U.S. patent application number 11/760919 was filed with the patent office on 2007-10-04 for method and apparatus for electrically connecting two substrates using a resilient wire bundle captured in an aperture of an interposer by a retention member.
Invention is credited to William Louis Brodsky, John Lee Colbert, Roger Duane Hamilton, Amanda Elisa Ennis Mikhail, Mark David Plucinski.
Application Number | 20070227769 11/760919 |
Document ID | / |
Family ID | 38139980 |
Filed Date | 2007-10-04 |
United States Patent
Application |
20070227769 |
Kind Code |
A1 |
Brodsky; William Louis ; et
al. |
October 4, 2007 |
Method and Apparatus for Electrically Connecting Two Substrates
Using a Resilient Wire Bundle Captured in an Aperture of an
Interposer by a Retention Member
Abstract
A method and apparatus for electrically connecting two
substrates using resilient wire bundles captured in apertures of an
interposer by a retention film. The interposer comprises an
electrically non-conductive carrier having two surfaces and
apertures extending from surface to surface. A resilient wire
bundle is disposed in each aperture. An electrically non-conductive
retention film is associated with one or both surfaces of the
carrier and has an orifice overlying each aperture. The width of
each orifice is smaller than that of the underlying aperture to
thereby enhance retention of the resilient wire bundle within the
aperture. Pin contacts of one or both of the substrates make
electrical contact with the resilient wire bundles by extending
through the orifices of the retention film and partially through
the apertures. In one embodiment, the interposer is a land grid
array (LGA) connector that connects an electronic module and a
printed circuit board (PCB).
Inventors: |
Brodsky; William Louis;
(Binghamton, NY) ; Colbert; John Lee; (Byron,
MN) ; Hamilton; Roger Duane; (Rochester, MN) ;
Mikhail; Amanda Elisa Ennis; (Rochester, MN) ;
Plucinski; Mark David; (Rochester, MN) |
Correspondence
Address: |
IBM CORPORATION;ROCHESTER IP LAW DEPT. 917
3605 HIGHWAY 52 NORTH
ROCHESTER
MN
55901-7829
US
|
Family ID: |
38139980 |
Appl. No.: |
11/760919 |
Filed: |
June 11, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11297307 |
Dec 8, 2005 |
|
|
|
11760919 |
Jun 11, 2007 |
|
|
|
Current U.S.
Class: |
174/264 ;
174/255; 174/265; 29/825; 439/66 |
Current CPC
Class: |
H01R 12/52 20130101;
Y10T 29/49204 20150115; Y10T 29/49169 20150115; Y10T 29/4913
20150115; Y10T 29/49208 20150115; Y10T 29/49155 20150115; H01R
13/2407 20130101; Y10T 29/49117 20150115; Y10T 29/49126
20150115 |
Class at
Publication: |
174/264 ;
029/825; 439/066; 174/265; 174/255 |
International
Class: |
H01R 12/00 20060101
H01R012/00; H05K 1/03 20060101 H05K001/03 |
Claims
1. An interposer, comprising: an electrically non-conductive
carrier having a first surface and a second surface, and an
aperture extending from the first surface to the second surface; an
electrically non-conductive first retention member associated with
the first surface of the carrier and having an orifice overlying
the aperture of the carrier, wherein the orifice of the first
retention member has a width smaller than that of the aperture of
the carrier; a resilient wire bundle disposed in the aperture of
the carrier.
2. The interposer as recited in claim 1, wherein the first
retention member comprises a thin polymer film.
3. The interposer as recited in claim 1, further comprising an
electrically non-conductive second retention member associated with
to the second surface of the carrier and having an orifice
underlying the aperture of the carrier, wherein the orifice of the
second retention member has a width smaller than that of the
aperture of the carrier.
4. The interposer as recited in claim 3, wherein the first and
second retention members each comprises a thin polymer film.
5. The interposer as recited in claim 1, wherein the carrier
includes a stop member projecting from the first surface thereof
and through a hole in the first retention member.
6. The interposer as recited in claim 1, wherein the carrier
includes a plurality of the apertures arranged in an array, wherein
the first retention member has a plurality of the orifices, and
wherein a plurality of the resilient wire bundles are disposed in
the apertures of the carrier.
7. The interposer as recited in claim 6, further comprising an
electrically non-conductive second retention member associated with
the second surface of the carrier and having a plurality of
orifices underlying the apertures of the carrier, wherein the each
orifice of the second retention member has a width smaller than
that of the overlying aperture of the carrier.
8. The interposer as recited in claim 7, wherein the first and
second retention members each comprises a thin polymer film.
9. The interposer as recited in claim 8, wherein the thin polymer
film has a thickness of about 0.006 inch.
10. An interposer, comprising: an electrically non-conductive
carrier having a first surface and a second surface, and a
plurality of apertures arranged in an array and extending from the
first surface to the second surface; an electrically non-conductive
first retention member attached to the first surface of the carrier
and having a plurality of orifices overlying the apertures of the
carrier, wherein each orifice of the first retention member has a
width smaller than that of the underlying aperture of the carrier;
a plurality of resilient wire bundles disposed in the apertures of
the carrier.
11. The interposer as recited in claim 10, wherein the first
retention member comprises a thin polymer film.
12. The interposer as recited in claim 10, further comprising an
electrically non-conductive second retention member attached to the
second surface of the carrier and having a plurality of orifices
underlying the apertures of the carrier, wherein the each orifice
of the second retention member has a width smaller than that of the
overlying aperture of the carrier.
13. The interposer as recited in claim 12, wherein the first and
second retention members each comprises a thin polymer film.
14. The interposer as recited in claim 13, wherein the thin polymer
film has a thickness of about 0.006 inch.
15. The interposer as recited in claim 10, wherein the carrier
includes a stop member projecting from the first surface thereof
and through a hole in the first retention member.
16. An interposer, comprising: an electrically non-conductive
carrier having a first surface and a second surface, and a
plurality of apertures arranged in an array and extending from the
first surface to the second surface; an electrically non-conductive
first retention member comprising a thin polymer film attached to
the first surface of the carrier and having a plurality of orifices
overlying the apertures of the carrier, wherein each orifice of the
first retention member has a width smaller than that of the
underlying aperture of the carrier; a plurality of resilient wire
bundles disposed in the apertures of the carrier.
17. The interposer as recited in claim 16, further comprising an
electrically non-conductive second retention member comprising a
thin polymer film attached to the second surface of the carrier and
having a plurality of orifices underlying the apertures of the
carrier, wherein the each orifice of the second retention member
has a width smaller than that of the overlying aperture of the
carrier.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This patent application is a continuation application of
U.S. patent application Ser. No. 11/297,307 (docket no.
ROC920050235US1), filed Dec. 8, 2005, entitled "METHOD AND
APPARATUS FOR ELECTRICALLY CONNECTING TWO SUBSTRATES USING A
RESILIENT WIRE BUNDLE CAPTURED IN AN APERTURE OF AN INTERPOSER BY A
RETENTION MEMBER", which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The present invention relates in general to the electrical
connector field. More particularly, the present invention relates
to the assembly of electrical connectors incorporating an
interposer having a resilient wire bundle that provides a
conductive path between two substrates and that is captured within
an aperture of the interposer by a retention member. The present
invention also relates to apparatus involved in the assembly of
such electrical connectors.
[0004] 2. Background Art
[0005] Electrical connectors are in widespread use in the
electronics industry. In many computer and other electronic circuit
structures, an electronic module such as a central processor unit
(CPU), memory module, application-specific integrated circuit
(ASIC) or other integrated circuit, must be connected to a printed
circuit board (PCB). In connecting an electronic module to a PCB, a
plurality of individual electrical contacts on the base of the
electronic module must be connected to a plurality of corresponding
individual electrical contacts on the PCB. This set of contacts on
the PCB dedicated to contacting the electronic module contacts is
known as a land grid array (LGA) site. Rather than permanently
soldering the electronic module contacts to the LGA site, it is
desirable to use LGA connectors that allow the electronic module to
be installed to and removed from the LGA site. LGA connectors are
also known as sockets, interconnects, interposers, carriers, and
button board assemblies.
[0006] LGA connectors provide the user with the flexibility to
upgrade or replace electronic modules during the manufacturing
cycle and in the field. A trend in the electronics industry has
been to increase both the quantity LGA sites and the density of
each LGA site, i.e., the number of contacts per unit area at the
LGA site. Another trend in the electronics industry is to reduce
the rated insertion force necessary to insert the electronic module
into the LGA connector.
[0007] One type of LGA connector that has proven to be very
reliable incorporates resilient wire bundles. Electrical connectors
having resilient wire bundles for providing conductive paths
between two electronic substrates, i.e., an electronic module and a
PCB, are well known to those skilled in the art. Such resilient
wire bundles are also well known as wadded wire, fuzz buttons,
button contacts, button wads, or contact wads, which are
collectively referred to hereafter as resilient wire bundles.
[0008] For example, U.S. Pat. No. 6,062,870 to Hopfer, III et al.,
the disclosure of which is incorporated by reference herein,
discloses an electrical interconnect that incorporates resilient
wire bundles that are retained in holes of a carrier by compressive
frictional engagement with a central section of the side wall of
each of the holes. In use, the carrier is placed between two
circuit boards and the resilient wire bundles provide conductive
paths between the two circuit boards.
[0009] A well known problem with electrical connectors that
incorporate resilient wire bundles is that one or more of the
resilient wire bundles may be jarred loose and fall out from the
interposer during transit or handling. If a resilient wire bundle
is missing from the interposer, an open circuit will result when
the interposer is used to connect two electronic substrates. In
this case, the interposer that is missing the resilient wire bundle
must be replaced for the two electronic substrates to be properly
connected. Such opens occur notwithstanding the teachings of
Hopfer, III et al. that the resilient wire bundles are force fitted
into holes in the interposer. In a related problem, instead of
being jarred completely out of the interposer, the resilient wire
bundle is instead jarred partially loose from the interposer such
that when the resilient wire bundle is compressed between the two
electronic substrates, the resilient wire bundle bends over and
makes contact with an adjacent resilient wire bundle or an adjacent
contact on the electronic substrate. If a bent-over resilient wire
bundle makes such an inadvertent contact, a short circuit will
result. Such a short can catastrophically damage to one or both of
the electronic substrates being interconnected. Accordingly, the
interposer that contains the bent-over resilient wire bundle, and
possibly also one or both of the electronic substrates being
interconnected, would have to be replaced.
[0010] These problems are recognized in U.S. Patent Application
Publication No. 2004/0002233 A1 to Advocate, Jr. et al., the
disclosure of which is incorporated by reference herein, which
discloses a method of assembling an interconnect device assembly
which consists of cylindrical resilient wire bundles captured with
a carrier. The interconnect device assembly is placed in a fixture
and the ends of the resilient wire bundles are deformed by shaping
dies in the fixture so that the resilient wire bundles now have a
dog bone shape. The dog bone shape of the resilient wire bundles
prevents the resilient wire bundles from being partially or totally
dislodged during handling and transit. However, one or more of the
shaping dies may insufficiently deform the resilient wire bundles
and thereby fail to prevent same from being dislodged. Also, the
shaping dies may inconsistently deform the resilient wire bundles
(i.e., some shaping dies will under-penetrate the resilient wire
bundles while other shaping dies will over-penetrate). The
resulting unequal resilient wire bundle height increases the
likelihood that one or more open circuits will occur when the
resilient wire bundles are compressed between two electronic
substrates. In this case, the interposer that contains the
resilient wire bundles of unequal height must be replaced for the
two electronic substrates to be properly connected.
[0011] Another problem with electrical connectors that incorporate
resilient wire bundles is that the strands of the resilient wire
bundles are not very robust. For example, the strands of resilient
wire bundles are prone to spreading or "mushrooming" upon repeated
insertions. If a resilient wire bundle is sufficiently mushroomed,
an open circuit or near-open circuit will result when the
mushroomed resilient wire bundle is subsequently compressed between
two electronic substrates. This occurs because mushrooming can
undesirably limit the compressive force on the resilient wire
bundle and thereby increase electrical resistance through the
resilient wire bundle to the point where an open circuit or
near-open circuit is created. In this case, the interposer that
contains the mushroomed resilient wire bundle must be replaced for
the two electronic substrates to be properly connected. Moreover,
the strands of resilient wire bundles can snag on mating features
during insertion and withdrawals. If either a snagged strand of a
resilient wire bundle or a mushroomed resilient wire bundle
subsequently makes contact with an adjacent resilient wire bundle
or an adjacent contact on the electronic substrate, a short circuit
will result. Such a short can catastrophically damage to one or
both of the electronic substrates being interconnected.
Accordingly, the interposer that contains the snagged strand or
mushroomed resilient wire bundle, and possibly also one or both of
the electronic substrates being interconnected, would have to be
replaced.
[0012] It should therefore be apparent that a need exists for an
enhanced mechanism for connecting two substrates using resilient
wire bundles.
SUMMARY OF THE INVENTION
[0013] According to the preferred embodiments of the present
invention, two substrates are electrically connected using
resilient wire bundles captured in apertures of an interposer by a
retention member. The interposer comprises an electrically
non-conductive carrier having two surfaces and apertures extending
from surface to surface. A resilient wire bundle is disposed in
each aperture. An electrically non-conductive retention member,
such as a thin polyimide film, is associated with one or both
surfaces of the carrier and has an orifice overlying each aperture.
The width of each orifice is smaller than that of the underlying
aperture to thereby enhance retention of the resilient wire bundle
within the aperture. Pin contacts of one or both of the substrates
make electrical contact with the resilient wire bundles by
extending through the orifices of the retention member and
partially through the apertures. In one embodiment of the present
invention, the interposer is a land grid array (LGA) connector that
connects an electronic module and a printed circuit board
(PCB).
[0014] The foregoing and other features and advantages of the
present invention will be apparent from the following more
particular description of the preferred embodiments of the present
invention, as illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The preferred exemplary embodiments of the present invention
will hereinafter be described in conjunction with the appended
drawings, where like designations denote like elements.
[0016] FIG. 1 is a side perspective view of a circuit card assembly
having an interposer that incorporates a retention member according
to the preferred embodiments of the present invention.
[0017] FIG. 2 is a partial, sectional view of the circuit card
assembly of FIG. 1, taken along the section line indicated in FIG.
1.
[0018] FIG. 3 is an enlarged partial, sectional view of the circuit
card assembly of FIG. 2, in an area of a single aperture of the
interposer.
[0019] FIG. 4 is an unassembled version of the enlarged partial,
sectional view of the circuit card assembly shown in FIG. 3.
[0020] FIG. 5 is a partial, top perspective view of an interposer
that incorporates a retention member according to the preferred
embodiments of the present invention. The retention member is shown
partially cut away to reveal a portion of an underlying
carrier.
[0021] FIG. 6 is a partial, sectional view of a circuit card
assembly having a hybrid interposer that incorporates a retention
member according to the preferred embodiments of the present
invention.
[0022] FIG. 7 is a flow diagram of a method for assembling an
interposer that incorporates a retention member according to the
preferred embodiments of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] 1.0 Overview
[0024] In accordance with the preferred embodiments of the present
invention, two subtrates are electrically connected using resilient
wire bundles captured in apertures of an interposer by a retention
member. The interposer comprises an electrically non-conductive
carrier having two surfaces and apertures extending from surface to
surface. A resilient wire bundle is disposed in each aperture. An
electrically non-conductive retention member, such as a thin
polyimide film, is associated with one or both surfaces of the
carrier and has an orifice overlying each aperture. The width of
each orifice is smaller than that of the underlying aperture to
thereby enhance retention of the resilient wire bundle within the
aperature. Pin contacts of one or both of the substrates make
electrical contact with the resilient wire bundles by extending
through the orifices of the retention member and partially through
the apertures. In one embodiment of the present invention, the
interposer is a land grid array connector that connects an
electronic module and a printed circuit board.
[0025] 2.0 Detailed Description
[0026] With reference to the figures and in particular FIG. 1,
there is depicted, in a side perspective view, a circuit card
assembly 100 having an interposer 102 that incorporates one or more
retention members, such as thin polymer films 104, 106, in
accordance with the preferred embodiments of the present invention.
In circuit card assembly 100, interposer 102 is sandwiched between
a ceramic module substrate 108 and a printed circuit board (PCB)
110. Although the preferred embodiments of the present invention
are described herein within the context of a land grid array (LGA)
connector that connects an electronic module to a PCB, one skilled
in the art will appreciate that many variations are possible within
the scope of the present invention. For example, the present
invention may be utilized in connecting any two substrates, such as
connecting a ribbon substrate to any of a PCB, an electronic
module, or another ribbon substrate.
[0027] A rectilinear heat sink 112 is connected to a bare die or
module cap 114, which is in turn connected to ceramic module
substrate 108. Heat sink 112 provides heat transfer functions, as
is well known in the art. Electronic components, such a
microprocessors and integrated circuits, must operate within
certain specified temperature ranges to perform efficiently.
Excessive heat degrades electronic component performance,
reliability, life expectancy, and can even cause failure. Heat
sinks, such as rectilinear heat sink 112, are widely used for
controlling excessive heat. Typically, heat sinks are formed with
fins, pins or other similar structures to increase the surface area
of the heat sink and thereby enhance heat dissipation as air passes
over the heat sink. In addition, it is not uncommon for heat sinks
to contain high performance structures, such as vapor chambers
and/or heat pipes, to further enhance heat transfer. Heat sinks are
typically formed of metals, such as copper or aluminum. The use of
a heat sink, per se, is not necessary for purposes of the present
invention, but is important in understanding an environment in
which the present invention may be used.
[0028] Electronic components are generally packaged using
electronic packages (i.e., modules) that include a module
substrate, such as ceramic module substrate 108, to which the
electronic component is electronically connected. In some cases,
the module includes a cap (i.e., capped modules) which seals the
electronic component within the module. In other cases, the module
does not include a cap (i.e., a bare die module). In the case of a
capped module, a heat sink is typically attached with a thermal
interface between a bottom surface of the heat sink and a top
surface of the cap, and another thermal interface between a bottom
surface of the cap and a top surface of the electronic component.
In the case of a bare die module, a heat sink is typically attached
with a thermal interface between a bottom surface of the heat sink
and a top surface of the electronic component.
[0029] Referring again to FIG. 1, a rigid insulator 116 is disposed
along the bottom surface of PCB 110 and is preferably fabricated
from fiberglass reinforced epoxy resin. Rigid insulator 116 is
urged upwards against PCB 110, and PCB 110 is thereby urged upward
towards interposer 102 and module substrate 108, by a clamping
mechanism. Preferably, the clamping mechanism is a
post/spring-plate type clamping mechanism 150 as shown in FIG. 1.
Because such clamping mechanisms are conventional, the
post/spring-plate type clamping mechanism 150 is only briefly
described below. Additional details about post/spring-plate type
clamping mechanisms may be found in U.S. Pat. No. 6,386,890 to
Bhatt et al., the disclosure of which is incorporated by reference
herein. One skilled in the art will appreciate that any of the many
different types and configurations of clamping mechanisms known in
the art may be used in lieu of the post/spring-plate type clamping
mechanism 150 shown in FIG. 1.
[0030] In the embodiment shown in FIG. 1, clamping mechanism 150
includes a stiffener 152, which is preferably a metal or steel
plate. An upward force is generated by a spring 154, which directs
force upward against stiffener 152 through interaction with a
spring-plate 156. It is preferred that spring-plate 156 is a square
structure with about the same overall footprint depth as heat sink
112. Four cylindrical posts 158 are connected at the four corners
of rectilinear heat sink 112 and disposed through cylindrical
interposer post apertures 160, PCB post apertures 162, post
apertures in insulator 116, stiffener post apertures 164, and
spring-plate post apertures 166. Post mushroom heads 168 are formed
at the ends of posts 158. The post mushroom heads 168 rest against
spring-plate 156 and thereby prevent spring-plate 156 from moving
downward. Downward expansion or deflection forces from spring 154
are exerted directly upon spring-plate 156, which translates the
forces through posts 158, heat sink 112, bare die or module cap 114
into module substrate 108, thereby forcing module substrate 108
downward until module substrate 108 comes into contact with and
exerts force upon stops (not shown in FIG. 1) of interposer 102.
Similarly, force from spring 154 is also exerted upwards by spring
154 and translated through stiffener 152 and insulator 116 into PCB
110, forcing PCB 110 upwards until PCB 110 comes into contact with
and exerts force upon stops (not shown in FIG. 1) of interposer
102. Accordingly, PCB 110 and module substrate 108 are forced
toward each other with compressive forces upon interposer 102
disposed therebetween.
[0031] Spring-plate 156 also has a threaded screw 170 in the center
of spring 154. When screw 170 is turned clockwise, its threads
travel along corresponding thread grooves in a spring-plate screw
aperture 172 in spring-plate 156 and, accordingly, screw 170 moves
upward toward and against stiffener 152. As screw 170 engages
stiffener 152 and exerts force upward against it, corresponding
relational force is exerted by the threads of screw 170 downward
against the thread grooves in spring-plate 156. As illustrated
above in the discussion of spring 154, the downward force exerted
by screw 170 is translated by spring-plate 156, post mushroom heads
168, posts 158, heat sink 112 and the bare die or module cap 114
into module substrate 108, thereby forcing module substrate 108
downward until module substrate 108 comes into contact with and
exerts force against stops (not shown in FIG. 1) of interposer 102.
Similarly, upward force from screw 170 is translated through
stiffener 152 and insulator 116 into PCB 110, forcing PCB 110
upwards until PCB 110 comes into contact with and exerts force
against stops (not shown in FIG. 1) of interposer 102. Accordingly,
after screw 170 is rotated clockwise into contact with stiffener
152, additional clockwise rotation of screw 170 results in
increasing compressive force exerted by PCB 110 and module
substrate 108 upon interposer 102 disposed therebetween.
[0032] Reference is now made to FIGS. 2-4. FIG. 2 illustrates, in a
partial, sectional view, circuit of card assembly 100 along the
section line 2-2 of FIG. 1. More particularly, FIG. 2 shows a
portion of a land grid array (LGA) site comprising pin contacts of
PCB 110 and corresponding pin contacts of module substrate 108. As
discussed in detail below, these pin contacts make electrical
contact with each other through resilient wire bundles captured in
apertures of interposer 102 by retention members. FIG. 3
illustrates, in an enlarged partial, sectional view, circuit card
assembly 100 in an area of a single aperture of interposer 102.
FIG. 4 is an unassembled version of FIG. 3. That is, FIG. 4
illustrates, in an enlarged partial, sectional view, circuit card
100 in an area of a single aperture of interposer 102 in an
unassembled state.
[0033] According to the preferred embodiments of the present
invention, interposer 102 includes an electrically non-conductive
carrier 202 and one or more electrically non-conductive retention
members 104, 106. The construction of carrier 202 is conventional,
and thus only briefly described herein. Additional details about
the construction of such carriers may be found in U.S. Pat. No.
6,062,870 to Hopfer, III et al., the disclosure of which was
already incorporated by reference herein. Preferably, carrier 202
is molded or machined with apertures 208. For example, carrier 202
may be formed by injection molding of suitable electrically
non-conductive materials. Those materials should have good flow
characteristics at molding temperatures to assure formation of the
fine detail required for the small aperture configurations,
particularly when molding a thin carrier 202. The mold typically
includes core pins that when withdrawn define apertures 208.
Specific examples of suitable moldable materials include
polyesters, such as the thermoplastic polyester resin product sold
by E.I. DuPont de Nemours & Co., Inc. under the tradename
Rynite and liquid crystal polymers such as the product sold by
Hoechst Celanese Corporation under the tradename Vectra. Smooth
inner wall surfaces of apertures 208 are assured by a molding
process, even when glass fiber fillers are included to enhance the
stability of the final interposer product.
[0034] Carrier 202 may alternatively be fabricated by machining
apertures 208 into a solid sheet or board. Each aperture 208 is
bored completely through carrier 202 so that it extends form
surface to surface with a desired diameter. Forming apertures 208
by such machining usually is more economical for short production
runs. However, more care is required to secure smooth inner wall
surfaces in apertures 208. Also, use of glass fiber fillers in
carrier 202 preferably is avoided when apertures 208 are to be
machined as the imbedded fibers tend to result in rough inner wall
surfaces in apertures formed by machining. Rough inner wall
surfaces can catch individual strands of wire which may interfere
with the desired resilient operation of the resilient wire
bundles.
[0035] Retention members 104, 106 are preferably machined with
orifices 210, 212. For example, retention members 104, 106 may be
fabricated by machining orifices 210, 212 into a solid film, sheet
or board of suitably electrically non-conductive materials. Those
materials should have good resilience to avoid wear as contact pins
are inserted into and withdrawn from orifices 210, 212, as
discussed in detail below. In addition, those materials should have
characteristics (e.g., coefficient of thermal expansion) compatible
with carrier 202, on which retention members 104, 106 are mounted.
Specific examples of suitable materials include thin polymer films,
such as the polyimide product sold by E.I. DuPont de Nemours &
Co., Inc. under the tradename Kapton. Each orifice 210, 212 is
bored completely through retention member 104, 106 so that it
extends form surface to surface with a desired diameter.
[0036] Alternatively, retention members 104, 106 may be molded with
orifices 210, 212 alone or together with carrier 202 as a one-piece
unit. For example, retention members 104, 106 may be formed by
injection molding of suitable electrically non-conductive
materials. In addition to having good resilience and compatible
characteristics as discussed above, those materials should have
good flow characteristics at molding temperatures to assure
formation of the fine detail required for the small orifice
configurations.
[0037] Inserted within each aperture 208 of carrier 202 is a
resilient wire bundle 220. Such resilient wire bundles are also
well known as wadded wire, fuzz buttons, button contacts, button
wads, or contact wads, which are collectively referred to herein as
resilient wire bundles. For example, U.S. Pat. No. 6,062,870 to
Hopfer, III et al., the disclosure of which was already
incorporated by reference herein, discloses an electrical
interconnect that incorporates resilient wire bundles that are
retained in holes in a carrier by compressive friction engagement
with a central section of the side wall of each of the holes. As
shown in FIGS. 2-4, the top end of each resilient wire bundle 220
mates with a pin contact 214 of module substrate 108 and the bottom
end of each resilient wire bundle 220 mates with a pin contact 216
of PCB 110. Alternatively, the interposer may be of a hybrid-type,
wherein contact pins are incorporated in only one of the
substrates, i.e., either the module substrate 108 or the PCB 110.
For example, as shown in FIG. 6, the top end of each resilient wire
bundle 220 mates with a pin contact 214 of substrate module 108
while the bottom end of each resilient wire bundle 220 mates with a
pad contact 226.
[0038] According to the preferred embodiments of the present
invention, the width of each orifice 210, 212 of retention members
104, 106 is smaller than that of aperture 208 to thereby enhance
retention of the resilient wire bundle 220 within aperture 208.
[0039] The upper end of each resilient wire bundle 220 is captured
within aperture 208 by an annular ledge formed where retention
member 104 overhangs aperture 208, while the bottom end of each
resilient wire bundle 220 is captured within aperture 208 by an
annular ledge formed where retention member 106 projects under
aperture 208. Preferably, the ledges retain physical contact with
resilient wire bundles 220 in a manner that is not a press-fit, but
which prevents resilient wire bundles 220 from rotating.
Accordingly, resilient wire bundles 220 preferably have relaxed
(non-stressed) diameters and heights approximately equal to those
of apertures 208.
[0040] These ledges substantially prevent any strand of resilient
wire bundle 220 from escaping aperture 208, and therefore the
possibility of shorting is much lower than in conventional button
boards (wherein the resilient wire bundles are retained solely by
compressive friction engagement with the side wall of the
aperture). Preferably, there is a slight interference between the
ledges and pin contacts 214, 216 (i.e., the diameter of pin
contacts is slightly larger than that of orifices 210, 212 of
retention members 104, 106) so that upon withdrawal of pin contacts
214, 216 from apertures 208 the ledges act as "wiper blades" to
scrape any snagged strands of resilient wire bundles 220 off the
pin contacts 214, 216. However, it may be desirable to dimension
pin contacts 214, 216 and orifices 210, 212 to avoid this slight
interference in certain applications, such as when insertion force
is to be minimized.
[0041] In addition, the ledges protect the resilient wire bundles
220 and prevent resilient wire bundles 220 from being jarred
completely or partially loose from interposer 102. Moreover,
resilient wire bundles 220 will not mushroom because the ledges
prevent the resilient wire bundles 220 from escaping the confines
of apertures 208.
[0042] Resilient wire bundles are typically formed from a single
strand of metal wire, which is preferably plated with a precious
metal such as gold. Resilient wire bundles typically have a wire
diameter in the range of approximately 0.002 inch. Preferably,
resilient wire bundles 220 are formed from a single strand of gold
plated beryllium copper wire having a wire diameter in the range of
approximately 0.002 inch. Each strand is preferably wadded together
in a random orientation to form a generally cylindrical "button" of
wadded wire. Generally, it is preferable that a precious metal wire
having a random orientation be used for resilient wire bundle 220
to provide multiple contact points on pin contacts 214, 216 (as
best seen in FIG. 3), increasing the reliability of the overall
electrical interconnection by providing multiple hertzian or high
localized stress contacts. Suitable resilient wire bundles are
exemplified by, but not limited to, resilient wire bundle products
sold by Cinch Connectors, Lombard, Ill. under the tradename
CIN::APSE and Tecknit, Inc., Cranford, N.J. under the tradename
Fuzz Button.
[0043] Pin contacts 214 are preferably soldered to conventional
electrically conductive pad contacts 224 on module substrate 108.
Similarly, pin contacts 216 are preferably soldered to conventional
electrically conductive pad contacts 226 on PCB 110. Pin contacts
214, 216 comprise an electrically conductive metal, such as a
copper alloy, aluminum alloy, or the like. Preferably, pin contacts
214, 216 comprise a copper alloy base that is Pd--Ni plated and
gold flashed. The gold-flash resides on top of the Pd--Ni plate and
prevents oxidation of the underlying copper alloy base, while the
gold-flash Pd--Ni plating combination allows less gold into the
solder bath than traditional (thicker) gold over nickel plating (if
too much gold is mixed with solder during the soldering process,
gold weakens the resulting solder joint).
[0044] In general, the size and shape of pin contacts 214, 216 as
well as the wire diameter of resilient wire bundles 220 can be
adjusted to trade off insertion force and contact reliability.
Preferably, each pin contact 214, 216 is tapered, chamfered,
semi-spherical or pointed at the end thereof that makes contact
with resilient wire bundle 220 so that at a given insertion force
the contact stress will be large. Accordingly, the reliability of
interposer 102 is likely to be greater than conventional
interposers having resilient wire bundles that mate with pad
contacts having a larger area of contact and consequently less
contact stress at a given insertion force.
[0045] Most of the insertion force of pin contacts 214, 216
preferably goes into making multiple high localized stress contacts
with resilient wire bundle 220, not compressing resilient wire
bundle 220. Accordingly, insertion force can be minimized because
it is used efficiently. Thus, the present invention facilitates the
use of an LGA connector for connecting a bare die module to a PCB
by minimizing the rated insertion and operating force. When bare
die modules are used, it is desirable to minimize the rated
insertion and operating force because the clamping mechanism
applies this force directly through the electronic component
itself.
[0046] Stops 230 set the length of penetration of pin contacts 214
of module substrate 108 into the top of apertures 208 of carrier
202. Similarly, stops 232 set the length of penetration of pin
contacts 216 of PCB 110 into the bottom of apertures 208 of carrier
202. As best seen in FIG. 4, stops 230, 232 preferably project from
carrier 202 through stop holes 502 (shown in FIG. 5) in the thin
polymer films that form retention members 104, 106. More
preferably, stops 230, 232 are integrally formed with carrier 202
as carrier 202 is formed by injection molding.
[0047] Preferably, stops 230, 232 are interspersed on both surfaces
of carrier 202 in a pattern that facilitates generally uniform
penetration of pin contacts 214, 216 into apertures 208. This is
best seen in FIG. 5, which illustrates, in a partial, top
perspective view, an interposer 102 that incorporates a retention
member 104 according to the preferred embodiments of the present
invention. In FIG. 5, for purposes of illustration, retention
member 104 is partially cut away to reveal a portion the underlying
carrier 202. As shown in FIG. 5, stops 230, 232 may be interspersed
on both surfaces (only one surface is shown in FIG. 5) of carrier
202 between apertures 208. Alternatively, or in addition, stops
230, 232 may be interspersed on both surfaces of carrier 202 along
the edges of interposer 102 outside the area of apertures 208.
Those skilled in the art will appreciate, however, that the stops
need not be present on both surfaces of carrier 202. For example,
in the case of a hybrid interposer, such as hybrid interposer 102'
shown in FIG. 6, the stops need only be present on a single surface
of carrier 202.
[0048] Stops 230, 232 may also serve to facilitate alignment of
retention members 104, 106 relative to carrier 202, i.e., the
retention member 104 is aligned relative to carrier 202 so that the
carrier's stops 230 will penetrate this retention member's stop
holes 502, and, likewise, retention member 106 is aligned relative
to carrier 202 so that the carrier's stops 230 will penetrate this
retention member's stop holes. Those skilled in the art will
appreciate, however, that other configurations of the stops are
possible without departing from the scope of the present invention.
For example, in lieu of projecting from carrier 202, the stops may
project from module substrate 108 and PCB 110, or may be integrally
formed with retention members 104, 106.
[0049] By way of example, and without limitation, for a carrier 202
having a thickness of in the range of approximately 0.040 inch,
retention members 104, 106 comprising Kapton polyimide films would
each have a thickness in the range of approximately 0.006 inch and
pin contacts 224, 226 would each penetrate in the range of
approximately 0.012 inch into aperture 208 in carrier 202. Also, by
way of example, and without limitation, for pin contacts 224, 226
each have a diameter of in the range of approximately 0.016 inch,
orifices 210, 212 in retention members 104, 106 would each have a
diameter of in the range of approximately 0.015 inch and apertures
208 in carrier 202 would each have a diameter of in the range of
approximately 0.025 inch. In this example, the annular ledge would
be in the range of approximately 0.005 inch (i.e., (0.025-0.015)/2)
and the pin contacts 224, 226 would fit into orifices 210, 212 with
a slight interference in the range of approximately 0.001 inch.
However, those skilled in the art will appreciate that alternative
compositions, configurations and dimensions are possible without
departing from the spirit and scope of the present invention. In
general, the compositions, configurations and dimensions will
change for different applications. For example, the dimensions will
typically vary in the range of 1/2 to 2.5 times the approximate
values provided above.
[0050] FIG. 6 illustrates, in a partial, sectional view, a circuit
card assembly having a hybrid interposer 102' that incorporates a
single retention member 104 according to the preferred embodiments
of the present invention. Hybrid interposer 102' shown in FIG. 6 is
similar to interposer 102 shown in FIG. 2, except that retention
member 106 and stops 232 are omitted from the bottom surface of
carrier 202. In some cases it may be desirable for one of the
substrates (i.e., either PCB 110 or module substrate 108) to have
conventional pad contacts rather than pin contacts. Hybrid
interposer 102' addresses such a case, i.e., the case where the PCB
has conventional pad contacts rather than pin contacts. As shown in
FIG. 6, the bottom of each resilient wire bundle 220 makes contact
with pad contacts 226 of PCB 110 in a conventional manner, such as
by compression force, solder, electrically-conductive adhesive,
etc. Although not shown in FIG. 6, it may be desirable to mount an
additional retention member on the bottom surface of carrier 202 to
enhance retention of resilient wire bundles 220 (i.e., similar to
retention member 106 in FIG. 2).
[0051] FIG. 7 is a flow diagram of a method 700 for assembling an
interposer that incorporates a retention member according to the
preferred embodiments of the present invention. Method 700 sets
forth the preferred order of the steps. It must be understood,
however, that the various steps may occur at any time relative to
one another. A first retention member having orifices therein is
mounted on a first surface of the carrier having apertures therein
(step 710). This step may be facilitated by aligning and inserting
stops of the carrier into stop holes of the first retention member.
Preferably, the first retention member is attached to the first
surface of the carrier through the use of a conventional fastening
mechanism, such as adhesive, thermal welding, or the like. Next,
resilient wire bundles are inserted in the apertures of the carrier
from the still-open second surface of the carrier (step 720). A
second retention member having orifices therein is then mounted on
the second surface of the carrier (step 730). This step may be
facilitated by aligning and inserting stops of the carrier into
stop holes of the second retention member. Preferably, the second
retention member is attached to the second surface of the carrier
through the use of a conventional fastening mechanism, such as
adhesive, thermal welding, or the like.
[0052] One skilled in the art will appreciate that many variations
are possible within the scope of the present invention. For
example, although the preferred embodiments of the present
invention are described herein within the context of a land grid
array (LGA) connector that connects an electronic module to a PCB,
the present invention may be utilized in connecting any two
substrates, such as connecting a ribbon substrate to any of a PCB,
an electronic module, or another ribbon substrate. Moreover,
different types and configurations of clamping mechanisms known in
the art may be used to force the substrates together in lieu of the
post/spring-plate type clamping mechanism described herein. Also,
although the dimensions of the pin contacts, apertures of the
carrier, and orifices of the retention members are set forth as
diameters, these features need not be round. Thus, while the
present invention has been particularly shown and described with
reference to the preferred embodiments thereof, it will be
understood by those skilled in the art that these and other changes
in form and detail may be made therein without departing from the
spirit and scope of the present invention.
* * * * *