U.S. patent application number 10/692174 was filed with the patent office on 2004-04-15 for microelectronic contact structures, and methods of making same.
This patent application is currently assigned to FormFactor, Inc.. Invention is credited to Eldridge, Benjamin N., Grube, Gary W., Khandros, Igor Y., Mathieu, Gaetan L..
Application Number | 20040072452 10/692174 |
Document ID | / |
Family ID | 21817623 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040072452 |
Kind Code |
A1 |
Eldridge, Benjamin N. ; et
al. |
April 15, 2004 |
Microelectronic contact structures, and methods of making same
Abstract
Microelectronic contact structures are fabricated by separately
forming, then joining together, various components thereof. Each
contact structure has three components: a "post" component, a
"beam" component, and a "tip" component. The resulting contact
structure, mounted to an electronic component, is useful for making
an electrical connection with another electronic component. The
post component can be fabricated on a sacrificial substrate, joined
to the electronic component and its sacrificial substrate removed.
Alternatively, the post component can be formed on the electronic
component. The beam and tip components can each be fabricated on a
sacrificial substrate. The beam component is joined to the post
component and its sacrificial substrate is removed, and the tip
component is joined to the beam component and its sacrificial
substrate is removed.
Inventors: |
Eldridge, Benjamin N.;
(Danville, CA) ; Grube, Gary W.; (Pleasanton,
CA) ; Khandros, Igor Y.; (Orinda, CA) ;
Mathieu, Gaetan L.; (Livermore, CA) |
Correspondence
Address: |
N. KENNETH BURRASTON
P.O. BOX 45898
201 SOUTH MAIN STREET, SUITE 1800
SALT LAKE CITY
UT
84145-0898
US
|
Assignee: |
FormFactor, Inc.
|
Family ID: |
21817623 |
Appl. No.: |
10/692174 |
Filed: |
October 23, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10692174 |
Oct 23, 2003 |
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10202768 |
Jul 25, 2002 |
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10202768 |
Jul 25, 2002 |
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09023859 |
Feb 13, 1998 |
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6520778 |
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Current U.S.
Class: |
439/69 |
Current CPC
Class: |
Y10T 29/49147 20150115;
Y10T 29/49204 20150115; H01L 2924/00013 20130101; H01L 2924/00013
20130101; Y10T 29/49218 20150115; H01L 2224/02335 20130101; Y10T
29/49316 20150115; G01R 1/07314 20130101; H01H 1/0036 20130101;
H01L 2224/13099 20130101 |
Class at
Publication: |
439/069 |
International
Class: |
H01R 012/00 |
Claims
What is claimed is:
1. In combination with an electronic component, a contact
structure, comprising: a post component; a beam component joined to
the post component; and a tip component joined to the beam
component.
2. A contact structure, according to claim 1, wherein: the beam
component is elongate, has a one end and an opposite end; the post
component is joined to the one end of the beam component; and the
tip component is joined to the opposite end of the beam
component.
3. A contact structure, according to claim 1, wherein: the beam
component has a one surface and an opposite surface; the post
component is joined to the one surface of the beam component; and
the tip component is joined to the opposite surface of the beam
component.
4. A contact structure, according to claim 1, wherein: the beam
component is elongate, has a one end, has an opposite end, has a
one surface and has an opposite surface; the post component is
joined to the one end and to the one surface of the beam component;
and the tip component is joined to the opposite end and to the
opposite surface of the beam component.
5. A contact structure, according to claim 1, wherein: the post
component is joined to an electronic component.
6. A contact structure, according to claim 1, further comprising an
electronic component with a terminal, wherein: the post component
is joined to a terminal of the electronic component.
7. A contact structure, according to claim 1, further comprising an
electronic component wherein: the post component is built up upon
the electronic component.
8. A contact structure, according to claim 1, further comprising an
electronic component with a terminal, wherein: the post component
is built up upon a terminal of the electronic component.
9. A contact structure, according to claim 1, wherein: the contact
structure is a spring contact element.
10. An electronic component, according to claim 1, further
comprising a second contact structure according to claim 1 mounted
thereon, wherein: a spacing between the tip components of the two
contact structures is different than a spacing between the post
components of the two contact structures.
11. An electronic component, according to claim 1, further
comprising a second contact structure according to claim 1 mounted
thereon, wherein: the beam component of a one of the two contact
structures is disposed at a different height from a surface of the
electronic component than the beam component of another of the two
contact structures.
12. A method of mounting a microelectronic contact structure to an
electronic component, comprising: providing a post component on an
electronic component; fabricating a beam component; fabricating a
tip component; joining the beam component to the post component;
and joining the tip component to the beam component.
13. Method, according to claim 12, further comprising providing the
post component on the electronic component by: fabricating a the
post component on a sacrificial substrate; joining the post
component to the electronic component; and removing the sacrificial
substrate.
14. Method, according to claim 12, wherein: the beam component is
fabricated on a sacrificial substrate; and further comprising
joining the beam component to the post component by: joining the
beam component to the post component; and removing the sacrificial
substrate.
15. Method, according to claim 12, wherein: the tip component is
fabricated on a sacrificial substrate; and further comprising
joining the tip component to the beam component by: joining the tip
component to the beam component; and removing the sacrificial
substrate.
16. Method, according to claim 12, wherein: the post component is
built up upon the electronic component.
17. Method, according to claim 12, wherein: the beam component is
elongate, has a one end and an opposite end; joining the post
component to the one end of the beam component; and joining the tip
component to the opposite end of the beam component.
18. Method, according to claim 12, wherein: the beam component has
a one surface and an opposite surface; joining the post component
to the one surface of the beam component; and joining the tip
component to the opposite surface of the beam component.
19. Method, according to claim 12, wherein: the beam component is
elongate, has a one end, has an opposite end, has a one surface and
has an opposite surface; joining the post component to the one end
and to the one surface of the beam component; and joining the tip
component to the opposite end and to the opposite surface of the
beam component.
20. Method of mounting two microelectronic contact structures to an
electronic component, comprising, for each microelectronic contact
structure: providing a post component on an electronic component;
fabricating a beam component; fabricating a tip component; joining
the beam component to the post component; and joining the tip
component to the beam component; further comprising: disposing the
beam of a one of the two microelectronic contact structures at a
different height from a surface of the electronic component than
the beam component of another of the two microelectronic contact
structures.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This patent application is a continuation-in-part of
commonly-owned, copending U.S. patent application Ser. No.
08/819,464 filed 17 Mar. 1997 and its counterpart PCT patent
application number US97/08606 filed 15 May 97 (published as
WO97/43653, 20 Nov. 1997), both of which are incorporated by
reference herein.
[0002] This patent application is a continuation-in-part of
commonly-owned, copending U.S. patent application Ser. No.
08/802,054 filed 18 Feb. 1997 and its counterpart PCT patent
application number US97/08271 filed 15 May 97 (published as
WO97/44676, 27 Nov. 1997), both of which are incorporated by
reference herein.
[0003] This patent application is a continuation-in-part of
commonly-owned, copending U.S. patent application Ser. No.
08/852,152 filed 06 May 97 and its counterpart PCT patent
application number US97/08634 filed 15 May 97 (published as
WO97/43654, 20 Nov. 1997), both of which are incorporated by
reference herein.
TECHNICAL FIELD OF THE INVENTION
[0004] The present invention relates to resilient (spring)
electrical contact (interconnection) elements (structures) suitable
for but not limited to effecting pressure connections between
electronic components and, more particularly, to microminiature
spring contacts such as may be used in probing (resiliently and
temporarily contacting) microelectronic components such as active
semiconductor devices.
BACKGROUND OF THE INVENTION
[0005] Commonly-owned U.S. patent application Ser. No. 08/152,812
filed 16 Nov. 1993 (now U.S. Pat. No. 4,576,211, issued 19 Dec.
1995), and its counterpart commonly-owned "divisional" U.S. patent
application Ser. Nos. 08/457,479 filed 01 Jun. 1995 (status:
pending) and 08/570,230 filed 11 Dec. 1995 (status: pending), all
by KHANDROS, disclose methods for making resilient interconnection
elements for microelectronics applications involving mounting an
end of a flexible elongate core element (e.g., wire "stem" or
"skeleton") to a terminal on an electronic component, and coating
the flexible core element and adjacent surface of the terminal with
a "shell" of one or more materials having a predetermined
combination of thickness, yield strength and elastic modulus to
ensure predetermined force-to-deflection characteristics of the
resulting spring contacts. Exemplary materials for the core element
include gold. Exemplary materials for the coating include nickel
and its alloys. The resulting spring contact element is suitably
used to effect pressure, or demountable, connections between two or
more electronic components, including semiconductor devices.
[0006] Commonly owned U.S. patent application Ser. No. 08/340,144
filed 15 Nov. 1994 and its corresponding PCT Patent Application No.
PCT/US94/13373 filed 16 Nov. 1994 (published as WO95/14314, 26 May
95), disclose a number of applications for the aforementioned
spring contact element, and also disclose techniques for
fabricating contact pads at the ends of the spring contact
elements. For example, in FIG. 14 thereof, a plurality of negative
projections or holes, which may be in the form of inverted pyramids
ending in apexes, are formed in the surface of a sacrificial layer
(substrate). These holes are then filled with a contact structure
comprising layers of material such as gold or rhodium and nickel. A
flexible elongate element is mounted to the resulting contact
structure and can be overcoated in the manner described
hereinabove. In a final step, the sacrificial substrate is removed.
The resulting spring contact has a contact pad having controlled
geometry (e.g., sharp points) at its free end.
[0007] Commonly-owned U.S. patent application Ser. No. 08/452,255
filed 26 May 95 (status: pending) and its corresponding PCT Patent
Application No. PCT/US95/14909 filed 13 Nov. 1995 (published as
WO96/17278, 06 Jun. 1996), disclose additional techniques and
metallurgies for fabricating contact tip structures on sacrificial
substrates, as well as techniques for transferring a plurality of
spring contact elements mounted thereto, en masse, to terminals of
an electronic component (see, e.g., FIGS. 11A-11F and 12A-12C
therein).
[0008] Commonly-owned U.S. patent application Ser. No. 08/788/740
filed 24 Jan. 1997 (status: pending) and its corresponding PCT
Patent Application No. PCT/US96/08107 filed 24 May 96 (published as
WO96/37332, 28 Nov. 1996), discloses techniques whereby a plurality
of contact tip structures (see, e.g., #620 in FIG. 6B therein) are
joined to a corresponding plurality of elongate contact elements
(see, e.g., #632 of FIG. 6D therein) which are already mounted to
an electronic component (#630). This patent application also
discloses, for example in FIGS. 7A-7E therein, techniques for
fabricating "elongate" contact tip structures in the form of
cantilevers. The cantilever tip structures can be tapered, between
one end thereof and an opposite end thereof. The cantilever tip
structures of this patent application are suitable for mounting to
already-existing (i.e., previously fabricated) raised
interconnection elements (see, e.g., #730 in FIG. 7F) extending
(e.g., free-standing) from corresponding terminals of an electronic
component (see. e.g., #734 in FIG. 7F).
[0009] Commonly-owned U.S. patent application Ser. No. 08/819,464
filed 17 Mar. 1997 (status: pending) and its corresponding PCT
Patent Application number US97/08606 filed 15 May 97 (published as
WO97/43653, 20 Nov. 1997), incorporated by reference herein,
disclose a number of processes and metallurgies for prefabricating
contact tip structures on sacrificial substrates, for later joining
to ends of spring contact elements, as well as mechanisms for
releasing prefabricated components of spring contact elements from
the sacrificial substrates. Many of the processes, metallurgies and
mechanisms disclosed therein are directly applicable to the methods
and apparatus of the present invention.
[0010] Commonly-owned, copending U.S. patent application Ser. No.
08/802,054 filed 18 Feb. 1997, and its corresponding PCT Patent
Application No. US97/08271 disclose a technique for making
microelectronic contact structures by masking and etching grooves
into a sacrificial substrate (e.g., a silicon wafer), then
depositing one or more layers of metallic material into the
grooves, then transferring the resulting structures onto an
electronic component such as by brazing, then removing the
sacrificial substrate so that the fabricated structures are secured
at one end to the electronic component and have another end for
contacting another electronic component and function as spring
contact elements. The present invention takes the concept a step
further, providing an alternate technique for fabricating such
spring contact elements and mounting them to terminals of
electronic components.
[0011] Commonly-owned, copending U.S. patent application Ser. No.
08/852,152 filed 06 May 97, and its corresponding PCT Patent
Application number US97/08634 filed 15 May 97 disclose a technique
for making microelectronic contact structures by applying a series
of masking layers patterned with openings onto a substrate such as
a semiconductor device, then depositing one or more layers of
metallic material into the openings, then removing the masking
layers. This results in a plurality of spring contact elements
having been fabricated on the substrate at lithographically-defined
locations.
[0012] The present invention addresses and is particularly
well-suited to making interconnections to modern microelectronic
devices having their terminals (bond pads) disposed at a
fine-pitch. The invention is useful for devices with arbitrarily
large pitch, but also is particularly useful for fine pitch. As
used herein, the term "fine-pitch" refers to microelectronic
devices that have their terminals disposed at a spacing of less
than 5 mils, such as 2.5 mils or 65 .mu.m. As will be evident from
the description that follows, this is preferably achieved by taking
advantage of the close tolerances that readily can be realized by
using lithographic rather than mechanical techniques to fabricate
the contact elements.
[0013] An exemplary application for making fine-pitch pressure
connections between electronic components can be found in
commonly-owned U.S. patent application Ser. No. 08/554,902 filed 09
Nov. 95 by ELDRIDGE, GRUBE, KHANDROS and MATHIEU (status: pending)
and its corresponding PCT Patent Application No. PCT/US95/14844
filed 13 Nov. 1995 (published as WO96/15458, 23 May 96) which
disclose a probe card assembly including elongate resilient
(spring) contact elements mounted to a "space transformer"
component. As used herein, a space transformer is a multilayer
interconnection substrate having terminals disposed at a first
pitch on a one surface thereof and having corresponding terminals
disposed at a second pitch on an opposite surface thereof, and is
used to effect "pitch-spreading" from the first pitch to the second
pitch. In use, the free ends (tips) of the elongate spring contact
elements make pressure connections with corresponding terminals on
an electronic component being probed (e.g., tested).
[0014] Another example of an application for fine pitch spring
contact elements can be found in commonly-owned U.S. patent
application Ser. No. 08/784,862 filed 15 Jan. 1997 by KHANDROS and
PEDERSEN (status: pending) and its corresponding PCT Patent
Application No. US97/08604 filed 15 May 97 (published as
WO97/43656, 20 Nov. 1997) which disclose mounting springs on active
semiconductor devices.
SUMMARY OF THE INVENTION
[0015] An object of the present invention is to provide an improved
technique for fabricating microelectronic contact structures, such
as spring contact elements.
[0016] Another object of the invention is to provide a technique
for fabricating microelectronic contact structures, such as spring
contact elements, using processes that are inherently well-suited
to the fine-pitch, close-tolerance world of microelectronics.
[0017] Another object of the invention is to provide a technique
for fabricating microelectronic contact structures, such as spring
contact elements, that are suitable for probing electronic
components such as semiconductor devices, and that is readily
scaleable to probing fine-pitch peripheral interconnect
structures.
[0018] Another object of the invention is to provide a technique
for fabricating microelectronic contact structures, such as spring
contact elements, that are suitable for socketing electronic
components such as semiconductor devices, such as for performing
burn-in on said devices.
[0019] According to the invention, microelectronic contact
structures are fabricated by forming various portions
("components") thereof on a corresponding number of sacrificial
substrates, then joining the portions to an electronic component
and to one another.
[0020] Each contact structure has three portions (components): a
base end portion or "post" component, a middle portion or "beam"
component, and a contact end portion or "tip" component.
[0021] The contact structure is useful for making an electrical
connection with a terminal of another electronic component, whether
by pure pressure connection or by soldering thereto.
[0022] For example, for a plurality of contact structures:
[0023] (a) The post components of a plurality of contact structures
are formed on a one sacrificial substrate, at prescribed spacing
from one another which may, for example, correspond to the terminal
layout of an electronic component. The post components can then be
joined to the terminals (e.g.) of the electronic component.
Alternatively, a post component can be fabricated directly on the
electronic component.
[0024] (b) The beam components of the plurality of contact
structures preferably are elongate, each having two opposite ends
and two opposite surfaces. One or more beam components are formed
on a sacrificial substrate, at prescribed spacing from one another
corresponding to the layout of the post components on the
electronic component. A beam component can then be joined, such as
by one of its ends and by one of its surfaces, to a corresponding
post component. A group of beam components can be joined as a group
to a corresponding group of post components.
[0025] (c) The tip components of the plurality of contact
structures are formed on another sacrificial substrate, at
prescribed spacing from one another, preferably corresponding to
the terminal layout of another electronic component which is to be
contacted by the contact structures. A tip component can then be
joined to a corresponding beam component at a position along the
beam component which is offset from the post component to which the
beam component is joined. The tip component may be joined to an
opposite (from the post component) end of the beam component, and
may be joined to an opposite (from the post component) surface of
the beam component. A group of tip components can be joined as a
group to a corresponding group of beam components.
[0026] In an embodiment of the invention, the post, beam and tip
components of each contact structure are fabricated by applying a
patterned masking layer onto a sacrificial substrate, the masking
layer having openings extending through to the sacrificial
substrate, then depositing one or more layers of metallic material
into the openings. The openings in the masking layer are at
positions whereat it is desired to fabricate the respective
component of the contact structures, and define the geometry
(shape) of the respective component of the contact structures. A
plurality of contact structures may be fabricated in this manner on
the sacrificial substrates, with lithographically-defined
tolerances (e.g., dimensions, spacing, alignment).
[0027] According to an aspect of the invention, a sacrificial
substrate may be provided with a release mechanism which may be a
dissolvable layer such as aluminum or multiple metallic layers,
either of which will permit the components of the contact
structures to be released from the respective sacrificial substrate
upon which they are fabricated.
[0028] An exemplary sacrificial substrate upon which the components
of the contact structures may be fabricated is a silicon wafer, in
which case the process of the present invention advantageously
utilizes the directionally selective etching of silicon (as, for
example, used for micro-machining processes) to create an
electroform which is used to plate up the components of the contact
structures. This approach may optionally employ laser-based
ablation of photoresist, as opposed to lithographic development of
the photoresist, in order to create the high aspect ratio of width
to height which is preferred for fine pitch spacing between the
contact structures.
[0029] The post, beam and tip components of the contact structures
are suitably formed of at least one layer of a metallic material.
In the case of the post components, the metallic material(s) should
preferably have good rigidity (high yield strength) and be suitable
for being joined, such as by brazing or soldering, with respective
ones of the beam components. In the case of the beam components,
the metallic material(s) should be appropriate to permit the
resulting contact structure to function, in use, as a spring
contact element (i.e., exhibit elastic deformation) when force is
applied to its (free) end, and should be suitable for being joined
with respective ones of the post and tip components. In the case of
the tip components, the metallic material(s) should have good
electrical contact characteristics, and should be suitable for
being joined with respective ones of the beam components. All of
the post, beam and tip components should include at least one layer
which is a good conductor of electricity. It is desirable that the
overall contact structure (which may be a spring contact element)
be a good electrical conductor.
[0030] In the main hereinafter, microelectronic contact structures
which are spring contact elements are discussed. However, the
present invention is not limited to contact structures which are
spring contact elements. Contact structures having more, or less,
rigidity than would be required to function usefully as spring
contact elements are within the scope of the present invention.
[0031] An exemplary contact structure formed in this manner has a
length "L" between its base (post) end and its contact (tip) end.
The base end is preferably offset in a first direction from a
central (beam) portion of the contact structure, and the contact
end is preferably offset in an opposite direction from the central
portion. In this manner, the overall contact structure base end is
mounted to a terminal of an electronic component, the beam portion
is offset from the electronic component and its contact end is
further offset, extending well away from the surface of the
electronic component to which it is mounted.
[0032] In one particularly preferred embodiment, the resulting
contact structure is preferably "long and low", having:
[0033] a length "L", as measured from one end to another end;
[0034] a height "H" measured transverse the length in a direction
that is normal (z-axis) to the surface of the sacrificial substrate
(and typically normal to the component to which the contact
structure is ultimately mounted);
[0035] a contact end (tip) portion which is offset in a one
direction (e.g., negative along the z-axis) from a central (beam)
portion of the spring element by a distance "d1"; and
[0036] a base end (post) portion which is offset in one direction
(e.g., positive z-axis) from the central (beam) portion of the
spring element by a distance "d2".
[0037] The beam portion of the contact structure is preferably
tapered from the one (base) end to the other (contact) end thereof,
the contact structure having the following dimensions:
[0038] a width "w1" at its base end as measured parallel to the
surface of the sacrificial substrate and transverse to the
longitudinal axis of the spring element;
[0039] a width "w2" at its contact end as measured parallel to the
surface of the sacrificial substrate and transverse to the
longitudinal axis of the spring element;
[0040] a thickness "t1" at its base end, measured along the z-axis;
and
[0041] a thickness "t2" at its contact end, measured along the
z-axis;
[0042] resulting in:
[0043] a widthwise taper angle ".alpha." (alpha); and
[0044] a thickness taper angle ".beta." (beta).
[0045] The tip portion of the contact structure is also suitably
provided with a projecting tip feature, said tip feature having a
dimension "d3" measured along the z-axis.
[0046] There is thus described herein an exemplary contact
structure suitable for effecting connections between two electronic
components, typically being mounted by its base (post) end to a one
of the two electronic components and effecting a pressure
connection with its contact (tip) end (e.g., by the projecting tip
feature) to an other of the two electronic components, having the
following dimensions (in mils, unless otherwise specified):
1 dimension range preferred L 10-1000 60-100 H 4-40 5-12 d1 3-15 7
.+-. 1 d2 0-15 7 .+-. 1 d3 0.25-5 3 w1 3-20 8-12 w2 1-10 2-8 t1
1-10 2-5 t2 1-10 1-5 .alpha. .sup. 0-30.degree. .sup. 2-6.degree.
.beta. .sup. 0-30.degree. .sup. 0-6.degree.
[0047] These dimensions are illustrative, and are not meant to
limit in any way the scope of the claims. Dimensions outside these
ranges may be useful according to various choices readily made by
one skilled in the art.
[0048] Other objects, features and advantages of the invention will
become apparent in light of the following description thereof.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] Reference will be made in detail to preferred embodiments of
the invention, examples of which are illustrated in the
accompanying drawings. The drawings are intended to be
illustrative, not limiting. Although the invention will be
described in the context of these preferred embodiments, it should
be understood that it is not intended to limit the spirit and scope
of the invention to these particular embodiments. Certain elements
in selected ones of the drawings are illustrated not-to-scale, for
illustrative clarity. Often, similar elements throughout the
drawings are referred to by similar reference numerals. For
example, the element 199 may be similar in many respects to the
element 299 in another figure. Also, often, similar elements are
referred to with similar numbers in a single drawing. For example,
a plurality of similar elements 199 may be referred to as 199a,
199b, 199c, etc.
[0050] FIG. 1A is a side cross-sectional view illustrating a spring
contact element, such as has been disclosed in the aforementioned
U.S. patent application Ser. No. 08/852,152.
[0051] FIG. 1B is a side cross-sectional view of the spring contact
element of FIG. 1A.
[0052] FIG. 1C is a perspective view of the spring contact element
of FIG. 1B.
[0053] FIG. 2A is a side cross-sectional view of an alternate
embodiment of a spring contact element, such as has been disclosed
in the aforementioned U.S. patent application Ser. No.
08/852,152.
[0054] FIG. 2B is a plan view of the spring contact element of FIG.
2A.
[0055] FIG. 2C is a side cross-sectional view of an alternate
embodiment of a spring contact element, similar to that shown in
FIG. 2B.
[0056] FIG. 3A is a cross-sectional view of a spring contact
element, such as has been disclosed in the aforementioned U.S.
patent application Ser. No. 08/802,054 and its counterpart PCT
patent application number US97/08271.
[0057] FIG. 3B is an enlarged cross-sectional view of the spring
contact element of FIG. 3A.
[0058] FIG. 3C is a cross-sectional view of an alternate embodiment
of a spring contact element, similar to that shown in FIG. 3B.
[0059] FIGS. 4A-4B are cross-sectional views illustrating a
technique for mounting a plurality of spring contact elements,
initially resident on a sacrificial substrate, to another component
such as a space transformer component of a probe card assembly,
such as has been disclosed in the aforementioned U.S. patent
application Ser. No. 08/802,054 and its counterpart PCT patent
application number US97/08271.
[0060] FIG. 4C is a cross-sectional view of a plurality of spring
contact elements mounted to a component, such as illustrated in
FIG. 4B, in use, probing (making temporary pressure connections
with) another component such as a semiconductor device.
[0061] FIG. 5A is a cross-sectional view illustrating fabricating
components of a spring contact element, according to the
invention.
[0062] FIG. 5B is a cross-sectional view of a subsequent step
related to FIG. 5A, according to the invention.
[0063] FIG. 5C is a cross-sectional view of a subsequent step
related to FIG. 5B, wherein the components are tip components
(contact tip structures) and are joined to ends of elongate spring
contact elements, such as has been disclosed in the aforementioned
U.S. patent application Ser. No. 08/819,464.
[0064] FIG. 5D is a cross-sectional view of a subsequent step
related to FIG. 5C, according to the invention.
[0065] FIG. 6 is a side cross-sectional view illustrating
fabricating components of spring contact elements on a sacrificial
substrate, according to the invention.
[0066] FIG. 7 is a side cross-sectional view illustrating forming
tip components (contact tip structures) on a sacrificial substrate
and a technique (means) for releasing the tip components from
sacrificial substrate, according to the invention.
[0067] FIG. 8A is a perspective view illustrating a first step in
fabricating a plurality of tip components (contact tip structures)
on a sacrificial substrate, according to the invention.
[0068] FIG. 8B is a side cross-sectional view, taken on the line
8B-8B through FIG. 8A, illustrating another step in fabricating tip
components (contact tip structures) on a sacrificial substrate,
according to the invention.
[0069] FIG. 8C is side cross-sectional view illustrating another
step in fabricating contact tip structures on a sacrificial
substrate, according to the invention.
[0070] FIG. 8D is a side cross-sectional view illustrating a
contact tip structure which has been fabricated on a sacrificial
substrate, such as has been disclosed in the aforementioned U.S.
patent application Ser. No. 08/819,464.
[0071] FIG. 8E is a perspective view of an elongate contact tip
structure joined to an existing interconnection element, such as
has been disclosed in the aforementioned U.S. patent application
Ser. No. 08/819,464.
[0072] FIG. 8F is a side cross-sectional view of an elongate
contact tip structure joined to an existing interconnection
element, such as has been disclosed in the aforementioned U.S.
patent application Ser. No. 08/819,464.
[0073] FIG. 9A is a cross-sectional view illustrating manufacturing
elongate contact tip structures on a sacrificial substrate, such as
has been disclosed in the aforementioned U.S. patent application
Ser. No. 08/819,464.
[0074] FIG. 9B is a perspective view of the elongate contact tip
structure of FIG. 9A.
[0075] FIG. 9C is a side cross-sectional view, illustrating
mounting the elongate contact tip structures of FIGS. 9A and 9B to
an electronic component.
[0076] FIG. 10A is perspective view illustrating forming a post
component of a spring contact structure, according to the
invention.
[0077] FIG. 10B is a side cross-sectional view taken on a line
10B-10B through FIG. 10A, according to the invention.
[0078] FIG. 10C is a side cross-sectional view illustrating a first
step in joining post components to an electronic component,
according to the invention.
[0079] FIG. 10D is a side cross-sectional view illustrating a
further step in joining post components to an electronic component,
according to the invention.
[0080] FIG. 10E is a side cross-sectional view illustrating a final
step in joining post components to an electronic component,
according to the invention.
[0081] FIG. 11A is perspective view illustrating forming a beam
component of a spring contact structure, according to the
invention.
[0082] FIG. 11B is a side cross-sectional view taken on a line
11B-11B through FIG. 11A, according to the invention.
[0083] FIG. 11C is a side cross-sectional view illustrating joining
beam components to post components on an electronic component,
according to the invention.
[0084] FIG. 11D is a side cross-sectional illustrating joining beam
components to post components on an electronic component, according
to the invention.
[0085] FIG. 11E is a side cross-sectional view illustrating joining
beam components to post components on an electronic component,
according to the invention.
[0086] FIG. 12A is perspective view illustrating forming a tip
component of a spring contact structure, according to the
invention.
[0087] FIG. 12B is a side cross-sectional view taken on a line
12B-12B through FIG. 12A, according to the invention.
[0088] FIG. 12C is a perspective cross-sectional view illustrating
the technique for forming a tip component of a spring contact
structure, according to the invention.
[0089] FIG. 12D is a side cross-sectional view illustrating joining
tip components to beam components on an electronic component,
according to the invention.
[0090] FIG. 12E is a side cross-sectional view further illustrating
joining tip components to beam components on an electronic
component, according to the invention.
[0091] FIG. 12F is a side cross-sectional view further illustrating
joining tip components to beam components on an electronic
component, according to the invention.
[0092] FIG. 13A is a side cross-sectional view illustrating
mounting spring contact elements on an electronic component,
according to the invention.
[0093] FIG. 13B is a top plan view of FIG. 13A, according to the
invention.
DETAILED DESCRIPTION OF THE INVENTION
A Spring Contact Element
[0094] FIGS. 1A-1C corresponding to FIGS. 1A-1C of the
aforementioned U.S. Patent Application No. U.S. patent application
Ser. No. 08/852,152 illustrate fabricating a plurality (one of many
shown) of spring contact elements 120 on an electronic component
102. Generally, a number of insulating layers having openings
formed therein are aligned and "seeded" with a layer of conductive
material. A mass of conductive material can then be formed (or
deposited) in the seeded opening(s), such as by electroplating (or
CVD, sputtering, electroless plating, etc.). After the insulating
layers are removed, the masses can function as free-standing spring
contact structures 120 which extend not only vertically above the
surface of the component 102, but also laterally from the location
whereat they are mounted. In this manner, the spring contact
structures are readily engineered to be compliant in both the
Z-axis as well as in the x-y plane (parallel to the surface of the
component).
[0095] FIG. 1A illustrates an exemplary technique for fabricating
one of a plurality of microelectronic contact structures 120 on a
substrate 102. The substrate 102, for example, may be an active
electronic component, including semiconductor devices, including
semiconductor devices resident on a semiconductor wafer (not
shown). More generally, the substrate can be a variety of
materials. This can be a passive device, such as an interposer or
space transformer, or an active device such as a semiconductor
device. The material of the substrate might be ceramic or silicon,
among other choices. In general, a preferred substrate is one which
is amenable to processing under typical semiconductor fabrication
conditions.
[0096] The substrate 102 has a plurality (one of many shown) of
areas 112 on its surface whereat the spring contact elements 120
will be fabricated. In the case of the substrate 102 being an
electronic component (such as a semiconductor device), an area 112
preferably would be a terminal (such as a bond pad) of the
electronic component.
[0097] Generally, a number (three shown) of patterned masking
layers 104, 106 and 108 are applied onto the surface of the
substrate. The layers are patterned to have openings (as shown)
aligned with the area 112, and the openings are sized and shaped so
that an opening in a one layer (e.g., 108, 106) extends further
from the area 112 than an opening in an underlying layer (e.g.,
106, 104, respectively). In other words, the first layer 104 has an
opening which may be directly over the area 112. A portion of the
opening in the second layer 106 is aligned over at least a portion
of the opening in the first layer 104 and, conversely, a portion of
the first layer 104 extends under a portion of the opening in the
second layer 106. Similarly, a portion of the opening in the third
layer 108 is aligned over at least a portion of the opening in the
second layer 106 and, conversely, a portion of the second layer 106
extends under a portion of the opening in the third layer 108. The
bottom portion of a given overall opening is directly over the
selected area 112 and its top portion is elevated from its bottom
portion. In one preferred embodiment, the top portion is laterally
offset from the area 112.
[0098] As discussed in greater detail hereinbelow, and as discussed
in greater detail in the aforementioned U.S. patent application
Ser. No. 08/819,464, a conductive metallic material is deposited
into the opening, and the masking layers are removed, resulting in
a free-standing contact structure having been fabricated directly
upon the substrate with its base end secured to the substrate 102
at the area 112 and its free end extending both above the surface
of the substrate and laterally-displaced from the area 112.
[0099] If required, such as for electroplating, a very thin (e.g.,
4500 .ANG.) "seed" layer of conductive material 114 such as
titanium/tungsten (TiW) may be deposited into the openings. Then, a
mass of conductive metallic material (e.g., nickel) 120 can be
deposited by electroplating into the openings.
[0100] FIGS. 1B and 1C illustrate a resulting spring contact
element 120 having its base end 122 adjacent the area 112, and its
free-end (tip) 124 elevated in the z-axis above the surface of the
substrate 102 as well as laterally offset in the x-axis and y-axis
from the base end 122.
[0101] As best viewed in FIG. 1C, the contact element 120 will
react pressure applied in the z-axis at its tip end 124, as
indicated by the arrow 132, such as would result from making a
temporary pressure electrical connection with a terminal (not
shown) of another electronic component (not shown). Compliance in
the z-axis ensures that contact force (pressure) will be
maintained, and also accommodates non-planarities (if any) between
terminals (not shown) on the other electronic component (not
shown). Such temporary electrical connections are useful for making
temporary connections to the electronic component 102, such as for
performing burn-in and/or testing of the component 102.
[0102] The tip end 124 is also free to move compliantly in the x-
and y-directions, as indicated by the arrows 134 and 136,
respectively. This would be important in the context of joining (by
soldering, or brazing, or with a conductive adhesive) the tip end
124 to a terminal (not shown) of another electronic component (not
shown) which has a different coefficient of thermal expansion than
the substrate (component) 102. Such permanent electrical
connections are useful for assemblies of electronic components,
such as a plurality of memory chips (each of which is represented
by the substrate 102) to another electronic component such as an
interconnection substrate such as a printed circuit board ("PCB";
not shown).
[0103] The plurality of spring contact elements 120 can be
fabricated with very precise dimensions and very precise spacing
from one another. For example, tens of thousands of such spring
contact elements 120 are readily precisely fabricated on a
corresponding number of terminals on semiconductor devices which
are resident on a semiconductor wafer (not shown).
[0104] In this manner, there has been shown a method of fabricating
spring contact elements (120) directly on a substrate (102) such as
an electronic component, such as a semiconductor device which may
be resident on a semiconductor wafer, by applying at least one
layer of masking material (104, 106, 108) on a surface of the
substrate (102) and patterning the masking layer to have openings
extending from areas (112) on the substrate to positions which are
spaced above the surface of the substrate and which also may be
laterally and/or transversely offset from the areas 112); by
optionally seeding (114) the openings; by depositing at least one
layer of a conductive metallic material into the openings; and by
removing the masking material so that the remaining conductive
metallic material forms free-standing contact elements extending
from the surface of the substrate, each contact element having a
base end which is secured to a one of the areas of the substrate
and having a tip end for making an electrical connection to a
terminal of an electronic component.
[0105] The structures (spring contact elements) 120 are
principally, preferably entirely, metallic, and may be formed
(fabricated) as multilayer structures. Suitable materials for the
one or more layers of the contact structures include but are not
limited to:
[0106] nickel, and its alloys;
[0107] copper, cobalt, iron, and their alloys;
[0108] gold (especially hard gold) and silver, both of which
exhibit excellent current-carrying capabilities and good contact
resistivity characteristics;
[0109] elements of the platinum group;
[0110] noble metals;
[0111] semi-noble metals and their alloys, particularly elements of
the palladium group and their alloys; and
[0112] tungsten, molybdenum and other refractory metals and their
alloys. Nickel and nickel alloys are particularly preferred.
[0113] In cases where a solder-like finish is desired, tin, lead,
bismuth, indium and their alloys can also be used.
Another Spring Contact Element
[0114] FIGS. 2A-2C corresponding to FIGS. 3A-3C of the
aforementioned U.S. patent application Ser. No. 08/852,152 are
schematic illustrations of spring contact elements 200 and 250
(compare 120) fabricated according to the techniques of the present
invention.
[0115] The spring contact element 200 of FIGS. 2A and 2B has a base
end portion 202, a contact (tip) end portion 204, a main body
portion 206 therebetween, an overall length "L" and an overall
height "H". As illustrated, the main body portion 206 is offset a
distance "d2" in a one direction from the base end portion 202, and
is offset a distance "d1" in another direction from the contact end
portion 304.
[0116] As best viewed in the top schematic view of FIG. 2B, the
contact element 200 can be provided with a widthwise taper
".alpha." so that it is narrower (width "w2") at its contact end
204 than at its base end 202 (width "w1")
[0117] FIG. 2C is a schematic representation of a similar (to the
contact element 200) spring contact element 250 that has a base end
portion 252 (compare 202), a contact (tip) end portion 254 (compare
204), and a main body portion 256 (compare 206) therebetween. In
this example, the contact element 250 can be provided with a
thickness taper ".beta." so that it is thinner (thickness "t2") at
its contact end 254 than at its base end 252 (thickness "t1")
Exemplary Dimensions
[0118] The spring contact elements of the present invention are
particularly well suited to making interconnections between
microelectronic components. Suitable dimensions for the spring
contact element are (in mils, unless otherwise specified):
2 dimension range preferred L 10-1000 60-100 H 4-40 5-12 d1 3-15 7
.+-. 1 d2 0-15 7 .+-. 1 d3 0.25-5 3 w1 3-20 8-12 w2 1-10 2-8 t1
1-10 2-5 t2 1-10 1-5 .alpha. .sup. 0-30.degree. .sup. 2-6.degree.
.beta. .sup. 0-30.degree. .sup. 0-6.degree.
[0119] These dimensions are illustrative, and are not meant to
limit in any way the scope of the claims. Dimensions outside these
ranges may be useful according to various choices readily made by
one skilled in the art.
[0120] The technique described hereinabove and resulting spring
contact elements 120, 200 and 250 are viable, but somewhat limited
in that:
[0121] (a) it is necessary to apply three masking layers (104, 106,
108), one atop the other, and pattern each masking layer with
openings registering with openings in previously-applied
layers;
[0122] (b) the entire resulting spring contact element is of
uniform composition (e.g., of one or more metallic layers
throughout its construction);
[0123] (c) there is no "tip feature" (described in greater detail
hereinbelow) associated therewith.
Another Spring Contact Element
[0124] FIGS. 3A-3C corresponding to FIGS. 1A, 1D and 1E,
respectively, of the aforementioned U.S. patent application Ser.
No. 08/802,054 and its counterpart PCT patent application number
US97/08271, and illustrate an elongate resilient (spring) contact
element 300 that is suitable for attachment as a free-standing
structure to an electronic component.
[0125] The structure 300 is elongate, has two ends 302 and 304, a
central portion 306 therebetween, and has an overall longitudinal
length of "L" between the two ends. The length "L" is in the range
of 10-1000 mils, such as 40-500 mils or 40-250 mils, preferably
60-100 mils.
[0126] The end 302 is a "base" whereat the contact element 300 will
be mounted to an electronic component (not shown). The end 304 is a
"free-end" (tip) which will effect a pressure connection with
another electronic component (e.g., a device-under-test, not
shown).
[0127] The structure 300 has an overall height of "H". The height
"H" is in the range of 4-40 mils, preferably 5-12 mils. (1
mil=0.001 inches=about 25 microns)
[0128] As best viewed in FIG. 3A, the structure is "stepped". The
base portion 302 is at a first height, the tip 304 is at another
height, and a middle (central) portion 306 is at a third height
which is between the first and second heights. Therefore, the
structure 300 has two "standoff" heights, labeled "d1" and "d2" in
the figure. In other words, the spring contact element 300 has two
"steps", a step up from the contact end 304 to the central body
portion 306, and a further step up from the central body portion
306 to the base end 302.
[0129] In use, the structure is often used as a resilient contact
member to allow a mechanical and electrical connection between a
second electronic device and the substrate upon which the structure
is mounted. When the structure is engaged, a pressure connection
moves the tip 304 closer to the substrate (not shown), thus
diminishing height "H". The distances d1 and d2 can be chosen to
allow displacement of tip 304 by a sufficient amount to provide the
desired contact. The contact force will be influenced by the
resilience of the structure as it resists compression when brought
into contact with the second electronic device. The design and the
resiliency of the central portion will influence how much the
central portion can flex near the tip 304 versus near the base
302.
[0130] The standoff height "d1", which is the "vertical" (as viewed
in FIG. 3A) distance between the tip 304 and the central portion
306, is selected in part to prevent bumping of the structure
(contact element) with a surface of a component being contacted by
the tip end 304.
[0131] In use, the standoff height "d2", which is the "vertical"
(as viewed in FIG. 3A) distance between the base 302 and the
central portion 306, is selected in part to allow the beam (contact
element) to bend and be displaced toward the surface of a substrate
to which the element is attached.
[0132] The dimensions for the standoff heights "d1" and "d2"
are:
[0133] "d1" is in the range of 3-15 mils, preferably approximately
7 mils.+-.1 mil; and
[0134] "d2" is in the range of 0-15 mils, preferably approximately
7 mils.+-.1 mil. In the case of "d2" being 0 mil, the structure
would be substantially planar (without the illustrated step)
between the central portion 306 and the base portion 302.
[0135] In use, the structure 300 is intended to function as a
cantilever beam, and is preferably provided with at least one taper
angle, in a manner such as was discussed with respect to FIGS. 2B
and 2C.
[0136] In contrast to the spring contact structures 120, 200 and
250 described hereinabove, the tip end 304 of the spring contact
structure 300 is preferably provided with an integral protruding
topological "tip feature" 308, for example in the geometric form of
a pyramid, to aid in effecting pressure connection to a terminal of
an electronic component (not shown).
[0137] The spring contact structure 300 is principally, preferably
entirely, metallic, and may be formed (fabricated) as a multilayer
structure, suitably employing, for its layers the materials listed
hereinabove for layers of other contact structures.
[0138] FIG. 3B shows an enlarged view of the contact end 304 of the
contact structure 300. In this enlarged view it can be seen that
the tip feature 308 is suitably quite prominent, projecting a
distance "d3", in the range of 0.25-5 mils, preferably 3 mils, from
the bottom (as viewed) surface of the contact end of the spring
contact element, and is suitably in the geometric shape of a
pyramid, a truncated pyramid, a wedge, a hemisphere, or the
like.
[0139] The resulting contact structure has an overall height "H"
which is approximately the sum of "d1", "d2" (and "d3") plus the
thickness of the central body portion when the contact structure is
not compressed.
[0140] The various dimensions set forth for the spring contact
element 300 are in the ranges set forth hereinabove for the spring
contact elements 200 and 250 (except for the dimension "d3" which
is relevant only to the contact element 300).
[0141] Another dimension is of interest--namely, the width and
length (i.e., footprint) of the overall tip end (304). In instances
where the tip end is expected to make contact with a terminal of an
electronic component which is recessed (e.g., a bond pad of a
semiconductor device which has passivation material surrounding the
bond pad), it may be desirable to ensure that the footprint of the
tip end is sufficiently small to make such contact, for example,
less than 4 mils by 4 mils. It is particularly useful to make the
footprint of the contact end relatively small, for example, 10
microns or even 2 or 3 microns square, to make a penetrating
contact feature which will tend to penetrate miscellaneous
contaminants on the surface of a contact.
[0142] It is desirable that the tip feature 308 is of sufficient
height (d3) to make contact with a terminal, which may be recessed
below the surface of the second electronic component. Generally
speaking, the selection of an appropriate tip end design will be
dictated by the peculiarities of the given application. For
example, for contacting bond pads on silicon devices, the tip end
design illustrated in FIG. 3B would likely be most appropriate. For
contacting C4 bumps, the tip end design illustrated in FIG. 3C
(described hereinbelow) would likely be most appropriate.
[0143] FIG. 3C illustrates an alternate embodiment of a spring
contact structure wherein separate and distinct (discrete) contact
tip structures 328, such as are described in the aforementioned
PCT/US96/08107 can be mounted to the contact end portions 304 of
the spring contact elements, such as by brazing 330 thereto. This
provides the possibility of the contact tip structure 328 having a
different metallurgy, than the spring contact element (300). For
example, the metallurgy of the spring contact element (300) is
suitably targeted at its mechanical (e.g., resilient, spring)
characteristics and its general capability to conduct electricity,
while the metallurgy of a contact tip structure 328 mounted thereto
is appropriately targeted to making superior electrical connection
with a terminal of an electronic component being contacted and, if
needed, can have superior wear-resistance.
[0144] According to an aspect of the invention, processes such as
photolithography are employed to fabricate the spring contact
elements of the present invention with tolerances, both of the
springs themselves and with regard to the relative locations of a
plurality of springs, suitable for use as interconnections in the
context of fine-pitch microelectronics.
Mounting and Contacting Spring Contact Elements
[0145] FIGS. 4A-4C, corresponding to FIGS. 4A-4C of the
aforementioned U.S. patent application Ser. No. 08/802,054 and its
counterpart PCT patent application number US97/08271, illustrate a
technique wherein a plurality (two of many shown) of contact
structures 402 (compare 120, 200, 250, 300) have been fabricated on
a sacrificial substrate 404. The base end portions of the contact
structures 402 are brought into contact with a corresponding
plurality of terminals 406 on an electronic component 408,
whereupon the base end portions are suitably joined by soldering,
brazing or with a conductive adhesive 410 to the terminals 406.
[0146] It is within the scope of this invention that any suitable
technique and/or material for affixing the base end portions of the
contact structures (402) to terminals of an electronic component be
employed, including brazing, welding (e.g., spot welding),
soldering, conductive epoxy, tacking the contact structure in any
suitable manner to the terminal and securely affixing the contact
structure to the terminal by plating (e.g., electroplating), and
the like.
[0147] The sacrificial substrate 404 is then removed, in any
suitable manner, such as by chemical etching or heating), resulting
in an electronic component 408 having a plurality (two of many
shown) of spring contact elements 402 affixed thereto, as
illustrated in FIG. 4B.
[0148] As is evident in FIG. 4B, a plurality of elongate spring
contact elements can be mounted to an electronic component having a
plurality of terminals on a surface thereof. Each spring contact
element has a base end and a contact end opposite the base end, and
is mounted by its base end to a corresponding terminal of the
electronic component. The contact end of each spring contact
element extends above the surface of the electronic component to a
position which is laterally offset from its base end.
[0149] FIG. 4C illustrates an application for the spring contact
elements 420 wherein the spring contact elements have been mounted
in the manner described with respect to FIG. 4B to a space
transformer component (408) of a probe card assembly (not shown) so
that the tip features (compare 308) at their contact ends (compare
304) make pressure connections with terminals 422 of an electronic
component 420 such as a semiconductor device which may or may not
be resident on a semiconductor wafer. As described hereinabove, it
is within the scope of this invention that separate and discrete
contact tip structures (328) be affixed to the contact end portions
of the spring contact elements.
[0150] It is within the scope of this invention that the substrate
(component) to which the structures 402 are mounted, for example
the component 408 illustrated in FIG. 4C is active electronic
components, such as memory devices or ASICs.
[0151] It is also within the scope of the invention, as is
illustrated in FIG. 4C, that the component or substrate to which
the structures (e.g., 402) are mounted can be provided with a
contiguous (as illustrated) or segmented ground plane to control
impedance. Such a ground plane may comprise a plurality of ground
lines 412 aligned directly underneath the structures 402, but
sufficient clearance for the tip of the structure to deflect must
be assured. Alternatively, the ground plane 412 can be covered with
an insulating layer. Another approach would be to dispose ground
plane lines 414 on the surface of the substrate 408 slightly (such
as 1 mil, in the x-axis) offset from directly underneath the
structures 402, and laying parallel to the structure 402.
Multilayer Structures
[0152] FIGS. 5A-5D, corresponding to FIGS. 2A-2D of the
aforementioned U.S. patent application Ser. No. 08/819,464
illustrate an exemplary technique for prefabricating metallic
structures 520 which suitably are components of a microelectronic
contact structure on a sacrificial substrate 502. In this example,
a silicon substrate (wafer) 502 having a top (as viewed) surface is
used as the sacrificial substrate.
[0153] A layer 504 of titanium is deposited (e.g., by sputtering)
onto the top surface of the silicon substrate 502, and suitably has
a thickness of approximately 250 .ANG. (1 .ANG.=0.1 nm=10.sup.-10
m). A layer 506 of aluminum is deposited (e.g., by sputtering) atop
the titanium layer 504, and suitably has a thickness of
approximately 20,000 .ANG.. The titanium layer 504 is optional and
serves as an adhesion layer for the aluminum layer 506. A layer 508
of copper is deposited (e.g., by sputtering) atop the aluminum
layer 506, and suitably has a thickness of approximately 5,000
.ANG..
[0154] A layer 510 of masking material (e.g., photoresist) is
deposited atop the copper layer 508, and suitably has a thickness
of approximately 2 mils. The masking layer 510 is processed in any
suitable manner to have a plurality (three of many shown) of holes
(openings) 512 extending through the photoresist layer 510 to the
underlying copper layer 508. For example, each hole 512 may be 6
mils in diameter, and the holes 512 may be arranged at a pitch
(center-to-center) of 10 mils. The sacrificial substrate 502 has,
in this manner, been prepared for fabricating a plurality of
contact tip structures at what are "lithographically-defined- "
locations on the sacrificial substrate 502, within the holes 512.
Exemplary metallic structures 520 may be formed, as follows.
[0155] A layer 514 of nickel is deposited, such as by plating,
within the holes 512, onto the copper layer 508, and suitably has a
thickness of approximately 1.0-1.5 mils. Optionally, a thin layer
(not shown) of a noble metal such as rhodium can be deposited onto
the copper layer 508 prior to depositing the nickel. Next, a layer
516 of gold is deposited, such as by plating, onto the nickel 514.
The multilayer structure of nickel and gold (and, optionally,
rhodium) will serve as a pre-fabricated metallic structure suitable
for use as one or more of the components of multipart, assembled
spring contact elements which are described in greater detail
hereinbelow.
[0156] Next, as illustrated in FIG. 5B, the photoresist 510 is
stripped away (using any suitable solvent), leaving a plurality of
pre-fabricated metallic structures 520 sitting atop the copper
layer 508. Next, the exposed (i.e., not covered by contact tip
structures 520) portion of the copper layer 508 is subjected to a
quick etch process, thereby exposing the aluminum layer 506. As
will be evident, aluminum is useful in subsequent steps, since
aluminum is substantially non-wettable with respect to most solder
and braze materials.
[0157] It bears mention that it is preferred to pattern the
photoresist with additional holes (not shown, comparable to 512)
within which "ersatz" metallic structures 522 may be fabricated in
the same process steps employed to fabricate the actual metallic
structures 520. These ersatz structures 522 will serve to
uniformize the aforementioned plating steps (514, 516) in a manner
that is well known and understood, by reducing abrupt gradients
(non-uniformities) from manifesting themselves across the surface
being plated. Such structures (522) are typically referred to in
the field of plating as "robbers".
[0158] In this manner, a plurality of metallic structures 520 have
successfully been pre-fabricated on a sacrificial substrate 502,
awaiting subsequent joining to terminals of electronic components
or to other metallic structures. Optionally, as part of the
pre-fabrication of metallic structures (alternatively, immediately
prior to joining the metallic structures 520 to terminals or other
metallic structures, solder or brazing paste ("joining material")
524 is deposited onto the top (as viewed) surfaces of the metallic
structures 520. (There is no need to deposit the paste onto the
tops of the ersatz structures 522). This is implemented in any
suitable manner, such as with a stainless steel screen or stencil
or by automated dispensing of solder paste, as is known in the art.
A typical paste (joining material) 524 would contain gold-tin alloy
(in a flux matrix) exhibiting, for example, 1 mil spheres
(balls).
[0159] The metallic structures 520, as fabricated upon and resident
upon a sacrificial substrate 502, constitute a product in and of
themselves.
[0160] As described in the aforementioned U.S. patent application
Ser. No. 08/819,464, the metallic structures 520 may be contact tip
structures suitable for joining to ends of free-standing resilient
contact structures resident on an electronic component, in which
case the sacrificial substrate 502 with contact tip structures 520
resident thereon is brought to bear upon tips (free ends) of
exemplary elongate interconnection elements extending from a
substrate which may be an electronic component.
[0161] As shown in FIG. 5C, the contact tip structures 520 (only
two contact tip structures are shown in the view of FIG. 5D, for
illustrative clarity) are aligned with the tips (distal ends) of
interconnection elements 552 extending from a surface of an
electronic component 554, using standard flip-chip techniques
(e.g., split prism), and the assembly is passed through a brazing
furnace (not shown) to reflow the joining material 524, thereby
permanently joining (e.g., brazing) the prefabricated contact tip
structures 520 to the ends of the interconnection elements 532.
[0162] During the reflow process, the exposed aluminum layer (506),
being non-wettable, prevents solder (i.e., braze) from flowing
between the contact tip structures 520, i.e., prevents solder
bridges from forming between adjacent contact tip structures.
[0163] In addition to this anti-wetting function of the aluminum
layer 506, the aluminum layer 506 also serves to provide a release
mechanism. Using a suitable etchant, the aluminum is preferentially
(to the other materials of the assembly) etched away, and the
silicon sacrificial substrate 502 simply "pops" off, resulting in a
substrate or electronic component 554 having "tipped"
interconnection elements 552, each having a prefabricated tip
structure 520, as illustrated in FIG. 5D. (Note that the joining
material 524 has reflowed as "fillets" 525 on end portions of the
interconnection elements 552.)
[0164] In a final step of the process, the residual copper (508) is
etched away, leaving the contact tip structures 520 with nickel (or
rhodium, as discussed hereinabove) exposed for making reliable
electrical pressure connections to terminals (not shown) of other
electronic components (not shown).
[0165] It is within the scope of the invention that the brazing
(soldering) paste (524) is omitted, and in its stead, alternating
layers of gold and tin in a eutectic ratio are plated onto the
interconnection elements (552) prior to mounting the contact tip
structures (520) thereto. In a similar manner, eutectic joining
layers can be plated onto the contact tip structures (520) prior to
joining with the interconnection elements (552).
[0166] Since the contact tip structures (520) are readily
fabricated to be coplanar and of uniform thickness, the resulting
"tipped" interconnection elements (FIG. 5D) will have tips (i.e.,
the exposed surfaces of the contact tip structures) which are
substantially coplanar. The electronic component (e.g., 554) to
which the interconnection elements (e.g., 552) are mounted may be
an ASIC, a microprocessor, a component (e.g., space transformer
component) of a probe card assembly, and the like.
A Multilayer Structure and a Release Mechanism
[0167] FIG. 6 corresponds to FIG. 4A of the aforementioned U.S.
patent application Ser. No. 08/819,464 and illustrates a useful
(e.g., preferred) technique for forming a multilayer metallic
component for a spring contact structure in (or on) a sacrificial
substrate, in the following manner, using a thin aluminum layer
(foil) 600 as the sacrificial substrate:
[0168] provide a temporary backing 602, such as a plastic sheet,
for the foil 600, to increase the structural integrity of the foil
(this backing layer 602 can also act as a plating
barrier/mask);
[0169] pattern the face (top, as viewed) of the foil 600 with a
thin (approximately 3 mil) layer of photoresist 604, or the like,
leaving (or creating) openings 616 at locations whereat it is
desired to form multilayer metallic components of spring contact
structures;
[0170] deposit (such as by plating) a thin (approximately 100
microinch (.mu.")) layer 606 of hard gold onto the foil 600, within
the openings 616 in the photoresist 604;
[0171] deposit (such as by plating) a very thin (approximately 5-10
.mu.") layer ("strike") of copper 608 onto the layer of hard gold
(it should be understood that such a copper strike is useful but
optional, and is provided principally to assist in subsequent
plating of the previous gold layer 606);
[0172] deposit (such as by plating) a relatively thick
(approximately 2 mil) layer 610 of nickel onto the copper strike
608 (or, if there is not copper strike, onto the layer 606 of hard
gold); and
[0173] deposit (such as by plating) a thin (approximately 100
.mu.") layer 612 of soft gold onto the nickel.
[0174] This results in a multilayer structure 620 (compare 520),
which is readily joined to either a terminal of an electronic
component (not shown) or to another component of a spring contact
structure (not shown). The multilayer structure 620 has, as its
principal layers, a hard gold surface (606) for contacting (e.g.,
making pressure connections to) terminals of electronic components
(not shown) making the structure 620 particularly useful as a tip
component of a spring contact element, a nickel layer (610)
providing strength, and a soft gold layer (612) which is readily
bonded to (joinable to) a terminal of an electronic component or to
another component of a spring contact structure.
[0175] Regarding depositing the materials for the structure 620
into the openings 616 of the masking material 604 atop the
sacrificial substrate, it should be noted that the sacrificial
substrate itself (e.g., 600), or one or more of the blanket layers
deposited thereon serve to electrically connect the openings to one
another, thereby facilitating the use of electroplating processes
to deposit the multiple metallic layers of the structure 620.
[0176] In use, the structures 620 can be joined to terminals of
electronic components or to other structures in the manner(s)
described with respect to FIGS. 4A, 5C and 5D, and the aluminum
sacrificial substrate 600 can be removed by means of chemical
etching (e.g., with potassium-hydroxide).
Another Multilayer Structure and another Release Mechanism
[0177] FIG. 7 corresponds to FIG. 4B of the aforementioned U.S.
patent application Ser. No. 08/819,464 and illustrates another
technique for making components of microelectronic contact
structures and releasing them from the sacrificial substrate upon
which they are formed. The technique is not dependent on chemical
etching (compare FIG. 6) to release the metallic structures from
the sacrificial substrate.
[0178] As mentioned hereinabove, a "plain" (i.e., no active devices
resident thereupon) silicon wafer can be used as the sacrificial
substrate upon which the post/beam/tip components of spring contact
elements of the present invention may be fabricated. An exemplary
metallurgy is set forth hereinabove (FIG. 6), wherein by using a
suitable chemical selective etching process, the components of
spring contact elements can be released from the sacrificial
substrate.
[0179] It is within the scope of this invention that an appropriate
metallurgy in conjunction with heat can be used to release the
components of the spring contact elements from the sacrificial
substrate, rather than by using chemical etching. For example, as
illustrated by FIG. 7:
[0180] Step 1. Etch a pit (one of one or more shown) 702 into a
silicon (sacrificial) substrate 704 at a location (one of several
shown) whereat it is desired to have a topological feature on a
contact tip structure. As discussed hereinbelow, etching of silicon
can be self-limiting.
[0181] Step 2. Apply a patterned masking layer 706 (e.g.,
photoresist) onto the surface of the silicon (sacrificial)
substrate 704. An opening 708 in the masking layer is at a
corresponding location where a corresponding tip component 720 will
be fabricated.
[0182] Step 3. Deposit (such as by sputtering) a thin layer 710 of
a non-wettable (as will be evident) material such as tungsten (or
titanium-tungsten) onto the substrate, within the opening 708 of
the masking layer 706.
[0183] Step 4. Deposit (such as by sputtering) a thin layer 712 of
a non-wetting material such as plateable lead (or indium) onto the
thin tungsten layer, within the opening 708 of the masking layer
706.
[0184] Step 5. Fabricate a tip component 720 having one or more
layers within the opening 708 of the masking layer 706, in the
manner described hereinabove (e.g., with respect to FIG. 6).
[0185] Step 6. Reflow (using heat) a tip component 720 onto an end
of a beam component (not shown) in the manner described
hereinabove. During reflow, the thin layer 712 will melt and ball
up. For example, tungsten (710) is not wettable with respect to
lead (712). This will cause the tip component 720 to be released
from the sacrificial substrate 704.
[0186] Optionally, a second layer of non-wettable material (e.g.,
tungsten) can be applied over the layer 712, between layer 712 and
tip component 720. Said material will become part of the resulting
contact tip structure, unless it is removed (e.g., by etching). In
some cases, lead will not ball up (e.g., lead tends to wet nickel),
in which cases it may be desired to deposit additional layers such
as lead, then tungsten, then lead, to ensure proper release of the
contact tip structures from the sacrificial substrate.
[0187] Optionally, another layer of material which will ball up
when heated (e.g., lead, indium) can be applied over the second
layer of non-wettable material (e.g., tungsten). Any residual lead
on the surface of the resulting contact tip structure is readily
removed, or may be left in place. Alternatively, a layer of a
"barrier" material can be deposited between the second layer of
material which will ball up and the first layer (e.g., rhodium) of
the resulting tip component 720. The "barrier" material may be
tungsten, silicon nitride, molybdenum, or the like.
Another Multilayer Structure
[0188] FIGS. 8A-8F correspond to FIGS. 5A-5F of the aforementioned
U.S. patent application Ser. No. 08/819,464 and illustrate a
technique for forming metallic structures having pyramid or
truncated pyramid tip features on a sacrificial substrate which is
a silicon wafer.
[0189] FIG. 8A illustrates a first step in the technique, wherein a
layer 804 of masking material, such as photoresist, is applied to
the surface of the silicon substrate 802, and is patterned to have
a plurality (two of many shown) of openings 806 extending to the
surface of the silicon substrate 802. The openings 806 are
preferably square, measuring approximately 1-4 mils, such as 2.5
mils on a side. However, the openings may be rectangular, or may
have other geometric shapes.
[0190] Next, as illustrated in FIG. 8B, the silicon substrate 802
is etched to form a like plurality (one of many shown) of
pyramid-shaped depressions 808 in the silicon substrate 802. Such
etching of silicon will tend to be self-limiting, as the etching
proceeds along the crystal plane at 54.74.degree. for (100)
silicon. In other words, the depression will extend to a depth
which is defined (dictated) by the size of the opening 806 and the
nature of the silicon substrate 802. For example, with a square
opening 2.5 mils per side, the depth of the depression will be
approximately 2 mils. Ultimately, depression 808 will become a
contact feature integrally formed upon the resulting contact tip
structure to be formed on the silicon substrate. This is preferably
a photolithographic process, so that the size and spacing of the
opening 806 and feature 808 will be extremely precise. Tolerances
of microns (10.sup.-6 meters) are readily attained.
[0191] Next, as illustrated in FIG. 8C, the masking material 804 is
removed, and a new masking layer 814 (compare 804), such as
photoresist, is applied to the surface of the silicon substrate 802
and is patterned to have a plurality (one of many shown) of
openings 816 (compare 806) extending to the surface of the silicon
substrate 802. The openings 816 are larger than the openings 806,
and are generally aligned therewith. (A typical opening 816 is over
a depression 808.) An exemplary opening 816 is a rectangle suitably
measuring approximately 7 mils (across the page, as shown) by 8-30
mils (into the page, as shown). Ultimately, an opening 816 will be
filled with conductive material forming the body of a contact tip
structure, being pre-fabricated on the sacrificial substrate 802.
This is also preferably a photolithographic process, but the size
and spacing of these openings 816 need not be as precise as
previous openings 806. Tolerances on the order of up to 1 mil
(0.001 inch) are generally acceptable.
[0192] Next, as illustrated by FIG. 8C, a multilayer contact tip
structure 820 is built up within the opening 816, with a
pyramid-shaped tip feature 830 extending from a surface thereof. In
this example, the multilayer buildup is suitably:
[0193] first deposit (apply) a release mechanism 822 such as has
been described hereinabove (e.g., a multilayer buildup of
lead/tungsten/lead);
[0194] then deposit a relatively thin layer 824 of rhodium or
tungsten (or ruthenium, or iridium, or hard nickel or cobalt or
their alloys, or tungsten carbide), such as 0.1-1.0 mils thick;
[0195] then deposit a relatively thick layer 826 of nickel, cobalt
or their alloys;
[0196] finally deposit a relatively thin layer 828 of soft gold,
which is readily brazed to.
[0197] In this manner, a plurality of elongate contact tip
structures 820 can be fabricated, each having a projecting
pyramid-shaped contact (tip) feature 830 projecting from a surface
thereof. It is this projecting contact feature that is intended to
make the actual contact with a terminal (not shown) of an
electronic component (not shown)(see FIG. 4C).
[0198] As shown in FIG. 8D (and evident in FIGS. 8C, 8E and 8F),
the pyramid-shaped contact feature 830 is suitably polished
(abraded) off, preferably at a level indicated by the dashed line
834, which will configure the pyramid-shaped feature as a truncated
pyramid-shaped feature. The relatively small flat end shape (e.g.,
a square measuring a few tenths of a mil on a side), rather than a
truly pointed end shape, will tend to be sufficiently "sharp" to
make reliable pressure connections with terminals (not shown) of
electronic components (not shown). This configuration will tend to
wear better than a truly pointed feature for making repeated
pressure connections to a large number of electronic components,
such as would be expected in an application of the tipped
interconnection elements of the present invention for probing
(e.g., testing silicon device wafers).
[0199] Another advantage of polishing off the point of the contact
feature 830 is that the second layer of the multilayer buildup can
be exposed for making contact with a terminal (not shown) of an
electronic component (not shown). For example, this layer can be of
a material with superior electrical characteristics, such as
rhodium. Or, it can be a material with superior wear
characteristics, such as titanium-tungsten. One preferred material
is palladium alloyed with cobalt. Other palladium alloys also are
preferred.
[0200] FIG. 8E illustrates the elongate contact tip structure 820
of the present invention joined to an end of an elongate
interconnection element 840. FIG. 8F illustrates a plurality of
elongate contact tip structures 820 of the present invention, each
joined to a contact bump 832 of a membrane probe 834. In these
exemplary applications, the contact tip structures 820 having
projecting topological contact features 830 provide:
[0201] a distinct metallurgy;
[0202] a distinct contact topology (topography);
[0203] tightly controlled positional tolerances; and
[0204] if desired, a degree of pitch spreading.
[0205] Regarding effecting pitch spreading, it can be seen in FIG.
8F that the contact tip structures can be arranged so that the
spacing between the contact features 830 is greater (as shown) or
lesser (not shown) than the spacing of the contact balls 832.
[0206] Generally, in use, the "tipped" interconnection element is
mounted to a first electronic component, and the apex (top, as
viewed in FIGS. 8E and 8F) portion of the pyramid effects an
electrical connection to a terminal (not shown) of a second
electronic component (not shown).
[0207] As mentioned above, by prefabricating contact tip structures
(e.g., 820) with topological contact features (e.g., 830) on a
surface thereof, it is possible to achieve extremely high
positional precision for the pressure connection to be made,
without requiring a comparable degree of precision in either the
body portion of the contact tip structure or the interconnection
element to which it is joined.
Joining Components Together
[0208] There have been described hereinabove some techniques for
joining prefabricated contact tip structures (e.g., 328, 520, 820
to ends of spring contact elements, elongate interconnection
elements or contact bumps membrane probe (e.g., 304, 552, 840,
832).
[0209] FIGS. 9A-9C correspond to FIGS. 7C, 7D and 7F, respectively,
of the aforementioned U.S. patent application Ser. No. 08/819,464
and illustrate another embodiment of making a contact structure and
joining it to an electronic component.
[0210] FIGS. 9A-9C illustrate a technique for fabricating contact
tip structures which are elongate and which, in use, will function
as cantilever (plated cantilevered beam) spring contact elements,
and mounting same to terminals of electronic components. These
techniques are particularly well suited to ultimately mounting
spring contact elements to electronic components such as
semiconductor devices, space transformer substrates of probe card
assemblies, and the like.
[0211] FIG. 9A illustrates a sacrificial substrate 902 such as a
silicon wafer, into a surface of which one or more trenches 904 are
etched. The trench 904 is illustrative of a surface texture
`template` for the contact tip structure 920 which will be
fabricated on the sacrificial substrate 902. The layout (spacing
and arrangement) of the trenches 904 can be derived from (e.g.
replicate or "mirror") the bond pad layout of a semiconductor die
(not shown) which is ultimately (in use) intended to be contacted
(e.g., probed). For example, the trenches 904 can be arranged in a
row, single file, down the center of the sacrificial substrate.
Many memory chips, for example, are fabricated with a central row
of bond pads ("lead on center" or LOC).
[0212] A hard "field" layer 906 has been deposited upon the surface
of the sacrificial substrate 902, including into trench 904.
Another layer 908, such as of a plateable material, can optionally
be deposited over the field layer 906, if the field layer is of a
material which is not amenable to plating such as
tungsten-silicide, tungsten, or diamond. (If, as will be evident
from the discussion hereinbelow, the layer 906 is difficult to
remove, it may be applied by selective deposition (e.g., patterning
through a mask), to avoid such removal.)
[0213] A masking material 910, such as photoresist, is applied to
define an opening 916 for the fabrication of plated cantilever tip
structure 920. The opening 916 in the masking layer 910 extends to
cover the trench 904. Next, a relatively thick (e.g., 1-3 mils)
layer 912 of a spring alloy material (such as nickel and its
alloys) is optionally deposited (such as by plating), over which a
layer 914 of material such as soft gold is deposited which is
amenable to brazing or soldering, in the event that the spring
alloy is not easy to bond, solder or braze to. The spring alloy
layer 912 is deposited by any suitable means such as plating,
sputtering or CVD. Another preferred spring alloy is palladium and
its alloys, particularly palladium-cobalt.
[0214] Next, as shown in FIG. 9B, the masking material 910 is
stripped (removed), along with that portion of the layers (906 and
908) which underlie the masking material 910, resulting in an
elongate contact tip structure 920 having been fabricated upon the
sacrificial substrate 902. Each elongate contact tip structure 920
has a tip portion 922 (directly over a corresponding one of the
trenches 904), a base portion 924, and an intermediate portion 926
between the tip and base portions 922 and 924.
[0215] A plurality of such structures 920 may be staggered
(oriented left-right-left-right), so that although their tip
portions (922) are all aligned in a row (corresponding, e.g., to a
central row of bond pads on a semiconductor device), their base
portions 924 are oriented opposite one another. In this manner, the
spacing between the base portions 924 of the contact tip structures
920 is at a greater (coarser) pitch (spacing) than the tip portions
922.
[0216] As mentioned hereinabove with respect to the spring contact
structures 200 and 250 is that the intermediate portion 926 can be
tapered, from narrowest at the (contact) tip portion 922 to widest
at the base portion 924. This feature provides for controllable,
determinate amount of deflection of the tip portion 922 when the
base portion 924 is rigidly mounted to a terminal of an electronic
component such as a space transformer of a probe card assembly or a
bond pad of a semiconductor device. Generally, deflection will be
localized at or near the tip end of each contact tip structure. The
mechanical design of springs in generally well known in the art,
including shape, taper, bending momentum and spring rate.
[0217] FIG. 9C illustrates the mounting of a cantilever tip
structure 920 to a rigid "pedestal" 930 extending (e.g.,
free-standing) from a corresponding terminal (one of many shown)
932 of an electronic component 934. Generally, the function of the
pedestal 930 is simply to elevate the cantilever tip structure 920
in the z-axis, above the surface of the component 934, so that
there is room for the tip end 922 to deflect (downwards, as viewed)
when making a pressure connection to a terminal (not shown) of an
electronic component (not shown). It is within the scope of this
invention that the pedestal 930 itself may be resilient, in which
case the cantilever tip structure 920 may or may not also be
resilient, as desired for a specific application (use).
[0218] As illustrated, a pre-fabricated cantilever tip structure
920 is mounted by its base portion 924 to an end (top, as shown) of
the pedestal 930, mounted in any suitable manner such as by brazing
or soldering. Here, another advantage of the base portion being the
widest portion of the cantilever tip structure 920 is evident, the
large base portion of the elongate contact tip structure providing
a relatively large surface area for performing such soldering or
brazing (shown by the fillet structure 936), affording the
opportunity to securely join the base of the elongate contact
structure to the pedestal.
[0219] It is within the scope of this invention that the pedestal
930 can be any free-standing interconnection element including, but
not limited to, a composite interconnection element, and
specifically including a contact bump of a probe membrane (in which
case the electronic component 934 would be a probe membrane) as
well as a tungsten needle of conventional probe card.
[0220] As best viewed in FIG. 9C, the tip portion 922 of the
cantilever tip structure 920 is provided with a raised tip feature
940 which, in use, effects the actual pressure connection to the
terminal (not shown) of the electronic component (not shown). The
shape and size of this feature 940 is controlled by the shape and
size of the trench 904 (see FIG. 9A).
[0221] In any cantilever beam arrangement, it is preferred that a
one end of the cantilever be "fixed" and the other end "movable".
In this manner, bending moments are readily calculated. Hence, it
is evident that the pedestal (930) is preferably as rigid as
possible. In the case of the elongate contact structure (920) being
joined to a contact bump on a membrane probe, much resilience
and/or compliance will be provided by the membrane (934), per
se.
A Three-Piece Microelectronic Contact Structure
[0222] According to the invention, a microelectronic contact
structure similar in many regards to the contact structures and
spring contact elements and components thereof described
hereinabove can be fabricated by joining together three components,
each component preferably having been fabricated on a distinct
sacrificial substrate, after which the components are joined to an
electronic component and to one another. Each contact structure has
three components: a "post" component for joining to an electronic
component, a "beam" component for joining to the post component,
and a "tip" component for joining to the beam component and adapted
in use to make an electrical connection with a terminal of another
electronic component. In one preferred embodiment, the post is
formed directly one the electronic component rather than on a
sacrificial substrate.
Making Post Components
[0223] FIGS. 10A and 10B illustrate a technique for fabricating a
plurality (two of many shown) of post components 1020 for
microelectronic contact structures on a sacrificial substrate 1002.
In FIG. 10A, which is similar to FIG. 8A, a plurality of openings
1012 (compare 806) are formed in a layer of masking material 1010
which is disposed on a surface of a sacrificial substrate 1002
(compare 802). Preferably, a release mechanism 1004 is disposed
between the sacrificial substrate 1002 and the masking layer 1010.
The release mechanism 1004 is any of the release mechanisms
described hereinabove, such as the multiple layers 504, 506 and 508
shown and described with respect to FIG. 5A. However, the present
invention is not limited to a particular release mechanism. As
shown in FIG. 10B, the openings 1012 in the masking layer 1010 are
filled, using any suitable process, with one or more layers of
metallic material, such as one of the multilayer buildups for
components of spring contact elements described hereinabove,
resulting in a post components 1020 for spring contact
elements.
Joining Post Components to Terminals
[0224] In a next step of the process, illustrated in FIG. 10C, the
masking material 1010 is removed and a joining material such as
solder paste 1024 or the like is applied to the exposed (top, as
viewed) surfaces of the post components 1020. Compare FIG. 5B. The
post components 1020, resident on the sacrificial substrate 1002,
with or without the masking material 1010, and preferably prior to
applying the solder paste 1024, constitute an interim product which
may be warehoused for future use.
[0225] In a next step of the process, shown in FIG. 10D, the
sacrificial substrate 1002 with post components 1020 resident
thereon and prepared with solder paste 1024 is brought into contact
with an electronic component 1030 which has a plurality (two of
many shown) of terminals 1032 on a surface (top, as viewed)
thereof. The layout of terminals 1032 on the electronic component
1030 `mirrors` the layout of post components 1020 on the
sacrificial substrate 1002, and vice-versa. The terminals and
corresponding post components are aligned. Then, by applying heat,
the solder paste 1024 is reflowed so that the post components 1020
become joined to the terminals 1032 of the electronic component
1030. With a suitable heat-release mechanism, such as has been
described hereinabove, the sacrificial substrate 1002 will release
the post components 1020 during the solder reflow heating step.
Else, as described hereinabove, the sacrificial substrate 1002 can
chemically be caused to release from the post components 1020.
[0226] The end result of the process is that a plurality of post
components 1020 has been joined to a corresponding plurality of
terminals 1032 on an electronic component, as illustrated in FIG.
10E. Compare the joining of contact tip structures 520 and 920 to
the interconnection element 552, 932 of FIGS. 5D and 9C,
respectively.
[0227] These post components 1020 will serve as base portions
(compare 122, 202, 302) of spring contact elements (compare 120,
200, 300) and establish a standoff distance "d2" (compare FIGS. 2A
and 3A) between the surface of the electronic component 1030 and a
main body portion (compare 206, 306) of a resulting spring contact
element in the manner described hereinabove with respect to FIGS.
2A and 3A.
[0228] In this and the following examples of joining components of
spring contact elements to terminals of electronic components and
to one another, the descriptions proceed in terms of solder paste
being the joining material and are illustrated prior to reflow as
circles, and after reflow in cross-hatch.
[0229] As an alternative to fabricating the post components on a
sacrificial substrate, then joining them to terminals of an
electronic component, the post components for the microelectronic
contact structures of the present invention can be built up
directly upon the terminals of the electronic components, by
applying a suitable masking layer on the component, patterning the
masking layer with openings, and depositing metallic material into
the openings, as described hereinabove. See Figure A and the
corresponding discussion.
[0230] Also, it is within the scope of this invention that the post
components can be joined to (or built-up upon) the electronic
component at locations other than directly on terminals thereof.
Such "remotely-located" post components may be associated with and
electrically-connected to corresponding ones of the terminals by
conductive traces upon the electronic component.
Making Beam Components
[0231] FIGS. 11A and 11B illustrate fabricating a plurality (two of
many shown) of beam components 1120 for microelectronic contact
structures on a sacrificial substrate 1102. In FIG. 11A, which is
similar to FIG. 10A, a plurality of openings 1112 (compare 1012)
are formed in a layer of masking material 1110 (compare 1010) which
is disposed on a surface of a sacrificial substrate 1102 (compare
1002). Preferably, a release mechanism 1104 (compare 1004) is
disposed between the sacrificial substrate 1102 and the masking
layer 1110. The release mechanism 1104 preferably can be any of the
release mechanisms described hereinabove.
[0232] For making a beam component 1120, an opening 1112 may be
elongate, having a one end 1112a and an opposite end 1112b which
will correspond to the one end 1120a and opposite end 1120b of the
beam component 1120 formed therein. As shown, the one end 1112a is
somewhat wider than the opposite end 112b of the opening 1112 and,
as will be seen, the one end 1120a of the resulting beam component
1120 will likewise be wider than the opposite end 1120b of the beam
component 1120 formed therein, in a manner similar to that
described hereinabove with respect to the middle portions 206 and
306 of the spring contact elements 200 and 300, respectively. Note
that other shapes suitable for making a beam, particularly a
resilient beam, are known or within the skill in the art.
[0233] As shown in FIG. 11B, the openings 1112 in the masking layer
1110 are filled, using any suitable process, with one or more
layers of metallic material, such as one of the multilayer buildups
for components of spring contact elements described hereinabove,
resulting in a plurality of beam components 1120 for spring contact
elements.
Joining Beam Components to Post Components
[0234] In a next step of the process 1100, shown in FIG. 11C, the
masking material 1110 is removed and a joining material such as
solder paste 1124 or the like is applied to a portion of the
exposed (top, as viewed) surfaces of the beam components 1120.
Compare FIG. 5B. The beam components 1120, resident on the
sacrificial substrate 1102, with or without the masking material
1110, and preferably prior to applying the solder paste 1124,
constitute an interim product which may be warehoused for future
use.
[0235] In a next step of the process, shown in FIG. 11D, the
sacrificial substrate 1102 with beam components 1120 resident
thereon and prepared with solder paste 1124 is brought into contact
with a top (as viewed) surface of the post components 1020 which
previously were joined to the terminals 1032 of the electronic
component 1030. The layout of the one ends 1120a of the beam
components 1120 `mirrors` the layout of the post components 1020 on
the sacrificial substrate 1002, and vice-versa. Then, by applying
heat, the solder paste 1024 is reflowed so that the beam components
1120 are joined to the post components 1020. With a suitable
heat-release mechanism, such as has been described hereinabove, the
sacrificial substrate 1102 will release the beam components 1020
during the solder reflow heating step. Else, as described
hereinabove, the sacrificial substrate 1102 can chemically be
caused to release from the beam components 1120.
[0236] The end result of the process 1100 is that a plurality of
elongate cantilever-like beam components 1120 have been joined by
one of their ends to a corresponding plurality of posts 1020 which
extend from terminals 1032 of an electronic component 1030, as
illustrated in FIG. 11E.
[0237] These beam components 1120 are comparable to the main body
portions 206 and 306 of the spring contact elements 200 and 300,
respectively, described hereinabove and are intended to provide the
principal situs of flexure when a contact force is brought to bear
upon the tip ends 1120b of the beam components 1120.
Making Tip Components
[0238] FIGS. 12A-12C are comparable to FIGS. 8A-8C, and illustrate
fabricating a plurality (two of many shown) of tip components 1220
on a sacrificial substrate 1102. In FIG. 12A a plurality of
openings 1212 (compare 806) are formed in a layer of masking
material 1210 (compare 804) which is disposed on a surface of a
sacrificial substrate 1202 (compare 802). Preferably, a release
mechanism is incorporated into the fabrication of the tip component
1220, but may alternatively be one or more layers (compare 1004 and
1104) between the sacrificial substrate and the masking layer. The
release mechanism preferably may be any of the release mechanisms
described hereinabove.
[0239] As shown in FIG. 12B, in a first etch step, a pit 1208
(compare 808) is etched into the sacrificial substrate 1202. Taking
advantages of the properties of silicon when it etches, a pit in
the form of an inverted pyramid can be formed in this manner, by
allowing the etching to proceed until it reaches a self-limiting
point. Alternatively, as shown, the etching process can be stopped,
resulting in the pit having the shape of an inverted truncated
pyramid with a small flat apex. Also alternatively, there may be no
pit 1208 at all to give, ultimately, a relatively flat tip
component 1220.
[0240] The masking layer 1210 is then removed, and another masking
layer 1214 (compare 814) is applied over the sacrificial substrate
1202 and is patterned to have openings 1216 aligned with the pits
1208. Then the openings 1216 in the masking layer 1216 are filled,
using any suitable process, with one or more layers of metallic
material, such as one of the multilayer buildups for components of
spring contact elements described hereinabove (see, e.g., FIG. 8C),
resulting in a plurality of tip components 1220 for spring contact
elements, each tip component 1220 having a pointed tip feature 1230
(compare 830) integrally formed therewith.
Joining Tip Components to Beam Components
[0241] FIGS. 12B and 12C, described hereinabove illustrate making
one or a plurality of tip components 1220 on a sacrificial
substrate 1202.
[0242] In a next step of the process, illustrated in FIG. 12D, the
masking material 1216 is removed and a joining material such as
solder paste 1224 or the like is applied to the exposed (top, as
viewed) surfaces of the tip components 1220. Compare FIG. 5B. The
tip components 1220, resident on the sacrificial substrate. 1202,
with or without the masking material 1216, and preferably prior to
applying the solder paste 1224, constitute an interim product which
may be warehoused for future use.
[0243] In a next step of the process, shown in FIG. 12E, the
sacrificial substrate 1202 with tip components 1220 resident
thereon (two tip components 1220 are illustrated in this figure)
and prepared with solder paste 1224 is brought into contact with
corresponding top (as viewed) surfaces of the opposite ends 1120b
of the beam components 1120 which were previously joined by their
one ends 1120a to the post components 1020 which were joined to the
terminals 1032 of the electronic component 1030. The layout of the
tip components 1220 `mirrors` the layout of the opposite ends 1120b
of the beam components 1120. The tip components 1220 and
corresponding opposite ends 1120b can be aligned and positioned as
precisely as desired. These elements can be secured, if desired,
before permanent joining. By applying heat, the solder paste 1224
is reflowed so that the tip components 1220 are joined to the beam
components 1120. With a suitable heat-release mechanism, such as
has been described hereinabove, the sacrificial substrate 1202 will
release the beam components 1220 during the solder reflow heating
step. Else, as described hereinabove, the sacrificial substrate
1202 can chemically be caused to release from the tip components
1220.
[0244] The end result of the process 1200 is that a plurality of
tip components 1220 have been joined to ends of beam components
1120 which were joined to post components 1020 extending from
terminals 1032 of an electronic component 1030, as illustrated in
FIG. 12F.
[0245] The end result of the three processes described with respect
to FIGS. 10A-12F is that a plurality of microelectronic contact
structures has been fabricated in separate pieces (components)
which are joined to one another and to the terminals of an
electronic component. In this manner, many of the limitations of
the prior art processes for forming microelectronic contact
structures are overcome. For example, the geometry and metallurgy
of each of the post, beam and tip components 1020, 1120 and 1220
can be controlled independently of the geometry and metallurgy of
the other of the three components. Similarly, different
manufacturing processes can be employed for each of the three
components. Additional advantages accrue to this three-piece
construction, making possible configurations of spring contact
elements on electronic components that otherwise would not be
practical using a one-piece construction of a spring contact
element.
The Joining Sequence
[0246] An example has been set forth hereinabove wherein:
[0247] (a) first, post components are joined to or built-up upon
the electronic component, such as upon selected terminals of the
electronic component;
[0248] (b) second, beam components are joined to post components;
and
[0249] (c) third, tip components are joined to the beam
components.
[0250] According to this exemplary sequence of events, one having
ordinary skill in the art to which the invention most nearly
pertains will readily appreciate that the material (e.g., solder
paste) used for joining the beam component to the post component
should preferably have a higher melting (reflow) temperature than
that of the material (e.g., solder paste) used for joining the tip
component to the beam component, so that joining the tip component
to the beam component does not adversely impact the joint between
the beam component and the post component. Moreover, in the case
where the post component is first joined (e.g., soldered) to the
terminal (or other location) of the electronic component, the
material (e.g., solder paste) used for joining the post component
to the terminal (e.g.) should preferably have an even higher
melting (reflow) temperature than that of the material joining the
beam component to the post component, so that joining the beam
component to the post component does not adversely affect the joint
between the post component and the electronic component. Solder and
braze formulations having a wide range of reflow temperatures are
readily available, from which appropriate materials can be selected
for each of the joints involved in assembling the microelectronic
contact structure. In some cases, conductive adhesive formulations
may also be appropriate for selected ones of the joints.
[0251] In a similar manner, one skilled in the art can select
release mechanisms such as 1004 and 1104 that are compatible with
reflow temperatures of the corresponding joining steps. It is
within the scope of this invention that other sequences can be
employed for joining components of a microelectronic contact
structure to one another. For example, the beam components can
first be joined to the tip components, then the sacrificial
substrate supporting the beam components can be removed (without
removing the sacrificial substrate supporting the tip components),
then the beam components with tip components already joined thereto
can be joined to the post components. This sequence affords the
opportunity to utilize a very high melting temperature joining
material to effect the joints between the beam components and the
tip components, since the electronic component to which the
microelectronic contact structures are ultimately joined preferably
would not be subjected to the very high temperatures involved. In a
similar manner the beam components can first be joined to the post
components, then the sacrificial substrate supporting the post
components can be removed (without removing the sacrificial
substrate supporting the beam components), then the post components
with beam components already joined thereto can be joined to the
electronic component. This sequence affords the opportunity to
utilize a very high melting temperature joining material to effect
the joints between the post components and the beam components,
since the electronic component to which the microelectronic contact
structures are ultimately joined would not be subjected to the very
high temperatures involved. Other variations of the joining
sequences described hereinabove are within the scope of the
invention.
The Resulting Contact Structure
[0252] An exemplary microelectronic contact structure having a post
component joined to a one end and a one surface of a beam
component, and having a tip component joined to an opposite end and
an opposite surface of the beam component has been described
hereinabove.
[0253] It is within the scope of this invention that the post
component is joined at other than the one end of the beam
component, and that the tip component is joined at other than the
opposite end of the beam component. Generally, it is preferred that
the tip component be joined at a position on the beam component
which is offset from the post component, so that the portion of the
beam component extending therebetween can function as a cantilever,
and the resulting microelectronic contact structure can function as
a spring contact element.
[0254] It is similarly within the scope of this invention that the
post component is joined to the one surface of the beam component,
and that the tip component is joined to the beam component at other
than the opposite surface of the beam component. For example, in
certain applications it may be desired to mount both of the post
and tip components to the same surface of the beam component. Or,
it may be desired to mount the tip component to a surface of the
beam component which is adjacent, rather than opposite, the surface
of the beam component to which the post component is joined.
Overlapping Spring Contact Elements
[0255] FIGS. 13A and 13B illustrate mounting a plurality (two of
many shown) of three-piece spring contact elements 1310 and 1312 to
a corresponding plurality of terminals 1302 and 1304, respectively,
of an electronic component 1306 in a configuration 1300 wherein the
beam components 1330 and 1332, respectively, of the spring contact
elements 1310 and 1312 are overlapping (e.g., have common
coordinate, but different z-axis coordinates).
[0256] The terminals 1302 and 1304 are spaced a distance "P1" apart
on the surface (top, as viewed) of the electronic component 1306.
The two terminals 1302 and 1304 need not be adjacent terminals, but
for adjacent terminals, this would be their "pitch".
[0257] In order that the beam component 1330 of the one spring
contact element 1310 may overlap or cross-over the beam component
1332 of the other spring contact element 1312, it should be
elevated (spaced) higher above the surface (top, as viewed) of the
electronic component 1306 than the beam component 1332 of the other
spring contact element 1312. To this end, the post component to
which the beam component 1330 is joined should be taller, overall,
than the post component to which the beam component 1332 is joined.
For contacting terminals of another electronic component (not
shown) which are coplanar, the tip components 1340 and 1342 of the
spring contact elements 1310 and 1312, respectively, should also be
coplanar, including any tip features projecting from the tip
components. Given that the beam component 1332 is disposed closer
to the surface (top, as viewed) of the electronic component 1306,
the tip component 1342 must be taller, overall, than the tip
component 1330. These objects may be achieved in the following
manner.
[0258] The overall post component of the spring contact element
1310 is fabricated as a post component 1320 joined (in the manner
described hereinabove) to the terminal 1302, and a spacer component
1350 joined (in the manner described hereinabove) to the top (as
viewed) surface of the post component 1320. Alternatively, the
spacer component 1350 could be joined to the terminal 1302 and the
post component 1320 could be joined to the spacer component 1350.
Alternatively, the post component 1320 and the spacer component
1350 could be formed as an integral unitary structure.
[0259] A one end of the beam component 1330 is joined to the top
(as viewed) surface of the spacer component 1350. The tip component
1340 of the spring contact element 1310 is joined to the opposite
end of the beam component 1330, in the manner described
hereinabove.
[0260] The overall tip component of the spring contact element 1312
is fabricated as a tip component 1342 joined (in the manner
described hereinabove) to a spacer component 1352 joined (in the
manner described hereinabove) to the opposite (right, as viewed)
end of the beam component 1332. Alternatively, the tip component
1342 and the spacer component 1352 could be formed as an integral
unitary structure. A one (left, as viewed) end of the beam
component 1332 is joined to the top (as viewed) surface of the post
component 1322, in the manner described hereinabove.
[0261] These same principles can be extended to a four-layer
structure, where each of two structures similar to those shown in
FIG. 13A have a post component and a tip component as shown.
However, spacer component 1350 is made of two components. A first
spacer component is approximately the thickness of beam component
1312 and preferably is formed in the same sacrificial substrate
together with beam component 1312 and attached to the corresponding
post component in the same sequence as beam component 1312 is
attached to its corresponding post component. Similarly, spacer
component 1352 is made of two components, a first component being
made together with beam component 1310, each attached to a
corresponding structure in the same way. A new group of spacer
components are fabricated on a separate sacrificial substrate using
the general methods described for making other components. Using
attaching techniques as taught above, each spacer component is
attached to a corresponding structure in sequence to form the
second portion ("top" as shown) of a spacer component such as 1350
and a first portion ("bottom" as shown) of another spacer component
such as 1352. Such a spacer should be sufficiently thick to provide
a desired offset between overlapping beam components. This can be
comparable in thickness to the thickness of a beam component, but
can be larger or smaller as selected by design.
[0262] As illustrated, the beam components 1330 and 1332 both
extend in the y-axis, at the same x-axis coordinates. (In other
words, the beam component 1330 is positioned directly over the beam
component 1332, as contrasted with simply crossing over it.) If the
two beam components 1330 and 1332 were the same length (as measured
between their two ends), the tip components 1340 and 1342 would be
spaced the same distance apart ("P2") as the terminals 1302 and
1304. However, as illustrated, the beam component 1332 is shorter
(in the y-axis) than the beam component 1330. In this manner, the
tip components 1340 and 1342 are space a distance "P2" apart which
can be less than the distance "P1" (P2<P1). This effects a
degree of space transformation (pitch spreading) with the spring
contact elements themselves. For example, the electronic component
1306 can be the space transformer component of a probe card
assembly, having terminals disposed at a one pitch (spacing from
one another), and the tip components can be spaced at a second
finer pitch.
[0263] The example of spacing the tip components at a finer pitch
than the post components (e.g., than of the terminals of the
electronic component) is but one example of many and various space
translations that can be implemented by having the beam components
of selected ones of a plurality of microelectronic contact
structures crossing over or disposed above the beam components of
selected other ones of the plurality microelectronic contact
structures which are mounted to an electronic component.
[0264] In the manner described hereinabove, various interconnection
schemes can be implemented, which would otherwise not be feasible
with the one piece spring contact elements (e.g., 120, 200, 250,
300) described hereinabove.
[0265] Although the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character it
being understood that only preferred embodiments have been shown
and described, and that all changes and modifications that come
within the spirit of the invention are desired to be protected.
Undoubtedly, many other "variations" on the "themes" set forth
hereinabove will occur to one having ordinary skill in the art to
which the present invention most nearly pertains, and such
variations are intended to be within the scope of the invention, as
disclosed herein.
* * * * *