U.S. patent application number 09/752992 was filed with the patent office on 2002-01-24 for microelectronic contacts with asperities and methods of making same.
Invention is credited to Distefano, Thomas H., Fjelstad, Joseph, Smith, John W., Walton, A. Christian, Zaccardi, James.
Application Number | 20020008966 09/752992 |
Document ID | / |
Family ID | 26944357 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020008966 |
Kind Code |
A1 |
Fjelstad, Joseph ; et
al. |
January 24, 2002 |
Microelectronic contacts with asperities and methods of making
same
Abstract
Microelectronic contacts, such as flexible, tab-like, cantilever
contacts, are provided with asperities disposed in a regular
pattern. Each asperity has a sharp feature at its tip remote from
the surface of the contact. As mating microelectronic elements are
engaged with the contacts, a wiping action causes the sharp
features of the asperities to scrape the mating element, so as to
provide effective electrical interconnection and, optionally,
effective metallurgical bonding between the contact and the mating
element upon activation of a bonding material.
Inventors: |
Fjelstad, Joseph;
(Sunnyvale, CA) ; Smith, John W.; (Palo Alto,
CA) ; Distefano, Thomas H.; (Monte Sereno, CA)
; Zaccardi, James; (Sunnyvale, CA) ; Walton, A.
Christian; (Belmont, CA) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,
KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Family ID: |
26944357 |
Appl. No.: |
09/752992 |
Filed: |
January 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09752992 |
Jan 2, 2001 |
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08845014 |
Apr 22, 1997 |
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6205660 |
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08845014 |
Apr 22, 1997 |
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08306205 |
Sep 14, 1994 |
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5632631 |
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08306205 |
Sep 14, 1994 |
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08254991 |
Jun 7, 1994 |
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5802699 |
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Current U.S.
Class: |
361/760 ;
257/E23.067; 257/E23.069; 257/E23.078; 361/774; 439/78; 439/886;
439/887 |
Current CPC
Class: |
H01L 2924/01049
20130101; H05K 3/4092 20130101; H01L 2224/81899 20130101; H01L
2924/01029 20130101; H01L 2924/01039 20130101; G01R 3/00 20130101;
H01L 2924/01082 20130101; Y10T 29/49126 20150115; H01L 2924/01004
20130101; H05K 7/1084 20130101; H01L 21/4853 20130101; H01L
2924/12042 20130101; G01R 1/0466 20130101; H01L 2924/01013
20130101; H01L 2924/01078 20130101; G01R 1/06727 20130101; H01L
2924/01006 20130101; H01L 2224/45144 20130101; H01L 2924/01032
20130101; G01R 1/06711 20130101; H01L 2924/01079 20130101; H01L
2924/14 20130101; Y10T 29/49117 20150115; Y10T 29/49155 20150115;
H01L 2924/01005 20130101; H01L 2924/30107 20130101; H01L 23/49816
20130101; H01L 2924/01033 20130101; H05K 2201/0397 20130101; H05K
1/118 20130101; H05K 2201/1059 20130101; H05K 2201/10734 20130101;
Y10T 29/49222 20150115; H01L 2924/01015 20130101; H05K 3/3431
20130101; H05K 3/3436 20130101; Y10T 29/4921 20150115; H05K
2201/0382 20130101; H05K 7/1069 20130101; H01L 2924/01027 20130101;
H05K 3/326 20130101; H01L 2924/01074 20130101; H01R 13/2485
20130101; H01L 2224/16237 20130101; Y10T 29/49156 20150115; G01R
1/06744 20130101; H01L 2924/01047 20130101; H01L 2924/01075
20130101; H01R 12/7076 20130101; Y02P 70/50 20151101; H01L
2924/01076 20130101; G01R 1/06733 20130101; H01L 2924/01046
20130101; Y10T 29/49204 20150115; H01L 23/49827 20130101; H01L
2224/8114 20130101; Y02P 70/613 20151101; H01L 2224/81385 20130101;
G01R 1/07357 20130101; H01L 24/81 20130101; Y10T 29/49224 20150115;
H01L 2924/01322 20130101; H01L 2924/12042 20130101; H01L 2924/00
20130101; H01L 2224/45144 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
361/760 ;
361/774; 439/78; 439/886; 439/887 |
International
Class: |
H05K 003/30; H01R
029/00; H05K 001/00; H01R 012/00; H01R 009/00; H05K 003/00; H01R
009/24; H01R 013/02 |
Claims
What is claimed is:
1. A contact for a microelectronic device comprising a base portion
defining a base surface and one or more asperities integral with
said base portion protruding upwardly from said base surface to a
height of less than about 40 microns, each said asperity defining a
tip surface and a substantially sharp edge bounding said tip
surface.
2. A contact as claimed in claim 1 wherein said base portion
includes a first metal at said base surface, each said asperity
including a column of said first metal extending from said base
surface and a cap of a second metal on such column defining said
sharp edge.
3. A contact as claimed in claim 2 wherein said second metal
consists essentially of one or more metals selected from the group
consisting of gold, osmium, rhenium, platinum and palladium and
alloys and combinations thereof.
4. A contact as claimed in claim 3 wherein said first metal
consists essentially of a metal selected from the group consisting
of copper and copper-bearing alloys.
5. A contact as claimed in claim 1 wherein each said top surface is
substantially flat.
6. A contact as claimed in claim 1 wherein each said asperity is
substantially cylindrical and each said edge is substantially
circular.
7. A contact as claimed in claim 1 wherein each said asperity is
substantially in the form of a elongated slab, each such slab
defining at least one generally vertical major surface intersecting
said tip surface so that the intersection of such major surface and
the tip surface defines at least a part of said sharp edge as an
elongated, generally straight edge.
8. A contact as claimed in claim 1 wherein said base portion
includes an anchor region and at least one flexible projection, at
least one said asperity being disposed on each said projection
remote from said anchor portion.
9. A contact as claimed in claim 8 wherein said anchor region is
substantially ring-like and defines a center, and said at least one
flexible projection includes a plurality of flexible projections
extending inwardly from the ring-like anchor region towards said
center.
10. A contact as claimed in claim 1 wherein each said asperity
protrudes upwardly from said base surface between about 10 .mu.m
and about 40 .mu.m.
11. A connector comprising a body having a top surface and a hole
extending into the body from said top surface, and a contact as
claimed in claim 9 mounted to said top surface so that said
ring-like anchor region encircles the hole at said top surface and
said projections extend inwardly over said hole.
12. A connector comprising a body and a contact as claimed in claim
8 mounted to the body so that the anchor region of the contact is
secured to the body and said projection is free to flex.
13. A contact assembly including a plurality of contact portions,
said contact portions being disposed in a regular contact pattern,
each said contact portion defining a base surface, and a plurality
of asperities on said contact portions each said asperity
protruding upwardly from the base surface of one said contact
portion and having a tip remote from the base surface, each said
asperity having a substantially sharp feature at its tip, said
asperities being disposed in a regular asperity pattern, said
asperity pattern being in registration with said contact pattern so
that at least one said asperity is disposed on each said contact
portion.
14. A contact assembly as claimed in claim 13 wherein said contact
portions are substantially identical to one another and said
asperities are disposed in substantially the same location on each
said contact portion.
15. A contact assembly as claimed in claim 13 wherein said contact
portions include a plurality of flexible projections connected to
at least one anchor region, each such projection having a distal
end remote from the associated anchor region, and wherein said
asperities are located on each said projection adjacent the distal
end thereof.
16. A contact assembly as claimed in claim 13 wherein each said
asperity protrudes upwardly from the associated base surface less
than about 50 .mu.m.
17. A contact assembly as claimed in claim 13 wherein each said
asperity includes a tip surface at its tip and said sharp feature
of each said asperity includes a substantially sharp edge bounding
the tip surface of the asperity.
18. A contact assembly as claimed in claim 13 wherein each said
sharp feature of each said asperity includes a point at the tip of
the asperity.
19. A method of making an electronic contact comprising the steps
of: (a) depositing an etch-resistant material in a plurality of
spots on a top surface of a sheet including a first metal at said
top surface; (b) etching said first metal in a first etching
process so that at least a portion of the first metal is removed in
areas other than said spots, whereby the etched areas will define a
base surface and the areas covered by said spots will form
asperities projecting upwardly from said base surface, said etching
step forming tips on said asperities remote from said base surface
and substantially sharp edges bounding said tips.
20. A method as claimed in claim 19 wherein said etch-resistant
material is a second metal and wherein said second metal at least
partially defines said sharp edges.
21. A method as claimed in claim 20 wherein said second metal
consists essentially of one or more metals selected from the group
consisting of gold, osmium, rhenium, platinum and palladium and
alloys and combinations thereof.
22. A method as claimed in claim 20 wherein said first metal
consists essentially of one or more metals selected from the group
consisting of copper and copper-bearing alloys.
23. A method as claimed in claim 19 wherein said sheet includes a
layer of an etch-resistant stop metal beneath said first metal.
24. A method as claimed in claim 23 wherein said etching step is
continued until said stop metal is exposed in said etched areas,
whereby said stop metal layer will define said base surface.
25. A method as claimed in claim 19 further comprising the step of
subdividing said sheet into a plurality of contact portions, said
subdividing and etching steps being conducted so that at least one
asperity is disposed on each said contact portion.
26. A method as claimed in claim 25 wherein said subdividing step
includes the step of etching said sheet in a second etching
process.
27. A method as claimed in claim 26 wherein said second etching
process includes the step of etching said sheet from a bottom
surface to form grooves in said bottom surface before said first
etching step, and wherein said first etching step is performed so
that said base surface is disposed adjacent said grooves.
28. A method as claimed in claim 19 wherein said step of depositing
said etch-resistant material in said spots includes the step of
applying a resist to said top surface of said sheet and exposing
said resist to radiant energy in a pattern constituting a positive
or negative image of said spots.
29. A method as claimed in claim 19 wherein said step wherein said
step of depositing said etch-resistant material in said spots
includes the step of applying a resist to said top surface of said
sheet and exposing said resist to energetic charged particles in a
pattern corresponding to a positive or negative image of said
spots.
30. A method as claimed in claim 29 wherein said top surface of
said sheet is non-planar at the time of said exposing step.
31. A method of making an electronic contact comprising the steps
of: (a) in a surface-forming step, etching a top surface of a sheet
including a first metal at said top surface so that at least a
portion of the first metal is removed except at locations in a
predetermined asperity pattern and so that the etched areas define
a base surface and asperities will projecting upwardly from said
base surface at said locations, said surface-forming etching step
forming tips on said asperities remote from said base surface and
sharp features at each said tip; and (b) severing said sheet to
form a plurality of contact portions according to a predetermined
severing pattern, said severing pattern and said asperity pattern
being in registration with one another so that at least one
asperity is disposed on each said contact portion.
32. A method as claimed in claim 31 wherein said severing step
includes the step of forming grooves in a bottom surface of said
sheet.
33. A method as claimed in claim 32 wherein said step of forming
said grooves is performed before said surface forming step and
wherein said surface forming step is performed so as to cut through
the sheet at said grooves.
34. A method of engaging a microelectronic device having electrical
elements thereon with a connector comprising the step of moving
said device and said connector relative to one another so that said
electrical elements of the device engage and deform resilient
contacts carried on a body of the connector, so that each
electrical element moves relative to the contact engaged therewith,
and so that sharp edges at tips of asperities protruding from the
contacts scrape the engaged electrical elements.
35. A method as claimed in claim 34 wherein each said asperity has
an edge portion facing opposite to the direction of motion of the
engaged electrical element.
36. A method as claimed in claim 35 wherein each said contact bears
on the engaged electrical element with a force between about 2 and
about 20 grams-force
37. A method as claimed in claim 34 wherein said connector body
includes a plurality of holes, said contacts include a plurality of
contacts extending inwardly over each said hole at a top surface of
the connector body, said electrical elements of said
microelectronic device include a plurality of bump leads protruding
from a lead-bearing surface, and said moving step includes the step
of moving said lead-bearing surface of said microelectronic element
toward said top surface of said connector body so that said bump
leads extend into said holes and said contacts bend downwardly into
said holes.
38. A microelectronic connector comprising a connector body and a
plurality of contact units, each contact unit including an anchor
region attached to the connector body and at least one resilient
tab extending from the anchor region, each such tab including a
bottom layer of a polymeric material and a conductive layer thinner
than said bottom layer overlying said bottom layer.
39. A connector as claimed in claim 38 wherein each said tab
includes a metallic asperity protruding upwardly from said
conductive layer, each said asperity having a sharp feature at a
tip remote from said conductive layer.
40. A connector as claimed in claim 39 wherein each said asperity
is between about 5 .mu.m and about 25 .mu.m high.
41. A connector as claimed in claim 39 wherein each said asperity
has a tip surface at its tip remote from said conductive layer and
a sharp edge bounding said tip surface.
42. A connector as claimed in claim 38 wherein each said conductive
layer is metallic an less than about 10 .mu.m thick.
43. A connector as claimed in claim 42 wherein each said bottom
layer is between about 10 and about 50 .mu.m thick.
44. A connector as claimed in claim 42 wherein each said tab is
between about 100 and about 300 .mu.m long.
45. A connector as claimed in claim 38 wherein said connector body
has a plurality of conductors therein, and wherein said bottom
layer and conductive layers of each said tab extend into the
associated anchor region, the connector further comprising
electrically conductive posts extending through the bottom layer in
said anchor regions and electrically connecting said conductive
layers to said conductors in said connector body.
46. A method of making a microelectronic connector comprising the
steps of: (a) providing a sheet having a polymeric bottom layer,
and at least one metallic layer on said bottom layer; (b)
selectively removing metallic material from said at least one
metallic layer so as to leave a conductive layer thinner than said
bottom layer overlying the bottom layer and a plurality of
asperities protruding upwardly from said conductive layer; and (c)
subdividing said conductive layer and said bottom layer to form at
least one elongated tab, each such tab having at least one said
asperity.
47. A method as claimed in claim 46 wherein said at least one
metallic layer includes a stop layer adjacent said bottom layer and
a first base metal layer overlying said stop layer, said step of
selectively removing metallic material including the step of
selectively etching said first base metal layer.
48. A method as claimed in claim 47 wherein said stop layer resists
etching in said step of selectively etching said first base metal
layer so that said stop layer remains and forms said conductive
layer.
49. A method as claimed in claim 46 wherein said subdividing step
includes the step of selectively etching said conductive layer so
as to expose said bottom layer at channel openings between the tabs
and then directing radiant energy through said channel openings so
as to ablate the bottom layer in said channel openings, whereby
said conductive layer will block radiant energy directed to
portions of said bottom layer in said tabs.
50. A method of making a microelectronic connector comprising the
steps of providing a sheet including a metallic layer and a
polymeric bottom layer, selectively etching said metallic layer so
as to form a plurality of tabs and channel openings between said
tabs and thereby expose said bottom layer at the channel openings,
and then directing radiant energy through said channel openings so
as to ablate the bottom layer in said channel openings, whereby
said metallic layer will block radiant energy directed to portions
of said bottom layer in said tabs.
Description
[0001] The present application is a continuation in part of U.S.
patent application Ser. No. 08/254,991 filed Jun. 7, 1994, the
disclosure of which is hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to contacts for
microelectronic devices such as semiconductor chips and the
associated circuit panels, connectors and related devices to
methods of making and using such contacts, and to components such
as sockets and other connectors including such contacts.
[0003] Microelectronic circuits require numerous connections
between elements. For example, a semiconductor chip may be
connected to a small circuit panel or substrate, whereas the
substrate may in turn be connected to a larger circuit panel. The
chip to substrate or "first level" interconnection requires a large
number of individual electrical input and output ("I/O") as well as
power and ground connections. As chips have become progressively
more complex, the number of I/O connections per chip has grown so
that hundreds of connections or more may be needed for a single
chip. To provide a compact assembly, all of these connections must
be made within a relatively small area, desirably an area about the
area of the chip itself. Thus, the connections must be densely
packed, preferably in an array of contacts on a regular grid,
commonly referred to as a "Bump Grid Array" or "BGA". The preferred
center-to-center distance between contacts or "contact pitch" for
chip mountings is on the order of 1.5 mm or less, and in some cases
as small as 0.5 mm. These contact pitches are expected to decrease
further. Likewise, chip mounting substrates and other circuit
panels used in microelectronics have become in the connected
elements. Such tolerances may cause varying degrees of
misalignment. Additionally, contamination on the surfaces of the
mating contact parts can interfere with the connection. This can
occur in metallurgically bonded connections and, particularly, in
mechanically interengaged connections. Therefore, the contact
system should be arranged to counteract the effects of such
contaminants. All of these requirements, taken together, present a
formidable engineering challenge.
[0004] Various approaches have been adopted towards meeting these
challenges. For example, Patraw, U.S. Pat. Nos. 4,716,049;
4,902,606 and 4,924,353, all disclose flexible, outstanding
projections on a substrate, each such projection being generally
dome-shaped. The chip itself is provided with a so-called "mesa"
member having multiple conductive pads coupled to the actual
contacts of the chip. A spring biases the chip and hence the pads
on the mesa member against the dome-shaped members. Minemura et al,
U.S. Pat. No. 4,950,173 discloses a relatively coarse-pitched
connector in which pin-shaped contacts, thread into holes in
insulating support. Contact tabs formed from a shape memory alloy
are then brought into engagement with the pin by changing the
temperature, causing the tabs to change shape and hence engage the
pin. This provides a so-called "zero insertion force" system in
which the pin is not engaged or wiped by the tabs. Hotine et al,
U.S. Pat. No. 3,275,736 also discloses a relatively coarse,
second-level interconnect structure. In this structure, all contact
including a ring with a plurality of fingers extending inwardly
from the ring is engaged on a pin-like lead extending from a
microelectronic component. Each of the fingers has a point at its
tip, and these points scrape the leads as the parts are engaged.
Once the parts are engaged, the fingers may be metallurgically
bonded to the leads as by welding. Shreve et al, U.S. Pat. No.
5,046,953 describes a tape automating bonding or "TAB" arrangement
using a dielectric tape with conductive leads thereon in which the
leads themselves are dimpled or in which sets of spherical
particles are interposed between the leads and the mating contacts
so as to provide an indenting and scrubbing action when the leads
of the tape are pressed against the contacts. Grabbe, U.S. Pat. No.
5,173,055 discloses a "area array connector" including plate-like
springs with upwardly projecting fingers to the main gauge
plate-like contacts on the mating part. U.S. Pat. No. 5,152,695
discloses similar arrangements, in which the fingers are provided
with apparently rounded or spherical raised bumps formed by adding
a raised area of gold using a wire bonding machine and then
"mechanically profiling" the raised area or by welding a gold wire
onto the contact finger and coining the wire into the final shape.
Grabbe et al, U.S. Pat. No. 5,131,852 discloses a tape-based
connection system in which contacts on a flexible tape are
supported by spring fingers and thus pressed against contact pads
on semiconductor chip. Here again, the contacts are provided with
rounded raised sections formed by electroforming, wire bonding or
the like.
[0005] Ikeya, U.S. Pat. No. 4,846,704 discloses a test socket for
testing large, second level interconnections, the test socket
having numerous spring fingers which engage the exposed leads
connected to the chip. Each of these spring fingers has sharp edges
for making contact with the exposed lead. Still other connectors
are disclosed in the text Multi-chip Module Technologies and
Alternatives; The Basics, Donn et al, EDS, Van Nostrand Rhinehold
Company 1993, Chapter 10, (pp. 487-524) entitled MCM To Printed
Wiring Board (Second Level) Connection Technology Options, by Alan
D. Knight.
[0006] Evans et al, U.S. Pat. No. 3,818,415 discloses a large-scale
electrical connector having a contact surface with adhering fine
particles of a grit, these particles being covered by tough, metal
coating. These particles are said to scrape away adhering
insulation on a mating conductor. Hill et al, Mechanical
Interconnection System For Solder Bump Dice, 1994 ITAP and Flip
Chip Proceedings (pp. 82-86) disclose a test connector for engaging
solder bumps on microelectronic chips. The connector includes a
flat surface with a set of pads in an array corresponding to the
array of solder bumps on the pads. Each pad on the fixture has a
so-called "dendritic" or "random pattern" of small palladium
needles, typically about 200-500 needles per square millimeter.
These needles or dendrites are forced against the solder bumps
during use, so that the dendrites penetrate contaminant films on
the solder bumps and make electrical contact.
[0007] Caine et al, U.S. Pat. No. 5,006,917 describes a tape
automated bonding system in which a dielectric tape is provided
with multiple leads, all having exposed inner tips. These tips are
provided with non-dendritic, rough surfaces having ridges spaced
apart from one another at a peak-to-peak distance of approximately
1 micron. These lead tips are then bonded to pads on a
semiconductor chip by thermocompression bonding.
[0008] Burns et al, U.S. Pat. No. 5,207,585 describes a "interface
pellicle" including a flexible, dielectric membrane and a large
number of electrodes extending through the dielectric membrane.
Each electrode has a dome-like upper surface disposed on the top
surface of the membrane and a roughened bottom surface disposed on
the bottom side of the membrane. The pellicle can be used by
placing the membrane between a mounting substrate having contact
pads and a chip or other component having solder balls so that the
textured bottom surface of the electrodes face the solder balls
whereas the dome-like top surfaces face the contact pads of the
substrate. The substrate and the component are then forced together
so that each electrode is squeezed between a contact pad and a
solder pad. The rough bottom surfaces indent the surfaces of the
solder balls.
[0009] Despite these efforts in the art, there has still been a
need for further improvement.
SUMMARY OF THE INVENTION
[0010] The present invention addresses this need.
[0011] One aspect of the present invention provides a contact for a
microelectronic device. The contact according to this aspect of the
invention includes a base portion defining a base surface, and one
or more asperities preferably integral with the base portion and
protruding upwardly from the base surface to a height of less than
about 40 microns, more preferably less than about 25 microns. Each
such asperity defines a tip surface remote from the base surface
and a substantially sharp edge bounding the tip surface. Each
asperity desirably includes a column of a first metal extending
upwardly from the base surface. Each asperity may also include a
cap of a second metal defining the sharp edge and the tip surface.
The second metal preferably is a substantially etch-resistant
metal, and may be harder than the first metal. The second metal may
be selected from the group consisting of gold, osmium, rhenium,
platinum, palladium and alloys and combinations thereof.
Alternatively or additionally, the tip surfaces of the asperities
may carry electrically conductive bonding materials adapted to form
metallurgical bonds with time mating electrical elements.
Preferably, the tip surfaces of the asperities are substantially
flat, and hence provide appreciable surface for carrying the
bonding material. The first metal may be selected from the group
consisting of copper and copper-bearing alloys. The base portion of
each contact may include one or more metallic layers such as copper
or copper-bearing alloys, and preferably includes a metal having
resilient characteristics such as beryllium copper or phosphor
bronze. Alternatively, the base portion of each contact may include
a polymeric structural layer in addition to a conductive, desirably
metallic, layer.
[0012] Each asperity may be substantially cylindrical, most
preferably in the form of a right circular cylinder, and each of
the aforementioned sharp edges may be substantially in the form of
a circle encircling the tip of the asperity. Alternatively, each
asperity may be substantially in the form of an elongated slab,
each such slab defining at least one generally vertical major
surface intersecting the tip surface of the asperity so that the
intersection defines an elongated straight edge, such straight edge
forming part of the sharp edge. The base portion of each contact
may include an anchor region and at least one tab or projection
formed integrally with the anchor region. The asperity or
asperities may be disposed on each tab remote from the anchor
region. In use, the anchor region of such a contact is fixed to a
connector body or other support, whereas the tab is free to bend.
When a lead, contact pad or other mating electrical element is
engaged with the tab, the tab bends and the mating element and tab
move relative to one another to provide a wiping motion. The
resilience of the tab causes the sharp edge of the asperity to bear
on the mating element and scrape the mating element. The anchor
region of each contact may be part of a substantially ring-like
common anchor region. A contact unit may include such common anchor
region and a plurality of tabs extending inwardly from the
ring-like anchor region towards a common center.
[0013] Further aspects of the present invention include connectors
including the contacts discussed above. Thus, a connector according
to this aspect of the invention may include a contact having a base
portion and one or more asperities thereon, each asperity having a
tip surface and a substantially sharp edge bounding the tip
surface, the contact being mounted to the body so that when a
mating element is engaged with the contact, the mating contact
element will be wiped across the asperity and pressed against the
asperity, causing the sharp edge of the asperity to scrape the
mating contact element. Preferably, the anchor region of the
contact is secured to the body and the projection is free to flex.
In this arrangement, the resilience of the projection causes the
asperity to engage the mating element. Where a contact unit
includes a ring-like anchor region and plural tabs extending
inwardly therefrom, the contact unit may be mounted to the body of
the connector so that the ring-like anchor region extends around a
hole and so that the tabs extend inwardly over the hole, with the
asperities pointing generally up, away from the body. When the
mating contact element is forced into the hole, the tabs bend
downwardly and the asperities engage the mating contact
element.
[0014] A further aspect of the present invention provides a
connector including a plurality of contact base portions, said base
portions being disposed in a regular contact pattern. Each contact
base portion defines a base surface. The contact assembly further
includes a plurality of asperities, each such asperity protruding
upwardly from the base surface of the associated contact base
portion. Each such asperity has a tip remote from the base surface
and a substantially sharp feature at such tip. The asperities may
be disposed in a regular, predetermined asperity pattern. The
asperity pattern is in registration with the contact pattern so
that at least one asperity is disposed on each contact base
portion. The contact base portions may be substantially identical
to one another and the asperities may be disposed in substantially
the same location on each such contact base portion. The connector
may further include at least one anchor region, and the contact
base portions may include a plurality of flexible tabs connected to
such anchor region or regions, each such tab having a distal end
remote from the associated anchor region. In such an arrangement,
the asperities desirably are located on each such tab adjacent the
distal end thereof.
[0015] In connectors according to this aspect of the invention, the
regular distribution of asperities on the contact portions assures
that the asperities are present on most or all of the contact
portions even where the spacings between adjacent asperities are
large relative to the size of the contact portions themselves.
Stated another way, there is no need to pack the surface with
closely spaced asperities in order to assure that each contact
portion is provided with an asperity. Accordingly, each asperity
may stand out from the base surface unencumbered by surrounding
asperities This promotes effective scraping action, particularly in
the case of very small contacts and asperities.
[0016] A further aspect of the present invention, provides methods
of engaging a microelectronic element with a connector. Such
methods include the step of moving the microelectronic element
relative to the body of the connector so that asperities carried on
contacts included in the connector scrape electrical elements, such
as leads or contact pads, on the sharp edges on the tips of the
asperities engage and scrape the conduct element of the
microelectronic device. Preferably, the contact portions include
flexible tabs and the asperities are disposed on the flexible tabs.
During the engagement step, the tabs are distorted by engagement
with the mating electrical mating elements of the microelectronic
device, so that the projections urge the asperities into engagement
with the contact elements. The method according to this aspect of
the present invention may further include the step of forming a
permanent metallurgical bond between the contacts and the terminals
of the microelectronic element. The bonding step can be performed
by activating an electrically conductive material carried by the
contacts or by the engaged elements of the microelectronic device.
Alternatively or additionally, the method may include the step of
actuating the microelectronic element by applying signals through
the contacts and the engaged elements of the microelectronic device
without formation of a metallurgical bond or before such a bond is
formed. Thus, the microelectronic element and its engagement with
the contacts can be tested before permanent bonding. Here again,
the scraping action provided by the sharp fractures on the
asperities promotes reliable contact before bonding, as well as
reliable bonding.
[0017] Further aspects of the present invention provides methods of
making microelectronic contacts. One method according to this
aspect of the present invention desirably includes the step of
depositing an etch-resistant material in a plurality of spots on a
top surface of a sheet which includes a first metal at the top
surface and then etching the first metal in a first etching process
so that at least a portion of the first metal is removed in areas
other than said spots, so that the etched areas defines a base
surface and so that areas covered by the spots form asperities
projecting upwardly from the base surface. The depositing and
etching steps form tips on the asperities, remote from the base
surface, and also forms substantially sharp edges bounding the
tips. The etch resistant material may be a second metal and the
second metal may at least partially define the sharp edges of the
tips. The second metal may be a metal selected from the group
consisting of gold, osmium, rhenium, platinum, palladium alloys and
combinations thereof, whereas the first metal desirably is selected
from the group consisting of copper and copper-bearing alloys.
[0018] The sheet may include a layer of a stop metal resistant to
the etchant used to etch the first metal. The stop layer may be
formed from a metal such as nickel which is substantially more
resistant than the first metal to etching by certain solutions. As
further discussed below, the stop layer may be susceptible to
etching by other solutions or procedures. The etching step may be
continued until the stop metal is exposed in the etched areas, so
that the stop metal layer defines the base surface. The method
desirably further includes the step of subdividing the sheet into a
plurality of contact units, each including one or more contacts,
the subdividing and etching steps being conducted so that at least
one asperity is disposed on each such contact. The subdividing step
may include a further etching process. This further etching process
may include the step of etching the sheet from a bottom surface,
opposite from the top surface.
[0019] The etch from the bottom surface may be performed before the
top surface etching step and may form grooves in the bottom
surfaces. The sheet may be secured to a body after the bottom
surface etching step but before the top surface etching step. Where
no stop layer is employed, the top surface etching step will break
through the sheet at the grooves, thereby severing the individual
contact units from one another. Where a stop layer is provided, the
bottom surface etching step, and hence the grooves formed in that
step, will terminate at the stop layer. After the top surface
etching step, the exposed stop layer is treated with a further
etchant or with another treatment to remove the stop layer at least
at the grooves, thereby severing the contact units from one
another. In either process, the sheet desirably remains coherent
until after the sheet has been mounted to the body. In further
processes according to the invention, the sheet may include a
bottom polymeric layer, and the step of subdividing the sheet may
include the step of forming channels in the stop layer and exposing
the sheet to radiant energy, so that the stop layer serves as a
mask and so that the polymeric layer is cut at the channels.
[0020] The step of depositing the etch-resistant tip material
desirably is performed by applying a resist to the top surface of
the sheet and then exposing the resist either to radiant energy in
a pattern constituting the positive or negative image of the spots
or else exposing the resist to energetic, charged particles, such
as alpha particles, also in a pattern corresponding to a positive
or negative image of the spots. The exposed resist is then
developed and treated to remove either the exposed or unexposed
regions leaving either a positive or negative image of the spots.
The resist itself may serve as the etch-resistant material, in
which case the resist is later removed after formation of the
asperities. Alternatively, the resist may be used to control
deposition of an etch-resistant metal in an electroplating step.
Use of energetic charged particles such as alpha particles to
expose the resist is particularly advantageous where the sheet is
embossed or otherwise non-planar at the time of the exposing
step.
[0021] Yet another aspect of the present invention provides methods
of making a microelectronic contact including the steps of etching
a sheet incorporating a first metal at such top surface so that at
least a portion of the first metal is removed except at locations
in a predetermined asperity pattern. Thus, the etched areas define
a base surface and asperities project upwardly from the base
surface at locations of said asperity pattern. The etching step
applied to the top surface is conducted so as to form tips on the
asperities remote from the base surface and sharp features at each
such tip. The method according to this aspect of the invention
desirably also includes the step of severing the sheet according to
a predetermined severing pattern, to form a plurality of contact
units, each including one or more contacts, the severing pattern
and the asperity pattern being in registration with another so that
at least one asperity is disposed on each contact. The severing
process may be conducted by etching as aforesaid.
[0022] These and other objects, features and advantages of the
present invention will be more readily apparent from the detailed
description of the preferred embodiments set forth below, taken in
conjunction with the accompany drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a fragmentary, diagrammatic perspective view
depicting portions of a contact assembly in accordance with one
embodiment of the present invention.
[0024] FIG. 2 is a fragmentary, diagrammatic partially sectional
view on an enlarged scale along lines 2-2 in FIG. 1.
[0025] FIG. 3 is a view similar to FIG. 2 but illustrating the
connector during engagement with microelectronic element.
[0026] FIGS. 4-8 are fragmentary, diagrammatic sectional views
depicting portions of the connector of FIGS. 1-3 at stages of a
manufacturing process in accordance with a further embodiment of
the invention.
[0027] FIGS. 9, 10 and 11 are fragmentary, partially sectional
views depicting a connector in accordance with a further embodiment
of the invention during successive states of fabrication
process.
[0028] FIG. 12 is a diagrammatic plan view depicting a connector in
accordance with a further embodiment of the invention.
[0029] FIG. 13 is a diagrammatic, perspective view depicting a
contact used in the connector of FIG. 12.
[0030] FIG. 14 is a diagrammatic elevational view of the connector
shown in FIGS. 12 and 13.
[0031] FIG. 15 is a diagrammatic, perspective view of a connector
in accordance with another embodiment of the invention.
[0032] FIG. 16 is a fragmentary, diagrammatic perspective view of a
connector in accordance with a further embodiment of the
invention.
[0033] FIGS. 17 through 21 are fragmentary, diagrammatic sectional
views depicting portions of a connector in accordance with a
further embodiment of the invention during successive stages of
manufacture and use.
[0034] FIG. 22 is a fragmentary top plan view of a the connector
depicted in FIGS. 17-21.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] A connector according to one embodiment of the invention
includes a plurality of independent, electrical contact ends 29.
Each contact unit includes four contacts 20. Each contact 20
includes a small metallic tab incorporating a base layer 22 (FIG.
2) defining an upwardly facing base surface 24. The base portion of
each contact desirably is formed from a resilient metal selected
from the group consisting of copper, copper-bearing alloys,
stainless steel and nickel. Beryllium copper is particularly
preferred. The base portion desirably may be between about 10 and
about 25 microns thick. A layer 25 of an etch metal such as nickel
used in the contact formation process as further described below
may be disposed on base surface 24. Layer 25 desirably is between
about 0.5 and 2.0 microns thick. Each such tab is joined to a
generally square, ring-like anchor portion 26 integral with the
tab. Each tab has a tip 28 at the end of the tab remote from the
anchor portion.
[0036] Four tabs extend inwardly from each anchor portion 26, the
tabs being separated from one another by channels 23. Each contact
or tab 20 has an asperity 30 projecting upwardly from the base
surface 24 adjacent the tip 28 of the tab. Each asperity includes a
column 32 of a first or base metal integral with base portion 22
and further includes a cap 34 overlying the column 32 at the
uppermost tip of the asperity, remote from base surface 24. Each
column 32 is generally cylindrical or frustoconical in shape, so
that the tip of each column is substantially circular. The cap of
each column defines a flat, circular tip surface and substantially
sharp edge 36 encircling the tip surface. Each asperity desirably
protrudes upwardly from the base surface less than about 50
microns, more preferably between about 5 microns and about 40
microns, and most preferably between about 12 microns and about 25
microns. Each asperity may be between about 12 and about 50 microns
in diameter, more preferably about 12 to about 35 microns in
diameter. The cap metal 34 may be selected from the group
consisting of metals resistant to etching by etchants which etch
the first or base metal. Cap metals selected from the group
consisting of gold, silver, platinum, palladium, osmium, rhenium
and combinations thereof are preferred. As further discussed below,
such etch-resistant metals aid in formation of sharp edges 36.
Moreover, the harder etch-resistant metals, particularly osmium and
rhenium, aid in preserving the edge during use.
[0037] The contact units are disposed on the top surface 38 of a
connector body 40, and spaced apart from one another so that there
are slots 42 between adjacent connector units. Connector body 40
incorporates a sheet-like, metallic element 44 having holes 46
therein. The metallic layer is covered by a bottom dielectric layer
48 and a top dielectric layer 50, which merge with one another
within holes 46, so that the dielectric layer cooperatively lines
the holes as well. A conductive metallic via liner 52 extends
through each hole 46 from the top surface 38 of the connector body
to the opposite, bottom surface 54. Each via liner 52 flares
radially outwardly, away from the central axis 56 of the associated
hole at the bottom surface so as to form an annular terminal 58 at
such bottom surface. Each via liner also flares outwardly, away
from the central axis at the top surface 38 so as to form a contact
support structure 60. The periphery of each contact support is
generally square.
[0038] Each contact unit 29 has four apertures 64 extending through
the ring-like anchor portion 26, from its bottom surface 21 to the
upwardly-facing base surface 24. One contact unit 29 is disposed on
each contact support 60, substantially in alignment with the square
boundary thereof. Each contact unit is secured to the associated
contact support by four posts 66 integrally with the contact
support 60 and extending upwardly through the hole 64 in the
contact unit. Each post 66 has an outwardly protruding ridge or
bulbous portion 68 at the end of the post remote from the contact
support 60, overlying base surface 24. These posts and bulbous
portion thus secure each contact unit 29 to the corresponding
contact support 60 so that the individual contacts or tabs 20, and
particularly the tips 28 thereof, protrude radially inwardly,
toward the axis 56 of the associated hole 46 in the connector body
so that tips of the contacts or tabs 20 overly the hole 46. The
posts and the contact supports 60 also electrically connect each
contact unit to the associated via liner and thus to the terminal
58 on the bottom surface.
[0039] Contact units 29, and hence the individual contacts or tabs
20 are disposed in a regular pattern corresponding to the patterns
of holes 46 in body 40. The asperities 30 on the contacts are also
disposed in a regular pattern, in registration with the pattern of
contacts 20, so that the same number of asperities are disposed on
each contact. In the embodiment of FIGS. 1 and 2, only one asperity
is disposed on each contact. However, because both the asperities
and the contacts are disposed in regular patterns, all of the
contacts are provided with asperities. Also, the asperity on each
contact is at the same location namely, adjacent the tip of the tab
or contact, remote from the anchor region of the contact unit.
[0040] The connector of FIGS. 1 and 2 may be engaged with a larger
substrate, such as a multilayer substrate 68 having leads 69
therein. Each such lead having an exposed end 71 at the surface of
the substrate. The terminals 58 of the connector, and thus the
contact units 29, may be electrically connected to the internal
leads 69 of the substrate by conventional lamination and/or solder
bonding methods, or by the lamination and interconnection methods
taught in International Patent Application 92/11395, the disclosure
which is hereby incorporated by reference herein. After assembly to
the substrate, the connector of FIGS. 1 and 2 is engaged with a
mating microelectronic element 70 so that a bump lead or solder
ball 72 engages each contact unit 29. Thus, the mating
microelectronic element 70 has bump leads 72 in a pattern
corresponding to the pattern of holes 46 and contact units 29.
Microelectronic element 70 is juxtaposed with the connector so that
one bump lead or solder ball 72 is aligned with each contact unit
and with the underlying hole 46 in the connector body 40. The
microelectronic element is then forced downwardly, towards the
connector body and towards the contact units 29 and individual tabs
or contacts 20. This downward motion brings each such ball 72 into
engagement with all four contacts or tabs 20 of the contact unit 29
and, in particular, engages the ball 72 with the asperities 30. As
illustrated in FIG. 3, the anchor portion or outer periphery 26 of
each contact unit remains substantially in fixed position, whereas
the distal regions of each tab 20, adjacent the tips 28 of the
tabs, bend downwardly, in the direction of motion of the engaged
ball 72. In this condition, a part of each sharp edge 36 faces
upwardly, in the direction opposite to the downward motion of
microelectronic element 70 and ball 72. Each asperity is biased
inwardly, towards the central axis 56 of the hole, by the
resilience of the tab 20. The upwardly facing portion of each edge
36 tends to dig into the surface of ball 72 and scrapes the surface
of the ball as the ball moves downwardly, into hole 46. The
sharp-edged asperity on each tab thus scrapes a path along the ball
or bump lead 72.
[0041] This scraping action effectively removes oxides and other
contaminants from the scraped paths. This assures reliable
electrical contact between contacts 20 and the balls or leads 72.
In particular, the tips of the asperities aid in making contact
with the balls or leads 72. Because the cap metal in layer 34 on
the tip of each asperity is a substantially oxidation resistant
metal, it normally does not have any substantial oxide or
contaminant layer. Thus, the ball and contacts form a firm,
reliable electrical interconnection. This action is repeated at
each contact unit and with each ball or lead 72 on the surface of
the microelectronic element, so that reliable interconnections are
formed simultaneously between all of the balls or leads and all of
the internal conductors 69 of substrate 68. These connections can
serve as the permanent or semi-permanent interconnections of the
assembly. Alternatively, the electrical connection achieved by
mechanical interengagement of the element may be used as a test
connection, so that microelectronic element 70, its connections to
substrate 68 and the other elements connected to the same substrate
can be tested and operated under power. If a defective connection
or component is identified during the test, the same can be removed
and replaced readily. Ordinarily, the connector and contacts can be
reused.
[0042] After completion of the test, the assembly can be
permanently bonded together. Each of bump leads 72 incorporates an
electrically conductive bonding material compatible with the
materials of contacts 20. Alternatively or additionally, the
contacts themselves may carry conductive bonding materials. Various
bonding materials known to those skilled in the art of
microelectronic assemblies can be used for these purposes. For
example, the bump leads 72 may be formed entirely from a solder or
from a solder layer overlying an interior core (not shown). In this
case, the electrically conductive bonding material or solder can be
activated by heating the assembly causing the solder to flow. A
flux such as a so-called "no-clean" flux can be provided either on
the microelectronic element around the solder ball or on contacts
20. Alternatively, a solder paste such as Koki RE4-95K, a 63%
tin-37% lead solder in 20-50 micron diameter particles distributed
in a no-clean flux can be provided on either the contact units or
the balls or leads 72.
[0043] Bonding materials other than solder can also be employed,
including a low temperature eutectic bonding material, a solid
state diffusion bonding material, a polymer-metal composite bonding
material or another heat-activatable bonding material. Thus,
polymer-metal bonding materials may include a dispersion of a metal
such as silver or gold particles in a thermoplastic polymer such as
ULTEM.backslash. material or a thermosetting polymer such as an
epoxy. Diffusion bonding materials may include layered structures
of gold on nickel; alloys of gold and tin such as 80% gold, 20% tin
and alloys of tin and silver such as 5% silver, 95% tin. Solders
may include alloys such as tin-lead and tin-indium-silver.
High-temperature bonding materials may be selected from the group
consisting of alloys of gold and tin; gold and germanium; gold and
silicon or combinations thereof, the gold and tin alloys being
preferred. In accordance with known principles, each type of
bonding material normally is employed to bond structures compatible
with that bonding material. For example, high-temperature bonding
materials and diffusion bonding materials are employed with contact
metals and bump lead or ball metals such as gold adapted to form
alloys with the bonding material. The bonding material may be
carried either on the contact units 29 or on the mating electrical
elements or leads 72. The cap metal carried on the tip surfaces of
the asperities may constitute the bonding material.
[0044] A fabrication process according to a further embodiment of
the invention may be utilized to fabricate contact units and
connectors as described above. The process begins with a sheet 100
of a base metal (FIG. 4), covered with a thin layer 102 of an
etch-stop metal and a further layer 104 of the base metal overlying
the etch-stop metal. Thus, sheet 104 defines the top surface 106 of
the composite, three-layer sheet whereas sheet 100 defines the
opposite, bottom surface 108. The thickness of layer 104
corresponds to the desired height of the base metal column 32 in
each asperity 30 (FIG. 2) whereas the thickness of bottom layer 100
corresponds to the desired thickness of the base metal layer 22
constituting each contact tab. In a bottom surface etching step,
the top surface is protected by a continuous mask 110, whereas the
bottom surface is covered by a layer 112 of a conventional
photoresist. The photoresist is patterned using conventional
photoexposure and selective removal techniques, so as to leave gaps
in the resist. The sheet is then subjected to etching by emerging
in an etch solution such as a solution of CuCl, NH.sub.4OH and
NH.sub.4Cl. The etch solution attacks the copper-based alloy of
lower layer 100 but does not substantially attack the stop layer
102. The patterning of resist 112 is controlled so that the
exposed, etched areas include channels 23 in base metal layer 100
bounding tabs 20, as well as apertures 66 in the anchor regions and
slots 42 bounding the anchor regions and subdividing lower layer
100 into individual portions corresponding to the separate contact
units discussed above.
[0045] In the next stage, top coating 110 is removed and replaced
by a top pattern resist 114 (FIG. 5), which again is patterned
using conventional photographic methods to leave openings 116
corresponding to the locations of the asperities 30. Thus, each
opening 116 is substantially in the form of a circular hole
corresponding to the circular asperity. The features on the bottom
surface are covered by a further bottom resist 118, and then the
assembly is electroplated with the cap metal 34. At this stage of
the process, top base metal layer 104 and stop layer 102 are still
solid and continuous. Although only a small portion of the sheet is
illustrated, corresponding to portions of one contact unit, it
should be appreciated that the sheet includes numerous contact
areas, sufficient to form one or more complete connectors. Stop
layer 102 and top layer 104 remain continuous and coherent and all
portions of the sheet are electrically continuous with one another
at this stage.
[0046] Following application of the cap metal, top surface holes 67
are formed in alignment with the apertures 66 previously formed in
the bottom surface. These top surface holes extend through top base
metal layer 104 and extend through stop layer 102. Top surface
holes 67 may be formed by applying radiant energy to the top
surface 106 of the sheet in a pattern corresponding to the desired
pattern of aperture 66 or by etching the top surface using a
further patterned mask (not shown). Such an etching process
desirably uses a CuCl NH.sub.4OH and NH.sub.4Cl etch solution to
etch from the top surface to top layer 102, followed by a further
etch using an FeCl and HCl etch solution to etch through stop layer
102. Following this procedure, any mask used in forming top holes
67 is removed, and the bottom masking 118 is also removed.
[0047] In this condition, the sheet is laminated to a connector
body 40 having the structure discussed above, with pre-existing
holes, via liners 52 and contact supports 60. At this stage of the
process however, the post 66 and bulbous portion 68 have not yet
been formed. The lamination procedure is conducted so as to align
each region which will ultimately become a contact unit 29 with the
corresponding hole 46 and with the corresponding contact support
60. The dielectric material on the top surface of the connector
body desirably softens and penetrates into the slots 42 between
adjacent connector units. In the next stage of the process, the
bottom surface of connector body 40 is covered with a masking layer
120 (FIG. 7), thus protecting the bottom surface of base metal
layer 100. The assembly is then immersed in a further etching
solution, such as a CuCl and HCl etching solution which attacks the
base metal. This further etch solution removes the base metal of
top layer 104 everywhere except at the spots covered by cap layers
34. This etching procedure thus forms base metal columns 32
extending upwardly from the base metal layer 100 and upwardly from
the stop metal layer 102. The etch procedure thus forms asperities
30 in the areas covered by cap layers 34. This etching procedure
also leaves each asperity with a sharp edge 36 defined by the cap
layer and surrounding the tip of the asperity.
[0048] Following this etch procedure, a further masking layer (not
shown) is applied on the stop layer 102 and on the other upwardly
facing features, leaving holes only in alignment with apertures 66.
The assembly is then electroplated with a metal compatible with
contact supports 60, such as copper, thereby forming post 66 and
outwardly extending or bulbous tips 68. Following this procedure,
the mask used is removed and a further mask is applied and
photodeveloped to leave a pattern of openings corresponding to the
desired pattern of channels 23 and slots 42. A further etch
solution, capable of attacking stop layer 102, such as an FeCl/HCl
solution, is applied and allowed to attack the stop layer in the
open areas of the mask until the etch solution breaks through stop
layer 102 at slots 42, thereby subdividing the original coherent
metallic sheet into individual contact units. The etch also breaks
through at channels 23, thereby converting individual portions of
each contact unit into individual contacts or tabs 20 in the
configuration discussed above. The bottom mask is then removed,
leaving the connector in the configuration discussed above with
reference to FIGS. 1 and 2.
[0049] During the process discussed above, the sheet remains
physically coherent and electrically conductive until the last
etching phase, so that the sheet can be successfully mounted on the
connector body and successfully electroplated to form the posts.
Each of the individual steps of the process requires only
conventional masking and etching techniques. Because the asperities
are performed in the same series of process steps as used to form
the contacts and contact units, the asperity pattern can be
provided in good registration with the contact pattern.
[0050] A process according to a further embodiment of the present
invention begins with a composite sheet 200 (FIG. 9) incorporating
a top base metal layer 204 and stop layer 202 similar to those
discussed above over a bottom layer 201 formed from a flexible but
resilient polymeric material, desirably a polyimide. Top layer 204
has a thickness approximately equal to the desired height of the
asperities, typically about 5 microns to about 25 microns, and may
be formed from a readily etchable metal such as copper or a copper
based alloy. Stop layer 202 includes a material, such as nickel,
which resists etchants that attack top layer 204. Stop layer 202
may be a composite layer, incorporating a sublayer about 0.5
microns to about 2.0 microns of the etch resistent metal over
another sublayer of copper or other metal less than about 10
microns thick. The bottom polyimide layer desirably is about 10
microns to about 50 microns thick. In the process, an etch
resistant material such as a photoresist is applied in a pattern of
spots 234 corresponding to the desired pattern of asperities. Here
again, although only a few asperities adapted to form parts of a
single contact unit are illustrated, the actual sheet encompasses a
relatively large area, corresponding to many contact units. The
sheet is then subjected to an etching process using an etchant
which attacks the top layer 204 but which does not attack either
the stop layer 202 or the bottom layer 201 as, for example,
CuCl/HCl solution. This leaves asperities 230 (FIG. 10) protruding
upwardly from stop layer 202, in a pattern corresponding to the
pattern of etch resistant spots 234, and leaves stop layer 202 as a
continuous electrically conductive layer. The resist constituting
spots 234 is then removed and a further resist is applied with open
areas corresponding to apertures 266. While this resist is in
place, the assembly is subjected to a further etching process, thus
removing stop or conductive layer 202 in the areas corresponding to
apertures 266. After removal of the stop layer in these areas, the
assembly is subjected to laser ablation using a KrF excimer laser,
or using other suitable radiation which is strongly absorbed by the
polymer of bottom layer 201. This extends apertures 266 entirely
through bottom layer 201. In this condition, the sheet is still
coherent and electrically conductive over its entire area.
[0051] The sheet is then laminated to a connector body 240 (FIG.
11) in the essentially the same manner as discussed above with
reference to FIG. 7. Thus, the sheet is aligned with the connector
body so that each zone of the sheet constituting an individual
contact unit is aligned with the corresponding hole and contact
support of the connector body. The sheet is laminated to the top
surface of the connector body so as to physically secure the sheet
to the connector body. In this operation, the polymeric material of
bottom layer 201 desirably merges with the dielectric material of
the connector body itself. Following this lamination operation, the
assembly is electroplated to form posts extending through apertures
266. These posts merge with the contact supports of the connector
body and with the stop layer 202 in substantially the same way as
post 66 described above with reference to FIG. 7. The posts provide
electrical continuity through bottom layer 201, so that each zone
of the stop or conductive layer 202 is electrically connected to
the corresponding contact support and via liner (not shown) of the
connector body.
[0052] In the next stage of the process, the stop layer is etched,
using a conventional masking and etching procedure, to form
channels 242 subdividing the stop layer into individual contact
units 229 (FIG. 11). The stop layer is further etched to form
channels 223 subdividing the stop layer within each contact unit
into individual tabs or contacts 220. Following this etching
procedure, the assembly is once again subjected to laser ablation
in the areas corresponding to channels 223. During this laser
ablation process, the surrounding regions of stop layer 202 serve
as a mask, and precisely limit the laser ablation process to the
channels 223. This laser ablation process removes the underlying
portions of layer 201 leaving the individual tabs or contacts 220
disconnected from one another at their tips 228. Thus, the
individual tabs of each contact unit 229 project inwardly over the
associated hole (not shown) in the connector body, in substantially
the same manner as discussed above with reference to FIGS. 1 and
2.
[0053] The tabs or contacts formed by this process are composite;
each tab incorporates a lower layer 201 formed from polymeric
material, a relatively thin electrically conductive layer overlying
that polymeric material and an asperity extending upwardly from the
polymeric layer and conductive layer. Desirably, the conductive
layer, formed from stop layer 202, is thinner than the polymeric
layer. Thus, the conductive layer may be less than about 10 microns
thick, desirably between about 0.5 micron and about 3 microns thick
and more preferably between about 0.5 micron and about 2.0 microns
thick. This construction makes it practical to provide relatively
low spring constants, and to allow for substantial deformation of
the tabs while maintaining relatively low stress levels in
relatively short tabs. For example, each tab may be between about
100 and about 300 microns long, from the anchor region to the
asperity. During use, each tab acts as a cantilever beam. Because
the polymeric layer has a modulus of elasticity far lower than a
metallic layer, the stiffness of the composite beam can be
relatively low, and can be controlled accurately. As described
above, the composite contacts most preferably are provided with
asperities to provide the scraping action. However, the composite
contacts provide significant advantages even where the scraping
action provided by the asperities is not required. For example, in
certain special bonding processes, such as gold-to-gold diffusion
bonding conducted under conditions where both the contacts and the
mating elements are maintained free of surface impurities,
acceptable bonding can be achieved without the scraping action.
Thus, a connector according to a further embodiment of the
invention, for use in such a process, may include composite
contacts with the polymeric layer and with the thin conductive
layer, but without the asperities. Such a connector provides the
advantage of well-controlled interengagement forces.
[0054] A connector in accordance with another embodiment of the
present invention includes a connector body 300 and a plurality of
individual contacts 302 mounted on a top surface 304 of the
connector body. Each contact 302 includes an anchor region 306
closely overlying connector body top surface 304 and secured to the
connector body. A terminal 308 formed integrally with the contact
is provided at a proximal end of each anchor region 306. A flexible
tab 310 extends from the opposite, distal end of each anchor region
306, the tab being joined to the anchor region along a hinge line
311. Each such tab is generally in the form of a strip extending
upwardly, away from the connector body top surface 304. Each such
strip defines a base surface 312 facing upwardly, away from the
connector body. Two asperities 314 are provided on each contact.
Each asperity is generally in the form of a rectilinear slab having
a generally vertical, generally planar front surface 316,
substantially perpendicular to base surface 312. Vertical surface
316 faces generally in the direction of the elongation of the strip
constituting tab 310, and faces towards the distal end of the tab,
away from the anchor region 306. Vertical surface 316 intersects
the tip surface of the asperity, remote from the base surface. The
intersection defines a generally linear sharp edge 318 partially
bounding the top surface of the asperity. Edge 318 faces away from
the anchor region and extends generally parallel to the line of
juncture or hinge line 311 between the anchor region and tab 310.
The asperity may also define a similar sharp edge facing in the
opposite or proximal direction towards the anchor region 306. Each
slab-like asperity includes a base metal portion 322 and a cap
portion 324 at the tip, the cap metal portion defining edge 318.
The cap metal and base metal may incorporate materials as discussed
above.
[0055] In use, the connector is engaged with a microelectronic
device 370 having connection pads 372 by juxtaposing the
microelectronic device with the connector so that the pad-bearing
surface of the microelectronic device faces the contacts of the
connector and then forcing the microelectronic device and connector
towards one another. The force used for this purpose may be applied
by conventional mechanical force-applying devices incorporated in a
test fixture (for temporary assembly) or in a package (for
permanent assembly). The force-applying device is symbolized in
FIG. 14 by a spring 374. However, the force-applying device may
include essentially any mechanical element capable of applying the
requisite force, such as a fluid power device, weights or springs
in fixtures and deformable elements such as flexible or crimped
enclosures, adhesives, elastomers, clamps or other force-applying
elements in permanent packages. As the contact pads 372 of the
microelectronic element engage the tabs 310 of the contacts, the
tabs flex bending generally about the line of joinder 311 between
each tab 310 and the associated anchor region 306. This flexing
movement causes the asperities 318 to move generally horizontally,
in the directions indicated by arrows 330 in FIG. 14, thus causing
the asperities to wipe across the contact pads 372 and causing
leading or distally facing edges of the asperities on each contact
to scrape the surfaces of the contact pad. Once again, the scraping
action removes contaminants from the contact pads and promotes
effective electrical interconnection between the contact pads 372
and the contacts of the connector. The same scraping action also
promotes formation of effective permanent bonds between the engaged
contacts and connection pads when the bonding material carried on
the contacts or applied separately is activate.
[0056] The connector illustrated in FIG. 15 has contacts 402 in the
form of elongated tabs, each such contact having an asperity 414
adjacent a distal end. Here again, the asperities are disposed in a
predetermined, regular pattern, as are the contacts so that a
predetermined number of asperities, in this case one asperity is
disposed on each contact, in a predetermined location on the
contact. The proximal end 416 of each contact is secured to the
underlying connector body 418, whereas the distal end overlies a
gap 420 in the connector body. Each asperity 414 is generally in
the form of a body of revolution about an axis perpendicular to the
upwardly facing base surface 422 of the contact. Each such body of
revolution tapers to a sharp point 424 at its end remote from the
base surface 422. In use, such contact is engaged with the mating
elements in the manner discussed above. The distal end of the
contact flexes downwardly, into opening 420 in the connector body
and hence applies a resilient, upward force tending to bias the
point 424 of each contact into engagement with the mating element.
Here again, the sharp asperities scrape the mating element as the
mating element moves relative to the contact and as the contact
deforms downwardly, to the position illustrated in broken lines at
402'. Sharp points as illustrated in FIG. 15 can be formed by
depositing small spots of an etch resistant material on the top
surface of a sheet and then subjecting the sheet to an isotropic
etching, so that the etch solution undercuts the spots.
[0057] A connector in accordance with a further embodiment of the
present invention may include a connector structure generally as
described in copending, commonly assigned U.S. patent application
Ser. No. 08/277,336, the disclosure of which is hereby incorporated
by reference herein. The connector may include a connector body 400
and a plurality of conductors extending in the body as, for
example, through conductors 402 extending between the top surface
404 and bottom surface 406 of the body. Contacts 408 may be
connected to the conductors, and each contact may flare radially
outwardly from the associated conductor. Each contact may be
arranged so that the periphery of the contact will expand radially
outwardly, away from the associated conductor, in response to a
vertical force directed toward the body applied to the contact.
Thus, each contact may include a plurality of tabs 420 arranged so
that the tabs can be bent downwardly towards the body when the tabs
are engaged with mating electrical elements such as contact pads
424 of a microelectronic device. The tabs may be spaced above the
top surface 404 of the connector body, or the body may incorporate
a material at the top surface which can be softened during
assembly, to permit downward movement of the tabs.
[0058] In this embodiment of the present invention, sharp-featured
asperities are provided on the contacts 408 at locations such that
the outward expansion of the contacts will cause the asperities to
scrape the mating contact pads 424. The asperities desirably have
sharp edges 436 extending at least around the outwardly-facing
portion of each asperity. These asperities may be formed by
processes as described above.
[0059] A manufacturing process in accordance with a further
embodiment of the invention begins with a sheet 502 of a first
metal such as beryllium copper, phosphor bronze or the other
resilient metals discussed above. A continuous protective layer 504
is applied on the bottom surface of the sheet. A photoresist is
applied on the top surface and selectively exposed and developed to
form numerous circular dots 506 on the top surface of the sheet.
The dots are arranged in groups 508, each group occupying a square
region corresponding to one contact unit. The regions are separated
from one another by linear spaces 510 about 0.1 mm wide. The dots
are about 12 to 35 microns in diameter. Within each group, the dots
are spaced apart from one another at a pitch of about 30 to about
50 microns. Each group 508 includes about 28 dots, and occupies a
region about 0.4 mm square, so that the groups are disposed in a
recurring rectilinear array with a group-to-group pitch of 0.5 mm.
In the next stage of the process, the sheet is etched, so as to
form a base surface 511 and asperities 512 protruding upwardly from
the base surface. After etching, the resist dots 506 are removed.
The asperities are disposed in the same arrangement as dots 506,
and disposed in asperity groups 514 corresponding to dot groups
508. Each asperity is generally fustoconical, and includes a
circular tip surface 516 remote from the base surface 511. A
substantially sharp, circular edge encircles each tip surface. In
this embodiment, the tip surfaces and edges are defined by portions
of the first metal corresponding to the original top surface of the
sheet. The height of the asperities, and the distance between the
base surface 511 and the bottom surface of the sheet, is controlled
by the depth of etching. Etch depth, in turn, is controlled by
known factors including concentration of the etch solution, time of
exposure, temperature and agitation. These factors preferably are
maintained substantially constant over the entire extent of the
sheet.
[0060] In the next stage of the process, a cover layer 518 is
applied over the top surface, so that the cover layer overlies the
tips of the asperities. An adhesive 520 fills the spaces between
asperities, including the linear spaces between asperity groups,
and holds the cover layer to the sheet. The cover layer and
adhesive may be provided in a prepared assemblage, such as the
material available under the trademark COVERLAY from the E.I.
DuPont Company. The bottom cover layer 504 is removed and replaced
by a bottom photoresist 522. The bottom photoresist is selectively
exposed and developed to form linear slots 526 aligned with the
linear spaces between groups of asperities, the slot channels being
narrower than the spaces. The bottom photoresist also includes
channel openings 524 arranged in an X-shaped pattern beneath each
asperity group. The sheet is then etched again, until the etch
breaks through to base surface 511 on the top side of the sheet, so
as to form slots 530 bounding each asperity group 514 and isolating
each such asperity group from the others. The same etching step
also forms channels 528 in an X-shaped pattern within each asperity
group. This step thus subdivides the sheet into individual contact
units corresponding to the individual asperity groups 514, and
forms four contacts or tabs 532 within each such contact unit.
[0061] The registration between the asperity pattern on the top
surface and the channel openings in the bottom photoresist is not
precise. Some asperities 512a (FIG. 20) overlie the areas etched to
form the channels. However, the spacing between asperities is small
in comparison to the dimensions of the tabs 532, so that each tab
includes at least one asperity.
[0062] In the next stage of the process, the bottom resist 522 is
removed, leaving the assemblage of the etched sheet and cover
layer. This assembly is then laminated to with an interposer 540
and a substrate 542. Interposer 540 includes a dielectric sheet 544
and flowable dielectric layers 546 and 548 on the top and bottom
surfaces of such sheet. The interposer further includes conductors
550 formed from flowable conductive material extending through the
dielectric sheet and flowable dielectric layers. The dielectric and
conductive materials may be those used in the interposers described
in U.S. Pat. No. 5,282,312, the disclosure of which is hereby
incorporated by reference herein. For example, the flowable
dielectric may be an epoxy, whereas the flowable conductive
material may include a polymer filled with metallic particles. The
interposer has through holes 552 disposed in a rectilinear grid
pattern corresponding to the pattern of contact units or asperity
groups 514. Conductors 550 are disposed in a similar grid offset
from the grid of holes. Substrate 542 includes contact pads 554
disposed in a similar grid, and internal circuitry (not shown)
connected to the contact pads. The substrate may also include other
elements (not shown) for connecting the internal circuitry to other
devices.
[0063] In the lamination process, the assemblage of etched sheet
and cover layer, interposer and substrate are aligned with one
another so that the center of each contact unit (at the center of
the X-shape defined by the channels 528) is aligned with a hole 552
of the interposer, whereas a conductor 550 of the interposer is
aligned with a corner of the contact unit. Each conductor 550 is
also aligned with a contact pad 554 of the substrate. The aligned
elements are subjected to heat and pressure so as to activate the
flowable dielectric and conductive materials and unite the sheet
assemblage, interposer and substrate. The flowable material in each
conductor 550 electrically connects the aligned contact unit 514
and contact pad 554. The flowable dielectric material on the top
surface of the interposer fills slots 530, and merges with the
adhesive 520 in the sheet assemblage.
[0064] The laminated assembly is then selectively exposed to
radiant energy, such as laser light, directed from the top surface
at the center of each contact unit. The radiant energy selectively
ablates the cover layer 518 and adhesive 520 in the areas overlying
the contacts or tabs 532 and channels 528, thus exposing these
elements at the top surface of the assembly. By removing the
surrounding adhesive and dielectric materials, the radiant energy
will also remove any loose fragments of asperities left overlying
the channels 528. However, the radiant energy does not
substantially melt asperities on the contacts, or substantially
dull their edges. The completed connector may now be used in
substantially the same manner as the connectors discussed above.
Thus, a microelectronic element 560 with bump leads 562 may be
engaged with the completed connector so that the bump leads
penetrate into holes 552 and engage contacts 552. Here again, the
bump leads are engaged and scraped by the asperities on the
contacts.
[0065] The various contacts described above can be adapted to
provide various levels of interengagement force between each
contact and the engaged mating electrical element. Interengagement
forces between about 0.5 and about 5 grams force per engaged
contact or tab are preferred in typical microelectronic
applications. The total interengagement force per contact unit, and
hence the total interengagement force per bump lead, desirably is
between about 2 and about 20 grams force. With the sharp-edged
asperity structures discussed above, these relatively small
interengagement forces nonetheless provide effective scraping and
wiping action. The ability to provide effective scraping action at
relatively low force levels is especially significant where
numerous contacts must be engaged with numerous mating elements.
The degree of wipe or relative movement between the asperity edge
and the mating electrical element surface during contact engagement
can be relatively small, typically less than about 20 microns and
usually between about 5 and 10 microns. Even this small relative
movement however is enough for the sharp features of the asperity
tips to break through the contaminants on the surface of the mating
element.
[0066] As these and other variations and combinations of the
features set forth above can be utilized without departing from the
invention, the foregoing description of the preferred embodiments
should be taken by way of illustration rather than by way of
limitation of the invention as defined by the claims.
* * * * *