U.S. patent application number 11/585462 was filed with the patent office on 2007-02-15 for process of forming socket contacts.
Invention is credited to Salman Akram, Warren M. Farnworth, David R. Hembree.
Application Number | 20070037418 11/585462 |
Document ID | / |
Family ID | 23012363 |
Filed Date | 2007-02-15 |
United States Patent
Application |
20070037418 |
Kind Code |
A1 |
Akram; Salman ; et
al. |
February 15, 2007 |
Process of forming socket contacts
Abstract
A socket contact formation process comprises forming a contact
head from a conductive material, forming a contact body from a
semiconductive material configured to be electrically conductive;
and joining the contact head and the contact body.
Inventors: |
Akram; Salman; (Boise,
ID) ; Hembree; David R.; (Boise, ID) ;
Farnworth; Warren M.; (Nampa, ID) |
Correspondence
Address: |
TRASK BRITT
P.O. BOX 2550
SALT LAKE CITY
UT
84110
US
|
Family ID: |
23012363 |
Appl. No.: |
11/585462 |
Filed: |
October 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09652585 |
Aug 31, 2000 |
|
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11585462 |
Oct 24, 2006 |
|
|
|
09265906 |
Mar 10, 1999 |
6725536 |
|
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09652585 |
Aug 31, 2000 |
|
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Current U.S.
Class: |
439/82 |
Current CPC
Class: |
Y10T 29/49126 20150115;
Y10T 29/49117 20150115; Y10T 29/4913 20150115; Y10T 29/49153
20150115; Y10T 29/4914 20150115; Y10T 29/49144 20150115; H01L
2924/00 20130101; H05K 7/1061 20130101; H01R 13/2421 20130101; H01L
2924/0002 20130101; G01R 1/0466 20130101; H01R 12/714 20130101;
H01L 2924/0002 20130101; Y10T 29/49149 20150115; G01R 1/0483
20130101; H01R 2201/20 20130101; Y10T 29/49128 20150115; Y10T
29/49222 20150115; Y10T 29/53174 20150115; Y10T 29/49204 20150115;
Y10T 29/49139 20150115; Y10T 29/49155 20150115; Y10T 29/49165
20150115; Y10T 29/49151 20150115; Y10T 29/49224 20150115; Y10T
29/49174 20150115 |
Class at
Publication: |
439/082 |
International
Class: |
H01R 12/00 20060101
H01R012/00 |
Claims
1. An electrical connector, comprising: an elongated conductive
body defining a central axis and having an end; an electrically
conductive annular portion at said end concentric to said central
axis; an electrically conductive frustoconical portion extending
inward from said annular portion toward said central axis; and an
electrically conductive planar portion below said annular portion,
concentric to said central axis, and coupled to said frustoconical
portion.
2. The electrical connector in claim 1, wherein said body comprises
a pogo pin.
3. A socket contact head, comprising: a flat area; a sidewall
extending upward and outward from said flat area; and a perimeter
portion extending outward from said sidewall; wherein a selection
of said flat area, said sidewall, said perimeter portion, and
combinations thereof is configured to receive an IC chip contact
and further configured to transmit an electrical signal along a
socket contact body.
4. The socket contact head of 3, wherein said sidewall comprises a
plurality of planar walls.
5. The socket contact head of claim 4, wherein said sidewall
comprises: a first planar wall; a second planar wall coupled to
said first planar wall; and a third planar wall coupled to said
first planar wall and said second planar wall.
6. An electrically conductive contact head, comprising: an upper
portion defining an opening; a sidewall coupled to said upper
portion at a first transition area and decliningly converging from
said first transition area; a lower portion coupled to said
sidewall at a second transition area; and an electrical connection
contact area at a selection of said upper portion, said sidewall,
said lower portion, and combinations thereof; wherein a selection
of said upper portion, said sidewall, said lower portion, and
combinations thereof is configured to contact a socket contact
body.
7. The electrically conductive contact head in claim 6, wherein
said electrical connection contact area defines a circle along said
sidewall.
8. The electrically conductive contact head in claim 6, wherein
said electrical connection contact area defines a plurality of
points along said sidewall.
9. The electrically conductive contact head in claim 6, wherein
said electrical connection contact area comprises: at least a
circle along said sidewall; and at least a point on said lower
portion.
10. The electrically conductive contact head in claim 6, wherein
said electrical connection contact area coincides with at least a
portion of said upper portion.
11. The electrically conductive contact head in claim 6, wherein
said electrical connection contact area coincides with said first
transition area.
12. The electrically conductive contact head in claim 11, wherein
said first transition area is rounded.
13. A receptacle for an IC chip contact, comprising: a metal layer
having a shape that is at least generally complimentary to said IC
chip contact, wherein said layer comprises: an outer surface, a
curved middle surface transitioning from said outer surface, and a
curved inner surface transitioning from said middle surface; and a
conductive material in electrical communication with said metal
layer and extending generally unidirectionally from said metal
layer.
14. The receptacle in claim 13, wherein said outer surface
comprises a curved surface.
15. An electrical connection device, comprising: a head defining an
inner frustum-shaped recess and sized to accommodate an IC chip
contact; and a resilient body coupled to said head.
16. The electrical connection device of claim 15, wherein said
resilient body comprises: a doped semiconductor shaft; and an
elastomer material contacting said shaft.
17. The electrical connection device of claim 15, wherein said
resilient body comprises a compressible metallic element.
18. The electrical connection device of claim 17, wherein said
resilient body comprises a tube defining at least one aperture
therein.
19. The electrical connection device of claim 17, wherein said
resilient body comprises: a spring coupled to said head; and a
shaft coupled to said spring.
20. The electrical connection device of claim 19, wherein said
resilient body further comprises a shell coupled to said head and
outwardly concentric to said shaft.
21. A pin for a socket, comprising: a head having a central recess;
and a shaft in electrical communication with said head and biased
from said head, wherein said shaft is configured to extend from
said socket.
22. The pin in claim 21, further comprising a spring coupled to and
interposed between said head and said shaft.
23. The pin in claim 22, wherein said spring defines a plurality of
coil circumferences.
24. The pin in claim 23, wherein said spring comprises: a first
section next to said head and defining a first coil circumference;
a second section next to said first section and defining a second
coil circumference; and a third section between said second section
and said shaft and defining a third coil circumference generally
equal to said first coil circumference.
25. The pin in claim 24 wherein said second coil circumference is
greater than said first coil circumference.
26. The pin in claim 25, wherein said second section of said spring
is configured to contact a nonconductive portion of said
socket.
27. A socket connector comprising: a cup-shaped head; and a
resilient tube next to said head and defining at least one aperture
in said tube, wherein said tube is configured to at least partially
extend into a socket hole.
28. The socket connector in claim 27, wherein said tube defines a
plurality of apertures at one length along said tube.
29. The socket connector in claim 27, wherein said tube defines a
first aperture at a first length along said tube; and a second
aperture at a second length along said tube.
30. The socket connector in claim 27, wherein said tube defines a
first aperture on a first side of said tube and a second aperture
on a second side of said tube.
31. The socket connector of claim 30, wherein said head is integral
to said tube.
32. A contact, comprising: a metal body sized to partially fit
within an IC chip socket, wherein said metal body defines: a
generally continuous profile; and at least one deformation of said
profile.
33. The contact in claim 32, wherein said generally continuous
profile comprises a cylindrical profile; and wherein said
deformation comprises a rectangular slit.
34. The contact in claim 32, wherein said deformation comprises a
semi-circular aperture.
35. A method of processing an array of contacts, comprising:
defining a general shape for each contact of a plurality of
contacts, such that said contacts are structurally interconnected;
reinforcing the positioning of said each contact relative to other
contacts in said plurality after said defining a general shape for
each contact of said plurality of contacts; singulating said
plurality of contacts after said maintaining a position of said
each contact relative to other contacts in said plurality; and
attaching said plurality of contacts to a substrate after said
singulating said plurality of contacts.
36. A method of forming a socket, comprising: providing a
semiconductor substrate; defining an arrangement of a plurality of
socket contacts from said substrate; preserving said arrangement;
providing a substrate having a plurality of conductive leads; and
attaching said plurality of socket contacts to said substrate,
wherein at least one socket contact is over at least one conductive
lead.
37. The method in claim 36, wherein said step of attaching said
plurality of socket contacts to said substrate comprises attaching
said plurality of socket contacts to said substrate with a
conductive elastomer.
38. The method in claim 37, wherein said step of attaching said
plurality of socket contacts to said substrate with a conductive
elastomer comprises: placing said elastomer onto said substrate;
and placing said plurality of socket contacts onto said
elastomer.
39. The method in claim 37, wherein said step of attaching said
plurality of socket contacts to said substrate with a conductive
elastomer comprises: placing said elastomer onto an underside of
said plurality of socket contacts; and placing said substrate onto
an underside of said elastomer.
40. The method in claim 39, wherein said step of preserving said
arrangement comprises preserving said arrangement with said
elastomer.
41. A method of supporting electrical communication through a
socket between an IC chip and a printed circuit board, comprising:
interposing a semiconductive shaft between said IC chip and said
printed circuit board; connecting said shaft to said printed
circuit board with an adhesive material; and allowing electrical
conductivity through said adhesive material in response to a
compression between said shaft and said printed circuit board.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of application Ser. No.
09/652,585, filed Aug. 31, 2000, pending, which is a divisional of
application Ser. No. 09/265,906, filed Mar. 10, 1999, now U.S. Pat.
No. 6,725,536, issued Apr. 27, 2004.
BACKGROUND OF THE INVENTION
[0002] 1. Technical Field
[0003] The present invention relates generally to devices and
methods for providing electrical connection between two electronic
components. More specifically, the present invention relates to a
socket contact configured to establish electrical communication
between a semiconductor die and a test device as well as methods
for forming the socket contact.
[0004] 2. State of the Art
[0005] Testing a semiconductor die often involves establishing an
electrical connection between testing equipment and the circuitry
of a die. Testing may be performed on an unpackaged die that has
been singulated from a semiconductor wafer, on a section of dice
that are still part of the wafer, or on all of the dice on a wafer.
Moreover, a bare die that has undergone packaging steps may also be
tested. One example of such a die is a "flip-chip," wherein
conductive material, such as solder balls, is attached directly to
the bond pads or electrical traces formed in the surface of the
die; the die is then "flipped," or mounted face down, so that the
solder balls may connect with contact members of another device.
Another example is a "chip-scale package," which includes a die
along with one or more package elements, such as encapsulating
material in the form of thin protective coatings formed of glass or
other materials bonded to the face and back side of the die; in
addition, solder balls may be attached to electrical traces in the
surface of the die or directly to the die's bond pads through
openings in the encapsulating material. A Ball-Grid-Array (BGA)
serves as yet another example that involves even more packaging:
the die is wire bonded to the top of a substrate and encapsulated,
and solder balls are bonded to electrical traces at the bottom of
the substrate that lead to the wire bonds.
[0006] The device to be tested will hereinafter be referred to as
an integrated circuit chip, or IC chip, regardless of the
singulation or packaging state of the die that forms all or part of
the IC chip. One method of testing the IC chip involves placing the
chip into a socket, which comprises a body with holes that span
through the body. These holes house contacts that are aligned with
electrical contact points of the IC chip. For purposes of
explanation only, it will be assumed that the contact points of the
IC chip are solder balls. Often, the socket includes a lid that,
when closed, pushes the solder balls of the IC chip against the
heads of the socket's contacts. Once the IC chip has been inserted,
the socket is then plugged into a printed circuit board (PCB). This
insertion often involves a biasing force in the opposite direction
of the lid's pushing force. To ensure electrical communication
between the IC chip and the PCB without the risk of breaking the
socket contacts, the socket contacts are configured to be resilient
to the compression resulting from these forces. One such
configuration for doing so involves the use of "pogo pin" contacts.
A pogo pin can comprise an electrically conductive inner shaft, an
electrically conductive outer shell concentric to the inner shaft
and defining the head of the contact, and an electrically
conductive spring between the inner shaft and outer shell. When the
pogo pin undergoes compression, the inner shaft is pushed into the
outer shell despite the spring's bias. Ideally, signals received at
the head of the outer shell will conduct through the spring to the
inner shaft and onward to devices that may be connected to the
inner shaft. However, such a design allows for unneeded electrical
communication along the entire surface of the outer shell.
[0007] As an alternate configuration, buckle beams may be used.
Buckle beams are essentially a thin, somewhat rigid length of
conductive material that will buckle in response to compression
from the IC chip and the PCB being pushed toward each other. The
problem with buckle beams is that the holes housing the beams must
be wide enough to accommodate the horizontal motion of the beams as
they buckle. The buckling space required limits the density of
beams per unit area that can be achieved. In addition, buckle beams
tend to rotate during buckling. Thus, in certain aspects, pogo pins
and buckle beams run contrary to the need in the art for electrical
contacts that require minimal space and material.
[0008] Returning to the testing process, the PCB with the connected
socket is placed in a chamber, wherein the IC chips are tested
while subjected to an elevated temperature. Such testing is
referred to as burn-in testing. The socket's contacts provide
electrical communication between the IC chip and signals sent
through the PCB from the test equipment. Once the test is complete,
the chip is removed from the socket. IC chips which do not pass the
testing are discarded, and chips that pass may undergo further
testing and ultimately be used as components in electronic
devices.
[0009] Further testing and use of these chips, however, depends
upon the ability of the solder balls to continue to function after
their interaction with the socket's contacts. Prior art socket
contacts have heads that are configured through their flexibility
to actively exert a force against the chip's solder balls, wherein
the force is generally transverse to the biasing force that pushes
the chip into the socket. The effect of this transverse force is to
pinch the solder balls, thereby severely damaging them and making
further communication with the chip difficult. Such socket contacts
include the aptly named "pinch contact" found in the Series 655
OTBGA Burn-in/Test Socket sold by Wells Electronics. Another series
655 OTBGA Socket by Wells uses a Y-shaped contact. The Y-shaped
contact is further described in U.S. Pat. No. 5,545,050, by Sato et
al., indicating that the head of the Y-shaped contact is flexible,
which allows it to "snugly" accommodate a hemispherical conductor
of an IC package. (Sato at col. 4, In. 25-30.) Thus, the Y-shaped
contact continues the tradition of applying a pinching action to
the electrical contacts of a device.
[0010] Still other examples of contact heads are illustrated by
references from Interconnect Devices, Inc. (IDI). Among the
examples are plunger probe tips having crown-shaped heads, whose
sharp prongs tend to gouge the surface of the chip's contact, be it
a solder ball or flat pad. In addition, IDI discloses a concave tip
that might accommodate hemispherical chip contacts such as solder
balls, but may provide insufficient electrical communication for
other contacts, such as those configured as flat pads.
[0011] Thus, in addition to the needs in the art discussed above
concerning the body of an electrical connector, there is also a
need in the art for an electrical connector having a head that
reduces the damage to the electrical contacts of IC chips during
connection and is configured to accommodate more than one type and
size of chip contact. More specifically, there is a need in the art
for a socket contact that minimizes the damage to various IC chip
contacts during IC chip testing.
BRIEF SUMMARY OF THE INVENTION
[0012] Accordingly, the current invention provides electrical
contacts as well as methods for forming them. One preferred
embodiment comprises a contact as part of a socket used for testing
semiconductor dice, wherein the contact has a head that defines a
recess, and the head is coupled to an elongated conductive body
configured to fit within a socket. More specifically, the head
comprises a portion defining the perimeter of the head, with other
portions of the head lower than the perimeter. In one exemplary
embodiment, this head takes the form of a planar ring with a
sidewall sloping downward from the ring toward the central axis
running the length of the contact. This sidewall transitions to a
generally planar section that is parallel to, yet lower than, the
perimeter ring. Various preferred embodiments address varying
degrees of transition and planarity of the portions of the contact
head.
[0013] Other preferred embodiments address the body of an
electrical contact, including one embodiment comprising a head, a
shaft, and a spring coupling the head to the shaft. In a more
specific embodiment, the spring's coils define circles of differing
circumferences. Another exemplary preferred embodiment comprises a
metallic tube for the contact body, wherein the tube defines at
least one slit. Yet other preferred exemplary embodiments address
silicon contacts and methods for forming them. Specifically,
semiconductor fabrication techniques are used to define an array of
silicon contacts, and the contacts are singulated while maintaining
their alignment within the array.
[0014] Still other preferred embodiments include the recessed
contact head as described above in combination with the contact
bodies just described. These embodiments include methods and
devices wherein the head is formed separately from the body and
attached thereto, as well as methods and devices wherein the head
is integral to the body.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0015] FIG. 1 is a cross-sectional view of one exemplary embodiment
of the current invention.
[0016] FIG. 2 is a close-up view of a portion of FIG. 1.
[0017] FIG. 3 is a top-down view of the illustration in FIG. 2.
[0018] FIGS. 4A and 4B are top-down views of a second and third
exemplary embodiment of the current invention.
[0019] FIGS. 5A and 5B are cross-sectional views of fourth and
fifth exemplary embodiments of the current invention.
[0020] FIGS. 6A-6D are cross-sectional views of sixth, seventh,
eighth, and ninth exemplary embodiments of the current
invention.
[0021] FIG. 7 is a cross-sectional view of a tenth exemplary
embodiment of the current invention.
[0022] FIG. 8 is a cross-sectional view of an eleventh exemplary
embodiment of the current invention.
[0023] FIG. 9 is a cross-sectional view of a twelfth exemplary
embodiment of the current invention.
[0024] FIG. 10 is a cross-sectional view of a thirteenth exemplary
embodiment of the current invention.
[0025] FIG. 11 is a cross-sectional view of a fourteenth exemplary
embodiment of the current invention.
[0026] FIGS. 12A-12F are cross-sectional views of additional
exemplary embodiments of the current invention.
[0027] FIGS. 13A-13H illustrate steps of another exemplary
embodiment of the current invention.
[0028] --FIGS. 14A-14C depict alternate steps of yet another
exemplary embodiment of the current invention.
[0029] FIGS. 15A-15C illustrate alternate steps of still another
exemplary embodiment of the current invention.
DETAILED DESCRIPTION OF THE INVENTION
[0030] FIG. 1 depicts one exemplary embodiment of the current
invention in the context of testing an IC chip. IC chip 20, which
could be a bare die, a flip-chip, a chip-scale package, or a die at
any stage of packaging, is enclosed within a socket 22. The socket
22 comprises a body 24 made of electrically nonconductive material
as well as a holding mechanism 26 for biasing the IC chip 20
against the body 24. In this particular example, the holding
mechanism 26 is a pair of hinged lids, but those skilled in the art
know that there are many ways to position the IC chip 20. In this
position, the IC chip's contacts 28, which are assumed to be solder
balls for purposes of explanation, are aligned with holes 30
extending in generally one direction through the body 24. Socket
contacts 32 extend through these holes 30 and electrically connect
the chip's contacts 28 and the PCB 34. Each socket contact body 36,
depicted in an exemplary generic form in FIG. 1, is configured to
be resilient along an axis defined by the biasing force that pushes
the PCB 34 against the socket contacts 32. This axis is often
referred to as the "z-axis" and is further described below. Such
resiliency can be achieved through known methods, such as with pogo
pins or buckle beams, or through embodiments of the current
invention which will be described below.
[0031] The socket contact head 38 of each socket contact 32 is
configured to receive a chip contact 28. Contrary to the prior art
contacts which have heads in the form of spears, chisels, needles,
crowns, or pinchers, exemplary embodiments of the current invention
include socket contacts having heads that define grooves or
recesses or cavities or cups. FIG. 2, for example, is a close-up of
the socket contact head 38 depicted in FIG. 1. In this
cross-sectional view, one can see that the socket contact head 38
comprises a first portion 40 defining a plane 41 and an opening. In
this embodiment, the plane 41 is parallel to the IC chip 20
positioned within the socket 22. Similarly, a second portion 42 is
parallel to plane 41 and is lower than the first portion 40, or at
least farther away from the positioned IC chip 20. Joining the
first portion 40 and the second portion 42 is a third portion 44.
In this exemplary embodiment, the third portion 44 defines a
frustum-shaped or frustoconical wall that slopes toward the center
of the socket contact 32 from the first portion 40 to the second
portion 42. In doing so, this socket contact head 38 offers a
continuous contact region along an entire cross-sectional
circumference C of the chip's contact 28. This can be seen better
in the top-down view of FIG. 3. Without limiting the invention, it
is believed that by providing such a continuous contact region, any
force biasing the chip contact 28 and the socket contact 32 toward
each other is distributed, thereby helping to maintain the
integrity of the chip contact 28. It is possible that the
compressive force applied to the chip contact 28 may be enough to
deform it. In that case, the chip contact 28 may flatten against
the third portion 44 and perhaps against the second portion 42 as
well. This would serve to increase the contact region without
inflicting the damage that prior art contacts would cause with
their sharp pikes and corners. It should be further noted that, in
this embodiment and from this viewpoint, the first portion 40 is
annular, or ring-shaped.
[0032] Despite the benefits from the area of connection offered by
the exemplary embodiment above, it may not be necessary to provide
connection along the entire circumference C. Accordingly, the
current invention includes within its scope electrical connectors
having heads that define polygons in a top-down view. FIG. 4A, for
example, illustrates a socket contact head 138 comprising a
triangular first portion 140, second portion 142, and third portion
144. Assuming the chip contact 28 is still a semipherical solder
ball, then electrical connection may occur at three points P1, P2,
and P3, along a particular cross-sectional circumference C. FIG. 4B
depicts yet another socket contact head 238 having a rectangular
first portion 240, second portion 242, and third portion 244.
Accordingly, electrical connection may occur at four points P4-P7
along a particular cross-sectional circumference C. While the
biasing force will be distributed to fewer points in the
embodiments shown in FIGS. 4A and 4B in comparison to FIG. 3, it
should be noted that the contact points P1-P3 and P4-P7 occur on
planar areas of the socket contact heads 138 and 238. As a result,
deformation of the chip's contact 28 will be minimal.
[0033] In the embodiments discussed above, the socket contact heads
38, 138, and 238 have been sized so that only the third portion 44,
144, or 244 is configured to touch the chip contact 28. However,
other embodiments are included wherein the head of the electrical
connector is sized differently in relation to the chip's contact.
In FIG. 5A, a socket contact head 338 is sized and shaped to allow
for connection not only along the cross-sectional circumference C
but also at a point B at the bottom of the chip contact 28. In FIG.
5B, socket contact head 438 is sized and shaped to initially touch
point B at the bottom of the chip contact 28. Once again it is
possible that some deformation of chip contact 28 will occur as it
is pressed against socket contact head 438, thereby increasing the
area of contact. However, since chip contact 28 is abutting a
generally flat plane 442, deformation will not be as damaging as it
would with prior art socket contact heads.
[0034] As shown in FIG. 6A, a socket contact head 538 can also be
sized so that the chip contact 28 touches the socket contact head
538 where the first portion 540 and third portion 544 meet. In the
FIG. 6A embodiment, the area where these two portions 540 and 544
meet defines a corner 500. As a result, it may be desirable in
certain embodiments to provide a more rounded area 600, as seen in
FIG. 6B, representing the transition from the first portion 640 to
the third portion 644 of socket contact head 638. Further, FIG.
6C's embodiment demonstrates that it may be beneficial in some
embodiments to include an area 700 providing a more gradual or
rounded transition from the third portion 744 to the second portion
742 of socket contact head 738. Moreover, it is not required in
some embodiments that the first and second portion be planar. The
socket contact head 838 in FIG. 6D comprises a first portion 840
that curves outward in a convex manner toward the positioned IC
chip 20 and its chip contact 28. On the other hand, the second
portion 842 and third portion 844 curve inward in a concave fashion
away from the positioned IC chip 20 and its chip contact 28. As a
result, the portions 840, 842, and 844 define a contact surface 800
that is generally if not completely complementary to the shape of
the chip contact 28. Specifically, the curved shape of contact
surface 800 corresponds to the curved shape of the chip contact
28.
[0035] However, it may be helpful in some embodiments to maintain
the planarity of at least the first portion 40. FIG. 7 depicts the
socket contact head 38 depicted in FIG. 2 with a different chip
contact 928. In this case, chip contact 928 is planar, as may be
found in Land Grid Array (LGA) packages. In LGA packages, a
plurality (array) of contact pads ("lands") are used to communicate
with the packaged die circuitry. As is preferred, the planar first
portion 40 of the socket contact head 38 corresponds to the planar
chip contact 928.
[0036] In the embodiments described above, it is noted that the
contact head's perimeter, or portion of the contact head that is
outermost from the central longitudinal axis of the contact, is
also the "highest" area of the head or farthest from the body of
the contact. In certain circumstances, the outermost portion could
also be described as being closest to the site in which the contact
of an IC chip will occupy while being housed in the socket. In
addition, because the remainder of the head declines and/or
converges toward the central longitudinal axis, these exemplary
embodiments can be considered to be defining a central or inner
recess or cavity.
[0037] In many embodiments, an electrical connector head such as
the socket contact heads described above is preferably made of an
electrically conductive material. More preferably, the embodiments
are made of metal. Exemplary materials for the electrical connector
head include gold, copper, beryllium copper, and stainless steel.
The shape of the electrical connector head may be formed through
chemical etching techniques, including wet or dry (plasma) etching,
or through stamping. Further, the head may be integral to the body
of the electrical connector or may be a discrete part that is
attached to the body. For example, it is possible to shape the head
by die-stamping a metal sheet, then attaching the completed head to
an electrical connector body using a conductive adhesive, such as a
Silva-based material (Silva Filled Conductive Chip Adhesive is a
conductive ink composed of silver flakes in an epoxy base which can
be purchased from Ablestick Laboratories of Gardena, Calif.). In
some exemplary embodiments, it is preferable to choose a metal type
and thickness so that flexibility in the head, if any, does not
result in any pinching action against the chip contact upon biasing
the IC chip and socket contact against each other.
[0038] As stated above, the electrical contact head may be
associated with an electrical contact body that is already known in
the art. In the context of socket contacts, for example, FIG. 8
illustrates the socket contact head 38 as part of a pogo pin 46.
The socket contact head 38 is connected to, if not an integral part
of, an outer shell 48. The socket contact head 38 is also connected
to an inner shaft 50 through a spring 52. However, if the outer
shell 48 is made of an electrically conductive material, then the
entire outer shell 48 is available to receive current, when all
that is really needed is for current to travel from the socket
contact head 38 to the inner shaft 50 through the spring 52 (as
well as in the reverse direction). In addition, the hole 30 in body
24 must be wide enough to accommodate the diameter of the outer
shell 48. As technology allows for smaller chip contacts 28 that
may then be more closely packed together, it is desirable to
densify the socket holes 30 in a corresponding manner. The
additional width needed for the outer shell 48 runs counter to that
desire.
[0039] Accordingly, the current invention includes electrical
contacts that dispense with an outer shell. As one example, FIG. 9
depicts a socket contact 1032 comprising a socket contact head 38
coupled to a shaft 1050 through a spring 1052. The spring 1052, in
turn, has sections defining varying widths. For instance, spring
1052 comprises a first section 54 and second section 58, whose
coils define a circle having a diameter of about 1 mil, as well as
a third section 56 having coils that define a circle having a
diameter of about two mils. The third section 56 is wide enough to
contact the socket's body 24. The absence of an outer shell allows
for a narrower hole 30 and therefore allows for a denser array of
holes 30 in the socket body 24.
[0040] Another electrical contact body that is known in the art is
the buckle beam, and the current invention includes electrical
contact heads such as the ones described above attached to such a
body. However, to avoid the problems associated with buckle beams,
the current invention also includes within its scope embodiments
such as the one in FIG. 10, wherein a socket contact 1132 comprises
a socket contact head 38 and a tube 60 having at least one aperture
62. Thus, when a compressive force is applied to the socket contact
1132, at least some of that force will cause the tube 60 to
collapse in on itself, initiating the closure of the aperture 62,
rather than cause the tube 60 to buckle laterally. Thus, hole 30
need not be as large as when it accommodates buckle beams. The tube
60 is, nevertheless, resilient enough to generally return to its
precompression shape once the compressive force eases. Further, the
tube 60 is configured to fit snugly against the socket body 24
somewhere along its length. Other embodiments have a plurality of
apertures, such as FIG. 11, wherein two apertures, 62 and 64,
appear at the same depth but on different sides of the tube 60.
FIG. 12A depicts two apertures, 62 and 66, at different depths
along the tube 60. The tube 60 in these and other embodiments is
preferably made of metal such as gold, copper, beryllium copper, or
stainless steel. The aperture or apertures can be formed by sawing.
In addition, since it is also preferred to make the socket contact
head from metal, it is possible to form the socket contact head 38
and tube 60 from the same piece of metal.
[0041] Still other embodiments include other contacts with bodies
defining a generally continuous profile but for at least one
deformation or deviation. For example, apertures of different
shapes may be formed. While the contacts in FIGS. 10, 11, and 12A
define a rectangular profile with a deformation in the form of a
second, smaller rectangle (or a slit), it is possible to define a
different deformation by using a different saw blade, by using a
particular etching technique, or simply by stamping a dent into the
contact body. FIG. 12B exemplifies such a different deformation; in
this case, a semicircular deformation 62' is defined from a body
60' having a generally rectangular profile defined by the body's
cylindrical shape. Moreover, the contact body in the embodiments
described above, as well as others, can be hollow. Methods for
making such a hollow body can be similar to those known in the art
for making the outer shell 48 of the pogo pin 46 depicted in FIG.
8. A hollow body allows embodiments such as the one depicted in
FIG. 12C, wherein metal strips 65 and 67 integrally extend from and
join cylindrical portions of the contact body 60'. That embodiment
can be formed by sawing on opposite ends of the hollow body, as
depicted in FIG. 12D. FIG. 12D is a top-down cross-sectional view
of the contact in FIG. 12C. Saw blades 69 move in the direction
indicated by arrows 71, thereby defining metal strips 65 and 67
from the cylindrical shell body 60'. Saw blades 69 can represent
two blades that saw the body 60' simultaneously or one saw blade
that saws the body 60' at different places and at different times.
FIG. 12E is another side view of this embodiment, similar to FIG.
12C, only at a slightly different angle than that of FIG. 12C. In
FIG. 12E, the metal strip 65 is closer to the viewer than metal
strip 67. In response to a compressive force along the length of
the contact body 60', the metal strips 65 and 67 can buckle,
allowing the body 60' to at least partially close the gap 73. In
yet another embodiment, seen in FIG. 12F, the metal strips 65 and
67 may be deformed or "pre-dented" through stamping or other
methods, to encourage an inward collapse in response to
compression. Once again, these embodiments can return to their
shape as the compression eases.
[0042] While all-metal electrical contacts are preferable in terms
of electrical conductivity, it may sometimes be preferable to use
semiconductive materials for at least the body of the electrical
contact, as this allows for the use of fabrication techniques that
support scaling on par with the techniques used to define the
contact pitch in the IC chip that is to be tested. FIGS. 13A
through 13H demonstrate such fabrication techniques that may be
used in embodiments of the current invention to form an electrical
contact. FIG. 13A shows a semiconductor substrate 68 that has been
patterned on the top and bottom with photoresist 70 so as to define
a plurality of contact bodies. For purposes of explanation, it is
assumed that the substrate is made of silicon that has been doped
to encourage electrical conductivity. Next, as seen in FIG. 13B,
the shapes of the top and bottom of the in-process contact bodies
are defined through etching. FIG. 13B indicates that an anisotropic
etch has been performed on the top and bottom. The fact that
plateaus 72 remain on the bottom suggests that the anisotropic etch
on the bottom was either shorter in time or involved a lower etch
rate than the anisotropic etch on the top; or that the openings
defined by the photoresist on the bottom were larger than the
openings on top. Partially defining the contacts also establishes
the placement of each prospective contact relative to the other
prospective contacts. Any silicon remaining between the designated
contact sites continues to determine the alignment of each contact
in the array of contacts until that silicon is replaced with
another material. Such a step is illustrated in FIG. 13C, where the
photoresist is removed and the position of each in-process contact
is maintained relative to the other in-process contacts, in this
case through the application of a z-axis elastomer 74 to the bottom
of the substrate 68. The z-axis elastomer 74 is an adhesive
material that is capable of conducting electricity along a
dimension in response to pressure applied along that dimension. The
direction of pressure is usually designated as being aligned with a
z-axis, wherein the elastomer sheet is generally parallel to a
plane defined by an x and y axis (and wherein the x, y, and z axes
are 90.degree. from each other). Such an elastomer is generally
nonconductive along the x and y axes.
[0043] Once the alignment of the in-process contacts has been
reinforced, the contacts are then singulated by removing the
remaining silicon interconnecting the in-process contacts. One
option for doing so is shown in FIG. 13D, wherein additional
photoresist 76 is patterned to protect the tops of the in-process
contacts, and the substrate 68 subsequently undergoes an isotropic
etch to form the sidewalls of the in-process contacts. Preferably,
the isotropic etch is continued to completely separate the contacts
1232, as depicted in FIG. 13D. Alternatively, the isotropic etch
may be used to partially define the sidewalls (FIG. 13E), with an
anisotropic etch completing the singulation (FIG. 13F). Once the
additional photoresist 76 has been removed, FIG. 13G shows that the
array of discrete contacts 1232, along with the z-axis elastomer 74
maintaining their placement, may then be moved to a substrate 78
such as a PCB having conductive leads 80 that end under the
contacts 1232. When the contacts 1232 undergo compression, the
z-axis elastomer 74 provides resiliency as well as electrical
communication between the contacts 1232 and the conductive leads
80. It may also be desirable in some embodiments to deposit an
insulation layer 82 between the contacts 1232 for added stability.
This can be accomplished with a blanket deposition of an insulating
layer followed by an etchback, with photoresist protecting the
contacts. The end result is the socket 1322 illustrated in FIG.
13H. As with previous sockets, an IC chip's contacts will connect
with the socket's contacts 1232, and the PCB's conductive leads 80
can be wire bonded to test equipment for testing the IC chip.
[0044] Variations of the processes described above also fall within
the scope of the current invention. For example, sidewall
definition and singulation of the contacts can be accomplished with
a saw such as those used to singulate dice from a wafer. In
addition, there are ways to retain the alignment of the contacts
1232 other than using the z-axis elastomer 74. For example, after
the step illustrated in FIG. 13B, an alternate step shown in FIG.
14A may be taken. FIG. 14A illustrates that the photoresist 70 has
been removed and another layer of resist 84 has been applied and
patterned to protect the tips of the in-process contacts. FIG. 14A
further indicates that the sidewalls of the in-process contacts
have been defined, either through etching or sawing. Subsequently,
the insulation layer 82 is provided to a desired height, and the
resist 84 is removed (FIG. 14B). In this embodiment, it is the
insulation layer 82 that maintains the alignment of the in-process
contacts. Singulation may then be completed by etching or sawing
from the bottom of the substrate 68, the result of which is seen in
FIG. 14C. The z-axis elastomer 74 may still be used, but in this
embodiment, it may be initially deposited on the substrate 78, with
the singulated contacts 1232 and insulation layer 82 being placed
thereover.
[0045] In addition, a metallization step may be added to make the
tips of the contacts 1232 more electrically conductive. Moreover,
it should be noted that the tips of the contacts may be formed in
accordance with the configurations described above for providing a
contact head with a groove or recess or cavity or defining a cup
shape, with the v-shaped recesses depicted in the contacts 1232 of
FIGS. 13H and 14C serving as one example. As another example, the
etch time, etch rate, or resist opening could be established, as is
known in the art, to define a contact tip that more closely
resembles the socket contact head 38 of FIG. 2. The result of such
a step appears in FIG. 15A. A metal layer could then be provided
and subsequently patterned using photoresist to define heads 1438
of the in-process contacts. Additional steps as illustrated in
FIGS. 13C-13H may be performed to reach the result depicted in FIG.
15C, wherein each contact 1232 has a metallic head 1438 comprising
a first portion 1540 defining a plane 1541 and an opening. In this
embodiment, the plane 1541 is parallel to the substrate 78.
Similarly, a second portion 1542 is parallel to plane 1541 and is
lower than the first portion 1540, or at least closer to the
substrate 78. Joining the first portion 1540 and the second portion
1542 is a third portion 1544. In this exemplary embodiment, the
third portion 1544 defines a frustum-shaped or frustoconical wall
that slopes in toward the center of the socket contact 1232 from
the first portion 1540 to the second portion 1542. As an
alternative to using a metallization step, it is also within the
scope of the current invention to form a metal head separately and
attach it to a silicon contact.
[0046] One skilled in the art can appreciate that, although
specific embodiments of this invention have been described for
purposes of illustration, various modifications can be made without
departing from the spirit and scope of the invention. For example,
just as embodiments concerning a socket contact head may be
associated with prior art socket contact bodies, so too can
embodiments of socket bodies be used in conjunction with prior art
socket heads. Moreover, concerning embodiments involving the
testing of electronic devices, the devices and methods covered by
the current invention could be used in tests including burn-in,
connectivity checks, open/short tests, and multichip module tests,
as well as others. As for embodiments addressing which IC chips
could be tested, the current invention includes embodiments that
involve testing packages such as dual in-line (DIP), zig-zag
in-line (ZIP), leadless chip carrier (LCC), small outline package
(SOP), thin small outline package (TSOP), quad flat pack (QFP),
small outline j-bend (SOJ), and pin grid array (PGA) packages in
addition to the bare die, chip-scale package, flip-chip, BGA, and
LGA mentioned above. Moreover, the methods and devices described
above are not limited to testing circumstances; rather, they could
also be used for interconnect devices in permanent or semipermanent
packaging. Accordingly, the invention is not limited except as
stated in the claims.
* * * * *