U.S. patent application number 11/382756 was filed with the patent office on 2006-08-31 for method of making microelectronic spring contact array.
This patent application is currently assigned to FormFactor, Inc.. Invention is credited to Benjamin N. Eldridge, Gaetan L. Mathieu, Carl V. Reynolds.
Application Number | 20060191136 11/382756 |
Document ID | / |
Family ID | 30769887 |
Filed Date | 2006-08-31 |
United States Patent
Application |
20060191136 |
Kind Code |
A1 |
Eldridge; Benjamin N. ; et
al. |
August 31, 2006 |
Method Of Making Microelectronic Spring Contact Array
Abstract
A method of making a microelectronic spring contact array
comprises forming a plurality of spring contacts on a sacrificial
substrate and then releasing the spring contacts from the
sacrificial substrate. Each of the spring contacts has an elongated
beam having a base end. The method of making the array includes
attaching the spring contacts at their base ends to a base
substrate after they have been released entirely from the
sacrificial substrate, so that each contact extends from the base
substrate to a distal end of its beams. The distal ends are aligned
with a predetermined array of tip positions. In an embodiment of
the invention, the spring contacts are formed by patterning
contours of the spring contacts in a sacrificial layer on the
sacrificial substrate. The walls of patterned recesses in the
sacrificial layer define side profiles of the spring contacts, and
a conductive material is deposited in the recesses to form the
elongated beams of the spring contacts.
Inventors: |
Eldridge; Benjamin N.;
(Danville, CA) ; Mathieu; Gaetan L.; (Varennes,
CA) ; Reynolds; Carl V.; (Pleasanton, CA) |
Correspondence
Address: |
N. KENNETH BURRASTON;KIRTON & MCCONKIE
P.O. BOX 45120
SALT LAKE CITY
UT
84145-0120
US
|
Assignee: |
FormFactor, Inc.
|
Family ID: |
30769887 |
Appl. No.: |
11/382756 |
Filed: |
May 11, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10202712 |
Jul 24, 2002 |
7047638 |
|
|
11382756 |
May 11, 2006 |
|
|
|
Current U.S.
Class: |
29/884 ; 29/837;
29/846; 29/876 |
Current CPC
Class: |
Y10T 29/49139 20150115;
G01R 1/06733 20130101; Y10T 29/49204 20150115; Y10T 29/49222
20150115; Y10T 29/49224 20150115; G01R 1/06744 20130101; G01R 3/00
20130101; Y10T 29/49155 20150115; Y10T 29/49208 20150115 |
Class at
Publication: |
029/884 ;
029/846; 029/837; 029/876 |
International
Class: |
H01R 43/00 20060101
H01R043/00; H05K 3/10 20060101 H05K003/10 |
Claims
1-40. (canceled)
41. A method of making a contact array structure, the method
comprising: providing a plurality of loose spring contact
structures; assembling the spring contact structures into an array
attached to a first substrate, wherein the assembling comprises
positioning the spring contact structures using an alignment
substrate; and removing the spring contact structures from the
alignment substrate.
42. The method of claim 41, wherein the assembling further
comprises inserting tips of the spring contact structures into
alignment features in the alignment substrate.
43. The method of claim 42, wherein the alignment features comprise
pits in the alignment substrate.
44. The method of claim 43, wherein the alignment substrate
comprises a semiconductor wafer into which the pits are etched.
45. The method of claim 41, wherein the assembling further
comprises: inserting bases of the spring contacts into holes in the
first substrate; and inserting tips of the spring contacts into
alignment features in the alignment substrate.
46. The method of claim 45, wherein the first substrate comprises
bonding material disposed adjacent the holes, and the assembling
further comprises activating the bonding material to bond the bases
in the holes.
47. The method of claim 46, wherein the bonding material comprises
solder.
48. The method of claim 41, wherein the assembling further
comprises: inserting tips of the contact structures into alignment
features in the alignment substrate; and securing bases of the
contact structures using holding plates.
49. The method of claim 48, forming a substrate around the
bases.
50. The method of claim 49, wherein the forming a substrate
comprises casting a substrate material around the bases.
51. The method of claim 41, wherein bases of the spring contacts
extend through the first substrate, the method further comprising
attaching the bases of the spring contacts to a second
substrate.
52. The method of claim 41 further comprising attaching the first
substrate to a probe card device, wherein the spring contacts
comprise probes of the probe card device.
53. The method of claim 41, wherein the providing comprises:
fabricating the spring contacts on a sacrificial substrate; and
releasing the spring contacts from the sacrificial substrate.
54. The method of claim 53, wherein: the fabricating comprises
fabricating the spring contacts in a first orientation on the
sacrificial substrate; and the assembling comprises attaching the
spring contacts in a second orientation to the first substrate,
wherein the second orientation is different than the first
orientation.
55. The method of claim 41, wherein the positioning the spring
contact structures using an alignment substrate comprises aligning
mechanical alignment features on the spring contacts with
structural alignment features on the alignment substrate.
56. A method of making a contactor device, the method comprising:
fabricating a plurality of loose spring contact structures;
assembling the spring contact structures into an array in which the
spring contact structures are aligned by an alignment structure and
attached to a first substrate; and removing the alignment
substrate.
57. The method of claim 56, wherein the fabricating comprises:
fabricating the spring contacts on a sacrificial substrate; and
releasing the spring contacts from the sacrificial substrate.
58. The method of claim 56, wherein the assembling comprises
inserting tips of the spring contact structures into alignment
features in the alignment substrate.
59. The method of claim 56, wherein the assembling the spring
contact structures into an array comprises aligning mechanical
alignment features on the spring contacts with structural alignment
features on the alignment substrate.
60. A method of making a contactor device, the method comprising:
providing a plurality of loose spring contact structures;
positioning the spring structures using an alignment substrate;
attaching the spring structures to a first substrate; and removing
the alignment substrate.
61. The method of claim 60, wherein the providing comprises:
fabricating the spring contacts on a sacrificial substrate; and
releasing the spring contacts from the sacrificial substrate.
62. The method of claim 60, wherein the positioning comprises
inserting tips of the spring contact structures into alignment
features in the alignment substrate.
63. The method of claim 60, wherein the attaching comprises
inserting bases of the spring contacts through holes in the first
substrate, and the method further comprises attaching the bases to
a second substrate.
64. The method of claim 60, wherein the positioning the spring
structures using an alignment substrate comprises aligning
mechanical alignment features on the spring contacts with
structural alignment features on the alignment substrate.
65. A probe card comprising: a plurality of probes attached to a
first substrate, tips of the probes positioned in locations
corresponding to alignment features in an alignment substrate by
which the tips were aligned while attaching the probes to the first
substrate; and an electronic component to which base ends of the
probes are attached, wherein the base ends of the probes are
opposite the tips of the probes.
66. The probe card of claim 65, wherein the locations in which the
tips of the probes are positioned corresponds to the alignment
features in the alignment substrate.
67. The probe card of claim 65, wherein the probes comprise
mechanical alignment features that correspond to the alignment
features of the alignment substrate.
68. The probe card of claim 67, wherein the mechanical alignment
features comprise shoulders configured to limit insertion of the
tips into the alignment features of the alignment substrate.
69. The probe card of claim 65, wherein the base ends of the probes
extend through holes in the first substrate and are attached to
terminals of the electronic component.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to methods of making
microelectronic spring contact arrays, such as contact arrays for
connecting to semiconductor devices (singulated or unsingulated),
for purposes of testing or assembly.
[0003] 2. Description of Related Art
[0004] Microelectronic spring contact arrays such as used for
contacting C4 or flat pad terminals of semiconductor devices have
previously been made in various different ways. Some older
techniques involve the assembly of fine, stiff components, such as
tungsten wires, onto a base, such as a probe card. Techniques using
tungsten wire and like components are generally limited to contact
arrays with relatively few contacts, because of practical
difficulties associated with achieving and maintaining a precise
contact tip alignment across the array.
[0005] A more recent method, involving forming composite spring
contacts on a substrate using a relatively soft, fine wire that is
coated with a layer of stiffer material, is capable of producing
higher contact densities than the older tungsten wire techniques.
The composite contacts may be formed directly on a contactor base
or tile, or may be formed on a sacrificial substrate and
transferred to a contactor base later. In the case of composite
contacts that are transferred, loose contacts may be assembled to
the contactor base or tile using a "pick-and-place" technique
(i.e., by individual handling), or by gang-transferring to a
contactor substrate. In a gang-transfer technique, the composite
spring contacts are first formed tips-down on the sacrificial
substrate. Then, while still attached to the sacrificial substrate,
the contacts are first attached to a contactor substrate at their
bases, and then, the sacrificial substrate is removed.
[0006] Composite contacts are subject to some limitations. The
shape of composite contacts is somewhat limited by the wire shaping
process. Also, the soft wire core of each composite contact
generally requires individual shaping before being coated with
stiffener. This may slow down the process of making an array,
particularly for arrays that include many thousands of such
contacts.
[0007] In yet another method, microelectronic spring contacts are
formed on a contactor base using lithographic techniques that are
similar to techniques for making semiconductor devices. The
contactor base is coated with one or more sacrificial layers, and
the sacrificial layers are patterned to define a contoured surface
extending up through the sacrificial layers from the contactor base
of each desired contact. A suitable spring contact material is then
deposited on each contoured surface, and the sacrificial layers are
removed to reveal freestanding spring contacts. Lithographic
techniques have the advantage of enabling more varied shapes to be
used for spring contacts, as well as eliminating the need for
individual handling of the spring contacts. However, relatively
complex lithographic processes may be needed to make spring
contacts of certain shapes, and to achieve certain configurations
of spring contacts on contactors, such as overlapping contacts.
[0008] In some prior art methods, the composite and lithographic
methods described above are combined to form a spring contact that
includes both a composite portion, and a lithographically formed
portion. Combination methods combine certain advantages of
composite and lithographic methods, while still being subject to
the disadvantages of both.
[0009] It is desirable, therefore, to provide a method of making
microelectronic spring contact arrays that overcomes the
limitations of prior art methods.
SUMMARY OF THE INVENTION
[0010] The present invention provides a method of making
microelectronic spring contact arrays that overcomes the
limitations of prior art methods. According to the method, spring
contacts of the desired shape are formed on a flat sacrificial
substrate by patterning a sacrificial layer on the substrate
according to the desired spring profile. The entire spring contact
(or plurality of contacts) may be formed using a single patterning
step. In the alternative, multiple patterning steps may be used, if
desired. A suitable spring material is deposited in the patterned
layer, and then the sacrificial substrate and layer are removed to
reveal free (unattached) spring contacts. The free spring contacts
may be attached to a contactor or tile base using a pick-and-place
method, or by a mass assembly method. In some embodiments, the
spring contacts may be attached directly to a semiconductor device.
Optionally, the spring contacts may be provided with separate
contact tip structures or additional coatings.
[0011] A more complete understanding of the method of making
microelectronic spring contact arrays will be afforded to those
skilled in the art, as well as a realization of additional
advantages and objects thereof, by a consideration of the following
detailed description of the preferred embodiment. Reference will be
made to the appended sheets of drawings which will first be
described briefly.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] FIG. 1 is a flow diagram showing exemplary steps of a method
according to the invention.
[0013] FIGS. 2A-2B are plan and cross-sectional views,
respectively, showing a suitable sacrificial substrate for use with
the method.
[0014] FIGS. 3A-3B are plan and cross-sectional views,
respectively, showing the sacrificial substrate covered by a
patterned layer of sacrificial material.
[0015] FIGS. 4A-4B are plan and cross-sectional views,
respectively, showing exemplary spring contacts attached to the
sacrificial substrate after the sacrificial layer is removed.
[0016] FIG. 5A is a plan view showing the exemplary spring contacts
after being freed from the sacrificial substrate.
[0017] FIG. 5B is a perspective view of a free spring contact in
relation to a tapered recess of a base substrate, according to an
alternative embodiment of the invention.
[0018] FIG. 5C is a plan view of a double-armed free spring contact
prior to assembly to a base substrate, according to an alternative
embodiment of the invention.
[0019] FIGS. 6A-6B are plan and cross-sectional views,
respectively, showing an exemplary base of insulating material for
mounting to the spring contacts.
[0020] FIGS. 7A-7C are side cross-sectional views showing the
exemplary base with springs contacts inserted therein during
exemplary steps of an attachment process.
[0021] FIG. 8 is a side cross-sectional view showing the base and
attached array of spring contacts attached to terminals of an
electronic component.
[0022] FIGS. 9A-9C are side cross-sectional views showing an
exemplary alignment substrate with springs contacts inserted
therein during exemplary steps of alternative attachment
methods.
[0023] FIG. 9D is a side cross-sectional view showing an exemplary
base substrate with springs contacts inserted therein during an
exemplary step of alternative attachment methods.
[0024] FIG. 10 is a side cross-sectional view showing exemplary
spring contacts assembled to have overlapping beam portions.
[0025] FIG. 11A is a plan view of a sacrificial substrate prepared
with a protrusion for forming a tip of a spring contact, according
to an embodiment of the invention.
[0026] FIG. 11B is a cross-sectional view of the sacrificial
substrate shown in FIG. 11A.
[0027] FIG. 11C is a plan view of the sacrificial substrate shown
in FIG. 11A, partially covered by a patterned sacrificial
layer.
[0028] FIGS. 11D-11F are cross-sectional views of the sacrificial
substrate and layer shown in FIG. 11C, at successive times during a
method according to the invention.
[0029] FIG. 12 is a perspective view of a tip region of a
bi-layered spring contact according to the invention.
[0030] FIG. 13 is a plan view of a contact tip with a rounded end,
for use with a spring contact according to the invention.
[0031] FIG. 14 is a plan view of a contact tip with multiple edges,
for use with a spring contact according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] The present invention provides a method of making a
microelectronic spring contact array that overcomes the limitations
of prior art methods. In the detailed description that follows,
like element numerals are used to indicate like elements appearing
in one or more of the figures.
[0033] Spring contacts arrays made using a method according to the
invention may be especially suitable for contacting very compact
semiconductor devices, such as, for example, devices with terminals
arranged at a pitch (average array spacing) of less than 5 mils
(about 130 .mu.m). The invention is also suitable for producing
wiping-type spring contacts having elongated beams, for example,
beams with an aspect ratio (ratio of length to width) of 3 or
greater, and more typically, 10 or greater. The method may be used
to produce straight or contoured beams having very precise
dimensions and performance characteristics. While the method is
especially suitable for making these types of spring contacts, it
may also be used to make other spring contacts, such as those in
arrays with a pitch greater than about 5 mils.
[0034] FIG. 1 shows exemplary high-level steps of a method 100
according to the invention. At step 102, a plurality of free spring
contacts are formed. Various methods may be used to form the
plurality of free spring contacts, of which exemplary methods are
described later in the specification. Preferably, the spring
contacts are formed on a sacrificial substrate using a lithographic
process, for more efficient production of fine-scale (e.g., less
than 5 mil) features. After being formed in a lithographic process,
the spring contacts are freed from the substrate or which they are
formed, thereby becoming "free spring contacts." In other words,
unlike prior art methods for assembling lithographically-formed
contacts into an array, the spring contacts are completely
unattached to any supporting substrate during a portion of method
100.
[0035] At step 104, the free spring contacts are assembled into a
base. Various methods may be used to assemble the spring contacts
onto a base substrate, of which exemplary methods are described in
more detail later in the specification. In an embodiment of the
invention, the base substrate is a tile of insulating material. The
base substrate may be provided with a plurality of through holes
for receiving base ends of the plurality of spring contacts.
Preferably, the base ends protrude through, or nearly through, the
base substrate, thereby providing an electrical connection from a
bottom surface of the base substrate to the plurality of spring
contacts protruding from the opposite top surface of the base
substrate. In addition, the base ends of the spring contacts may be
configured to provide a plurality of terminals on the bottom
surface of the base substrate.
[0036] In the alternative, the base substrate may have a plurality
of pads for bonding to base ends of the spring contacts. The
plurality of pads on a top surface of the base substrate may be
electrically connected to corresponding terminals on a bottom
surface (or other surface) of the base substrate, such as by vias
passing through the substrate. In another alternative embodiment,
the base substrate is itself an electronic component, such as a
package that includes electronic circuits, devices, and so forth.
In this embodiment, the method is essentially completed after step
104 by the assembly to the base substrate/electronic
components.
[0037] For many applications, however, it may be advantageous for
the base substrate to be separate from an electronic component. For
such applications, step 106 may be performed to attach the base
substrate to an electronic component, when desired. Terminals of
the base substrate are connected to terminals of the electronic
component, such as by soldering. If desired, a plurality of base
substrates, each with an assembled array of spring contacts, may be
tiled over the surface of an electronic component. Tiling may
reduce the costs of assembling and/or repairing a very large array
of spring contacts.
[0038] FIGS. 2A-5 relate to an exemplary method for making spring
contacts (step 102 of method 100). FIGS. 2A and 2B show a
sacrificial substrate 202, which is essentially a slab of passive
material having a working surface 204 that is substantially flat
and smooth, relative to the scale of the spring contacts that are
to be formed thereon. Various passive materials may be used for
substrate 202. Silicon of the type used for manufacturing
semiconductor devices is an example of a suitable passive material.
Any other material that is stable and compatible with the materials
used in method 100 may be selected.
[0039] Substrate 202 may be prepared by depositing a thin release
layer 206 over the working surface 204, such as by sputtering.
Release layer 206 may be an aluminum/copper bi-layer formed by
sequential deposition, or other suitable material. Layer 202 may
also serve as a seed layer for a subsequent electroplating step, in
addition to serving as a release layer. It should be appreciated
that the relative thickness of the substrate 202 and seed layer 204
are not drawn to scale. One of ordinary skill may select a suitable
thickness for layer 204 as appropriate for the selected deposition
material and the intended use as a release and/or seed layer.
[0040] After substrate 202 has been suitably prepared, a
sacrificial layer 208 is deposited on the substrate and patterned
to define contours of the desired spring contacts. FIGS. 3A and 3B
show the substrate with an exemplary patterned sacrificial layer
208. Various suitable materials and deposition methods may be used
for sacrificial layer 206. Layer 208 may be comprised of a suitable
photoresist material, and may be patterned using a
photo-lithographic technique such as known in the art. It should be
appreciated that the relative thickness of the substrate 202 and
sacrificial layer 208 are not drawn to scale. One of ordinary skill
may select a suitable thickness for layer 208, such as within the
range of about 0.2 to 100 mil (about 5 to 2500 .mu.m), and more
typically, about 2 to 20 mil (about 50 to 500 .mu.m). Layer 208 is
preferably slightly thicker, for example, 5% thicker, than the
desired thickness of the spring contacts defined by the profiles
patterned in layer 208. Layer 208 may be comprised of multiple
laminated layers, if desired.
[0041] In an embodiment of the invention, contours 212 of the
desired spring contacts are patterned by defining a side profile of
each desired spring contact using side walls 214 of patterned
recesses 210 in sacrificial layer 208, as shown in FIGS. 3A and 3B.
Recesses 210 extend to and expose release layer 206. Sidewalls may
be substantially perpendicular to working surface 204 as shown, or
may be inclined at ay desired angle. It should be apparent that the
contours 212 are shown greatly enlarged relative to the size of
typical spring contacts, and that in general, many more than the
three contours shown would be defined on a single substrate. It is
of course much more efficient to form many more spring contacts on
a single substrate, such as, for example, many tens of thousands of
spring contacts. Recesses 210 may readily be formed using any of
various known photo-lithographic methods.
[0042] Prior art patterning methods, such as methods in which a
plan profile of each desired spring contact is defined using side
walls of recesses in a sacrificial layer, may also be used to form
spring contacts according to the method. An example of such prior
art patterning methods is provided by U.S. application Ser. No.
08/802,054, filed Feb. 18, 1997 and published as Publication No. US
2002/0019152 A1, which is incorporated herein by reference.
[0043] While the distinction between a "side profile" and a "plan
profile" is not readily apparent from inspection of FIGS. 3A and 3B
alone, it is clarified by the disclosures below. In brief, a side
profile refers to the shape of spring contact projected through a
viewing plan perpendicular to the surface to which the spring
contact is mounted to and free-standing from. Plan profile refers
to the shape of the spring contact as projected through a viewing
plan above and parallel to the surface to which the spring contact
is mounted to and free-standing from. It is evident that spring
contacts formed using a plan-profile patterning method may be
formed directly on the surface to which they will be mounted during
use, while spring contacts formed using a side-profile patterning
method must be removed from the sacrificial substrate on which they
are formed, re-oriented, and re-mounted to a connector substrate.
Side-profile patterning methods can be advantageous in that
relatively complex spring contacts may be patterned using as few as
one photo-lithographic patterning step.
[0044] Referring again to the side-profile patterns shown in FIGS.
3A and 3B, after the desired recesses 210 are created in layer 208,
a layer of resilient, conductive material is selectively deposited
over the contours 212. For example, a material deposited by
electroplating may be selectively deposited over the seed/release
layer 206 exposed by recesses 210. Any suitable resilient and
conductive material may be deposited. Suitable materials for the
resilient and conductive material include nickel and nickel alloys.
After the desired depth of material has been deposited, the upper
surface 216 of layer 208 and the deposited resilient conductive
material may be lapped or polished so as to achieve a precise
uniform thickness of resilient conductive material.
[0045] Sacrificial layer 208 may then be removed from substrate 202
using any suitable stripping agent. FIGS. 4A-4B show a plurality of
spring contacts 218 adhered along a length of their elongated beams
218 to sacrificial substrate 202. Release layer 206 may then be
stripped from substrate 202 using a suitable stripping agent, such
as an etchant that will selectively etch the release layer, to
release the spring contacts 218 entirely from substrate 202.
[0046] While spring contacts 220 are adhered to substrate 202, it
may be advantageous to slightly magnetize the contacts 220 in a
common direction. A slight amount of magnetization may be useful
for later re-orienting the spring contacts after they are released
from substrate 202. For embodiments wherein magnetization is
desirable, suitable resilient and conductive materials for spring
contacts 220 include nickel, iron or alloys of nickel and iron
containing cobalt, rhenium, nickel, iron, or other appropriate
materials.
[0047] FIG. 5A shows a plan view of a plurality of free spring
contacts 226 comprised of contacts 220. Each contact 220 further
comprises an elongated beam 218, a base end 224, and a contact tip
222 at an end of the elongated beam 218 distal from base end 224.
In the alternative, contact tip 222 may be omitted and the distal
end of the elongated beam may be shaped to receive a separately
formed contact tip (not shown) after assembly step 104 of method
100. In such case, attachment of separately formed contact tips may
be accomplished using steps essentially similar to those disclosed
in U.S. Pat. No. 5,974,662, which is incorporated herein, in its
entirety, by reference; and more particularly, those steps
disclosed in connection with FIGS. 8A-8E of U.S. Pat. No.
5,974,662, with spring contacts 220 of the present invention
substituted for elements 832 shown in FIGS. 8C-8E.
[0048] It should be apparent that spring contacts 220 may be formed
in a great many alternative shapes other than the shapes shown
herein. For example, the shape of spring contact 230 shown in FIG.
5B may be formed. Spring contact 230 is provided with a tapered
base end 234, designed to fit into a tapered recess of 238 of base
substrate 236. Tapered features, such as recess 238, may readily be
formed at microscopic scales in crystalline substrates such as
silicon, using etching techniques such as known in the art. The use
of matching tapered bases and recesses may aid in orienting and
assembling contact 230 to base 236.
[0049] An alternative, double-armed contact 240 is shown in FIG.
5C. Contact 240 is radially symmetrical about its centroid 241,
which lies in the center of base end 244. Arms 242, 246 extend
outwards from base end 244. Being radially symmetrical, either of
arms 242, 246 may be inserted into the through hole of a base
substrate during assembly, without affecting the configuration of
the resulting array of spring contacts. Either way, when the base
end 244 is seated in a mating recess of a base substrate (e.g., a
recess similar to recess 238 shown in FIG. 5B), arms 242, 246 will
be oriented the same as each other relative to the mounting surface
of the base substrate. An unwanted one of arms 242, 246 may then be
trimmed off, or, in the alternative, spring contact 240 may be used
as a double-ended contact. The relative insensitivity of radially
symmetrical contact 240 to deviations in radial orientation may be
useful where mass assembly techniques, such as fluidic-assisted
assembly, vibration-assisted assembly, or magnetic-assisted
assembly, are used to assemble the spring contact to a base
substrate. A radially symmetrical contact with more than two arms,
such as three arms, may also be useful for similar reasons.
[0050] FIGS. 6A-6B shows an exemplary base substrate 250 for
assembling to free contacts 226 during assembly step 104 of method
100. It should be apparent that substrate 250 is shown at a greatly
enlarged scale, and that, while a substrate 250 with nine mounting
locations is depicted, it would be generally desirable to include a
much greater number of mounting locations.
[0051] Base substrate 250 may be prepared from any suitable
insulating material. Alumina, silicon nitride, and like materials
may be especially suitable. It may also be possible to make base
substrate 250 from silicon, or from polymer materials. If materials
such as alumina or silicon nitride are used, through holes 252 may
be made using a deep reactive ion etch, or any other suitable
process, to match the shape of base ends 224 of spring contacts
220.
[0052] A suitable bonding material, such as solder material 254,
may be deposited adjacent to each through hole 252. For example, a
solder material, such as a gold-tin solder, may be deposited in a
precise pattern near each hole 252, using a photo-lithographic
patterning and plating technique. After the substrate 252 is thus
prepared, the desired spring contacts 220 may be inserted into the
holes 252, as shown in FIG. 7A.
[0053] To assist in locating and retaining the spring contacts 220
in holes 252 during the assembly process, base ends 224 may be
configured with locating and retaining features, such as shown in
FIG. 7B. For example, base end 224 may be provided with shoulders
257 to prevent over-insertion of contact 220 into hole 252; one or
more tapered surfaces 258 as previously described, to aid in
insertion of spring contact 220; and at least one slot 260 to
provide for compressibility of base 224 and help retain spring
contact 220 in hole 252 before solder 254 is activated. A snap-fit
feature (not shown) may also be provided.
[0054] While the exemplary embodiment described above shows
mounting the spring contacts 220 by inserting peg-like bases 224
into through holes 252; other mounting geometries may also be used.
For example, substrate 250 may be provided with a plurality of
mounting pegs or protrusions configured to fit into holes or
recesses in a base of a free spring contact (not shown). In the
alternative, the free spring contacts may be mounted to relatively
flat terminals or pads on a base substrate; or any combination of
the foregoing mounting geometries may be used. The use of through
holes for mounting advantageously provides for a direct electrical
connection between the spring contact protruding from the top
surface of the substrate and a terminal on the bottom surface of
the substrate, without the need for additional manufacturing
steps.
[0055] Various methods may be used to insert free spring contacts
into or onto a base substrate. Pick-and-place methods involve
manipulation of individual spring contacts by a robotic or human
operator. To manipulate very small loose free contacts, a human
operator may use a teleoperation system that de-amplifies spatial
motion inputs to allow for precise manipulation of parts under a
microscope. Mass assembly techniques utilize the random motion of a
group of excited spring contacts, coupled with a force that draws
them towards the base substrate, to accomplish insertion of the
spring contacts. Using the spring contact forming method of the
invention, spring contact shapes may readily be optimized for
pick-and-place or mass assembly techniques. Radially symmetrical
contact 240 (FIG. 5C) is an example of a spring contact optimized
for mass assembly. Mass assembly and pick-and-place techniques may
also be combined; for example, mass assembly may be used to insert
the majority of the contacts, followed by a pick-and-place
operation to insert any remaining spring contacts.
[0056] Various methods may be used for mass assembly. In fluidic
mass assembly, the free spring contacts are suspended in a fluid
reservoir, and fluid from the reservoir containing suspended
contacts is drawn through, or directed towards, the holes of the
base substrate. A vibration-assisted mass assembly method uses a
combination of gravity and mechanical vibration to insert springs
into mounting holes. For example, free spring contacts may be
placed or dropped onto a vibrating base substrate. An
magnetic-assisted method using a magnetic field to orient
individual spring contacts while they are drawn towards the based
substrate using gravity or other motive force. Various alignment
fixtures may also be used in combination with mass assembly
techniques. For example, spring contacts may first be inserted en
masse into a specialized fixture (not shown), and then the fixture
used to assemble the spring contacts to a base substrate.
[0057] To assemble a useful spring contact array, the distal ends
of the spring contacts should be located within a controllable
error to a predetermined array of desired tip positions. In an
embodiment of the invention, when the contacts 220 are first
inserted into holes 252, there may be a substantial amount of free
play between individual spring contacts and the base substrate
before the bonding material 254 is activated. Accordingly, it may
be desirable to use a tip alignment fixture 256 with a plurality of
precisely located alignment features, such as pits 260, as shown in
FIG. 7A. Tip alignment fixture 256 may be a silicon wafer or slab,
and pits 260 may be formed by isotropic etching of the silicon
through a patterned layer of photo-resist. Tapering the side walls
of the pits as shown may assist in alignment of the contact tips.
After the tip alignment fixture 256 is in place, the spring
contacts 220 may be fixed in position by activating the solder 254,
or by plating or otherwise coating a thin layer or hard material
(such as a nickel layer) over the contact array, before fixture 256
is removed.
[0058] Other methods may be used to align the distal ends of the
spring contacts in the array. In an embodiment of the invention, it
is not necessary to use a separate tip alignment fixture such as
fixture 256. Instead, a sufficient degree of alignment may be
provided by controlling the tolerance of the spring contact base
ends and mating mounting holes of the base substrate. For example,
a precisely shaped tapered base 234 as shown on contact 230 (FIG.
5) may provide an acceptable degree of alignment when coupled with
a precisely tapered mounting hole 238. In an alternative
embodiment, the need for a bonding material and for alignment may
both be eliminating by ensuring a tight fit, such as a friction
fit, snap fit, or press fit, between the mounting holes or other
mounting features of the base substrate and the base ends of the
spring contacts. To facilitate assembly of tight-fitting
components, the base substrate may be heated to enlarge the
mounting holes 252 relative to the base ends 224 of the contacts,
and/or the spring contacts may be cooled, prior to assembly. Yet
another alternative assembly method is described below with respect
to FIGS. 9A-D.
[0059] FIG. 7C shows an array 270 of microelectronic spring
contacts 220 after assembly to base substrate 250. Solder 254 has
been activated and has fixed each contact 220 in place. Array 270
may now be attached to an electronic component 272, such as, for
example, a semiconductor probe card, or an interposer for a testing
probe, as shown in FIG. 8. In the alternative, component 272 may be
a semiconductor device or connector. When attached directly to a
semiconductor device, contact array 270 may provide a convenient
package for applications such as flip-chip assembly. Base ends 224
may be positioned on terminals 274 of component 272, and bonded in
place using a suitable bonding material, such as solder 276.
Preferably, solder 276 has a lower activation temperature than
solder 254 used to attach contacts 220 to base substrate 250. For
example, if solder material 254 is a gold-tin solder, solder 276
may be a lead-tin solder. Plural arrays of spring contacts on
separate base substrates may be tiled over a single electronic
component, if desired. Suitable over-compression stops (not shown)
may be placed on the base substrate and/or the electronic component
to prevent inadvertent over-compression of spring contacts 220.
[0060] FIGS. 9A-D show views of spring contacts 320 during
exemplary steps of alternative assembly methods that utilize the
shape of the contacts' distal ends 322 for positioning the contacts
in an array. With the base ends 324 free, distal ends 322 are
inserted into holes 354 of alignment substrate 356, as shown in
FIG. 9A. As previously described, the alignment substrate may be a
semiconductor wafer or like material, with holes 354 formed by
etching in a desired array pattern. Any suitable adhesive material
(not shown) may be used to temporarily retain free spring contacts
320 in holes 354.
[0061] As previously described, any suitable pick-and-place or mass
insertion technique may be used to insert distal ends 322 into
holes 356. In an embodiment of the method, the holes 356 are made
somewhat oversized, i.e., larger than the corresponding distal ends
322, so as to facilitate insertion of contacts into the alignment
substrate 356, as shown in FIGS. 9A and 9B. Accordingly, contacts
320 may be partially free to move, and base ends 324 may fall out
of alignment. To ensure that contacts 320 are held in proper
alignment, one or more temporary holding plates 330, 331 (e.g.,
thin metal or dielectric plates) may be used to hold the base ends
324 of the spring contacts. FIG. 9B shows base ends 324 inserted
into oversized holes 332, 333 in holding plates 330, 331,
respectively. The holding plates 330, 331 have been moved to a
position in which opposite ends of the oversized holes capture
opposite sides of the spring contact bases 324, thereby bringing
them into alignment. Prior to this, the oversized holes 331, 332
may be aligned with one another to facilitate insertion of the base
ends 324.
[0062] In an alternative embodiment, distal ends 322 are inserted
into an alignment substrate 357 having holes 355 that closely match
the geometry of the distal ends. The contacts 320 accordingly are
substantially aligned by the holes 355 and uniform geometry of ends
322, as shown in FIG. 9C. Instead of holes 355, one of ordinary
skill may devise other features for holding a plurality of free
spring contacts in alignment in a desired array pattern. For
example, springs 320 may be retained in a desired aligned position
using an array of posts (not shown) protruding from an alignment
substrate. In addition, to assist in the positioning and alignment
of spring contacts 320 over the alignment substrate, the spring
contacts may be provided with alignment features, for example,
shoulders 326. Such features may be shaped as desired to interact
with features of the alignment substrate. For example, as shown in
FIG. 9C, the shoulders 326 help prevent over-insertion of distal
ends 322 into holes 355, and ensure that contacts 320 extend from
substrate 357 at substantially the same angle.
[0063] After the spring contacts 324 are positioned and aligned as
desired, a casting process may then be used to cast a base
substrate 340 around the base ends 324. The base substrate 340 may
be in the form of a tile. An array 350 of spring contacts 320
inserted into a base substrate (tile) is shown in FIG. 9D. Suitable
casting materials for substrate 340 include epoxies, polyimides,
organic resins, thick film ceramics, low temperature firing
ceramics, organic materials with strength enhancing fillers (e.g.,
silicon carbon or alumina), or any other suitable material. As an
alternative to casting, base ends 324 may be inserted into holes of
the base substrate 340, and bonded to the base substrate using any
suitable method, such as those described above in connection with
FIGS. 7A-B. After base ends 324 are retained by substrate 340, the
alignment substrates 356, 357 and/or the temporary holding plates
330, 331 may be removed, leaving the array 350 as shown.
[0064] One of the advantages provided by the present invention is
the relative ease with which spring contact arrays that include
overlapping portions of spring contacts may be made. FIG. 10 shows
an exemplary spring contact array 400 assembled with a base
substrate 450 and electronic component 472, similarly to the
assembly to substrate 250 and component 272 as previously
described. Contact array 400 includes spring contacts 420, 421,
422, each having an elongated beam 485 extending from the base
substrate 450 to a contact tip at its distal end. Contacts 420,
421, 422 are configured such that a portion of beam 485 of contact
421 is interposed between contact 420 and substrate 450. Similarly,
a portion of contact 422 is interposed between contact 421 and
substrate 450. This overlapping pattern may be repeated across the
entire array.
[0065] The overlapping pattern may allow contacts with relatively
long beam spans across the substrate surface to be spaced at a
pitch spacing less than their average beam span. "Span" is defined
herein as the horizontal distance (i.e., in FIG. 10, as measured
along the top surface of substrate 450) between the contact tip and
its fixed base. Long beam spans may advantageously provide high
resiliency and a relatively large amount of wiping action at their
contact tips. The methods of the present invention overcome the
limitations of prior art methods with respect to making spring
contact arrays with long beam spans and pitch spacing less than the
beam span.
[0066] It may be beneficial to provide free spring contacts
according to the invention, wherein the spring contact has a tip
region covered by a suitable electrical contact material that is
different from a material in other parts of the spring contact.
This may be accomplished by assembling a separate tip structure to
the spring contact, but assembly of a separate tip structure may
entail additional handling and/or process steps. Accordingly, the
invention provides a method whereby the tip region (or any other
desired part) of a free spring contact can be covered by a distinct
material during its formation. Thus, the tip region may be finished
along with the rest of the free spring contact, and additional
assembly may be avoided. This method is described below in
connection with FIGS. 11A-11F.
[0067] FIGS. 11A-11B show plan and cross-sectional views,
respectively, of a sacrificial substrate 502 prepared for use in a
method for forming an integral tip region. Substrate 502 may be any
suitable material, for example, silicon. An exposed surface 505 of
substrate 502 is prepared with a protrusion 501 in a location where
it is desired to form a contact tip of a spring contact. One
skilled in the art will recognize suitable methods for providing a
protrusion 501 at a size and scale appropriate for forming a
microelectronic spring contact tip. For example, structures at a
very small scale may be provided by masking selected regions of
substrate 502 with a suitable resist material, and etching the
substrate. Surface 505 may accordingly be etched except underneath
the resist to create protrusion 501. It should also be appreciated
that although FIGS. 11A-11B show a single protrusion 501, for many
applications, a large plurality of protrusions for use in forming a
large plurality of spring contacts may be desirable.
[0068] Protrusions such as protrusions 501 may be provided in
different shapes. Although a pyramidal shape is depicted, other
shapes may be suitable. Protrusion 501 should include at least one
surface 503 in a location where the tip region of a contact is to
be formed. Surface 505 is configured for forming a spring contact
adjacent to surface 503, for example, it is flat in this region.
Although surface 503 is depicted as inclined at an acute angle to
surface 505, it may in the alternative be perpendicular to surface
505, or inclined at an obtuse angle. By inclining surface 503 at an
acute angle to surface 505, release of materials deposited on the
surface of substrate 502 may be facilitated. Instead of a single
surface 503, a multi-faceted region of protrusion 501 may be used
for tip formation.
[0069] After a suitable protrusion has been provided on substrate
502, the surface 505 of the substrate is covered with a sacrificial
layer 508, as known in the art. The exemplary substrate 502 with a
deposited sacrificial layer 508 is shown in FIGS. 11C-11 D. Prior
to depositing layer 508, the substrate may be coated with a
suitable release/seed layer, for example, a thin aluminum layer
(not shown), as previously described. Sacrificial layer 508 is then
patterned as known in the art to create an opening 510 in the shape
of a spring contact having a tip region positioned over surface 503
of protrusion 501. As described above, opening 510 defines a side
profile of a spring contact. In an embodiment of the invention,
opening 510 reveals a conductive seed layer (not shown) on surface
505.
[0070] A suitable layer of tip material 512 may then be deposited
over the substrate 502 at the bottom of opening 510 by any suitable
method, such as electroplating or sputtering. Any suitable tip
material may be used, for example, palladium, gold, rhodium,
nickel, cobalt, or alloys including at least one of these
materials. Tip material layer 512 may be deposited to any desired
depth. A view of substrate 502 after layer 512 has been deposited
is shown in FIG. 11E.
[0071] A second layer of spring contact material 518 may then be
deposited over tip material layer 512. Again, electroplating or
other suitable methods may be used. Spring contact material for
layer 514 may be stiffer, stronger, and/or less costly than the tip
material selected for layer 512. It should be selected to impart
desired structural properties to the finished spring contact. For
example, nickel, iron, cobalt, or alloys of these materials may be
suitable, as described above. A view of spring material layer 514
deposited over tip material layer 512 is shown in FIG. 11F.
[0072] Depending on the configuration of opening 510, layer 514 may
protrude above a generally flat top surface 518 at a portion 516
over surface 503. It may be desirable to remove any such protruding
portion 516, to thereby expose tip material layer 512. If so,
substrate 502 and its attached layers may be leveled to at or below
top surface 518, such as by machining and/or electromechanical
polishing. In addition, or in the alternative, a third layer (not
shown), such as another layer of tip material, may be deposited
over layer 514.
[0073] After layers 512, 514 are prepared as desired, sacrificial
layer 508 is removed as known in the art. Layers 512, 514 may then
be removed as an integrated piece from sacrificial substrate 502,
to provide a free spring contact 520 similar to free spring
contacts described hereinabove. Contact 520 is comprised of
integrated material layers 512 and 514, as shown in FIG. 12.
Characteristically, a tip region 522 of free spring contact 520 is
at least partially covered by layer 512, which may enhance
electrical performance of contact 520.
[0074] Although contact 520 is depicted as having a single-edged
tip 524, other contact tip configurations may also be used. For
example, a rounded tip 530 may be used, as shown in FIG. 13. For
further example, a multiple-edged tip 540 may be used, as shown in
FIG. 14. These and other tip configurations, including tip 524, may
be used for free spring contacts, with or without a layer of
distinct tip material.
[0075] Having thus described a preferred embodiment of the method
of making a microelectronic spring contact array, it should be
apparent to those skilled in the art that certain advantages of the
within system have been achieved. It should also be appreciated
that various modifications, adaptations, and alternative
embodiments thereof may be made within the scope and spirit of the
present invention. For example, the method as applied to make
particular shapes of contacts has been illustrated, but it should
be apparent that the inventive concepts described above would be
equally applicable to making and assembling contacts of various
other shapes.
* * * * *