824;
5,630,981; 5,637,169; 5,651,934; 5,667,820; 5,672,312; 5,676,904;
5,688,464; 5,693,144; 5,695,707; 5,711,911; 5,776,409; 5,779,967;
5,814,265; 5,850,239; 5,854,748; 5,855,718; 5,855,836; 5,885,511;
5,897,825; 5,902,537; 5,902,538; 5,904,889; 5,943,235; and
5,945,058. The disclosure of each of the foregoing patents is
hereby incorporated herein by this reference. As noted in more
detail below, however, a significant modification is made to
conventional stereolithographic apparatus, such as those offered by
3D Systems, Inc., in the context of initiation and control of the
stereolithographic disposition and fixation of materials.
Specifically, the apparatus of the present invention employs a
so-called "machine vision" system in combination with suitable
programming of the computer controlling the stereolithographic
process to eliminate the need for accurate positioning or
mechanical alignment of workpieces to which material is
stereolithographically applied, and expands the use of conventional
stereolithographic apparatus and methods to application of
materials to large numbers of workpieces which may differ in
orientation, size, thickness, and surface topography. The
workpieces employed in the practice of the preferred embodiment of
the method of the invention are substrates for forming interposers
100 wherein adaptability for rapidly fabricating large numbers of
parts having the aforementioned variations in orientation, size,
thickness and surface topography is very important.
[0066] With reference again to FIG. 9 and as noted above, a 3-D CAD
drawing of an object to be fabricated in the form of a data file is
placed in the memory of a computer 12 controlling the operation of
apparatus 10 if computer 12 is not a CAD computer in which the
original object design is effected. In other words, an object
design may be effected in a first computer in an engineering or
research facility and the data files transferred via wide or local
area network, tape, disc, CD-ROM or otherwise as known in the art
to computer 12 of apparatus 10 for object fabrication.
[0067] The data is preferably formatted in an STL (for
STereoLithography) file, STL being a standardized format employed
by a majority of manufacturers of stereolithography equipment.
Fortunately, the format has been adopted for use in many
solid-modeling CAD programs, so often translation from another
internal geometric database format is unnecessary. In an STL file,
the boundary surfaces of an object are defined as a mesh of
interconnected triangles.
[0068] Apparatus 10 also includes a reservoir 14 (which may
comprise a removable reservoir interchangeable with others
containing different materials) of liquid material 16 to be
employed in fabricating the intended object. In the currently
preferred embodiment, the liquid is a photocurable polymer
responsive to light in the UV wavelength range. The surface level
18 of the liquid material 16 is automatically maintained at an
extremely precise, constant magnitude by devices known in the art
responsive to output of sensors within apparatus 10 and preferably
under control of computer 12. U.S. Pat. No. 5,174,931, referenced
above and previously incorporated herein by reference, discloses
one suitable level control system. A support platform or elevator
20, precisely vertically movable in fine, repeatable increments
responsive to control of computer 12, is located for movement
downward into and upward out of liquid material 16 in reservoir 14.
A laser 22 for generating a beam of light 26 in the UV wavelength
range has associated therewith appropriate optics and scan
controller 24 to shape and define beam 26 into beam 28, which is
directed downwardly to the surface 30 of platform 20 and traversed
in the X-Y plane, that is to say, in a plane parallel to surface
30, in a selected pattern under control of computer 12 to at least
partially cure liquid material 16 disposed over surface 30 to at
least a semisolid, or partially consolidated, state.
[0069] Data from the STL files resident in computer 12 is
manipulated to build an object 50 one layer at a time. Accordingly,
the data mathematically representing object 50 is divided into
subsets, each subset representing a slice or layer of object 50.
This is effected by mathematically sectioning the 3-D CAD model
into a plurality of horizontal layers, a "stack" of such layers
representing object 50. Each slice or layer may be from about
0.0025 to 0.0300 inch thick. As mentioned previously, a thinner
slice promotes higher resolution by enabling better reproduction of
fine vertical surface features of object 50. In some instances, a
base support or supports for an object 50 may also be programmed as
a separate STL file, such supports being fabricated before the
overlying object 50 in the same manner and facilitating fabrication
of an object 50 with reference to a perfectly horizontal plane and
removal of object 50 from surface 30 of elevator 20. Where a
"recoater" blade 32 is employed as described below, the
interposition of the base supports precludes inadvertent contact of
blade 32 with surface 30.
[0070] Before fabrication of object 50 is initiated with apparatus
10, the primary STL file for object 50 and the file for the base
support(s) are merged. It should be recognized that, while
reference has been made to a single object 50, multiple objects may
be concurrently fabricated on surface 30 of platform 20. In such an
instance, the STL files for the various objects and supports, if
any, are merged. Operational parameters for apparatus 10 are then
set, for example, to adjust the size (diameter, if circular) of the
laser light beam used to cure material 16.
[0071] Before initiation of a first layer for a support or object
50 is commenced, computer 12 automatically checks and, if
necessary, adjusts by means known in the art, as referenced above,
the surface level 18 of liquid material 16 in reservoir 14 to
maintain same at an appropriate focal length for laser beam 28.
Alternatively, the height of scan controller 24 may be adjusted
responsive to a detected surface level 18 to cause the focal point
of laser beam 28 to be located precisely at the surface of liquid
material 16 at surface level 18 if level 18 is permitted to vary.
The platform 20 may then be submerged in liquid material 16 in
reservoir 14 to a depth greater than the thickness of one layer or
slice 60 of the object 50 (FIG. 10(F)), then raised to a depth
equal to the thickness of a layer 60, and the liquid surface level
18 readjusted as required to accommodate liquid material 16
displaced by submergence of platform 20 while the surface of the
material 16 in reservoir 14 settles to be free of ripples and other
surface discontinuities which might result in an uneven layer when
material 16 is subjected to laser beam 28. Laser 22 is then
activated so that laser beam 28 will scan liquid material 16 over
surface 30 of platform 20 to at least partially cure (e.g., at
least partially polymerize) liquid material 16 at selected
locations, defining the boundaries of a first layer 60 (of object
50 or a support therefor, as the case may be) and filling in solid
portions thereof. Platform 20 is then lowered by a distance greater
than the thickness of a layer 60, raised to a depth equal to the
thickness thereof, and the laser beam 28 scanned again to define
and fill in the second layer 60 while simultaneously bonding the
second layer to the first. The process is then repeated, layer by
layer, until object 50 is completed.
[0072] If a recoater blade 32 is employed, the process sequence is
somewhat different. In this instance, surface 30 of platform 20 is
lowered into liquid material 16 below surface level 18 a distance
greater than a thickness of a single layer of material 16 to be
cured, then raised thereabove until it is precisely one layer's
thickness below blade 32. Blade 32 then sweeps horizontally over
surface 30, or (to save time) at least over a portion thereof on
which object 50 is to be fabricated, to remove excess liquid
material 16 and leave a film thereof of the precise, desired
thickness on surface 30. Platform 20 is then lowered so that the
surface of the film and material level 18 are coplanar and the
surface of the material 16 is still. Laser 22 is then initiated to
scan with laser beam 28 and define the first layer 60. The process
is repeated, layer by layer, to define each succeeding layer 60 and
simultaneously bond same to the next lower layer 60 until object 50
is completed. A more detailed discussion of this sequence and
apparatus for performing same is disclosed in U.S. Pat. 5,174,931,
previously incorporated herein by reference.
[0073] Each layer 60 of object 50 is preferably built by first
defining any internal and external object boundaries of that layer
60 with laser beam 28, then hatching solid areas of object 50 with
laser beam 28. The internal and external object boundaries of all
layers 60 comprise an envelope 80 whose boundaries are set by the
software (see FIGS. 10(B)-10(E)). If a particular part of a
particular layer 60 is to form a boundary of a void in the object
above or below that layer 60, then the laser beam 28 is scanned in
a series of closely spaced, parallel vectors so as to develop a
continuous surface, or skin, with improved strength and resolution.
The time it takes to form each layer 60 depends upon its geometry,
surface tension and viscosity of material 16, and thickness of the
layer.
[0074] Once object 50 is completed, platform 20 is elevated above
surface level 18 of liquid material 16, and the platform 20 with
object 50 may be removed from apparatus 10. Excess, uncured liquid
material 16 on the surface of object 50 may be manually removed,
and object 50 then solvent-cleaned and removed from platform 20,
usually by cutting it free of any base supports. Object 50 may then
require postcuring, as material 16 may be only partially
polymerized and exhibit only a portion (typically 40% to 60%) of
its fully cured strength. Postcuring to completely harden object 50
may be effected in another apparatus projecting UV radiation in a
continuous manner over object 50 and/or by thermal completion of
the initial, UV-initiated partial cure.
[0075] In practicing the present invention, a commercially
available stereolithography apparatus operating generally in the
manner as that described with respect to apparatus 10 of FIG. 9 is
preferably employed. For example and not by way of limitation, the
SLA-250/50HR, SLA-5000 and SLA-7000 stereolithography systems, each
offered by 3D Systems, Inc. of Valencia, Calif., are suitable for
modification. Photopolymers believed to be suitable for use in
practicing the present invention include Cibatool SL 5170 and SL
5210 resins for the SLA-250/50HR system, Cibatool SL 5530 resin for
the SLA-5000 and Cibatool SL 7510 resin for the SLA-7000 system.
All of these resins are available from Ciba Specialty Chemicals
Inc. By way of example and not limitation, the layer thickness of
material 16 to be formed, for purposes of the invention, may be on
the order of 0.001 to 0.002 inch, with a high degree of uniformity
over a field on a surface 30 of a platform 20. It should be noted
that different material layers may be of different heights, so as
to form a structure of a precise, intended total height or to
provide different material thicknesses for different portions of a
structure. The size of the laser beam "spot" impinging on the
surface of liquid material 16 to cure same may be on the order of
0.002 inch to 0.008 inch. Resolution is preferably .+-. 0.0003 inch
in the X-Y plane (parallel to surface 30) over at least a 0.5
inch.times.0.25 inch field from a center point, permitting a high
resolution scan effectively across a 1.0 inch.times.0.5 inch area.
Of course, it is desirable to have substantially this high a
resolution across the entirety of surface 30 of platform 20 to be
scanned by laser beam 28, which area may be termed the "field of
exposure," such area being substantially coextensive with the
vision field of a machine vision system employed in the apparatus
of the invention as explained in more detail below. The longer and
more effectively vertical the path of laser beam 26/28, the greater
the achievable resolution.
[0076] Referring again to FIG. 9 of the drawings, it should be
noted that apparatus 10 of the present invention includes a camera
70 which is in communication with computer 12 and preferably
located, as shown, in close proximity to scan controller 24 located
above surface 30 of platform 20. Camera 70 may be any one of a
number of commercially available cameras, such as
capacitive-coupled discharge (CCD) cameras available from a number
of vendors. Suitable circuitry as required for adapting the output
of camera 70 for use by computer 12 may be incorporated in a board
72 installed in computer 12, which is programmed as known in the
art to respond to images generated by camera 70 and processed by
board 72. Camera 70 and board 72 may together comprise a so-called
"machine vision system," and specifically a "pattern recognition
system" (PRS), the operation of which will be described briefly
below for a better understanding of the present invention.
Alternatively, a self-contained machine vision system available
from a commercial vendor of such equipment may be employed. For
example, and without limitation, such systems are available from
Cognex Corporation of Natick, Mass. For example, the apparatus of
the Cognex BGA Inspection Package.TM. or the SMD Placement Guidance
Package.TM. may be adapted to the present invention, although it is
believed that the MVS-8000.TM. product family and the
Checkpoint.RTM. product line, the latter employed in combination
with Cognex PatMax.TM. software, may be especially suitable for use
in the present invention.
[0077] It is noted that a variety of machine vision systems are in
existence, examples of which and their various structures and uses
are described, without limitation, in U.S. Pat. Nos. 4,526,646;
4,543,659; 4,736,437; 4,899,921; 5,059,559; 5,113,565; 5,145,099;
5,238,174; 5,463,227; 5,288,698; 5,471,310; 5,506,684; 5,516,023;
5,516,026; and 5,644,245. The disclosure of each of the immediately
foregoing patents is hereby incorporated by this reference.
[0078] In order to facilitate practice of the present invention
with apparatus 10, a data file representative of at least one
physical parameter, such as the size, configuration, thickness and
surface topography of a particular type and design of interposer
substrate 110 to which fence 120 is to be secured to form an
interposer 100 of the invention, is placed in the memory of
computer 12. If the interposer 100 is to be formed to accept a
particular type of semiconductor device 150, data representative of
semiconductor device 150, including the arrangement of conductive
structures 152 protruding therefrom, is provided.
[0079] Camera 70 is then activated to locate the position and
orientation of each interposer substrate 110 by scanning platform
20 and comparing the features of interposer substrates 110 disposed
thereon with those in the data file residing in memory, the
locational and orientational data for each interposer substrate 110
then also being stored in memory. It should be noted that the data
file representing the design size, shape and topography for
interposer substrates 110 may be used at this juncture to detect
physically defective or damaged interposer substrates 110 prior to
forming a fence 120 thereon and to automatically delete such from
the interposer manufacturing operation. It should also be noted
that data files for more than one type (size, thickness,
configuration, surface topography) of interposer substrate 110 may
be placed in computer memory and computer 12 programmed to
recognize not only substrate locations and orientations, but which
type of interposer substrate 110 is at each location so that
material 16 may be cured by laser beam 28 in the correct pattern
and to the height required to define interposer sidewalls and area
coverage, providing a receptacle 130 of the correct size, height
and location on each interposer 100.
[0080] If structural material in the form of the aforementioned
photopolymer is to be applied to top surfaces 104 (see FIG. 1) of
interposer substrates 110, or to top surfaces 104 and portions or
all of peripheral edges 112 of interposer substrates 110, a large
plurality of such substrates 110 may be placed, bottom side 108
down, on surface 30 of platform 20 for formation of fences 120. If
bottom protective layers 134 are to be fabricated on bottom
surfaces 108 of interposer substrates 110, it may be desirable to
first mount interposer substrates 110 upside down on platform 20 to
form bottom protective layer 134, then reposition interposer
substrates 110 right-side up to fabricate the remainder of fence
120.
[0081] Continuing with reference to a stereolithographic method
shown in FIG. 9 of the drawings, the use of stereolithography to
fabricate a bottom protective layer 134 of fence 120 on bottom
surface 108 of interposer substrate 110 is illustrated. An
interposer substrate 110 may be inversely mounted on platform 20 so
that structure may be formed on bottom surface 108 (see FIG.
10(A)). Interposer substrate 110 may then be submerged partially
below the surface level 18 of liquid material 16 to a depth greater
than the thickness of a first layer 60 of material on bottom
surface 108. The layer or "slice" 60 is then at least partially
cured to a semisolid state to form the lowest layer of a bottom
protective layer 134. Curable material overlying contact pads 106
is left uncured by not exposing those areas to radiation. If
additional layers 60 are required to obtain a particular desired
bottom protective layer 134, the process is repeated by further
submerging interposer substrate 110 to raise the liquid level to a
depth equal to the desired layer thickness, allowing the surface of
liquid material 16 to settle, and selectively curing the curable
material to form a bottom protective layer 134.
[0082] The material 16 selected for use in forming the interposer
100 may be a photopolymer such as one of the above-referenced
resins from Ciba Specialty Chemicals Inc. which are believed to
exhibit a desirable dielectric constant and low shrinkage upon
cure, are of sufficient (i.e., semiconductor grade) purity, exhibit
good adherence to other materials used in semiconductor devices,
and have a coefficient of thermal expansion (CTE) sufficiently
similar to that of the interposer substrate 110 so that the
substrate and the fence 120 are not stressed during thermal cycling
in testing and use. One area of particular concern in determining
resin suitability is the substantial absence of mobile ions and,
specifically, fluorides.
[0083] It may be desirable that surface 30 of platform 20 comprise,
or be coated or covered with, a material or stereolithographically
fabricated structures from which the at least partially cured
material 16 defining the lowermost layers of the interposer 100 may
be easily released to prevent damage to fence 120 and other parts
of interposer 100 during removal of a completed interposer 100 or
fence 120 from platform 20. Alternatively, a solvent may be
employed to release the completed interposer 100 or fence 120 from
platform 20. Such release and solvent materials are known in the
art. See, for example, U.S. Pat. No. 5,447,822 referenced above and
previously incorporated herein by reference.
[0084] To describe the stereolithography curing process in more
detail, as depicted in FIG. 9, laser 22 is activated and scanned to
direct beam 28, under control of computer 12, about the periphery
or over each interposer substrate 110 to effect the aforementioned
partial cure of material 16 to form a first layer 60. The platform
20 is then lowered into reservoir 14 and raised another layer
thickness-equaling depth increment and laser 22 activated to add
another layer 60. This sequence continues, layer 60 by layer 60,
until fence 120 is built up.
[0085] As shown in FIG. 10(B), interposer substrate 110 with
attached bottom protective layer 134 is inverted and remounted on
the platform 20. At this point, platform 20 is again lowered to
submerge a lower portion of interposer substrate 110 below surface
level 18 and then positioned a desired additional depth increment
below the surface of material 16. Layers 60 of at least semicured
material are formed in sequence by repeating the method.
[0086] FIGS. 10(C) and 10(D) illustrate fabrication of an upper
protective layer 122 over top surface 104 of interposer substrate
110. Contact pads 102 are exposed through recesses 124 formed in
upper protective layer 122.
[0087] FIGS. 10(E) and 10(F) depict an alternative interposer
structure without an upper protective layer 122. FIGS. 10(E) and
10(F) show interposers 100 which have fences 120 thereon that are
completed except for a final cure.
[0088] The thickness of layer 60 may be preprogrammed for each
layer over a relatively wide range. The greatest precision is
attained by forming thin layers, while thickness may be increased
to save time where extremely high precision is not necessary.
Layers of greater thickness in FIGS. 10(C)-10(F) are identified by
the numeral 60A.
[0089] In an alternative stereolithographic method, fence 120 is
fabricated by merely curing a "skin" over a surface of the
structure envelope 80, the final cure of the material of fence 120
being effected subsequently by broad-source UV radiation in a
chamber, or by thermal cure in an oven. In this manner, an
extremely thick protective layer of material 16 may be formed in
minimal time within apparatus 10.
[0090] The stereolithographic method as described enables precise
positioning by machine vision of a receptacle 130 on an interposer
substrate 110 irrespective of the location of interposer substrate
110 on platform 20. Thus, the use of stereolithography to fabricate
fence 120 facilitates the formation of an interposer 100 having a
receptacle 130 within which a semiconductor device 150 may be
accurately aligned with and connected to interposer substrate
110.
[0091] It is notable that the stereolithographic method of the
present invention, in addition to eliminating the capital equipment
expense of transfer molding processes, is extremely frugal in its
use of dielectric encapsulant material 16, since all such material
in which cure is not initiated by laser 22 remains in a liquid
state in reservoir 14 for use in forming fences 120 on the next
plurality of interposer substrates 110. Also, surprisingly, the
structure dimensional tolerances achievable through use of the
present invention are more precise, e.g., three times more precise,
than those of which a transfer molding system is capable, and there
is no need for an inclined mold sidewall (and thus extra packaging
material) to provide a release angle to facilitate removal of an
interposer 100 from a mold cavity. Moreover, there is no potential
for mold damage, or mold wear, or requirement for mold
refurbishment. Finally, the extended cure times at elevated
temperatures, on the order of, for example, four hours at
175.degree. C., required after removal of batches of interposers
100 from the transfer mold cavities are eliminated. Post-cure of
interposers 100 formed according to the present invention may be
effected with broad-source UV radiation emanating from, for
example, flood lights in a chamber through which interposers are
moved on a conveyor, either singly or in large batches.
Additionally, if some portion of an interposer 100 is shadowed by
another part of itself or another interposer, curing of material 16
in that shadowed area will eventually occur due to the
cross-linking initiated in the outwardly adjacent photopolymer. The
curing of any uncured photopolymer, in shadowed areas or elsewhere,
may be accelerated as known in the art, such as by a thermal cure
(e.g., heating the polymer at a relatively low temperature such as
160.degree. C.).
[0092] It should also be noted that the stereolithographic method
of the present invention is conducted at substantially ambient
temperature, the small beam spot size and rapid traverse of laser
beam 28 around and over the substrates 110 resulting in negligible
thermal stress thereon. Physical stress on the fence 120 is also
significantly reduced, in that material 16 is fixed in place and
not moved over the structure in a viscous, high-pressure wave front
as in transfer molding, followed by cooling-induced stressing of
the package.
Molding Method for Fabricating the Fence
[0093] Although stereolithography is a preferred method for forming
an interposer 100 of the invention, having many advantages
described above, known molding processes may nonetheless be used to
fabricate fence 120 of interposer 100. FIG. 11 schematically
illustrates an exemplary mold 170 in which an interposer substrate
110 may be positioned to form a fence 120, 120', 120'', 120''' (see
FIGS. 1, 1A, 2, 3, 6-8) thereon. As illustrated, mold 170 has an
upper mold half 172 and a lower mold half 174. Upper mold half 172
is shown with receptacles 184 for receiving any protecting,
projecting portions of contact pads 102. Lower mold half 174 is
shown with upwardly extending projections 186 which form apertures
through the lower protective layer of fence 120, through which
contact pads 106 will be exposed. In addition, when biased against
an interposer substrate 110, projections 186 prevent leakage of
mold material onto contact pads 102, 106, as well as damage that
may be caused to interposer substrate 110 as mold material is
introduced into cavity 180.
[0094] When assembled, mold halves 172 and 174 are joined at a
periphery 182 of mold 170. When mold halves 172 and 174 are so
assembled, one or more cavities 180 are formed internally within
mold 170. In use of mold 170, a flowable mold material, such as a
thermoplastic material, is introduced into each cavity 180 through
an inlet port 176. As the flowable mold material enters and fills
each cavity 180, air or gas within cavity 180 is driven therefrom
through vent(s) 178. As the flowable mold material is shaped by
cavity 180 and begins to harden, fence 120 is formed.
Further Processing of the Interposer
[0095] Following the fabrication of fence 120 and assembly thereof
with interposer substrate 110, conductive structures 142 can be
secured by known processes to contact pads 106 exposed at bottom
surface 108 of interposer substrate 110. Conductive structures 142
can be bumps, balls, pillars, or structures having any other
suitable configuration that are fabricated from a suitable
conductive material, such as solder, metal, metal alloy,
conductor-filled epoxy, or conductive elastomer.
[0096] Interposers incorporating teachings of the present invention
are useful for connecting semiconductor devices, including, without
limitation, flip-chips, chip scale packages, and ball grid array
packages, to a substrate, such as a test substrate or a higher
level carrier substrate.
[0097] While the present invention has been disclosed in terms of
certain preferred embodiments, those of ordinary skill in the art
will recognize and appreciate that the invention is not so limited.
Additions, deletions and modifications to the disclosed embodiments
may be effected without departing from the scope of the invention
as claimed herein. Similarly, features from one embodiment may be
combined with those of another while remaining within the scope of
the invention.
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