U.S. patent application number 13/226606 was filed with the patent office on 2012-03-15 for electrically conductive pins for microcircuit tester.
This patent application is currently assigned to Johnstech International Corporation. Invention is credited to Patrick J. Alladio, Gary W. Michalko, John E. Nelson, Russell F. Oberg, Jeffrey C. Sherry, Brian Warwick.
Application Number | 20120062261 13/226606 |
Document ID | / |
Family ID | 45806060 |
Filed Date | 2012-03-15 |
United States Patent
Application |
20120062261 |
Kind Code |
A1 |
Nelson; John E. ; et
al. |
March 15, 2012 |
Electrically Conductive Pins For Microcircuit Tester
Abstract
The terminals of a device under test are temporarily
electrically connected to corresponding contact pads on a load
board by a series of electrically conductive pin pairs. The pin
pairs are held in place by an interposer membrane that includes a
top contact plate facing the device under test, a bottom contact
plate facing the load board, and a vertically resilient,
non-conductive member between the top and bottom contact plates.
Each pin pair includes a top and bottom pin, which extend beyond
the top and bottom contact plates, respectively, toward the device
under test and the load board, respectively. The top and bottom
pins contact each other at an interface that is inclined with
respect to the membrane surface normal. When compressed
longitudinally, the pins translate toward each other by sliding
along the interface.
Inventors: |
Nelson; John E.; (Brooklyn
Park, MN) ; Sherry; Jeffrey C.; (Savage, MN) ;
Alladio; Patrick J.; (Santa Rosa, CA) ; Oberg;
Russell F.; (Beldenville, WI) ; Warwick; Brian;
(Ben Lomond, CA) ; Michalko; Gary W.; (Ham Lake,
MN) |
Assignee: |
Johnstech International
Corporation
Minneapolis
MN
|
Family ID: |
45806060 |
Appl. No.: |
13/226606 |
Filed: |
September 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61380494 |
Sep 7, 2010 |
|
|
|
61383411 |
Sep 16, 2010 |
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Current U.S.
Class: |
324/755.09 ;
324/756.01 |
Current CPC
Class: |
G01R 31/2889 20130101;
G01R 1/06744 20130101; G01R 3/00 20130101; H01R 43/16 20130101;
G01R 1/06738 20130101; G01R 31/2891 20130101; G01R 1/0416 20130101;
G01R 1/0735 20130101; G01R 31/2887 20130101; Y10T 29/49204
20150115 |
Class at
Publication: |
324/755.09 ;
324/756.01 |
International
Class: |
G01R 1/067 20060101
G01R001/067; G01R 31/00 20060101 G01R031/00 |
Claims
1. A replaceable, longitudinally compressible membrane (10) for
forming a plurality of temporary mechanical and electrical
connections between a device under test (1) having a plurality of
terminals (2) and a load board (3) having a plurality of contact
pads (4), each contact pad (4) being laterally arranged to
correspond to exactly one terminal (2), comprising: a flexible,
electrically insulating top contact plate (40) longitudinally
adjacent to the terminals (2) on the device under test (1); a
flexible, electrically insulating bottom contact plate (60)
longitudinally adjacent to the contact pads (4) on the load board
(3); a longitudinally resilient, electrically insulating interposer
(50) between the top and bottom contact plates (40, 60); a
plurality of longitudinally compressible, electrically conductive
pin pairs (20, 30) extending through longitudinal holes in the top
contact plate (40), the interposer (50) and the bottom contact
plate (60), each pin pair in the plurality being laterally arranged
to correspond to exactly one terminal (2) on the device under test
(1); the plurality of pin pairs including a top and bottom contact,
the top contact having a top engagement surface which engages
electrical connections to a device under test, said top engagement
surface including a sharp longitudinal contact ridge rising above
the engagement surface, said ridge extending at least along the
major portion of the engagement surface; wherein when a particular
pin pair (20, 30) is longitudinally compressed, the pins (20, 30)
in the pair slide past each other along a virtual interface surface
(70) that is inclined with respect to a surface normal of the
interposer (50).
2. A method of lowering the resistance between a terminal on an
integrated circuit and test fixture having an electrically
conductive pin having a top surface engagable with the terminal,
the method comprising; forming the top surface to include a
longitudinal ridge along the surface, forming the ridge to have a
sharp edge at its apex whereby engagement of the ridge with the
terminal will focus contact pressure over a small surface area and
further cause ablation of oxides on the terminal.
3. The membrane (10) of claim 1, wherein the two pins (20, 30) in
the particular pin pair include mating surfaces (23, 33) that form
the virtual interface surface (70) when brought together.
4. The membrane (10) of claim 1, wherein the virtual interface
surface (70A) is generally planar.
5. The membrane (10) of claim 1, wherein the virtual interface
surface (70B) is curved along one dimension.
6. The membrane (10) of claim 1, wherein the virtual interface
surface (70C) is curved along two dimensions.
7. The membrane (10) of claim 1, wherein the virtual interface
surface (70D) is saddle-shaped.
8. The membrane (10) of claim 1, wherein the virtual interface
surface (70E) includes one or more locating features.
9. The membrane (10) of claim 1, wherein the virtual interface
surface includes one or more non-contiguous regions.
10. The membrane (10) of claim 9, wherein the non-contiguous
regions include collinear centers of curvature.
11. The membrane (10) of claim 9, wherein the non-contiguous
regions are separated by a matching groove and ridge disposed on
the mating surfaces.
12. The membrane (10) of claim 1, wherein one of the pins (20) in
each pin pair (20, 30) includes a contact pad (21) capable of
wiping through any oxide layers on the surface of the terminal (2)
on the device under test (1).
13. The membrane (10) of claim 1, wherein one of the pins (20) in
each pin pair (20, 30) includes a textured contact pad (21E) for
contacting the terminal (2) on the device under test (1).
14. The membrane (10) of claim 1, wherein one of the pins (20) in
each pin pair (20, 30) includes a contact pad (21) having at least
one rounded edge (25).
15. The membrane (10) of claim 1, wherein one of the pins (20) in
each pin pair (20, 30) includes an engagement feature (26) for
securing the pin (20) to the top contact plate (40).
16. The membrane (10) of claim 1, wherein one of the pins (20) in
each pin pair (20, 30) includes a depression (26) for securing the
pin (20) to the top contact plate (40).
17. The membrane (10) of claim 1, wherein one of the pins (30) in
each pin pair (20, 30) includes an engagement feature (36) for
securing the pin (30) to the bottom contact plate (60).
18. The membrane (10) of claim 1, wherein one of the pins (30) in
each pin pair (20, 30) includes a depression (36) for securing the
pin (30) to the bottom contact plate (60).
19. The membrane (10) of claim 1, wherein the top contact plate
(40) and the bottom contact plate (60) are made from a
polyimide.
20. The membrane (10) of claim 1, wherein the top contact plate
(40) and the bottom contact plate (60) are made from kapton.
21. The membrane (10) of claim 1, wherein the top contact plate
(40) and the bottom contact plate (60) are made from
polyetheretherketone (PEEK).
22. The membrane (10) of claim 1, wherein the interposer (50) is
made from foam.
23. The membrane (10) of claim 1, wherein the interposer (50) is
made from an elastomer.
24. The membrane (10) of claim 1, wherein the interposer (50)
includes at least one hollow region.
25. The membrane (10) of claim 1, wherein the two pins in each pin
pair (20, 30) are made from different metals.
26. The membrane (10) of claim 1, wherein when a particular pin
pair (20, 30) is longitudinally compressed between the terminal (2)
on the device under test (1) and the contact pad (4) on the load
board (3), one of the pins (30) remains stationary and in contact
with the contact pad (4) on the load board (3), and the other of
the pins (20) moves while maintaining contact with the terminal (2)
on the device under test (1).
27. The membrane (10) of claim 25, wherein the other of the pins
(20) includes a relief feature (24) that avoids contact with the
interposer (50) over the full range of the longitudinal
compression.
28. The membrane (10) of claim 1, wherein each terminal (2) on the
device under test (1) corresponds to up to two contact pads (4) on
the load board (3).
29. The membrane (10) of claim 1, wherein each terminal (2) on the
device under test (1) corresponds to exactly one contact pad (4) on
the load board (3).
30. The membrane (10) of claim 1, wherein at least two of the
longitudinal holes in the top contact plate (40), the interposer
(50) and the bottom contact plate (60) accommodate respective
lateral alignment pins that extend therethrough.
31. A test fixture (5), comprising: a membrane (10) extending
laterally between a device under test (1) and a load board (3), the
device under test (1) including a plurality of electrical terminals
(2) arranged in a predetermined pattern, the load board (3)
including a plurality of electrical contact pads (4) arranged in a
predetermined pattern corresponding to that of the terminals (2),
the membrane having a top side facing the terminals (2) of the
device under test (1) and a bottom side facing the contact pads (4)
of the load board (3); a plurality of electrical pin pairs (20, 30)
supported by the membrane (10) in a predetermined pattern
corresponding to that of the terminals (2), each pin pair in the
plurality comprising: a top pin (20) extending through the top side
of the membrane (10) and having a top pin mating surface (23); and
a bottom pin (30) extending through the bottom side of the membrane
(10) and having a bottom pin mating surface (33); wherein the top
and bottom pin mating surfaces (23, 33) have complementary surface
profiles; wherein when the corresponding electrical terminal (2) is
forced against the pin pair, the top and bottom pin mating surfaces
(23, 33) slide along each other along a virtual interface surface
(70); and wherein the virtual interface surface (70) is inclined
with respect to a surface normal of the membrane (10).
32. The test fixture (5) of claim 31, wherein the membrane (10)
includes a plurality of membrane layers.
33. The test fixture (5) of claim 32, wherein at least two of the
membrane layers in the plurality have different mechanical
properties.
34. The test fixture (5) of claim 31, wherein the membrane (10) is
monolithic.
35. A test fixture (5) for forming a plurality of temporary
mechanical and electrical connections between a device under test
(1) having a plurality of terminals (2) and a load board (3) having
a plurality of contact pads (4), the terminals (2) and contact pads
(4) being arranged in a one-to-one correspondence, comprising: a
replaceable interposer membrane (10) disposed generally parallel to
and adjacent to the load board (3), the interposer membrane (10)
including a plurality of pin pairs (20, 30) arranged in a
one-to-one correspondence with the plurality of terminals (2), each
pin pair (20, 30) including a top pin (20) adjacent to the
corresponding terminal (2) and extending into the interposer
membrane, and a bottom pin (30) adjacent to the corresponding
contact pad (4) and extending into the interposer membrane (10);
wherein each contact pad (4) corresponding to a particular pin pair
(20, 30) is configured to mechanically and electrically receive the
terminal (2) on the device under test (1) corresponding to the
particular pin pair (20, 30); and wherein when the device under
test (1) is attached to the test fixture (5), the top pins (20)
contact the corresponding terminals (2) on the device under test
(1), the bottom pins (30) contact the corresponding contact pads
(4) on the load board (3), each top pin (20) contacts the
corresponding bottom pin (30) along a virtual interface surface
that is inclined with respect to a surface normal of the interposer
membrane (10), and the plurality of terminals (2) on the device
under test (1) are electrically connected in a one-to-one
correspondence to the plurality of contact pads (4) on the load
board (3).
36. The test fixture (5) of claim 35, wherein the membrane (10)
includes a plurality of membrane layers.
37. The test fixture (5) of claim 36, wherein at least two of the
membrane layers in the plurality have different mechanical
properties.
38. The test fixture (5) of claim 35, wherein the membrane (10) is
monolithic.
39. An electrical contact pin for engagement with an a device under
test having electrical contact array on an integrated circuit or
similar device having a plurality of adjacent contacts, the pin
being having a top surface, said top surface comprising: a
projecting land extending generally orthogonally upwardly from said
top surface, said projection including a generally narrow
longitudinal contact area which is engagable with a contact of the
integrated circuit, said contact area being substantially narrower
than that of the top surface and the contact area having a surface
area substantially less than that of the top surface.
40. The pin of claim 39 wherein said narrow contact area comprises
a peak formed of two converging sidewalls rising from the top
surface.
41. The pin of claim 40 wherein the sidewall are generally
hemispherical.
42. The pin of claim 40 wherein the sidewalls are generally
convex.
43. The pin of claim 40 wherein said sidewalls are first sidewalls
generally hemispherical and further includes a secondary set of
sidewall rising from the first sidewalls and converging to an
apex.
44. The pin of claim 39 wherein said narrow contact area is flat
and includes a pair of parallel sidewalls rising from the top
surface, thereby creating a land.
45. The pin of claim 44 wherein said narrow contact surface area is
an apex rising from said parallel sidewalls.
46. The pin of claim 39 wherein said projecting land include a
plurality of adjacent spaced apart lands each having an apex for
contacting a single integrated circuit contact at a plurality of
point on said contact.
47. The pin of claim 46 wherein said plurality of lands are
parallel to each other.
48. The pin of claim 46 wherein at least two of the lands are
non-parallel to each other.
49. The pin of claim 39 wherein said longitudinal contact area is
not smooth.
50. The pin of claim 39 wherein said longitudinal contact area
includes notches therealong.
51. The pin of claim 39 wherein said longitudinal contact area is
skewed along the top surface of the pin.
52. The pin claim of 51 wherein the skew follows a generally
diagonal path across the top surface of the pin.
53. The method of claim 2 further including the steps of slideably
engaging the pin and terminal then they are brought together and
skewing the longitudinal ridge placement on the pin to increase
drag between the ridge and the terminal when brought together.
Description
BACKGROUND OF THE DISCLOSURE
[0001] 1. Field of the Disclosure
[0002] The present disclosure is directed to equipment for testing
microcircuits.
[0003] 2. Description of the Related Art
[0004] As microcircuits continually evolve to be smaller and more
complex, the test equipment that tests the microcircuits also
evolves. There is an ongoing effort to improve microcircuit test
equipment, with improvements leading to an increase in reliability,
an increase in throughput, and/or a decrease in expense.
[0005] Mounting a defective microcircuit on a circuit board is
relatively costly. Installation usually involves soldering the
microcircuit onto the circuit board. Once mounted on a circuit
board, removing a microcircuit is problematic because the very act
of melting the solder for a second time ruins the circuit board.
Thus, if the microcircuit is defective, the circuit board itself is
probably ruined as well, meaning that the entire value added to the
circuit board at that point is lost. For all these reasons, a
microcircuit is usually tested before installation on a circuit
board.
[0006] Each microcircuit must be tested in a way that identifies
all defective devices, but yet does not improperly identify good
devices as defective. Either kind of error, if frequent, adds
substantial overall cost to the circuit board manufacturing
process, and can add retest costs for devices improperly identified
as defective devices.
[0007] Microcircuit test equipment itself is quite complex. First
of all, the test equipment must make accurate and low resistance
temporary and non-destructive electrical contact with each of the
closely spaced microcircuit contacts. Because of the small size of
microcircuit contacts and the spacings between them, even small
errors in making the contact will result in incorrect connections.
Connections to the microcircuit that are misaligned or otherwise
incorrect will cause the test equipment to identify the device
under test (DUT) as defective, even though the reason for the
failure is the defective electrical connection between the test
equipment and the DUT rather than defects in the DUT itself.
[0008] A further problem in microcircuit test equipment arises in
automated testing. Testing equipment may test 100 devices a minute,
or even more. The sheer number of tests cause wear on the tester
contacts making electrical connections to the microcircuit
terminals during testing. This wear dislodges conductive debris
from both the tester contacts and the DUT terminals that
contaminates the testing equipment and the DUTs themselves.
[0009] The debris eventually results in poor electrical connections
during testing and false indications that the DUT is defective. The
debris adhering to the microcircuits may result in faulty assembly
unless the debris is removed from the microcircuits. Removing
debris adds cost and introduces another source of defects in the
microcircuits themselves.
[0010] Other considerations exist as well. Inexpensive tester
contacts that perform well are advantageous. Minimizing the time
required to replace them is also desirable, since test equipment is
expensive. If the test equipment is off line for extended periods
of normal maintenance, the cost of testing an individual
microcircuit increases.
[0011] Test equipment in current use has an array of test contacts
that mimic the pattern of the microcircuit terminal array. The
array of test contacts is supported in a structure that precisely
maintains the alignment of the contacts relative to each other. An
alignment template or board aligns the microcircuit itself with the
test contacts. The test contacts and the alignment board are
mounted on a load board having conductive pads that make electrical
connection to the test contacts. The load board pads are connected
to circuit paths that carry the signals and power between the test
equipment electronics and the test contacts.
[0012] For the electrical tests, it is desired to form a temporary
electrical connection between each terminal on the device under
test and a corresponding electrical pad on a load board. In
general, it is impractical to solder and remove each electrical
terminal on the microcircuit being contacted by a corresponding
electrical probe on the testbed. Instead of soldering and removing
each terminal, the tester may employ a series of electrically
conductive pins arranged in a pattern that corresponds to both the
terminals on the device under test and the electrical pads on the
load board. When the device under test is forced into contact with
the tester, the pins complete the circuits between respective
device under test contacts and corresponding load board pads. After
testing, when the device under test is released, the terminals
separate from the pins and the circuits are broken.
[0013] The present application is directed to improvements to these
pins.
[0014] There is a type of testing known as "Kelvin" testing, which
measures the resistance between two terminals on the device under
test. Basically, Kelvin testing involves forcing a current to flow
between the two terminals, measuring the voltage difference between
the two terminals, and using Ohm's Law to derive the resistance
between the terminals, given as the voltage divided by the current.
Each terminal on the device under test is electrically connected to
two contact pads on the load board. One of the two pads supplies a
known current amount of current. The other pad is a high-impedance
connection that acts as a voltmeter, which does not draw any
significant amount of current. In other words, each terminal on the
device under test that is to undergo Kelvin testing is
simultaneously electrically connected to two pads on the load
board--one pad supplying a known amount of current and the other
pad measuring a voltage and drawing an insignificant amount of
current while doing so. The terminals are Kelvin tested two at a
time, so that a single resistance measurement uses two terminals on
the load board and four contact pads.
[0015] In this application, the pins that form the temporary
electrical connections between the device under test and the load
board may be used in several manners. In a "standard" test, each
pin connects a particular terminal on the device under test to a
particular pad on the load board, with the terminals and pads being
in a one-to-one relationship. For these standard tests, each
terminal corresponds to exactly one pad, and each pad corresponds
to exactly one terminal. In a "Kelvin" test, there are two pins
contacting each terminal on the device under test, as described
above. For these Kelvin tests, each terminal (on the device under
test) corresponds to two pads (on the load board), and each pad (on
the load board) corresponds to exactly one terminal (on the device
under test). Although the testing scheme may vary, the mechanical
structure and use of the pins is essentially the same, regardless
of the testing scheme.
[0016] There are many aspects of the testbeds that may be
incorporated from older or existing testbeds. For instance, much of
the mechanical infrastructure and electrical circuitry may be used
from existing test systems, and may be compatible with the
electrically conductive pins disclosed herein. Such existing
systems are listed and summarized below.
[0017] An exemplary microcircuit tester is disclosed in United
States Patent Application Publication Number US 2007/0202714 A1,
titled "Test contact system for testing integrated circuits with
packages having an array of signal and power contacts", invented by
Jeffrey C. Sherry, published on Aug. 30, 2007 and incorporated by
reference herein in its entirety.
[0018] For the tester of '714, a series of microcircuits is tested
sequentially, with each microcircuit, or "device under test", being
attached to a testbed, tested electrically, and then removed from
the testbed. The mechanical and electrical aspects of such a
testbed are generally automated, so that the throughput of the
testbed may be kept as high as possible.
[0019] In '714, a test contact element for making temporary
electrical contact with a microcircuit terminal comprises at least
one resilient finger projecting from an insulating contact membrane
as a cantilevered beam. The finger has on a contact side thereof, a
conducting contact pad for contacting the microcircuit terminal.
Preferably the test contact element has a plurality of fingers,
which may advantageously have a pie-shaped arrangement. In such an
arrangement, each finger is defined at least in part by two
radially oriented slots in the membrane that mechanically separate
each finger from every other finger of the plurality of fingers
forming the test contact element.
[0020] In '714, a plurality of the test contact elements can form a
test contact element array comprising the test contact elements
arranged in a predetermined pattern. A plurality of connection vias
are arranged in substantially the predetermined pattern of the test
contacts elements, with each of said connection vias is aligned
with one of the test contact elements. Preferably, an interface
membrane supports the plurality of connection vias in the
predetermined pattern. Numerous vias can be embedded into the pie
pieces away from the device contact area to increase life. Slots
separating fingers could be plated to create an I-beam, thereby
preventing fingers from deforming, and also increasing life.
[0021] The connection vias of '714 may have a cup shape with an
open end, with the open end of the cup-shaped via contacting the
aligned test contact element. Debris resulting from loading and
unloading DUTs from the test equipment can fall through the test
contact elements where the cup-shaped vias impound the debris.
[0022] The contact and interface membranes of '714 may be used as
part of a test receptacle including a load board. The load board
has a plurality of connection pads in substantially the
predetermined pattern of the test contacts elements. The load board
supports the interface membrane with each of the connection pads on
the load board substantially aligned with one of the connection
vias and in electrical contact therewith.
[0023] In '714, the device uses a very thin conductive plate with
retention properties that adheres to a very thin non-conductive
insulator. The metal portion of the device provides multiple
contact points or paths between the contacting I/O and the load
board. This can be done either with a plated via hole housing or
with plated through hole vias, or bumped surfaces, possibly in
combination with springs, that has the first surface making contact
with the second surface, i.e., the device I/O. The device I/O may
be physically close to the load board, thus improving electrical
performance.
[0024] One particular type of microcircuit often tested before
installation has a package or housing having what is commonly
referred to as a ball grid array (BGA) terminal arrangement. A
typical BGA package may have the form of a flat rectangular block,
with typical sizes ranging from 5 mm to 40 mm on a side and 1 mm
thick.
[0025] A typical microcircuit has a housing enclosing the actual
circuitry. Signal and power (S&P) terminals are on one of the
two larger, flat surfaces, of the housing. Typically, terminals
occupy most of the area between the surface edges and any spacer or
spacers. Note that in some cases, a spacer may be an encapsulated
chip or a ground pad.
[0026] Each of the terminals may include a small, approximately
spherical solder ball that firmly adheres to a lead from the
internal circuitry penetrating surface, hence the term "ball grid
array." Each terminal and spacer project a small distance away from
the surface, with the terminals projecting farther from the surface
than the spacers. During assembly, all terminals are simultaneously
melted, and adhere to suitably located conductors previously formed
on the circuit board.
[0027] The terminals themselves may be quite close to each other.
Some have centerline spacings of as little as 0.4 mm, and even
relatively widely spaced terminals may still be around 1.5 mm
apart. Spacing between adjacent terminals is often referred to as
"pitch."
[0028] In addition to the factors mentioned above, BGA microcircuit
testing involves additional factors.
[0029] First, in making the temporary contact with the ball
terminals, the tester should not damage the S&P terminal
surfaces that contact the circuit board, since such damage may
affect the reliability of the solder joint for that terminal.
[0030] Second, the testing process is more accurate if the length
of the conductors carrying the signals is kept short. An ideal test
contact arrangement has short signal paths.
[0031] Third, solders commonly in use today for BGA terminals are
mainly tin for environmental purposes. Tin-based solder alloys are
likely to develop an oxide film on the outer surface that conducts
poorly. Older solder alloys include substantial amounts of lead,
which do not form oxide films. The test contacts must be able to
penetrate the oxide film present.
[0032] BGA test contacts currently known and used in the art employ
spring pins made up of multiple pieces including a spring, a body
and top and bottom plungers.
[0033] United States Patent Application Publication No. US
2003/0192181 A1, titled "Method of making an electronic contact"
and published on Oct. 16, 2003, shows microelectronic contacts,
such as flexible, tab-like, cantilever contacts, which are provided
with asperities disposed in a regular pattern. Each asperity has a
sharp feature at its tip remote from the surface of the contact. As
mating microelectronic elements are engaged with the contacts, a
wiping action causes the sharp features of the asperities to scrape
the mating element, so as to provide effective electrical
interconnection and, optionally, effective metallurgical bonding
between the contact and the mating element upon activation of a
bonding material.
[0034] According to United States Patent Application Publication
No. US 2004/0201390 A1, titled "Test interconnect for bumped
semiconductor components and method of fabrication" and published
on Oct. 14, 2004, an interconnect for testing semiconductor
components includes a substrate, and contacts on the substrate for
making temporary electrical connections with bumped contacts on the
components. Each contact includes a recess and a pattern of leads
cantilevered over the recess configured to electrically engage a
bumped contact. The leads are adapted to move in a z-direction
within the recess to accommodate variations in the height and
planarity of the bumped contacts. In addition, the leads can
include projections for penetrating the bumped contacts, a
non-bonding outer layer for preventing bonding to the bumped
contacts, and a curved shape which matches a topography of the
bumped contacts. The leads can be formed by forming a patterned
metal layer on the substrate, by attaching a polymer substrate with
the leads thereon to the substrate, or by etching the substrate to
form conductive beams.
[0035] According to U.S. Pat. No. 6,246,249 B1, titled
"Semiconductor inspection apparatus and inspection method using the
apparatus" and issued on Jun. 12, 2001 to Fukasawa, et al., a
semiconductor inspection apparatus performs a test on a
to-be-inspected device which has a spherical connection terminal.
This apparatus includes a conductor layer formed on a supporting
film. The conductor layer has a connection portion. The spherical
connection terminal is connected to the connection portion. At
least a shape of the connection portion is changeable. The
apparatus further includes a shock absorbing member, made of an
elastically deformable and insulating material, for at least
supporting the connection portion. A test contact element of the
disclosure for making temporary electrical contact with a
microcircuit terminal comprises at least one resilient finger
projecting from an insulating contact membrane as a cantilevered
beam. The finger has on a contact side thereof, a conducting
contact pad for contacting the microcircuit terminal.
[0036] In U.S. Pat. No. 5,812,378, titled "Microelectronic
connector for engaging bump leads" and issued on Sep. 22, 1998 to
Fjelstad, et al., a connector for microelectronic includes a
sheet-like body having a plurality of holes, desirably arranged in
a regular grid pattern. Each hole is provided with a resilient
laminar contact such as a ring of a sheet metal having a plurality
of projections extending inwardly over the hole of a first major
surface of the body. Terminals on a second surface of the connector
body are electrically connected to the contacts. The connector can
be attached to a substrate such a multi-layer circuit panel so that
the terminals on the connector are electrically connected to the
leads within the substrate. Microelectronic elements having bump
leads thereon may be engaged with the connector and hence connected
to the substrate, by advancing the bump leads into the holes of the
connector to engage the bump leads with the contacts. The assembly
can be tested, and if found acceptable, the bump leads can be
permanently bonded to the contacts. According to United States
Patent Application Publication No. US 2001/0011907 A1, titled "Test
interconnect for bumped semiconductor components and method of
fabrication" and published on Aug. 9, 2001, an interconnect for
testing semiconductor components includes a substrate, and contacts
on the substrate for making temporary electrical connections with
bumped contacts on the components. Each contact includes a recess
and a support member over the recess configured to electrically
engage a bumped contact. The support member is suspended over the
recess on spiral leads formed on a surface of the substrate. The
spiral leads allow the support member to move in a z-direction
within the recess to accommodate variations in the height and
planarity of the bumped contacts. In addition, the spiral leads
twist the support member relative to the bumped contact to
facilitate penetration of oxide layers thereon. The spiral leads
can be formed by attaching a polymer substrate with the leads
thereon to the substrate, or by forming a patterned metal layer on
the substrate. In an alternate embodiment contact, the support
member is suspended over the surface of the substrate on raised
spring segment leads.
BRIEF SUMMARY OF THE DISCLOSURE
[0037] An embodiment is a replaceable, longitudinally compressible
membrane (10) for forming a plurality of temporary mechanical and
electrical connections between a device under test (1) having a
plurality of terminals (2) and a load board (3) having a plurality
of contact pads (4), each contact pad (4) being laterally arranged
to correspond to exactly one terminal (2), comprising: a flexible,
electrically insulating top contact plate (40) longitudinally
adjacent to the terminals (2) on the device under test (1); a
flexible, electrically insulating bottom contact plate (60)
longitudinally adjacent to the contact pads (4) on the load board
(3); a longitudinally resilient, electrically insulating interposer
(50) between the top and bottom contact plates (40, 60); a
plurality of longitudinally compressible, electrically conductive
pin pairs (20, 30) extending through longitudinal holes in the top
contact plate (40), the interposer (50) and the bottom contact
plate (60), each pin pair in the plurality being laterally arranged
to correspond to exactly one terminal (2) on the device under test
(1). When a particular pin pair (20, 30) is longitudinally
compressed, the pins (20, 30) in the pair slide past each other
along a virtual interface surface (70) that is inclined with
respect to a surface normal of the interposer (50).
[0038] Another embodiment is a test fixture (5), comprising: a
membrane (10) extending laterally between a device under test (1)
and a load board (3), the device under test (1) including a
plurality of electrical terminals (2) arranged in a predetermined
pattern, the load board (3) including a plurality of electrical
contact pads (4) arranged in a predetermined pattern corresponding
to that of the terminals (2), the membrane having a top side facing
the terminals (2) of the device under test (1) and a bottom side
facing the contact pads (4) of the load board (3); a plurality of
electrical pin pairs (20, 30) supported by the membrane (10) in a
predetermined pattern corresponding to that of the terminals (2),
each pin pair in the plurality comprising: a top pin (20) extending
through the top side of the membrane (10) and having a top pin
mating surface (23); and a bottom pin (30) extending through the
bottom side of the membrane (10) and having a bottom pin mating
surface (33). The top and bottom pin mating surfaces (23, 33) have
complementary surface profiles. When the corresponding electrical
terminal (2) is forced against the pin pair, the top and bottom pin
mating surfaces (23, 33) slide along each other along a virtual
interface surface (70). The virtual interface surface (70) is
inclined with respect to a surface normal of the membrane (10).
[0039] A further embodiment is a test fixture (5) for forming a
plurality of temporary mechanical and electrical connections
between a device under test (1) having a plurality of terminals (2)
and a load board (3) having a plurality of contact pads (4), the
terminals (2) and contact pads (4) being arranged in a one-to-one
correspondence, comprising: a replaceable interposer membrane (10)
disposed generally parallel to and adjacent to the load board (3),
the interposer membrane (10) including a plurality of pin pairs
(20, 30) arranged in a one-to-one correspondence with the plurality
of terminals (2), each pin pair (20, 30) including a top pin (20)
adjacent to the corresponding terminal (2) and extending into the
interposer membrane, and a bottom pin (30) adjacent to the
corresponding contact pad (4) and extending into the interposer
membrane (10). Each contact pad (4) corresponding to a particular
pin pair (20, 30) is configured to mechanically and electrically
receive the terminal (2) on the device under test (1) corresponding
to the particular pin pair (20, 30). When the device under test (1)
is attached to the test fixture (5), the top pins (20) contact the
corresponding terminals (2) on the device under test (1), the
bottom pins (30) contact the corresponding contact pads (4) on the
load board (3), each top pin (20) contacts the corresponding bottom
pin (30) along a virtual interface surface that is inclined with
respect to a surface normal of the interposer membrane (10), and
the plurality of terminals (2) on the device under test (1) are
electrically connected in a one-to-one correspondence to the
plurality of contact pads (4) on the load board (3).
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0040] FIG. 1 is a side-view drawing of a portion of the test
equipment for receiving a device under test (DUT).
[0041] FIG. 2 is a side-view drawing of the test equipment of FIG.
1, with the DUT electrically engaged.
[0042] FIG. 3 is a side-view cross-sectional drawing of an
exemplary interposer membrane in its relaxed state.
[0043] FIG. 4 is a side-view cross-sectional drawing of the
interposer membrane of FIG. 3, in its compressed state.
[0044] FIG. 5 is a side-view drawing of an exemplary pin pair in
its relaxed state.
[0045] FIG. 6 is a side-view drawing of the pin pair of FIG. 5, in
its compressed state.
[0046] FIG. 7 is a plan drawing of the planar interface surface
shown in FIG. 3.
[0047] FIG. 8 is a plan drawing of the cylindrically curved
interface surface shown in FIG. 5.
[0048] FIG. 9 is a plan drawing of a curved interface surface that
has curvature in both horizontal and vertical directions.
[0049] FIG. 10 is a plan drawing of a saddle-shaped interface
surface, in which the vertical and horizontal curvatures have
opposite concavity.
[0050] FIG. 11 is a plan drawing of an interface surface having a
locating feature, such as a groove or ridge.
[0051] FIG. 12 is a plan drawing of a generally planar top contact
pad.
[0052] FIG. 13 is a plan drawing of a top contact pad that extends
out of the plane of the pad.
[0053] FIG. 14 is a plan drawing of a top contact pad that includes
a protrusion out of the plane of the pad.
[0054] FIG. 15 is a plan drawing of a top contact pad that includes
multiple protrusions out of the plane of the pad.
[0055] FIG. 16 is a plan drawing of an inclined top contact
pad.
[0056] FIG. 17 is a plan drawing of an inclined top contact pad
with multiple protrusions out of the plane of the pad.
[0057] FIG. 18 is a plan drawing of a textured top contact pad.
[0058] FIG. 19 is a plan drawing of a radially enlarged top contact
pad.
[0059] FIG. 20 is a side-view drawing of a top pin with a top
contact pad that has rounded edges.
[0060] FIG. 21 is a side-view cross-sectional drawing of a top pin
having a top pin engagement feature on one side.
[0061] FIG. 22 is a side-view cross-sectional drawing of a top pin
having a top pin engagement feature on two opposing sides.
[0062] FIG. 23 is a side-view cross-sectional drawing of a top pin
having a two top pin engagement features engaging the top contact
plate, and one engagement feature engaging the foam interposer.
[0063] FIG. 24 is a side-view cross-sectional drawing of a bottom
pin having a bottom pin engagement feature.
[0064] FIG. 25 is a perspective-view cross-sectional drawing of an
exemplary interposer membrane.
[0065] FIG. 26 is an end-on cross-sectional drawing of the
interposer membrane of FIG. 25.
[0066] FIG. 27 is a plan drawing of the interposer membrane of
FIGS. 25 and 26.
[0067] FIG. 28 is a plan drawing of an exemplary top contact pad
for Kelvin testing, with an insulating portion that separates the
two halves of the pad.
[0068] FIG. 29 is a side-view drawing of an exemplary pin pair for
Kelvin testing, with an insulating ridge that extends outward from
the top pin mating surface.
[0069] FIG. 30 is a plan drawing of an interposer membrane,
inserted into a frame.
[0070] FIG. 31 is a plan drawing of the interposer membrane of FIG.
30, removed from the frame.
[0071] FIG. 32a is a top-view schematic drawing of the interposer
membrane of FIGS. 30-31.
[0072] FIG. 32b is a plan drawing of the interposer membrane of
FIGS. 30-31.
[0073] FIG. 32c is a front-view schematic drawing of the interposer
membrane of FIGS. 30-31.
[0074] FIG. 32d is a right-side-view schematic drawing of the
interposer membrane of FIGS. 30-31.
[0075] FIG. 33a is a top-view schematic drawing of the interposer,
from the interposer membrane of FIGS. 30-32.
[0076] FIG. 33b is a plan drawing of the interposer, from the
interposer membrane of FIGS. 30-32.
[0077] FIG. 33c is a front-view schematic drawing of the
interposer, from the interposer membrane of FIGS. 30-32.
[0078] FIG. 33d is a right-side-view schematic drawing of the
interposer, from the interposer membrane of FIGS. 30-32.
[0079] FIG. 34 includes 24 specific designs for the interposer
supporting members, shown in cross-section.
[0080] FIG. 35 is a plan drawing of an interposer having supporting
members that extend between adjacent holes within a particular
plane.
[0081] FIG. 36 is a plan drawing of an interposer having a
supporting plane that completely fills the area between adjacent
holes, but is absent above or below that plane.
[0082] FIG. 37 includes 18 specific designs for the interposer,
shown in cross-section, where the top and bottom contact plates are
horizontally oriented, and the pin direction is generally
vertical.
[0083] FIG. 38 is a perspective view of an alternate embodiment of
a top pin.
[0084] FIG. 39 is a top plan view of the subject matter of FIG.
38.
[0085] FIG. 40 is a side plan view of the subject matter of FIG.
38.
[0086] FIG. 41 is an end plan view of the subject matter of FIG.
38.
[0087] FIG. 42 is a perspective view of an alternate embodiment of
a top pin having a skewed knife edge top surface.
[0088] FIG. 43 is a perspective view of an alternate embodiment of
a top pin having a double sided peaked knife edge top surface.
[0089] FIG. 44 is a perspective view of an alternate embodiment of
a top pin similar to FIG. 43 except having steep sidewall toward
the top surface.
[0090] FIG. 45 is a perspective view of an alternate embodiment of
a top pin having a projecting land knife edge top surface.
[0091] FIG. 46 is a perspective view of an alternate embodiment of
a top pin similar to FIG. 45 except the projecting land has a
peaked knife edge atop the land on the top surface.
[0092] FIG. 47 is a perspective view of an alternate embodiment of
a top pin like FIG. 46 except the sidewalls of the land are tapered
to a sharp peak.
[0093] FIG. 48 is a perspective view of an alternate embodiment of
a top pin having a plurality of lands extending from the pin, in
this case with tapered side walls rising to a sharp peak of
generally parallel surfaces.
[0094] FIGS. 49-51 are similar to FIG. 48 except they show a top
pin having two lands instead of three. FIG. 49, is a perspective
view, FIG. 50 is a side view and FIG. 51 is a top view.
DETAILED DESCRIPTION OF THE DISCLOSURE
[0095] Consider an electrical chip that is manufactured to be
incorporated into a larger system. When in use, the chip
electrically connects the device to the larger system by a series
of pins or terminals. For instance, the pins on the electrical chip
may plug into corresponding sockets in a computer, so that the
computer circuitry may electrically connect with the chip circuitry
in a predetermined manner. An example of such a chip may be a
memory card or processor for a computer, each of which may be
insertable into a particular slot or socket that makes one or more
electrical connections with the chip.
[0096] It is highly desirable to test these chips before they are
shipped, or before they are installed into other systems. Such
component-level testing may help diagnose problems in the
manufacturing process, and may help improve system-level yields for
systems that incorporate the chips. Therefore, sophisticated test
systems have been developed to ensure that the circuitry in the
chip performs as designed. The chip is attached to the tester, as a
"device under test", is tested, and is then detached from the
tester. In general, it is desirable to perform the attachment,
testing, and detachment as rapidly as possible, so that the
throughput of the tester may be as high as possible.
[0097] The test systems access the chip circuitry through the same
pins or terminals that will later be used to connect the chip in
its final application. As a result, there are some general
requirements for the test system that perform the testing. In
general, the tester should establish electrical contact with the
various pins or terminals so that the pins are not damaged, and so
that a reliable electrical connection is made with each pin.
[0098] Most testers of this type use mechanical contacts between
the chip pins and the tester contacts, rather than soldering and
de-soldering or some other attachment method. When the chip is
attached to the tester, each pin on the chip is brought into
mechanical and electrical contact with a corresponding pad on the
tester. After testing, the chip is removed from the tester, and the
mechanical and electrical contacts are broken.
[0099] In general, it is highly desirable that the chip and the
tester both undergo as little damage as possible during the
attachment, testing, and detachment procedures. Pad layouts on the
tester may be designed to reduce or minimize wear or damage to the
chip pins. For instance, it is not desirable to scrape the device
I/O (leads, pins, pads or balls), bend or deflect the I/O, or
perform any operation that might permanently change or damage the
I/O in any way. Typically, the testers are designed to leave the
chips in a final state that resembles the initial state as closely
as possible. In addition, it is also desirable to avoid or reduce
any permanent damage to the tester or tester pads, so that tester
parts may last longer before replacement.
[0100] There is currently a great deal of effort spent by tester
manufacturers on the pad layouts. For instance, the pads may
include a spring-load mechanism that receives the chip pins with a
prescribed resisting force. In some applications, the pads may have
an optional hard stop at the extreme end of the spring-load force
range of travel. The goal of the pad layout is to establish a
reliable electrical connection with the corresponding chip pins,
which may be as close as possible to a "closed" circuit when the
chip is attached, and may be as close as possible to an "open"
circuit when the chip is detached.
[0101] Because it is desirable to test these chips as quickly as
possible, or simulate their actual use in a larger system, it may
be necessary to drive and/or receive electrical signals from the
pins at very high frequencies. The test frequencies of current-day
testers may be up to 40 GHz or more, and the test frequencies are
likely to increase with future generation testers.
[0102] For low-frequency testing, such as that done close to DC (0
Hz), the electrical performance may be handled rather
simplistically: one would want an infinitely high resistance when
the chip is detached, and an infinitesimally small resistance when
the chip is attached.
[0103] At higher frequencies, other electrical properties come into
play, beyond just resistance. Impedance (or, basically, resistance
as a function of frequency) becomes a more proper measure of
electrical performance at these higher frequencies. Impedance may
include phase effects as well as amplitude effects, and can also
incorporate and mathematically describe the effects of resistance,
capacitance and inductance in the electrical path. In general, it
is desirable that the contact resistance in the electrical path
formed between the chip I/O and the corresponding pad on the load
card be sufficiently low, which maintains a target impedance of 50
ohms, so that the tester itself does not significantly distort the
electrical performance of the chip under test. Note that most test
equipment is designed to have 50 ohm input and output
impedances.
[0104] For modern-day chips that have many, many closely spaced
I/O, it becomes helpful to simulate the electrical and mechanical
performance at the device I/O interface. Finite-element modeling in
two- or three dimensions has become a tool of choice for many
designers. In some applications, once a basic geometry style has
been chosen for the tester pad configuration, the electrical
performance of the pad configuration is simulated, and then the
specific sizes and shapes may be iteratively tweaked until a
desired electrical performance is achieved. For these applications,
the mechanical performance may be determined almost as an
afterthought, once the simulated electrical performance has reached
a particular threshold.
[0105] A general summary of the disclosure follows.
[0106] The terminals of a device under test are temporarily
electrically connected to corresponding contact pads on a load
board by a series of electrically conductive pin pairs. The pin
pairs are held in place by an interposer membrane that includes a
top contact plate facing the device under test, a bottom contact
plate facing the load board, and a vertically resilient,
non-conductive member between the top and bottom contact plates.
Each pin pair includes a top and bottom pin, which extend beyond
the top and bottom contact plates, respectively, toward the device
under test and the load board, respectively. The top and bottom
pins contact each other at an interface that is inclined with
respect to the membrane surface normal. When compressed
longitudinally, the pins translate toward each other by sliding
along the interface. The sliding is largely longitudinal, with a
small and desirable lateral component determined by the inclination
of the interface. The interface may optionally be curved along one
or two dimensions, optionally with different curvatures and/or
concavities in each direction, and may optionally include one or
more locating features, such as a ridge or groove. The top and
bottom contact plates may be made from a polyimide or
non-conductive, flexible material, such as KAPTON.RTM., which is
commercially available from the DuPont Corporation. Another example
material is polyetheretherketone (PEEK), an engineering plastic
commercially available from manufacturers such as Victrex. The
material between the contact plates may be a foam or elastomeric
material. The pins in each pair may optionally be made from
different metals.
[0107] The preceding paragraph is merely a summary of the
disclosure, and should not be construed as limiting in any way. The
test device is described in much greater detail below.
[0108] FIG. 1 is a side-view drawing of a portion of the test
equipment for receiving a device under test (DUT) 1. The DUT 1 is
placed onto the tester 5, electrical testing is performed, and the
DUT 1 is then removed from the tester 5. Any electrical connections
are made by pressing components into electrical contact with other
components; there is no soldering or de-soldering at any point in
the testing of the DUT 1.
[0109] The entire electrical test procedure may only last about a
fraction of a second, so that rapid, accurate placement of the
device under test 1 becomes important for ensuring that the test
equipment is used efficiently. The high throughput of the tester 5
usually requires robotic handling of the devices under test 1. In
most cases, an automated mechanical system places the DUT 1 onto
the tester 5 prior to testing, and removes the DUT 1 once testing
has been completed. The handling and placement mechanism may use
mechanical and optical sensors to monitor the position of the DUT
1, and a combination of translation and rotation actuators to align
and place the DUT 1 on the testbed. Such automated mechanical
systems are mature and have been used in many known electrical
testers; these known robotic systems may also be used with any or
all of the tester elements disclosed herein. Alternatively, the DUT
1 may be placed by hand, or placed by a combination of hand-fed and
automated equipment.
[0110] Likewise, the electrical algorithms that are used to test
each terminal on the DUT 1 are well established, and have been used
in many known electrical testers. These known electrical algorithms
may also be used with any or all of the tester elements disclosed
herein.
[0111] The device under test 1 typically includes one or more
chips, and includes signal and power terminals that connect to the
chip. The chip and terminals may be on one side of the device under
test 1, or may be on both sides of the device under test 1. For use
in the tester 5, all the terminals 2 should be accessible from one
side of the device under test 1, although it will be understood
that there may be one or more elements on the opposite side of the
device under test 1, or that there may be other elements and/or
terminals on the opposite side that may not be tested by accessing
terminals 2.
[0112] Each terminal 2 is formed as a small, generally spherical
ball of solder. Prior to testing, the ball 2 is attached to an
electrical lead that connects internally to other leads, to other
electrical components, and/or to one or more chips on the device
under test 1. The volume and size of the solder balls may be
controlled quite precisely, and there is typically not much
difficulty caused by ball-to-ball size variations or placement
variations. During testing, the terminals 2 remain solid, and there
is no melting or re-flowing of any solder balls 2.
[0113] The terminals 2 may be laid out in any suitable pattern on
the surface of the device under test 1. In some cases, the
terminals 2 may be in a generally square grid, which is the origin
of an expression that describes the device under test 1, "ball grid
array". There may also be deviations away from a rectangular grid,
including irregular spacings and geometries. It will be understood
that the specific locations of the terminals may vary as needed,
with corresponding locations of pads on the load board and pin
pairs on the membrane being chosen to match those of the device
under test terminals 2. In general, the spacing between adjacent
terminals 2 is in the range of 0.25 to 1.5 mm, with the spacing
being commonly referred to as a "pitch".
[0114] When viewed from the side, as in FIG. 1, the device under
test 1 displays a line of terminals 2, which may optionally include
gaps and irregular spacings. These terminals 2 are made to be
generally planar, or as planar as possible with typical
manufacturing processes. In many cases, if there are chips or other
elements on the device under test 1, the protrusion of the chips is
usually less than the protrusion of the terminals 2 away from the
device under test 1.
[0115] The tester 5 of FIG. 1 includes a load board 3.
[0116] The load board 3 includes a load board substrate 6 and
circuitry that is used to test electrically the device under test
1. Such circuitry may include driving electronics that can produce
one or more AC voltages having one or more particular frequencies,
and detection electronics that can sense the response of the device
under test 1 to such driving voltages. The sensing may include
detection of a current and/or voltage at one or more frequencies.
Such driving and sensing electronics is well known in the industry,
and any suitable electronics from known testers may be used with
the tester elements disclosed herein.
[0117] In general, it is highly desirable that the features on the
load board 3, when mounted, are aligned with corresponding features
on the device under test 1. Typically, both the device under test 1
and the load board 3 are mechanically aligned to one or more
locating features on the tester 3. The load board 3 may include one
or more mechanical locating features, such as fiducials or
precisely-located holes and/or edges, which ensure that the load
board 3 may be precisely seated on the tester 5. These locating
features typically ensure a lateral alignment (x, y) of the load
board, and/or a longitudinal alignment (z) as well. The mechanical
locating features are well known in the industry, and any suitable
electronics from known testers may be used with the tester elements
disclosed herein. The mechanical locating features are not shown in
FIG. 1.
[0118] In general, the load board 3 may be a relatively complex and
expensive device. In many cases, it may be advantageous to
introduce an additional, relatively inexpensive element into the
tester 5 that protects the contact pads 4 of the load board 3 from
wear and damage. Such an additional element may be an interposer
membrane 10. The interposer membrane 10 also mechanically aligns
with the tester 3 with suitable locating features (not shown), and
resides in the tester 5 above the load board 3, facing the device
under test 1.
[0119] The interposer membrane 10 includes a series of electrically
conductive pin pairs 20, 30. In general, each pin pair connects one
contact pad 4 on the load board 3 to one terminal 2 on the device
under test 1, although there may be testing schemes in which
multiple contact pads 4 connect to a single terminal 2, or multiple
terminals 2 connect to a single contact pad 4. For simplicity, we
assume in the text and drawings that a single pin pair connects a
single pad to a single terminal, although it will be understood
that any of the tester elements disclosed herein may be used to
connect multiple contact pads connect to a single terminal, or
multiple terminals to a single contact pad. Typically, the
interposer membrane 10 electrically connects the load board pads
and the bottom contact surface of the test contactor. It may
alternatively be used to convert an existing load board pad
configuration to a vehicle, which is a test socket used to connect
and test a device under test.
[0120] Although the interposer membrane 10 may be removed and
replaced relatively easily, compared with removal and replacement
of the load board 3, we consider the interposer membrane 10 to be
part of the tester 5 for this document. During operation, the
tester 5 includes the load board 3, the interposer membrane 10, and
the mechanical construction that mounts them and holds them in
place (not shown). Each device under test 1 is placed against the
tester 5, is tested electrically, and is removed from the
tester.
[0121] A single interposer membrane 10 may test many devices under
test 1 before it wears out, and may typically last for several
thousand tests or more before requiring replacement. In general, it
is desirable that replacement of the interposer membrane 10 be
relatively fast and simple, so that the tester 5 experiences only a
small amount of down time for membrane replacement. In some cases,
the speed of replacement for the interposer membrane 10 may even be
more important than the actual cost of each membrane 10, with an
increase in tester up-time resulting in a suitable cost savings
during operation.
[0122] FIG. 1 shows the relationship between the tester 5 and the
devices under test 1. When each device 1 is tested, it is placed
into a suitable robotic handler with sufficiently accurate
placement characteristics, so that a particular terminal 2 on the
device 1 may be accurately and reliably placed (in x, y and z) with
respect to corresponding pin pairs 20, 30 on the interposer
membrane 10 and corresponding contact pads 4 on the load board
3.
[0123] The robotic handler (not shown) forces each device under
test 1 into contact with the tester 5. The magnitude of the force
depends on the exact configuration of the test, including the
number of terminals 2 being tested, the force to be used for each
terminal, typical manufacturing and alignment tolerances, and so
forth. In general, the force is applied by the mechanical handler
of the tester (not shown), acting on the device under test 1. In
general, the force is generally longitudinal, and is generally
parallel to a surface normal of the load board 3.
[0124] FIG. 2 shows the tester and device under test 1 in contact,
with sufficient force being applied to the device under test 1 to
engage the pin pairs 20, 30 and form an electrical connection 9
between each terminal 2 and its corresponding contact pad 4 on the
load board 3. As stated above, there may alternatively be testing
schemes in which multiple terminals 2 connect to a single contact
pad 4, or multiple contact pads 4 connect to a single terminal 2,
but for simplicity in the drawings we assume that a single terminal
2 connects uniquely to a single contact pad 4.
[0125] FIGS. 3 and 4 are side-view cross-sectional drawings of an
exemplary interposer membrane 10 in its relaxed and compressed
states, respectively. In its relaxed state, there is no electrical
connection between terminal 2 on the device under test 1 and
contact pad 4 on the load board 3. In its compressed state, in
which the device under test 1 is forced toward the load board 3,
there is an electrical connection 9 between terminal 2 on the
device under test 1 and contact pad 4 on the load board 3.
[0126] In some cases, the interposer membrane 10 may extend across
essentially the entire lateral extent of the load board, or at
least over the lateral area subtended by the load board contact
pads 4. The membrane 10 includes a sandwich structure that
mechanically supports electrically conductive pin pairs, with each
pin pair corresponding to a terminal 2 on the device under test 1
and a contact pad 4 on the load board 3. The sandwich structure is
described below, followed by a detailed description of the pin
pairs.
[0127] The membrane 10 may be formed as a sandwich structure, with
an interposer 50 being surrounded by a top contact plate 40 and a
bottom contact plate 60. In some cases, the layers 40, 50, 60 of
the membrane 10 are held together by relatively thin layers of
adhesive 41, 61.
[0128] The interposer 50 is an electrically insulating, vertically
resilient material, such as foam or an elastomer. When the device
under test is forced toward the load board, the interposer 50
compresses in the longitudinal (vertical) direction, as is the case
in FIG. 4. The vertical compression is generally elastic. When the
device under test is released, the interposer 50 expands in the
longitudinal (vertical) direction to its original size and shape,
as is the case in FIG. 3.
[0129] Note that there may optionally be some transverse
(horizontal) compression as well, although the transverse component
is generally smaller than the longitudinal component. In general,
the interposer 50 material does not substantially "flow" laterally
when a longitudinal force is applied. In some cases, there may be a
resisting lateral force supplied by the interposer 50 material,
which can help constrain the pair of pins 20, 30 to a particular
columnar volume and prevent or reduce any lateral spreading of the
overlapping portions of the pins in each pair.
[0130] On either side of the interposer 50 is a contact plate, with
a top contact plate 40 facing the device under test 1 and a bottom
contact plate 60 facing the load board 3. The contact plates 40, 60
may be made from an electrically insulating, flexible material,
such as a polyimide or Kapton.RTM.. Alternatively, the contact
plates 40, 60 may be made from any semi-rigid thin film material,
which can include a polyester, a polyimide, PEEK, Kapton.RTM.,
nylon, or any other suitable material. In some cases, the contact
plates 40, 60 are adhered to the interposer 50 by an adhesive 41,
61. In other cases, the contact plates 40, 60 are made integral
with the interposer 50. In still other cases, the contact plates
40, 60 are free floating and not physically attached to the
interposer 50, which may allow for quick removal and replacement.
For these cases, there is no adhesive 41, 61 that binds the
interposer 50 to the contact plates 40, 60.
[0131] The contact plates 40, 60 (Kapton.RTM.) are structurally
stronger than the interposer 50 (foam), and provide a durable
exterior to the interposer membrane 10. In addition, they deform
less than the interposer 50 when the device under test 1 is forced
toward the load board 3. Note that in FIG. 4, the top contact plate
40 may bend longitudinally to accommodate the longitudinal
compression, but the material that actually compresses is the foam
or elastomer of the interposer 50. In other words, during
compression, the top and bottom contact plate 40, 60 may be pushed
toward each other and one or both may longitudinally deform, but
neither one significantly compresses or changes thickness.
[0132] A membrane 10 that uses Kapton.RTM. contact plates 40, 60
may have several advantages.
[0133] First, it is easy and relatively inexpensive to cut and
place holes into the semi-rigid film, which may be made from a
material such as Kapton.RTM.. As a result, once the lateral
locations of the contact pads 4 and the corresponding terminals 2
are determined (usually by the manufacturer of the device under
test 1), the locations and sizes may be fed into a machine that
drills or etches the holes in the desired locations. Note that the
machining/processing of Kapton.RTM. is far less expensive for
comparable processing of a metallic layer.
[0134] Second, after machining, the Kapton.RTM. layers are very
strong, and resist lateral deformation of the hole shapes or
locations. As a result, the Kapton.RTM. layers themselves may be
used to determine the lateral locations of the pin pairs, during
assembly of the interposer membrane 10. In other words, the pins
may be inserted into the existing holes in the Kapton.RTM.,
eliminating the need for an additional, expensive tool to precisely
place the pins in (x, y).
[0135] The exemplary membrane 10 shown in FIG. 3 shows the top pin
20 and bottom pin 30 as being spatially separated when the membrane
10 is in its relaxed state. When the membrane 10 is compressed, as
in FIG. 4, the top pin 20 and bottom pin 30 are brought into
physical and electrical contact.
[0136] Note that having a pin separation in the relaxed state is
optional. Alternatively, the top and bottom pins may be in physical
and electrical contact even when the membrane is in its relaxed
state; this is the case of the design discussed below with
reference to FIGS. 5 and 6.
[0137] Having discussed the sandwich structure of the interposer
membrane 10, we turn now to the top pin 20 and bottom pin 30.
[0138] The top pin 20, also known as a slider pin 20, has a top
contact pad 21 that extends generally laterally around the pin 20
and comes into contact with the terminal 2 on the device under test
1. This lateral extension makes the top contact pad 21 a "larger
target" for the terminal 2 during testing, and helps relax some
fabrication and alignment tolerances on all the tester and device
elements. The top contact pad 21 need not be flat or rectangular in
profile; other options are discussed below with reference to FIGS.
12-18.
[0139] The top pin 20 has a longitudinal member 22 that extends
away from the top contact pad 21 toward the load board 3. In some
cases, the longitudinal member 22 may include all of the top pin 20
except the top contact pad 21.
[0140] The longitudinal member 22 may include at least one mating
surface 23. The mating surface 23 is shaped to contact an analogous
mating surface 33 on the bottom pin 30 during longitudinal
compression of the pin pair, so that the mating surfaces 23 and 33
on the pin pair provide good mechanical and electrical contact
between the top and bottom pins. Here, the element numbers "23" and
"33" refer to general mating surfaces. The surfaces themselves may
take on many shapes and orientations, and specific shapes are
labeled in the drawings as "23A", "33A", "23B", "33B", and so
forth. FIGS. 3 and 4 show flat mating surfaces 23A and 33A. Some
other suitable shapes are shown below in subsequent drawings.
[0141] The bottom pin 30, also known as a base pin 30, has a bottom
contact pad 31, a longitudinal member 32 and a mating surface 33A,
all of which are similar in construction to the analogous
structures in the top pin 20.
[0142] In some cases, the top and bottom pins are formed from
different metals, so that the pins avoid "sticking" together over
the course of repeated contact along the mating surfaces 23A and
33A. Examples of suitable metals include copper, gold, solder,
brass, silver, and aluminum, as well as combinations and/or alloys
of the above conductive metals.
[0143] In the exemplary design of FIGS. 3 and 4, the mating
surfaces 23A and 33A are essentially planar. When brought together,
the mating surfaces 23A and 33A form a so-called virtual "interface
surface" 70A, which in this example is a plane. Other examples are
provided below.
[0144] Note that the hole in the membrane 10, and likewise the
cross-section of the longitudinal members 22 and 32, may be
circular, elliptical, elongated, rectangular, square, or any other
suitable shape. In all of these cases, the membrane 10 holds the
top and bottom pins together, in a manner similar to having a
rubber band around the pins' circumference in the vicinity of their
overlapping longitudinal portions. The membrane 10 provides
resistance to motion in the lateral direction.
[0145] Whereas the interface surface 70A of FIGS. 3 and 4 is
generally planar, the interface surface may alternatively take on
other shapes. For instance, the interface surface 70B in FIGS. 5
and 6 is curved. The top pin mating surface 23B is convex, and the
bottom pin mating surface 33B is concave, with both having the same
radius of curvature so that they fit together.
[0146] In FIG. 5, when the membrane is in its relaxed state, the
top pin 20 and bottom pin 30 have generally parallel longitudinal
members. In FIG. 6, when the device under test is forced against
the load board, the top pin 20 has slid along the curved interface
surface 70B, thereby translating the top pin 20 downward and
pivoting the top pin 20 so that the top contact pad is inclined
with respect to the terminal 2 on the device under test, and the
top pin longitudinal member is inclined with respect to the bottom
pin longitudinal member.
[0147] This angular incline may be useful. Note in FIG. 6 that when
the electrical connection 9 is made between the terminal (ball) 2
and the load board contact pad 4, that the top contact pad 21 on
the top pin 20 contacts the ball 2 away from the center of the ball
2. This shift in contact area may cause a desirable "wiping"
function, in which the top contact pad 21 on the top pin 20 can
break through any oxide layers that have formed on the solder ball
2. This, in turn, may result in an improved electrical connection
between the ball 2 and the top contact pad 21 of the top pin
20.
[0148] In addition, depending on the location of the center of
rotation of the interface surface 70B, there may be an additional
lateral translation of the top pin 20 as the device under test is
forced against the load board. Generally, this lateral (x, y)
translation is smaller than the longitudinal (z) translation of the
top pin, but is desirable nonetheless because it may also cause the
"wiping" function described above.
[0149] Note that this lateral translation is also present on the
designs of FIGS. 3 and 4, in which the interface surface 70A is
planar, and is inclined away from a surface normal of the
interposer membrane 10. As a result, the designs of FIGS. 3 and 4
display the desirable "wiping" function described above.
[0150] Note also that while "wiping" may be desirable for the
solder ball terminals 2 on the devices under test, "wiping" is
typically not desirable for the contact pads 4 on the load board 3.
In general, persistent and repeated wiping of the load board
contact pads 4 may lead to deterioration of the pads themselves,
and may eventually lead to failure of the load board 3, which is
highly undesirable. For the designs considered herein, the top pin
20 is the pin that moves and performs the wiping, while the bottom
pin 30 remains generally stationary, and does not wipe against the
load board contact pad 4.
[0151] Note that the top pin 20 has a top relief surface 24, which
is cut away from the top pin longitudinal member so that the top
pin may pivot without bumping into the resilient membrane (not
shown--on the left portion of FIG. 6). In some cases, when the top
pin 20 is at full compression, as in FIG. 6, the top relief surface
24 is perpendicular to the plane of the interposer membrane 10. In
the case shown in FIG. 6, the bottom pin 30 includes a bottom
relief surface 34 that is perpendicular to the membrane surface,
which does not cause any interference with the membrane foam
because the bottom pin 30 generally does not pivot.
[0152] FIGS. 3 and 4 showed a planar interface surface 70A, and
FIGS. 5 and 6 showed a curved interface surface 70B. These and
other configurations are shown more clearly in FIGS. 7 through
11.
[0153] FIG. 7 is a plan drawing of the planar interface surface 70A
shown in FIG. 3.
[0154] Note that the plane itself is inclined with respect to the
surface normal of the interposer membrane 10. In other words, the
plane is not truly vertical, but is inclined away from vertical by
an angle, such as 1 degree, 5 degree, 10 degrees, 15 degrees, 20
degrees, or an angle within a range of angles, such as 1-30
degrees, 5-30 degrees, 10-30 degrees, 15-30 degrees, 20-30 degrees,
5-10 degrees, 5-15 degrees, 5-20 degrees, 5-25 degrees, 10-15
degrees, 10-20 degrees, 10-25 degrees, 15-20 degrees, 15-25
degrees, or 20-25 degrees. To form this planar interface surface
70A, top pin mating surface 23A and bottom pin mating surface 33A
are both planar.
[0155] With a planar interface surface 70A, there is no restriction
of movement of the top mating surface 23A with respect to the
bottom mating surface 33A. The mating surfaces are free to
translate and rotate with respect to each other while remaining in
contact with each other.
[0156] FIG. 8 is a plan drawing of the curved interface surface 70B
shown in FIG. 5. In this case, the curvature is only along one
dimension, so that the interface surface 70B assumes a cylindrical
profile. There is curvature along a vertical direction, but no
curvature along a horizontal direction. To form this cylindrically
curved interface surface 70B, the top pin mating surface 23B is
cylindrically curved and convex, and the bottom pin mating surface
33B is cylindrically curved and concave. Each mating surface has
the same radius of curvature. Note that in other cases, the
concavity may be reversed, so that the top pin mating surface 23B
is concave and the bottom pin mating surface 33B is convex.
[0157] The curved interface surface 70B does restrict movement of
the pins with respect to each other. The mating surfaces of the
pins may translate horizontally, along the dimension that has no
curvature, and may pivot about the center of curvature (the mating
surfaces and interface surface all have the same center of
curvature), but may not translate vertically without rotation with
respect to each other.
[0158] The placement of the center of curvature does determine the
amount of rotation and/or lateral translation one may achieve for a
given longitudinal translation of the pins. In general, it is
desirable to have enough translation and/or rotation to provide
adequate "wiping" of the ball terminal 2, as described above.
[0159] FIG. 9 is a plan drawing of a curved interface surface 70C
that has curvature in both horizontal and vertical directions. In
some applications, the horizontal and vertical radii of curvature
are the same, meaning that the interface surface 70C is spherically
curved. This is the case as drawn in FIG. 9. In other applications,
the horizontal and vertical radii of curvature are different,
meaning that the interface surface has a single concavity but a
more complex shape.
[0160] FIG. 10 is a plan drawing of a saddle-shaped interface
surface 70D, in which the vertical and horizontal curvatures have
opposite concavity. Note that the top pin mating surface and the
bottom pin mating surface are both saddle-shaped, with surface
profiles that are mated to form the interface surface 70D.
[0161] Finally, FIG. 11 is a plan drawing of an interface surface
70E having a locating feature, such as a groove or ridge. Note that
the mating surface of one pin may have a groove, while the mating
surface of the other pin has the complementary feature of a ridge
that fits into the groove. Such a locating feature may restrict
motion along a particular dimension or axis. As drawn in FIG. 11,
the only possible relative motion of the mating surfaces is a
largely vertical pivoting around the center of curvature; no
horizontal relative motion is allowed by the locating feature.
[0162] Other suitable shapes, radii of curvature, concavity, and/or
locating features are certainly possible, in addition to those
shown in FIGS. 7 through 11. In each case, the top pin mating
surface and bottom pin mating surface have complementary features,
which may optionally restrict motion in a particular dimension or
rotation along a particular direction. During use of the pins
during testing, the compression of the pins retains intimate
contact between the mating surfaces, and the contact is along the
interface surface.
[0163] The top contact pad 21 can include any of a variety of
features that may help enhance electrical contact with the ball
terminal 2 on the device under test 1. Several of these are shown
in FIG. 12-18.
[0164] FIG. 12 is a plan drawing of a generally planar top contact
pad 21A.
[0165] FIG. 13 is a plan drawing of a top contact pad 21B that
extends out of the plane of the pad. In the example shown in FIG.
13, the center of the contact pad 21B extends farther away from the
top pin than the edges do, although this is not a requirement. In
some cases, the top contact pad 21B is curved and is convex.
[0166] FIG. 14 is a plan drawing of a top contact pad 21C that
includes a protrusion out of the plane of the pad. In the example
shown in FIG. 14, the protrusion is essentially a line that extends
through the center of the pad. In other cases, the line may be
perpendicular to the one drawn in FIG. 14. In still other cases,
the protrusion may be a point or protruding region, rather than a
line. Alternatively, other protrusion shapes and orientations are
possible. In some cases, the top contact pad 21C is curved and is
concave. In other cases, the top contact pad 21C includes both
concave and convex portions.
[0167] FIG. 15 is a plan drawing of a top contact pad 21D that
includes multiple protrusions out of the plane of the pad. In the
example shown in FIG. 14, the protrusions are essentially linear
and parallel, although other shapes and orientations may also be
used. In some cases, the top contact pad 21D includes only flat
portions. In other cases, the top contact pad 21D includes both
curved and flat portions. In some cases, the top contact pad 21D
includes one or more edges or blades, which may be useful for the
"wiping" action described above.
[0168] FIG. 16 is a plan drawing of an inclined top contact pad
21E. One possible advantage of having an inclination to the top
contact pad is that it may encourage "wiping" of the terminal
2.
[0169] FIG. 17 is a plan drawing of an inclined top contact pad 21F
with multiple protrusions out of the plane of the pad. In addition
to the inclination, the protrusions may also enhance "wiping" of
the terminal 2. Here, the protrusions are grooves or ridges that
are parallel to the direction of the ball wiping action.
Alternatively, the grooves may be perpendicular to the ball wiping
action, as in FIG. 15.
[0170] FIG. 18 is a plan drawing of a textured top contact pad 21G.
In some case, the texture is a series of repeating structures,
which may be useful for "wiping" the terminal 2. In some cases, the
top contact pad 21G is knurled. In some cases, the knurl or texture
may be superimposed on a curved or otherwise shaped top contact
pad.
[0171] FIG. 19 is a plan drawing of a radially enlarged top contact
pad 21H. In practice, the maximum size that may be used may depend
on the two-dimensional layout of the pins on the devices under test
1, the mechanical response of the interposer membrane (i.e., will
the membrane longitudinally distort enough to ensure good contact
between top and bottom pins), and so forth. In some cases, the
shape or footprint of the top contact pad may be round, elliptical,
skewed, rectangular, polygonal, square, or any other suitable
shape. Furthermore, the top contact pad may have an enlarged
footprint in combination with any of the inclinations, protrusions
and textures described above.
[0172] FIG. 20 is a side-view drawing of a top pin 20 with a top
contact pad 21 that has rounded edges 25. In general, any or all of
the edges in the top pin 20, and likewise, the bottom pin 30, may
be rounded or sharp. Any rounded edges may be used with any or all
of the pin features shown herein.
[0173] It should be noted that any combination of the features
shown in FIGS. 12-20 may be used simultaneously. For instance,
there may be a generally flat top pin contact pad (21A) that also
has grooves in the length dimension (21F), or a top pin extending
out of the plane (21B) that also has grooves in the length
dimension (21F) and rounded edges (25). Any or all of these
features may be mixed and matched as needed.
[0174] The top pin 20 and bottom pin 30 may optionally include one
or more features that can allow the pins to be snapped into the
interposer membrane 10. Some exemplary engagement and/or retention
features are shown in FIG. 21-24.
[0175] FIG. 21 is a side-view cross-sectional drawing of a top pin
20 having a top pin engagement feature 26A on one side. In this
case, the engagement feature is a horizontal depression, or lip,
running along the underside of the top contact pad. Note that in
some cases, the longitudinal member of the top pin is rectangular
in profile, and the lip may run along one, two, three or all four
edges of the top pin. When inserted into the hole in the interposer
membrane, the top pin engagement feature 26A may engage all or a
part of the top contact plate 40, and may optionally engage a
portion of the foam or elastomer interposer 50. Such engagement
allows the top pin 20 to be connected to the rest of the interposer
membrane without adhesives and without any additional connection
components. Additionally, such an engagement feature 26A may allow
the interposer membrane to be assembled by first having the
sandwich structure of the top plate, the foam and the bottom
plates, with holes in the locations that will ultimately house
pins, then by inserting each pin into a hole until the engagement
feature catches the Kapton.RTM. contact plate. Each hole itself
should be suitably sized to allow the pin to be snugly inserted up
to the lip, albeit with a tight fit.
[0176] FIG. 22 is a side-view cross-sectional drawing of a top pin
20 having a top pin engagement feature 26B on two opposing sides.
This has the advantages of feature 26A shown in FIG. 21, with
additional engagement and retention strength. For top pin
longitudinal members that have a round cross-section, the lip 26B
may extend all or partway around the circumference of the
longitudinal member.
[0177] FIG. 23 is a side-view cross-sectional drawing of a top pin
20 having a two top pin engagement features 26B engaging the top
contact plate, and one engagement feature 26C engaging the foam
interposer 50. This also has additional engagement and retention
strength. In some cases, it may be preferable to engage the bottom
plate to the foam, rather than the top plate, so that the top plate
is free to move without restriction. In some cases, the foam may
not fully extend into the engagement feature, or may not extend at
all into the engagement feature.
[0178] The bottom pin 30 may also have similar engagement and
retention features. For instance, FIG. 24 shows an engagement
feature or lip 36A that engages a portion of the bottom contact
plate 60. Other configurations are possible, analogous to those for
the top pin 20.
[0179] Several of the figures above show individual features or
elements. FIGS. 25 through 27 show a more detailed example, in
which many of the features are combined. Note that this is merely
an example and should not be construed as limiting in any way.
[0180] FIG. 25 is a perspective-view cross-sectional drawing of an
exemplary interposer membrane 10. FIG. 26 is an end-on
cross-sectional drawing of the interposer membrane 10 of FIG. 25.
FIG. 27 is a plan drawing of the interposer membrane 10 of FIGS. 25
and 26.
[0181] The terminals from a device under test contact respective
top pins 20, and the contact pads 4 from a load board contact
respective bottom pins 30. In this example, the top contact pad 21B
is cylindrically curved and convex, and the bottom contact pad 31
is flat. The top and bottom contact pins slide past each other
along mating surfaces 23B and 33B, which in this example are
cylindrically curved. The mating surfaces 23B and 33B contact each
other along a virtual, cylindrically curved interface surface 30B,
denoted by the dashed line in FIG. 26. The pins have top and bottom
relief surfaces 24, 34, which in this example are both oriented
generally perpendicular to the membrane 10 when the pins are fully
compressed. In this example, the top and bottom pin contact pads
have rounded edges 25, 35. The top and bottom pins have engagement
features 26A, 36A that engage the top and bottom contact plates,
40, 60, respectively, as well as optional engagement features 26C,
36C that engage the foam layer 50.
[0182] FIG. 27 shows an exemplary layout for the pins 20 in the
membrane 10. In this example, the pins themselves are laid out in a
generally square grid, corresponding to both the terminal and
contact pad layouts of the device under test and the load board,
respectively. Note that the footprint of the contact pad is
oriented at a 45 degree angle with respect to the square grid,
which allows for a larger contact pad than would be possible if the
pad were extended along the square grid itself. Note also that the
orientation of the interface surface 70B is at a 45 degree angle
with respect to the square grid. In practice, the interface surface
70B may alternatively be oriented along the grid, or at any
suitable angle with respect to the grid.
[0183] It is instructive to consider some elements that are
particularly useful for so-called "Kelvin" testing. Unlike the one
terminal/one contact pad testing described above, Kelvin testing
measures the resistance between two terminals on the device under
test. The physics of such a measurement is straightforward--we pass
a known current (I) between the two terminals, measure the voltage
difference (V) between the two terminals, and use Ohm's Law (V=IR)
to calculate the resistance (R) between the two terminals.
[0184] In a practical implementation, each terminal on the device
under test is electrically connected to two contact pads on the
load board. One contact pad is effectively a current source or
current sink, which supplies or receives a known amount of current.
The other contact pad acts effectively as a voltmeter, measuring a
voltage but not receiving or supplying a significant amount of
current. In this manner, for each terminal on the device under
test, one pad deals with I and the other deals with V.
[0185] While it is possible to use two separate pin pairs for each
terminal, each pin pair corresponding to a single contact pad on
the load board, there are drawbacks to this method. For instance,
the tester would have to make two reliable electrical connections
at each terminal, which would prove difficult for exceedingly small
or closely spaced terminals. In addition, the membrane that holds
the pin pairs would include essentially twice as many mechanical
parts, which may increase the complexity and cost of such a
membrane.
[0186] A better alternative is a pin mechanism that combines the
electrical signals from two contact pads on the load board
internally, so that only one top pin pad need make reliable contact
with each terminal, rather than two distinct pins contacting each
terminal. There are five possible pin schemes that can combine the
two load board signals into a single top pin, each described
briefly below.
[0187] First, the electrical signals are combined at the load board
itself, as is the case for a single bottom contact pad that
subtends two adjacent pads on the load board.
[0188] Second, the electrical signals are combined at the bottom
pin. For this case, the membrane would include two distinct bottom
contact pads, or a single bottom contact pad with an insulating
portion that electrically separates one load board contact pad from
the other.
[0189] Third, the electrical signals are combined at the top pin.
For this case, the entire bottom pin is divided into two halves
separated by an electrical insulator.
[0190] Fourth, the electrical signals are combined at the top
contact pad, or equivalently, as close as possible to the terminal
of the device under test. For this case, the entire bottom pin and
much or all of the longitudinal member of the top pin are divided
into two halves separated by an electrical insulator. The halves
are electrically joined at the top contact pad, and are
electrically isolated from each other below the top contact pad,
i.e., between the top contact pad and the respective load board
contact pad.
[0191] Finally, fifth, the electrical signals are combined only at
the terminal of the device under test. The top contact pad, the top
pin, the bottom pin, and the bottom contact pad(s) all include an
electrical insulator that divides the pins and pad(s) into two
electrically conductive portions that are electrically insulated
from each other. In practical terms, the pins may be symmetrically
bisected by the insulating material, so that a "left" half may be
electrically insulated from a "right" half, where the "left" half
electrically contacts one pad on the load board and the "right"
half electrically contacts another pad on the load board.
[0192] In some cases, there are advantages to keeping the
electrical signals isolated from each other along most or all of
the longitudinal extent of the pins. If the signals are connected
at the load board, there is an unnecessary redundancy, as if there
were to two independent signal paths. In addition, connecting the
signals at the load board may actually lower the associated
inductances, since two inductances in parallel result in half the
inductance.
[0193] An example of the fifth case above is shown in FIGS. 28 and
29.
[0194] FIG. 28 is a plan drawing of an exemplary top contact pad
121 for Kelvin testing, with an insulating portion 128 that
separates the two conducting halves 127, 129 of the pad. In many
cases, the insulating portion extends throughout the full
longitudinal extent of the top pin, and effectively separates the
pin into two conducting portions that are electrically insulated
from each other. In many cases, the bottom pin may also include an
analogous insulating portion that separates the bottom pin into two
conducting portions that are electrically insulated from each
other.
[0195] FIG. 29 is a side-view drawing of an exemplary pin pair 120,
130 for Kelvin testing, with an insulating ridge 180 that extends
outward from the top pin mating surface 123. The ridge 180 may be
generally planar and may extend through the entire top pin 120. The
ridge 180 effectively bisects the top pin 120, and electrically
insulates one half (facing the viewer in FIG. 29) from the other
half (facing away from the viewer in FIG. 29). The ridge may be
made from any suitable insulating material, such as Kapton.RTM.,
and so forth.
[0196] The ridge 180 itself extends outward from the mating surface
123, and electrically insulates one half of the surface from the
other. The mating surface 123 now includes two non-contiguous
halves, separated by a ridge that extends outwardly from the
surface. The corresponding mating surface 133 on the bottom pin 130
includes a suitable groove for accepting the ridge; the groove is
an indentation along the mating surface 133 and is not shown in
FIG. 29. In some cases, the groove may extend deeper than the
ridge, so the "top" of the ridge does not contact the "bottom" of
the groove at any point in the range of travel. This may be
desirable, in that the mating surfaces 123 and 133 may share less
common surface area, and may produce less friction as they move
past each other. In other cases, the "top" of the ridge does
contact the "bottom" of the groove. The ridge and groove structure
serves to keep the mating surfaces aligned, as with the cases
described above.
[0197] In some cases, the groove and ridge are both made from
electrically insulating material, which separate the top and bottom
pins each into two conducting portions that are electrically
insulated from each other. This allows a single mechanical pin to
be used for two independent electrical contacts, which is
beneficial for Kelvin testing. Note that in FIG. 29, the groove on
the bottom pin is hidden by surface 133, and would appear to the
right of surface 133, much in the way that ridge 180 appears to the
right of surface 123 in the top pin. The groove may be as deep or
deeper than the ridge 180.
[0198] In some cases, the groove (not shown) would be sized to
receive the ridge or land 180 and just wider than the ridge. With
this sizing, the elements can slide by each other freely. In
addition, the ridge-groove engagement provides a reliable track for
sliding of the top and bottom elements 120, 130, thereby preventing
skew or misalignment as the elements move with respect to each
other. It is also possible to make the ridge and groove of an
electrically conductive material (i.e., not a dielectric) where
Kelvin testing capabilities are not needed. This may provide the
same tracking capability and may also increase the electrical
contact surface area.
[0199] The virtual interface surface 170 may differ slightly from
the cases described above, in that it may not include the portion
occupied by the ridge and groove structure. In these cases, the
interface surface 170 may include two non-contiguous regions, one
in the "front" and one in the "back", as drawn in FIG. 29. Each
region may include planar, a cylindrically curved, or a spherically
curved surface, as described above.
[0200] Note that in some cases, the interface surface may include
discontinuities, such as a change in the radius of curvature. In
general, such discontinuities are perfectly acceptable as long as
the two mating surfaces 123 and 133 remain in contact for most or
all of their full ranges of travel. For instance, the "front"
portion may have one particular radius of curvature, and the "rear"
portion may have a different radius of curvature, and the two
centers of curvature may be coincident or collinear, to permit the
mating surfaces to move and remain in contact. Other variations may
include "stripes" along the mating surfaces, where each stripe may
have its own particular radius of curvature, the radii all being
coincident or collinear.
[0201] It will be understood that the ridge and groove of the top
and bottom pins may be exchanged for a groove and ridge on the top
and bottom pins, respectively. It will also be understood that the
concavities of the top and bottom mating surfaces may be reversed
as well.
[0202] Note that in the text and figures thus far, the membrane 10
has been shown as a sandwich structure, with two outer layers
surrounding an inner layer. In general, the outer layers of this
sandwich structure have different mechanical properties than the
inner layer, with the outer layers being a semi-rigid thin film and
the inner layer being a vertically resilient material. As an
alternative, the sandwich structure may be replaced by a monolithic
membrane, which may be formed as a single layer having a single set
of mechanical properties. The outer surfaces of such a single
monolithic layer would face the load board and device under test.
In such cases, the membrane itself may be formed as a single layer
having a set of vertically-oriented holes. The two pins are placed
into the holes from the top and bottom.
[0203] Finally, we describe the interposer 50 in more detail.
[0204] The simplest design for the interposer is just a monolithic
structure, with holes extending from the top contact plate to the
bottom contact plate that can accommodate the pins. In this
simplest design, the interposer material completely surrounds the
holes, and has no internal structure aside from the holes
themselves.
[0205] Other designs for the interposer are possible as well,
including designs that incorporate some hollow space within the
interposer itself. In these designs, the holes for the pins may
resemble those in the monolithic design, but the interposer that
surrounds these holes may have some structured hollow space in the
regions surrounding the pin holes.
[0206] A specific example for such a structured interposer is shown
in FIGS. 30-33. FIG. 30 is a plan drawing of an interposer
membrane, inserted into a frame. FIG. 31 is a plan drawing of the
interposer membrane of FIG. 30, removed from the frame. FIG. 32 is
a four-view schematic drawing of the interposer membrane of FIGS.
30-31, with FIGS. 32a-d including top-view, plan view, front view
and right-side view drawings, respectively. FIG. 33 is a four-view
schematic drawing of the interposer, from the interposer membrane
of FIGS. 30-32, with FIGS. 33a-d including top-view, plan view,
front view and right-side view drawings, respectively.
[0207] In this specific example, the interposer 50 is structured as
a honeycomb, with supporting members 230 that extend between the
pin-supporting holes 210, and generally empty space 240 between the
supporting members 230.
[0208] There are many possible designs for the supporting members
230 within the interposer. FIGS. 34 includes 24 specific designs
for the interposer supporting members, shown in cross-section. The
holes 210 and the supporting members 230 may take on any of a
number of shapes, sizes and orientations. In these examples, the
supporting members 230 may extend from one pin-supporting hole to a
directly-adjacent hole, or from one pin-supporting hole to a
diagonally-adjacent hole. Other orientations, shapes and sizes are
possible, as well.
[0209] In general, the specific design for the interposer is chosen
to have particular mechanical characteristics, rather than specific
aesthetic traits. It is desirable that the interposer be vertically
resilient, and provide support and suitable resistance for the
pins.
[0210] As seen in FIG. 34 showing 24 alternative structures, in
addition to interposer structure that is generally cylindrical
(i.e., each cross-section of the structure is the same, for all
planes within the interposer that are parallel to the contact
plates), there may also be out-of-the-plane structure. For
instance, FIG. 35 is a plan drawing of an interposer having
supporting/bridging members 260 that extend between adjacent holes
within a particular plane, which may or may not be in the same
plane as the top or bottom edges of the cylindrical structures. As
another example, FIG. 36 is a plan drawing of an interposer having
a supporting plane 270 that completely fills the area between
adjacent holes, but is absent above or below that plane. FIG. 37
includes 18 specific designs for the interposer, shown in
cross-section, where the top and bottom contact plates are
horizontally oriented, and the pin direction is generally vertical.
As seen from the drawing, many possible cross-sectional designs are
possible.
[0211] In general, the interposer 50 need not be monolithic, and
can include one or more hollow regions with a design that can vary
within the plane of the interposer membrane (as in FIG. 34) and can
vary out of the plane of the interposer membrane (as in FIG. 35).
Mechanical performance of any interposer design may be simulated
readily using finite element analysis.
[0212] In applications where there is a need to reduce contact
resistance to a minimum, an effective solution lies is increasing
the point contact pressure between the contact pin and the array
contact. Of course, this could be done by increasing the insertion
force but it has its limits. In addition, increasing the
ablating/scraping action can remove oxide build up. Combining
solutions provides the optimum result.
[0213] To increase the point contact pressure/force, without
increasing the insertion/actuator force overall, it is possible to
reduce the contact surface area with the embodiment shown in FIG.
38 which has a blade like constructions. The point contact pressure
is actually increased (due to the decrease in contact surface area.
This has the additional benefit of decreasing the contact
resistance, because the sharp blade construction produces a
penetrating effect which reduces resistance by ablating oxide and
by penetrating slighting into the ball contact to a place were
oxide has not yet formed. In FIG. 38, top pin 320 has a similar
basic shape as pin 20 in previous embodiments except that the top
surface 321 has been altered to provide the benefits mentioned
above. The top pin has a top engagement surface 321 which engages
electrical connections to a device under test (20), the top
engagement surface may include sharp longitudinal contact ridge 326
rising above the engagement surface 322, to an apex, the ridge
extending at least along the major portion of the engagement
surface. The ridge can be straight, planar, or curved and or non
linear. Sharp is desirable.
[0214] Unlike the fully planar surface 21 of pin 20, pin 320 has a
split top surface, with a first portion 322 being a planar strip
extending longitudinally from one end to the other, and then a
projection portion 324 which rises from the surface 322 to a sharp
or knife edge peak 326, creating a step to a planar wall 328. As
visible in FIG. 41, on the back side of the wall 328, is a sloped
wall 330 which terminates at an obtuse angle intersection 322 and
rejoins the rear wall of the pin 320. Wall 328 is position
generally at a mid point along the lateral dimension of surface 322
so that the knife edge 326 is likely to strike the ball 2 likewise
near its midpoint where contact pressure will be greatest. The back
slope surface 320 need not be flat as shown but may follow any
shape so long as it can support the knife edge. Wall 328 likewise
does not have to be planar, and may be sloped.
[0215] This above embodiment is only exemplary, as other designs
are possible so long as that increase point contact pressure,
without increasing overall pressure, and reduce resistance.
[0216] These goals are accomplished by making edge 326 sharp enough
to penetrate (even microscopically), the surface on the contact 2.
The first few atoms on the surface of the ball are often oxidized
but even slight penetration can bypass that resistive layer.
[0217] For example, knife edge 326 may be skewed instead of
parallel to the longitudinal dimension. As seen in FIG. 39 in
dotted lines or in a complete view of its own in FIG. 42, it could
follow a skewed path shown as line 326a from points 400 to 402. By
electing a now parallel path between longitudinal ends of the pin
top surface, there will be increased ablation of the exterior
surface of ball 2. This can be further increased by making line
326a follow a curved or serpentine path (non-linear). This will
further increase the ablation of the ball surface. Likewise, a
plurality of spaced apart notches/serrations in and along the major
part of the length of the knife edge would create additional
ablation and thus lower electrical resistance by scrape away
oxides.
[0218] The additional forms shown in FIGS. 12-19 also provide
advantages similar to the embodiment in FIG. 38 and could be
further enhanced if their surface was hemispherical or domed shaped
(similar to the curvature of FIG. 13 but having the features of
FIGS. 12, 15-19. Some specific examples of alternate configurations
are shown in FIGS. 43-48
[0219] FIGS. 43 and 44 illustrate double sided domed knife edge
peaks with curved or hemispherical sidewalls 434 in FIG. 43 and
steeper sidewalls 436 in FIG. 44. The steep curved sidewalls of
FIG. 44 provide for a sharper knife edge which may be desirable in
certain configurations. FIG. 45 shows a protecting land structure
426 having a generally planar top surface, generally planar
parallel side wall 424 and generally planar shelf or ledge portions
422a and 422b on either side of the land 426. The location of land
426 shown at the midpoint across the top surface of the pin is not
required. It can be offset left or right or the entire land can be
skewed as in FIG. 42, but unlike FIG. 42, the top edge 428 is
planar and not knife edged.
[0220] FIGS. 46 and 47 are variations of FIG. 45 where land 426
terminates in a peaked structure 430 with converging sidewalls. In
FIG. 46, the sidewalls are first generally parallel from their base
422a and then transform into a triangular peaked shape with
converging planar sidewalls. In FIG. 47 the parallel sidewalls are
replaced with converging sidewalls which taper from their base
422c, which as shown may be hemispherical, rounded or curved to a
plateau where the tapered converging sidewalls 432 rise to a
peak
[0221] FIGS. 48-51 illustrates an embodiment which may be used in
combination with all of the previous embodiments but is shown only
in a knife edge configuration for simplicity. Here a plurality of
lands 440 (with recess 440a in FIG. 49 for example), 442, and 444
extend upwardly from the base of the top pin are oriented into two
or three parallel knife edge lands. They are shown as knife edged
but can be any other top edge. Furthermore, they are shown as
parallel but may be skewed as in FIG. 42, and the skew angle of
each of the lands may be different so that the lines of the top
edges form may intersect (in actual fact or at an imaginary point
distant from the pin).
[0222] The knife edge ridge 326 should be hardened if possible,
such as by plating with hard gold under a beryllium copper which
provides strength and low resistance.
[0223] The spacing between lands 440 and 442 in FIG. 49 can be such
that a ball--style contact can reside partway received with in the
recess 440a. In the preferred embodiment, one-third to one half of
the contact would be received in the recess thereby providing for
substantial contact surface area and still create the scraping
action which removes oxides.
[0224] The disclosure also includes a method of lowering contact
resistance without increasing insertion force by creating a sharp
edge of contact which can engage the IC circuit contact with a
small surface area and consequently high point pressure according
to the disclosure herein. It is also possible to also increase the
drag (resistance) by slideably engaging the pin and terminal then
they are brought together and skewing the longitudinal ridge on the
top in. Various embodiments are shown which increase drag, thereby
removing oxide build up. The pin surface is slideably engaged with
the contacts on the IC by even the slightest lateral movement which
occurs when the IC is seated during insertion. This lateral
movement can be taken advantage of in addition to the above
mentioned methodology of increasing contact force by reducing
contact area and increasing contact depth by penetration of the
contact.
[0225] There is one notable further feature of FIGS. 30 and 31. The
frame in FIGS. 30 and 31 includes a series of preferably peripheral
mounting posts 220 that extend through corresponding locating holes
215 in the interposer membrane. In FIGS. 30 and 31, the locating
holes and posts are located around the perimeter of the membrane,
although any suitable post and hole locations may be used. In
general, these posts 220 are arranged with great lateral precision,
so that when a membrane is placed onto the frame, the pins in the
membrane are also placed with great lateral precision.
[0226] The description of the disclosure and its applications as
set forth herein is illustrative and is not intended to limit the
scope of the disclosure. Variations and modifications of the
embodiments disclosed herein are possible, and practical
alternatives to and equivalents of the various elements of the
embodiments would be understood to those of ordinary skill in the
art upon study of this patent document. These and other variations
and modifications of the embodiments disclosed herein may be made
without departing from the scope and spirit of the disclosure.
* * * * *