U.S. patent application number 09/794101 was filed with the patent office on 2001-12-20 for method and apparatus for interconnecting devices using an adhesive.
This patent application is currently assigned to Xerox Corporation. Invention is credited to Chua, Christopher L., Fork, David K., Kim, Patrick G., Romano, Linda.
Application Number | 20010053620 09/794101 |
Document ID | / |
Family ID | 23831581 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053620 |
Kind Code |
A1 |
Chua, Christopher L. ; et
al. |
December 20, 2001 |
Method and apparatus for interconnecting devices using an
adhesive
Abstract
A method and apparatus for interconnecting at least two devices.
Each of the interconnected devices includes a contact structure for
electrically and/or physically interconnecting the devices.
Preferably, the contact structure for at least one of the devices
includes a spring contact. An adhesive, such as a UV-curable
adhesive, is applied to at least a portion of one of the devices,
and once the adhesive is applied, the devices are assembled, i.e.,
brought into sufficient proximity so that the contact structures
interconnect the devices. The adhesive can be applied directly to
contact structures of one of the devices and/or can be applied to
other portions of the devices so that the adhesive flows around the
contact structures during assembly. The adhesive is then cured to
bond the devices together. Applying the adhesive before assembling
the devices prevents interference with the interconnection between
the contact structures, especially if the contact structures
include spring contacts to be electrically connected with
corresponding contact pads.
Inventors: |
Chua, Christopher L.; (San
Jose, CA) ; Fork, David K.; (Los Altos, CA) ;
Kim, Patrick G.; (Santa Clara, CA) ; Romano,
Linda; (Sunnyvale, CA) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. Box 19928
Alexandria
VA
22320
US
|
Assignee: |
Xerox Corporation
|
Family ID: |
23831581 |
Appl. No.: |
09/794101 |
Filed: |
February 28, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09794101 |
Feb 28, 2001 |
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09461195 |
Dec 15, 1999 |
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6213789 |
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Current U.S.
Class: |
439/149 ;
257/E21.503; 257/E23.021; 257/E23.078 |
Current CPC
Class: |
H01L 2924/01039
20130101; H01L 2224/13 20130101; H01L 2924/01074 20130101; H01L
2924/00 20130101; H01L 2924/00 20130101; H01L 2924/00 20130101;
H01L 2924/12042 20130101; H01R 4/04 20130101; H01L 2924/01024
20130101; H01L 2924/01022 20130101; H01L 24/13 20130101; H01L
2924/01045 20130101; H01L 2924/0104 20130101; H01L 2924/12042
20130101; H05K 3/325 20130101; H01L 2924/01079 20130101; H01L 24/10
20130101; H01L 2924/01049 20130101; H01L 2924/01033 20130101; H01L
2224/73203 20130101; H01L 2224/13 20130101; H01L 2924/181 20130101;
H01L 2924/014 20130101; H01L 2924/181 20130101; H01L 2924/01013
20130101; H01L 2224/13099 20130101; H01L 2924/01029 20130101; H01L
2924/14 20130101; H01L 2924/01018 20130101; H01L 2924/01004
20130101; H01L 24/72 20130101; H01L 2924/01042 20130101; H01L
2924/01078 20130101; H01L 2924/12041 20130101; H01L 21/563
20130101; H01L 2924/01046 20130101; H01R 12/52 20130101 |
Class at
Publication: |
439/149 |
International
Class: |
H05K 001/00; H01R
012/00; H01R 013/44 |
Claims
What is claimed is:
1. A method for interconnecting two devices, the method comprising:
providing a first device having a first contact structure that
includes at least one spring contact; providing a second device
having a second contact structure; applying an adhesive to at least
one of the first and second devices; aligning the first and second
devices; bringing the first and second devices into sufficient
proximity so that the first and second contact structures
interconnect and the adhesive surrounds at least a portion of the
contact structures; and curing the adhesive; wherein the step of
applying the adhesive is performed before the step of bringing the
first and second devices into sufficient proximity.
2. The method of claim 1, wherein both of the first and second
contact structures include a spring contact.
3. The method of claim 1, wherein at least one of the first and
second contact structures includes a spring contact that is formed
by fixing an elastic material having an inherent stress gradient to
a substrate and releasing a portion of the elastic material so that
the released portion is biased away from the substrate by the
inherent stress gradient.
4. The method of claim 1, wherein at least one of the first and
second contact structures includes at least one of a contact pad, a
gold contact pad, a contact pad having a conductive and inert
material coating, a spring contact, a gold spring contact, a metal
trace, a wirebond pad, a solder bump, a electrical interconnection
tab, a spacer, and a device alignment feature.
5. The method of claim 1, wherein the first and second contact
structures include complementary electrical interconnect contact
structures so that when the first and second devices are brought
into sufficient proximity, the first and second devices are
electrically interconnected.
6. The method of claim 1, wherein at least one of the first and
second devices includes at least one of a circuit board, an
electrical interconnection device, a laser emitting element, a
light modulating element, a light detecting element, a vertical
cavity surface emitting laser, a light emitting diode, an edge
emitting laser, a switching element, a controller, a data
processing apparatus, a semiconductor chip, a semiconductor memory
or logic chip, an optoelectronics module, and a
micro-electro-mechanical device.
7. The method of claim 1, wherein the step of applying the adhesive
comprises applying an ultraviolet (UV) curable adhesive, a
multi-component adhesive or a thermal setting compound.
8. The method of claim 1, wherein the step of applying the adhesive
comprises applying the adhesive to a portion of the first or second
contact structure.
9. The method of claim 1, wherein the step of applying the adhesive
comprises applying an insulating, conductive semiconductive or
anisotropically conductive compound.
10. The method of claim 1, wherein the step of aligning the first
and second devices comprises aligning complementary contact
structures on the first and second devices in preparation for
electrically contacting the complementary contact structures.
11. The method of claim 1, wherein the step of bringing the first
and second devices comprises moving the first and second devices
toward each other along a straight line.
12. The method of claim 1, wherein the step of bringing the first
and second devices comprises moving the first and second devices
toward each other along a straight line and in a direction
perpendicular to the straight line to ensure that the contact
structures are properly interconnected.
13. The method of claim 1, wherein the step of bringing the first
and second devices comprises moving the first and second devices
toward each other until the first and second contact structures are
properly physically and electrically interconnected.
14. An apparatus formed by the method of claim 1.
15. An apparatus formed by the method of claim 1, wherein at least
one contact pad on one device is mechanically scrubbed by a
corresponding spring contact tip.
16. An apparatus formed by the method of claim 3.
17. An apparatus formed by the method of claim 4.
18. An apparatus formed by the method of claim 5.
19. An apparatus formed by the method of claim 6.
20. A liquid crystal display formed by the method of claim 1,
wherein the first device is an active matrix backplane, and the
second device is a display front plane.
21. The liquid crystal display of claim 20, further comprising an
off-display board interconnected with the display front plane.
22. The method of claim 1, wherein the first device is an
electronic switching device comprising at least one transistor
switching element and the second device is a laser array
device.
23. The method of claim 1, further comprising interconnecting a
photodetector device with the electronic switching device by the
method of claim 1.
24. An apparatus including two interconnected devices, comprising:
a first device having a first contact structure that includes at
least one spring contact; a second device having a second contact
structure interconnected with the first contact structure; and a
rubbery adhesive that surrounds at least a portion of the contact
structures and bonds the first and second devices together, wherein
the rubbery adhesive allows accommodation of physical movement of
the devices relative to each other while keeping the contact
structures interconnected.
25. A liquid crystal display apparatus comprising: an active matrix
backplane having a first contact structure; a display frontplane
having a second contact structure interconnected with the first
contact structure; and an adhesive that surrounds at least a
portion of the contact structures and bonds the frontplane and the
backplane together, and the adhesive forms a surface that contains
a liquid crystal material between the frontplane and the
backplane.
26. The apparatus of claim 25, wherein: at least one of the first
contact structure and the second contact structure includes a
spring contact.
27. The apparatus of claim 26, wherein: at least one spring contact
extends from the adhesive into the liquid crystal material to
contact a corresponding contact pad.
Description
INCORPORATED PATENTS
[0001] This Application is related to U.S. Pat. Nos. 5,613,861 and
5,944,537, which are hereby incorporated by reference in their
entirety. U.S. Pat. Nos. 5,665,648 and 3,842,189 are also hereby
incorporated by reference in their entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] This invention generally relates to interconnecting devices,
such as integrated circuits, circuit boards, electrode arrays, or
other devices.
[0004] 2. Description of Related Art
[0005] As described in U.S. Pat. No. 5,613,861, standard bonding
techniques for electrically connecting integrated circuits, or
chips, to a circuit board or other device include wire bonding, tab
bonding, solder-bump and gold-bump flip-chip bonding and other
techniques. However, these standard bonding techniques suffer from
various problems and limitations, including relatively low
resistance to thermal and mechanical shock and being incapable of
being made very small, e.g., allowing a contact pad pitch of
several microns.
SUMMARY OF THE INVENTION
[0006] The invention provides a method and apparatus for
interconnecting two devices by using an adhesive that surrounds the
contact structures on the devices and adheres to the device
substrates. According to the invention, the two devices are
interconnected by first applying an adhesive to at least one of the
devices. The adhesive can be applied so that the adhesive surrounds
at least some of the contact structures on the device or can be
applied away from the contact structures. As used herein, the term
"contact structure" can include contact pads, spring contact
structures or other physical or electrical connection structures,
and the term "device" can include any type of apparatus including
circuit boards, semiconductor chips, a laser device, an
optoelectronics module, etc. After the adhesive is applied, the
devices and their corresponding contact structures are aligned and
the devices are brought into sufficient proximity to allow the
contact structures on the devices to interconnect, e.g.,
electrically interconnect. As the devices are brought into
sufficient proximity, the adhesive can flow into areas where
contact structures are present. Thus, even if the adhesive is
applied to a device in an area where no contact structure is
present, adhesive can flow around the contact structures during
assembly. The adhesive is cured or otherwise hardened to bond the
devices together.
[0007] The inventors have discovered that if an adhesive is
applied, e.g., injected in a conventional fashion, between devices
after the devices are electrically connected, the adhesive can
disrupt the connection between the devices, especially if delicate
spring contacts are used to interconnect the devices. Thus, the
adhesive is applied to at least one of the devices before the
devices are assembled.
[0008] In one aspect of the invention, the contact structure of at
least one of the interconnected devices includes at least one
spring contact.
[0009] In one aspect of the invention, a spring contact that is
part of a device's contact structure includes a stress gradient
formed in the spring contact, which causes the spring contact to
bend away from the substrate and thus provide compliant contact
with a corresponding contact pad.
[0010] In one aspect of the invention, spring contacts included in
a contact structure of a first device are formed of a thin metal
strip which is in part fixed to a substrate and electrically
connected to a via on the substrate. The free portion of the metal
strip not fixed to the substrate bends up and away from the
substrate. When a contact pad on a second device is brought into
pressing contact with the free portion of the metal strip, the free
portion deforms and provides compliant contact with the contact
pad. Since the metal strip is electrically conductive or coated
with a conductive material, the via on the substrate is
electrically connected to the contact pad on the second device via
the spring contact.
[0011] In one aspect of the invention, spring contacts can have
various tip configurations, including a single point, multiple
points, a deformable tab, a flat end, etc.
[0012] In one aspect of the invention, spring contacts can have
various configurations such that portions other than a tip of
spring contact are connected to a corresponding contact pad. For
example, a spring contact can curl to form an arc of 180 degrees or
more.
[0013] In one aspect of the invention, the contact structures of
the devices can include various connection devices. in one aspect
of the invention, at least one of the interconnected devices can be
or include an LED device, a laser emitting device or devices, a
photodetector, microelectronics devices, an LCD device, a driver
device, etc.
[0014] Other aspects of the invention will be apparent and/or
obvious from the following description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention is described in relation to the following
drawings, in which reference numerals refer to like elements and
wherein:
[0016] FIG. 1 is a spring contact in an undeformed free state and
another spring contact deformed when contacting a contact pad;
[0017] FIGS. 2-4 show steps in a method of interconnecting two
devices in accordance with the invention;
[0018] FIGS. 5-10 show a plurality of types of spring contact
tips;
[0019] FIG. 11 shows an alternate contact structure for
interconnecting two devices;
[0020] FIGS. 12 and 13 show inverted "shepherd's hook"-type spring
contacts;
[0021] FIG. 14 shows an alternate contact structure for
interconnecting two devices;
[0022] FIG. 15 shows an exemplary device interconnection structure
for a liquid crystal display; and
[0023] FIG. 16 shows steps of a method of interconnecting two
devices.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0024] The invention is described below as interconnecting two
different devices by applying an adhesive to at least one of the
devices, aligning the contact structures of the two devices,
bringing the devices into sufficient proximity (i.e., to allow the
contact structures to interconnect) and curing or otherwise
hardening the adhesive. The contact structures on the devices can
include any type of interconnect structure, such as electrical
interconnect structures like contact pads and corresponding solder
bumps. However, the invention is described below in connection with
using spring contacts as part of the contact structure of at least
one of the interconnected devices. Accordingly, a brief description
of a spring contact and how a spring contact can be made, as is
fully described in U.S. Pat. Nos. 5,613,861 and 5,944,537, is
provided before describing the device interconnect invention. It
should be appreciated that the following description is only one
example. Thus, the spring contacts can be made in any desired way,
such as that described in U.S. Pat. Nos. 5,665,648 and 3,842,189,
for example.
[0025] FIG. 1 shows a side view of an interconnected device
structure 100 including a first device 14 that is connected to a
second device 21. The first device 14 has a contact structure that
includes a plurality of spring contacts 15 (although only one
spring contact 15 is shown). Each spring contact 15 comprises a
free portion 1 1 and an anchor portion 12 fixed to a release layer
13 and electrically connected to a via 32. Each spring contact 15
is made of an extremely elastic material, such as a
chrome-molybdenum alloy or a nickel-zirconium alloy. Preferably,
the spring contacts 15 are formed of an elastic conductive
material, although they can be formed of a non-conductive or
semi-conductive material if they are coated or plated with a
conductor material (assuming the devices 14 and 21 are to be
electrically interconnected). More preferably, the spring contacts
15 are formed of a nickel-zirconium alloy having 1% zirconium, a
chrome-molybdenum alloy (20% Cr--80% Mo), a tungsten (W)-based
alloy, or a chronium (Cr) based alloy. Zirconium is added to the
nickel in the nickelzirconium alloy to improve the elastic
properties of the alloy while not greatly reducing the conductivity
of the nickel. When the elastic material is not conductive, it is
coated on at least one side with a conductive material, such as a
metal or metal alloy.
[0026] The via 32 and the contact pad 3 on the first and second
devices 14 and 21 can be the terminal ends of a communication line
that electrically communicates with an electronic device formed on
the first and second devices 14 and 21, such as a transistor, a
display electrode, or other electrical device, or can communicate
with other contact structures such as wirebond pads, solder bumps,
etc. The via 32 and the contact pad 3 are typically made of
aluminum, but can be made of any conductive material. If the
contact pad 3 is made of aluminum, the contact pad 3 is preferably
coated with a conductive and preferably inert material, such as
gold, gold alloys, indium tin oxide, nickel, palladium, platinum,
rhodium, etc. This allows the spring contact 15 to make better
electrical contact with the contact pad 3, since the spring contact
15 is not required to "scrub" the uncoated contact pad 3 to break
through the aluminum oxide that forms on an uncoated aluminum
contact pad 3. Preferably, a thin coating of Titanium (Ti) is
applied to the uncoated aluminum contact pad 3 to promote good
adhesion of the gold to the contact pad 3.
[0027] The release layer 13 is made of silicon nitride or other
etchable material, and can be electrically insulating or
conducting. However, the release layer 13 is not necessary and can
be eliminated. The release layer 13 and the via 32 are formed on or
over a first device 14, which can have a substrate formed of an
insulating material, such as oxidized silicon or glass.
[0028] The spring contacts 15 on the device 14 can be formed as
follows. A via 32 is formed on or over a substrate in the first
device 14. Additionally, a release layer 13 can be formed on or
over the first device 14. However, as mentioned above, the release
layer 13 is not required and can be eliminated.
[0029] A layer of metal is then deposited on or over a portion of
the first device 14. In a preferred embodiment, the metal is the
nickel-zirconium alloy described above. Part of the metal layer is
electrically connected to or directly contacts the via 32 and
another portion of the metal layer is deposited on or over the
release layer 13, if present. There are many methods available for
depositing a metal layer on or over the first device 14, including
electron-beam deposition, thermal evaporation, chemical vapor
deposition, sputter deposition and other methods. Preferably, the
metal layer is sputter deposited.
[0030] When sputter-depositing a metal, a plate of the metal,
called the target, is placed on a cathode, which is set to a high
negative potential and immersed in a low-pressure, typically 1 to
100 millitorr, gas. This causes a glow-discharge plasma to ignite,
from which positive ions are accelerated into the negatively
charged target. This ion bombardment knocks metal atoms off the
target, and many of these deposit on nearby surfaces, such as on
the first device 14.
[0031] The metal layer can be thought of as deposited in several
sub-layers to a final thickness of any desired thickness, e.g.,
approximately 1 .mu.m. A stress gradient is introduced into the
metal layer by altering the stress inherent in each of the
sub-layers of the metal layer so that each sub-layer has a
different level of inherent stress.
[0032] Different stress levels can be introduced into each
sub-layer of the deposited metal layer during sputter deposition in
a variety of ways, including adding a reactive gas to the plasma,
depositing the metal at an angle, and changing the pressure of the
plasma gas. Preferably, the different levels of stress are
introduced into the metal layer by varying the pressure of the
plasma gas, which is preferably argon. The pressure of the plasma
gas can be varied in a stepwise fashion, or continuously, as
desired.
[0033] To form the spring contact 15 shown in FIG. 1, the metal
layer is formed so that a sub-layer near the device 14 substrate
has a compressive stress and upper layers have increasingly tensile
stress toward the top of the metal layer. Although the stress
gradient in the metal layer biases the layer to bend into an arc,
the metal layer adheres to the release layer 13, the first device
14, and the contact pad 3, and thus lies flat.
[0034] After the metal layer is deposited, the metal layer is
photolithographically patterned into the spring contacts 15.
Photolithographic patterning is a well-known technique and is
routinely used in the semiconductor chip industry and allows the
spring contacts to be formed in almost any shape or
configuration.
[0035] Next, the free portion 11 of the spring contact 15 is
released from the release layer 13, preferably by a process of
under-cut etching, i.e., removing at least a portion of the release
layer 13 or other substrate under the free portion 11. Thus, the
spring contacts 15 are released from the release layer 13 and are
allowed to bend up and away from the release layer 13 due to the
stress gradient in the spring contacts 15.
[0036] Only those areas of the release layer 13 under the free
portion 11 of the spring contact 15 are under-cut etched. Thus, the
anchor portion 12 of the spring contact 15 remains fixed to the
release layer 13 and does not pull away from the release layer
13.
[0037] When the contact pad 3 on the device 21 is aligned with the
tip of the spring contact 15 and the first and second devices 14
and 21 are moved toward each other, the spring contact 15 contacts
the pad 3 and elastically deforms. Therefore, the tip 30 of the
spring contact 15 is compliantly forced into the contact pad 3 to
establish an electrical contact between the contact pads 3.
[0038] A layer of gold or other resistance lowering material such
as copper, nickel, palladium, etc., can be formed over the outer
surface of each spring contact 15 to reduce the resistance in the
spring contacts 15, but can be replaced with any other resistance
lowering material.
[0039] Since the process for forming the spring contacts 15 is
limited only by the design rules of photolithographic patterning,
many hundreds or thousands of spring contacts 15 can be formed
closely together in a relatively small area on the first device 14.
The typical width w of the spring contact 15 can be 10-100 .mu.m.
Therefore, the spring contacts 15 can be formed close together, at
a spacing of approximately 10-20 .mu.m, and less if necessary. This
makes the center-to-center distance between adjacent spring
contacts 15 approximately 20-120 .mu.m, which is within or less
than the typical center-to-center distance between adjacent contact
pads 3 on a standard semiconductor chip.
[0040] FIGS. 2-4 show steps in a method for interconnecting two
devices in accordance with the invention. In FIG. 2, a first device
14 is provided that has a contact structure including at least a
contact pad 3. The contact structure can of course include other
interconnect structures including spring contacts, solder bumps,
alignment structures that ensure alignment between interconnected
devices, spacing structures that ensure proper spacing between
interconnected devices, etc. Next, an adhesive 40, or molding
compound, is applied to the first device 14. The adhesive 40 can be
applied to portions of the first device 14 that include contact
structures and/or to portions of the first device 14 that do not
include contact structures. FIG. 2 shows an example where adhesive
40 is applied over a contact structure on the first device 14.
[0041] The adhesive 40 can be a UV-curable optically transparent
adhesive, such as Loctite 352, but other compounds, such as other
UV-curable adhesives, thermal setting compounds, multi-component
adhesives such as a two-part epoxy, or other compounds can be used.
Preferably, the adhesive 40, or molding compound, is electrically
insulating, but semiconductive, anisotropically conductive or
conductive compounds could be used if desired. For example, an
adhesive 40 that is only electrically conductive along an applied
electric field, but otherwise insulating, could be used to
interconnect contact pads 3 on the first and second devices 14 and
21 without requiring the contact pads 3 to physically touch.
[0042] The adhesive 40 can be applied to the first device 14 in
various different ways, including using a micro-actuated
applicator. When using a micro-actuated applicator, a wire is
dipped into a pool of viscous adhesive solution. When the wire is
lifted from the pool, an amount of adhesive 40 is carried by the
wire, and the adhesive 40 can be applied by lowering the wire to
the desired portions of the first device 14. Of course, the
adhesive 40 can also be applied to the second device 21, if
desired. The adhesive 40 can also be applied in other ways,
including spraying, injecting, etc.
[0043] As shown in FIG. 3, the contact structures of the first and
second devices 14 and 21 are next aligned with each other. That is,
the contact structures, e.g., spring contacts, contact pads, etc.,
on the first and second devices 14 and 21 are aligned with each
other so that when the first and second devices 14 and 21 are moved
into sufficient proximity with each other, as shown in FIG. 4, the
contact structures interconnect the devices 14 and 21. The
interconnection can be electrical interconnection and/or physical
interconnection.
[0044] The process of bringing the first and second devices 14 and
21 into sufficient proximity can involve steps other than simply
moving the devices 14 and 21 together. For example, the first and
second devices 14 and 21 and or elements in the respective contact
structures can be moved laterally relative to each other to scrub
the spring contacts 15 into the corresponding contact pads 3. As
the first and second devices 14 and 21 are moved together, excess
adhesive 40 is squeezed out and a thin layer of adhesive 40 is
trapped between the devices 14 and 21 to encapsulate the entire
package. When the first and second devices 14 and 21 are moved to a
final relative position, the adhesive 40 is cured or otherwise
hardened to bond the devices 14 and 21 as well as their contact
structures together.
[0045] Although only two devices 14 and 21 are shown, of course
three or more devices can be bonded together according to the
invention. Further, the devices can be or include any type of
apparatus such as a circuit board or other electrical
interconnection device, a laser emitting element, a light
modulating element, a light detecting element, a vertical cavity
surface emitting laser, a light emitting diode, an edge emitting
laser, a switching element, a controller, a data processing
apparatus, a semiconductor chip, a semiconductor memory or logic
chip, an optoelectronics module, and a micro-electro-mechanical
device The inventors have discovered that when at least one of the
devices 14 and 21 includes spring contacts 15 as part of its
contact structure, the devices 14 and 21 should be interconnected
by first applying adhesive to at least one of the devices 14 and 21
and then assembling the devices 14 and 21 into a final package,
especially when the spring contacts 15 are very thin, e.g., 5-20
microns. That is, the inventors have found that the interconnection
between contact structures of the devices 14 and 21 can be
disrupted if the adhesive 40 is injected between the devices in a
conventional fashion after the contact structures are
interconnected, e.g., injecting adhesive 40 after somewhat delicate
spring contacts 15 and corresponding contact pads 3 are
electrically connected. The electrical interconnect between the
spring contacts 15 and the contact pads 3 is disrupted by the
surface tension of the adhesive 40 as it flows between the devices
14 and 21, and some of the adhesive 40 forces itself between the
spring contacts 15 and their corresponding contact pads 3.
Accordingly, applying the adhesive 40 to at least one of the
devices 14 and 21 before the devices 14 and 21 are moved together
and the contact structures interconnected can be critical to proper
assembly of two devices having spring contacts 15 as part of a
contact structure.
[0046] Applying the adhesive 40 to one of the devices 14 and 21
before assembly also has the benefit of reducing the likelihood of
void formation in the adhesive 40 since pressure is applied to the
adhesive 40 when the devices 14 and 21 are moved together and the
adhesive 40 is squeezed out from between the devices 14 and 21.
Interconnecting the devices 14 and 21 according to the invention
also has the benefit of shorter assembly time since adhesive 40 can
be forced out from between the devices 14 and 21 more quickly than
adhesive 40 can be injected or wicked into the space between
devices 14 and 21 after the devices 14 and 21 have been brought
together.
[0047] The adhesive 40 can also provide a sealing function against
atmospheric contaminants and, if properly selected, the adhesive 40
does not contribute contaminants of its own. When the adhesive 40
is cured, the adhesive 40 can undergo a slight contraction, e.g.,
up to 4%, which increases the compressive force of the spring
contact 15 into the contact pad 3. This compression is caused by
shrinkage of the adhesive 40 in the y direction, as shown in FIG.
4. The adhesive 40 shrinks in the y direction rather than the x
direction because when the adhesive 40 is bonded to the first
device 14 and the second device 21, the first device 14 and the
second device 21 resist shrinkage of the adhesive 40 in the x
direction. The additional compressive force provided between the
spring contact 15 and the contact pad 3 will remain over a
relatively wide temperature range, providing of course that the
differential thermal expansion of the adhesive 40 relative to the
contacts does not exceed the initial contraction value of, for
example, 4%. The adhesive 40 can also perform a heat sink function
to remove heat from elements of the devices 14 and 21.
[0048] FIGS. 5-10 show various tip 30 configurations for spring
contacts 15 used with the invention. The shape of the spring
contact tip 30 can take different forms, depending on the
application. Since the spring contacts 15 are photolithographically
patterned, the spring contact tips 30 are easily formed in a
variety of shapes. FIG. 5 shows a spring contact tip 30 having a
flat end. The spring contact tip 30 shown in FIG. 6 has a pointed
end which concentrates the force exerted by the spring contact 15
at a single point on the contact pad 3. This pointed shape aids the
spring contact tip 30 when breaking through native oxides which may
be present on the contact pads 3. FIGS. 7 and 8 show spring contact
tips 30 having multiple points for applications where contact
redundancy is required. FIG. 9 shows a spring contact tip 30 having
a deformable tab. The deformable tab increases the contact area
with the contact pad 3 by deforming as shown in FIG. 10 when the
spring contact 15 forces the tip 30 against the contact pad 3. For
example, when contacting a gold spring contact tip 30 to a gold
contact pad 3, a tip 30 having a flat or deformable end has been
found to reduce resistance at the point of contact.
[0049] FIG. 11 shows an alternate type of spring contact that can
be used with the invention. In this example, the spring contact 15
is formed so that when it is released from the surface of the first
device 14, the free end of the spring contact 15 curls back to form
an arc of 180 degrees or more. This arrangement can be advantageous
when a large contact area is needed between the spring contact 15
and the contact pad 3, or when relative movement between the second
device 21 and the first device 14 in the x direction might stress
the spring contact 15/contact pad 3 joint. Relative movement in the
x direction is compensated for by flexure in the curved portion of
the spring contact 15 between the contact pad 3 and the first
device 14.
[0050] Other possible spring contact 15 configurations include that
shown in FIGS. 12 and 13. In these examples, the bottom-most
portion of the spring contacts 15 have a tensile stress, while
upper portions have decreasing levels of tensile stress and/or
increasing levels of compressive stress. Therefore, when the free
portion 11 of the spring contact 15 is released from the first
device 14, the free portion 11 bends so that the spring contact 15
moves up and away from the first device 14. These configurations
have an advantage over other configurations where the free portion
11 does not contact the first device 14 after the free portion 11
is released, e.g., FIG. 1, in that the free portion 11 tends not to
move too freely in the z direction shown in FIGS. 12 and 13. This
can be an advantage in fine-pitch contact applications where the
spring contacts 15 are spaced closely together, e.g., less than 10
.mu.m apart, and can become entangled with each other.
[0051] FIG. 14 shows another configuration of two interconnected
devices 14 and 21 where the contact structures, or one of the
contact structures, of the devices 14 and 21 include an aligning or
spacing structure 36. The structure 36 can, for example, have
aligning grooves or bumps that interlock when the devices 14 and 21
are moved together, thus ensuring that the contact structures of
the devices 14 and 21 are properly aligned. The structure 36 can
also ensure that the devices 14 and 21 are properly spaced apart,
e.g., when the device 14 is an LCD panel backplane and the device
21 is an LCD panel front plane. The structure 36 can also function
to contain the adhesive 40 and/or prevent the adhesive 40 from
contacting certain portions of the contacting structures, e.g.,
particularly sensitive or fine structures.
[0052] As also shown in FIG. 14, the first and second devices 14
and 21 can include any type of elements, such as switching elements
(transistors), data processing elements, light emitting elements,
etc. Thus, the element 35 can be an LED or laser emitter and can
communicate through the spring contact 15 to a driver on the first
device 14 that controls the element 35 to selectively emit light.
In this example, the adhesive 40 and the substrate of the first
device 14 can be transparent so that the element 35 can emit light
through the adhesive 40 and the device 14 substrate while being
protected from a harmful environment.
[0053] As discussed above, the devices 14 and 21 can be any desired
set of devices that are interconnected, including, a circuit board,
a semiconductor chip, a probe card, or other electronic devices.
FIG. 15 shows one detailed example of how three devices in a liquid
crystal display (LCD) can be interconnected using the invention. In
this example, an active matrix backplane 22 for the LCD and an
off-display board 24, such as a device driver, are interconnected
with an LCD front plane 23. The contact structure of the active
matrix backplane 22 and the off-display board 24 can include
contact pads 3, spring contacts 15, metal traces, wirebond pads,
bumps, tabs, etc. The contact structure of the LCD front plane 23
can include metal traces (including indium-tin oxide (ITO) traces),
spring contacts 15, contact pads 3, wirebond pads, bumps, tabs,
etc. In the cross section shown in FIG. 15, the front plane 23
includes spring contacts 15 that connect with contact pads 3,
traces or other structures (not shown) on the active matrix
backplane 22 and the off-display board 24. A conductive trace 51 or
other structure electrically connects the two spring contacts 15
shown so that appropriate elements in the active matrix backplane
22 and the off-display board 24 can communicate.
[0054] As described above, adhesive 40 is applied to the active
matrix backplane 22, the LCD front plane and/or the off-display
board 24. After application of the adhesive, the backplane 22, the
front plane 23 and the off-display board 24 are aligned and moved
into sufficient proximity so that the respective contact structures
interconnect. The adhesive 40 is then cured or otherwise hardened
to bond the devices 22, 23 and 24 together. Once the adhesive 40 is
cured, a liquid crystal material 52 can be provided between the
backplane 22 and the front plane 23 in a conventional fashion.
Thus, the adhesive 40, typically an epoxy, can function to both
bond the devices 22, 23 and 24 together in accordance with the
invention as well as provide a sealing function for the liquid
crystal material 52. The spring contacts 15 can also be arranged so
that the spring contact tips 30 extend from the adhesive 40 into
the liquid crystal material 52 to contact a structure on the
backplane 22.
[0055] Although the devices 22, 23 and 24 are described as a
backplane, front plane and off-display board, the devices 22, 23
and 24 could be replaced with other devices such as a laser
emitting or laser array device for the device 22, an electronic
device, such as an array of transistors and/or other switching
elements for the device 23 and a photodetector or array of
photodetectors for the device 24. Such an arrangement could be
used, for example, as a scanning device.
[0056] FIG. 16 shows steps of a method for interconnecting two
devices. In step S10, a first device is provided having a contact
structure. The first device can include a single device or a group
of devices that perform any desired function, such as a display
driver, data processor, display, electrical interconnect, heat
sink, light or other radiation emitter, detector or modulator, data
storage, interface, etc. The contact structure associated with the
first device can include any desired physical or electrical
interconnect structure, such as contact pads, spring contacts,
metal traces, wirebond pads, bumps, tabs, spacers, alignment
features, etc. Preferably, the contact structure includes spring
contacts for electrical interconnection with a corresponding
contact pad.
[0057] In step S20, an adhesive is applied to either the first or
second device. The adhesive can be applied to the contact structure
or portions of the contact structure of either of the devices
and/or to portions of the device that include no contact structure.
The adhesive can be any kind of compound having various different
mechanical and/or electrical properties. The adhesive can be a
UV-curable optically transparent adhesive, such as Loctite 352, but
other compounds, such as other UV-curable adhesives, thermal
setting compounds, multi-component adhesives such as two-part epoxy
or other compounds can be used. Preferably, the adhesive is
electrically insulating, but semiconductive, anisotropically
conductive or conductive compounds could be used if desired. For
example, an adhesive that is only electrically conductive along an
applied electric field, but otherwise insulating, could be used to
interconnect contact pads on the first and second devices without
requiring the contact pads to physically touch.
[0058] The adhesive can be applied to the devices in various
different ways, including using a micro-actuated applicator. When
using a micro-actuated applicator, a wire is dipped into a pool of
viscous adhesive solution. When the wire is lifted from the pool,
an amount of adhesive is carried by the wire, and the adhesive can
be applied by lowering the wire to the desired portions of the
first device.
[0059] In step S30, the second device having a complementary
contact structure to the first device is aligned with the first
device. As with the first device, the second device can be a single
device or a group of devices that perform any desired function. The
second device can also have a contact structure including any of
the elements mentioned above.
[0060] In step S40, the first and second devices are brought into
sufficient proximity to each other, preferably so that the contact
structures interconnect either physically and/or electrically.
Bringing the devices into sufficient proximity also can cause
adhesive to flow in the space between the devices and preferably
allows the adhesive to surround at least some of the contact
structures of the first and second devices. This adhesive flow can
prevent voids from forming in the adhesive and ensure the contact
structures on the devices are surrounded by adhesive.
[0061] In step S50, the adhesive is cured or otherwise hardened,
e.g., by exposing the adhesive to UV radiation. Of course, other
methods for hardening or setting the adhesive can be used depending
on the type of adhesive.
[0062] While the invention has been described with reference to
specific embodiments, the description of the specific embodiments
is illustrative only and is not to be construed as limiting the
scope of the invention. Various other modifications and changes may
occur to those skilled in the art without departing from the spirit
and scope of the invention as set forth in the following
claims.
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