U.S. patent application number 09/870420 was filed with the patent office on 2002-01-03 for contact probe and fabrication method thereof.
Invention is credited to Haga, Tsuyoshi, Hayasaka, Nobuo, Matsunaga, Noriaki, Okumura, Katsuya, Shibata, Hideki.
Application Number | 20020000821 09/870420 |
Document ID | / |
Family ID | 18668029 |
Filed Date | 2002-01-03 |
United States Patent
Application |
20020000821 |
Kind Code |
A1 |
Haga, Tsuyoshi ; et
al. |
January 3, 2002 |
Contact probe and fabrication method thereof
Abstract
A contact probe is fabricated by a method including a
lithography step and a plating step. The contact probe includes a
plunger unit to form contact with a circuit to be tested, a spring
unit, and a lead wire connection unit, all formed integrally so as
to have a three dimensional configuration with uniform thickness
with respect to a predetermined plane configuration in a thickness
direction perpendicular to the predetermined plane configuration.
Preferably, a guide unit parallel to the spring unit is also formed
integrally. Further preferably, the contact probe is formed
integrally also including a stopper for each unitary configuration
of the spring unit constituted by a leaf spring.
Inventors: |
Haga, Tsuyoshi; (Ako-gun,
JP) ; Okumura, Katsuya; (Tokyo, JP) ;
Hayasaka, Nobuo; (Yokosuka-shi, JP) ; Shibata,
Hideki; (Yokohama-shi, JP) ; Matsunaga, Noriaki;
(Chigasaki-shi, JP) |
Correspondence
Address: |
FASSE PATENT ATTORNEYS, P.A.
P.O. BOX 726
HAMPDEN
ME
04444-0726
US
|
Family ID: |
18668029 |
Appl. No.: |
09/870420 |
Filed: |
May 30, 2001 |
Current U.S.
Class: |
324/755.05 |
Current CPC
Class: |
G01R 1/06716 20130101;
G01R 1/06738 20130101; G01R 1/06733 20130101; G01R 1/06722
20130101 |
Class at
Publication: |
324/761 |
International
Class: |
G01R 031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 1, 2000 |
JP |
2000-164407 |
Claims
What is claimed is:
1. A contact probe comprising: a plunger unit to form contact with
a circuit to be tested, a spring unit supporting said plunger unit
at one end, and a lead wire connection unit electrically connecting
another end of said spring unit with a lead wire, wherein said
plunger unit, said spring unit and said lead wire connection unit
are formed integrally.
2. The contact probe according to claim 1, wherein said plunger
unit, said spring unit and said lead wire connection unit are
formed integrally so as to have a three dimensional configuration
with uniform thickness with respect to a predetermined plane
configuration in a thickness direction perpendicular to said
predetermined plane configuration.
3. The contact probe according to claim 1, comprising a guide unit
arranged parallel to said spring unit to maintain said spring unit
at a constant posture, wherein said plunger unit, said spring unit,
said lead wire connection unit and said guide unit are formed
integrally.
4. The contact probe according to claim 3, wherein said plunger
unit, said spring unit, said lead wire connection unit and said
guide unit are formed integrally so as to have a three dimensional
configuration with uniform thickness with respect to a
predetermined plane configuration in a thickness direction
perpendicular to said predetermined plane configuration.
5. The contact probe according to claim 1, comprising a cylindrical
member including a conductor having an inner wall covered with an
insulator, said cylindrical member surrounding an outer side of
said spring unit, and said plunger unit protruding from said
cylindrical member.
6. The contact probe according to claim 5, wherein said lead wire
connection unit and said cylindrical member are fixed to each
other.
7. The contact probe according to claim 1, wherein said spring unit
includes a configuration in which a unitary configuration of a leaf
spring is repeated several times and connected.
8. The contact probe according to claim 7, wherein said spring unit
includes a stopper for each said unitary configuration, said
stopper arranged so as to abut against the leaf spring forming said
unitary configuration to prevent further elastic deformation when
the elastic deformation of said spring unit in a longitudinal
direction exceeds a predetermined value.
9. The contact probe according to claim 1, wherein said plunger
unit includes a top portion and inclination portions sandwiching
said top portion, wherein said inclination portions are angled at
not more than 90.degree. with respect to each other, and a radius
of curvature of a transverse section of said top portion is not
more than 5 .mu.m.
10. The contact probe according to claim 1, wherein a portion or
entire surface of said plunger unit including said top portion is
covered with a material of a volume resistivity lower than the
volume resistivity of the material inside said plunger unit.
11. A method of fabricating a contact probe, said contact probe
including a plunger unit to form contact with a circuit to be
tested, a spring unit supporting said plunger unit at one end, and
a lead wire connection unit electrically connecting another end of
said spring unit with a lead wire, wherein said plunger unit, said
spring unit and said lead wire connection unit are formed
integrally so as to have a three dimensional configuration with
uniform thickness with respect to a predetermined plane
configuration in a thickness direction perpendicular to said
predetermined plane configuration, said method of fabricating a
contact probe comprising: a resist formation step of coating a
resist on a substrate having conductivity, an exposure step of
exposing said resist using an integral mask, a first resist removal
step of removing a portion of said resist that is exposed by said
exposure step, a forming step of filling with metal a portion of
said resist removed at said first resist removal step, a second
resist removal step of removing a remaining portion of said resist,
and a substrate removal step of removing said substrate, wherein
said integral mask employs a mask of a configuration in which said
contact probe is projected in said thickness direction.
12. The method of fabricating a contact probe according to claim
11, wherein said contact probe further includes a guide unit
arranged parallel to said spring unit to maintain said spring unit
at a constant posture.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a contact probe to
electrically test semiconductor substrates, liquid crystal displays
and the like, and a method of fabricating such a contact probe.
[0003] 2. Description of the Background Art
[0004] Testing of circuitry formed on semiconductor substrates,
liquid crystal displays and the like is generally performed using a
testing device with a plurality of contact probes. The conventional
structure of each of such contact probes is as described in, for
example, Japanese Utility Model Laying-Open Nos. 6-22964 and
6-22965. A structure thereof is shown in FIG. 18. Referring to FIG.
18, a contact probe 100 has a barrel 103 placed in a socket 104. A
spring 102 employing a coil spring is arranged in barrel 103. A
plunger 101 to make contact with a circuit that is to be tested is
urged by spring 102 in a direction protruding from the end of
barrel 103.
[0005] According to this structure, plunger 101, spring 102, barrel
103 and socket 104 are individual components. In assembly thereof,
plunger 101 and spring 102 are inserted into barrel 103 so that
spring 102 urges plunger 101 outwards, followed by inserting this
barrel 103 into socket 104.
[0006] In accordance with the higher density and
microminiaturization of the circuitry that is the subject of
testing, more contact probes are now being mounted at higher
density per one testing device. As a result, a plurality of contact
probes must be arranged at small pitches of not more than 0.1
mm.
[0007] The conventional contact probe 100 as described with
reference to FIG. 18 had to be assembled from individual components
such as plunger 101, spring 102, barrel 103 and socket 104.
Therefore, in accordance with the fine geometry of the contact
probe, the assembly process has become more difficult since
respective components are correspondingly reduced in size. Since
each component is conventionally fabricated by machining, the size
of each component is also reduced in accordance with the
microminiaturization of contact probes. The machining process of
each component has become more difficult. Particularly when
components formed by machining are to be arranged at the pitch of
not more than 0.1 mm, the thickness of each component will become
the bottleneck in the arrangement.
[0008] In the case where many contact probes are to be mounted in
one testing device, the cost for component machine work will become
higher in proportion to the increase of the number of contact
probes since each contact probe component was conventionally formed
by machining. The demand in the field of art could not be satisfied
sufficiently.
[0009] In accordance with the increase in speed of the circuit
operation and reduction in the pitch, crosstalk noise between
contact probes has become noticeable. Such noise will degrade the
detection sensitivity.
SUMMARY OF THE INVENTION
[0010] In view of the foregoing, an object of the present invention
is to provide an ultra fine contact probe to correspond to
reduction in the pitch, and a method of fabricating such a contact
probe.
[0011] Another object of the present invention is to provide a
contact probe that has the shielding function to prevent crosstalk
noise even when of an ultra fine structure.
[0012] According to an aspect of the present invention, a contact
probe includes a plunger unit to form contact with a circuit to be
tested, a spring unit supporting the plunger unit at one end, and a
lead wire connection unit electrically connecting the other end of
the spring unit with a lead wire. The plunger unit, the spring unit
and the lead wire connection unit are formed integrally. This
structure eliminates the need to form each component and assembly
thereof. Reduction in the size of the contact probe and increase in
the number of contact probes can be accommodated more easily.
[0013] In the invention of the present aspect, the plunger unit,
the spring unit and the lead wire connection unit are formed
integrally so as to have a three dimensional configuration with
uniform thickness with respect to a predetermined plane
configuration in a thickness direction perpendicular to the
predetermined plane configuration.
[0014] By employing the above-described structure, a contact probe,
even of an ultra fine structure, can easily be fabricated as an
integral object according to a fabrication method of a combination
of lithography and plating using a predetermined mask.
[0015] In the invention of the present aspect, the contact probe
preferably includes a guide unit arranged parallel to the spring
unit to maintain the spring unit at a constant posture. The plunger
unit, spring unit, lead wire connection unit and guide unit are
formed integrally. By this structure, the step of assembling the
guide unit can be eliminated even if a guide unit is required
depending upon the usage status of the contact probe.
[0016] In the invention of the present aspect, the plunger unit,
spring unit, lead wire connection unit and guide unit are
preferably formed integrally so as to form a three dimensional
configuration with uniform thickness with respect to a
predetermined plane configuration in a thickness direction
perpendicular to said predetermined plane configuration.
[0017] By the above structure, a contact probe including a guide
unit, even of an ultra fine structure, can be easily fabricated as
an integral object according to a fabrication method of a
combination of lithography and plating using a predetermined
mask.
[0018] In the invention of the present aspect, the contact probe
preferably includes a cylindrical member including a conductor
having the inner wall covered with an insulator. The cylindrical
member surrounds the outer side of the spring unit. The plunger
unit protrudes from the cylindrical member. This structure allows
the cylindrical member to function as a guide unit. Since the
cylindrical member includes a conductor, the spring unit is
shielded by the cylindrical member to prevent crosstalk noise.
[0019] In the invention of the present aspect, the lead wire
connection unit and the cylindrical member are fixed with respect
to each other. By this structure, displacement of the cylindrical
member during usage can be prevented.
[0020] Preferably, the spring unit has a configuration in which a
leaf spring of a unitary configuration is repeated several times
and connected. By this structure, a mask of only a simple pattern
is required. A spring unit having a uniform spring constant at all
sites can be provided.
[0021] Preferably, the spring unit includes a stopper for each of
said unitary configuration. The stopper is arranged so as to abut
against the leaf spring of the above-described unitary
configuration to prevent further elastic deformation when the
elastic deformation in the longitudinal direction of the spring
unit exceeds a predetermined value. This structure prevents the
spring from exceeding the elasticity limit to achieve plastic
deformation and become disabled.
[0022] Preferably, the plunger unit includes a top portion and
inclination portions sandwiching the top portion. The inclination
portions are angled at not more than 90.degree. with respect to
each other. The radius of curvature of the transverse section of
the top portion is not more than 5 .mu.m. By this structure, the
insulating film such as a natural oxide film formed at the surface
of the circuit to be tested can easily be broken through to ensure
electrical contact.
[0023] Preferably, a portion or all of the surface of the plunger
unit including the top portion is covered with a material of low
volume resistivity that is lower than the volume resistivity of the
material inside the plunger unit. By this structure, the electrical
contact resistance when the plunger unit is brought into contact
with the circuit to be tested can be reduced to ensure stable
electrical contact.
[0024] According to another aspect of the present invention, a
method of fabricating a contact probe is provided. The contact
probe includes a plunger unit to form contact with a circuit to be
tested, a spring unit supporting the plunger unit at one end, and a
lead wire connection unit electrically connecting the other end of
the spring unit with the lead wire. The plunger unit, the spring
unit and the lead wire connection unit are formed integrally so as
to have a three dimensional configuration with uniform thickness
with respect to a predetermined plane configuration in a thickness
direction perpendicular to the predetermined plane configuration.
The contact probe fabrication method includes a resist formation
step of coating a resist on a substrate having conductivity, an
exposure step of exposing the resist using an integral mask, a
first resist removal step of removing the portion of the resist
exposed at the exposure step, a forming step of filling the portion
of the resist removed at the first resist removal step with metal,
a second resist removal method of removing the remaining portion of
the resist, and a substrate removal step of removing the substrate.
As the integral mask, a mask of a configuration having the contact
probe projected in the thickness direction is employed.
[0025] By the above-described fabrication method, a contact probe
having the plunger unit, spring unit and lead wire connection unit
formed integrally can be easily fabricated. Reduction in the size
and complexity of the contact probe can be accommodated.
Furthermore, the assembly process is unnecessary.
[0026] Preferably, the contact probe further includes a guide unit
arranged parallel to the spring unit to maintain the spring unit at
a constant posture.
[0027] By the fabrication method, a contact probe having the
plunger unit, spring unit, lead wire connection unit and guide unit
formed integrally can be easily fabricated. Also, reduction in the
size and complexity of the contact probe can be accommodated.
Furthermore, the assembly process is unnecessary.
[0028] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 is a perspective view of a contact probe according to
a first embodiment of the present invention.
[0030] FIG. 2 is a plan view of an integral mask employed in the
fabrication method of a contact probe according to the first
embodiment of the present invention.
[0031] FIGS. 3, 4, 5, 6 and 7 are sectional views of the contact
probe of the first embodiment in a first step, second step, third
step, fourth step, and fifth step, respectively, in the fabrication
method of the contact probe.
[0032] FIG. 8 is a diagram to describe the usage status of the
contact probe of the first embodiment.
[0033] FIGS. 9A-9C are enlarged plan views of the plunger unit of
the contact probe of the first embodiment.
[0034] FIG. 10A is an enlarged perspective view and FIG. 10B is a
transverse sectional view, respectively, of the plunger unit of the
contact probe of the first embodiment.
[0035] FIG. 11 is a perspective view of another contact probe
according to the first embodiment of the present invention.
[0036] FIG. 12 is a perspective view of a contact probe according
to a second embodiment of the present invention.
[0037] FIG. 13 is a plan view of an integral mask employed in the
fabrication method of a contact probe of the second embodiment.
[0038] FIG. 14 is a perspective view of another contact probe of
the second embodiment.
[0039] FIG. 15 is a perspective view of a further contact probe of
the second embodiment.
[0040] FIG. 16 is a perspective view of still another contact probe
of the second embodiment.
[0041] FIG. 17A is a diagram to describe the assembly of the
contact probe of a third embodiment, and FIG. 17B is a perspective
view of a completed product thereof.
[0042] FIG. 18 is a sectional view of a contact probe according to
conventional art.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] First Embodiment
[0044] Referring to FIG. 1, a structure of a contact probe 50
according to a first embodiment of the present invention will be
described hereinafter. Contact probe 50 includes a plunger unit 1
to form contact with a circuit to be tested, a spring unit 2, and a
lead wire connection unit 3. Spring unit 2 supports plunger unit 1
at one end. The other end of spring unit 2 is connected to lead
wire connection unit 3. Lead line connection unit 3 functions to
electrically connect the end of spring unit 2 with a lead wire (not
shown).
[0045] This structure is formed integrally from a conductive
material. As shown in FIG. 1, a three dimensional configuration is
established with uniform thickness with respect to a predetermined
plane configuration in a thickness direction perpendicular to the
predetermined plane configuration. Therefore, the thickness is
substantially identical at all portions. The thickness direction is
the direction from the left bottom side towards the right upper
side in FIG. 1.
[0046] In the exemplary contact probe 50 of FIG. 1, spring unit 2
has a configuration in which a leaf spring constituting a ring as a
unitary configuration is repeatedly formed. The plurality of the
rings are connected.
[0047] A method of fabricating contact probe 50 will be described
hereinafter with reference to FIGS. 2-7.
[0048] A resist 22 is formed (not shown) at the surface of a
conductive substrate 21. An Si substrate sputtered with Ti is used
as substrate 21. Other conductive substrates such as an aluminum
substrate may be employed alternatively.
[0049] Using an integral mask 30 shown in FIG. 2, the surface of
resist 22 is irradiated with an X-ray 23 as shown in FIG. 3.
Although a method employing X ray lithography will be described
here, UV (Ultra Violet) lithography may be employed instead of X
ray lithography. Whichever type of lithography is employed, the
resist of exposed portion 24 is removed after development. As a
result, a recessed portion 25 as shown in FIG. 4 is formed.
[0050] Referring to FIG. 5, forming is applied to fill recessed
portion 25 with a metal layer 26. Possible material for metal layer
26 includes nickel, or nickel based alloy such as Ni--Co, Ni--W,
and Ni--Mn. Also, palladium (Pd), rhodium (Rh) or ruthenium (Ru)
may be employed.
[0051] Resist 22 remaining on substrate 21 is removed by ashing
using oxygen plasma or by a development process after radiation. As
a result, the structure shown in FIG. 6 is obtained. Using
potassium hydroxide (KOH), the region of substrate 21 is dissolved
away to leave only the portion of metal layer 26. As a result,
contact probe 50 is produced as shown in FIG. 7. In other words,
this corresponds to contact probe 50 of FIG. 1.
[0052] In order to reduce the electrical contact resistance of
plunger unit 1, the entire surface or the surface around the
leading end of plunger unit 1 can be plated with gold (Au) or
rhodium (Rh).
[0053] A specific method of testing a circuit to be tested 65
formed at the surface of an under-test substrate 64 using contact
probe 50 will be described with reference to FIG. 8. A plurality of
guide holes 62 corresponding to the arrangement pitch of under-test
circuit 65 are provided at an insulating substrate 61 of the
testing device. A contact probe 50 is arranged in each of guide
holes 62. The leading end of each contact probe 50 protrudes
outwards from the side of insulating substrate 61 facing under-test
substrate 64. At the other side of insulating substrate 61 opposite
to under-test substrate 64, a lead wire such as a flexible printed
circuit (FPC) 63 is arranged so as to be electrically connected to
lead wire connection unit 3 of each contact probe. Under-test
circuit 65 is tested using such a testing device.
[0054] Since the above contact probe has a three dimensional
configuration with uniform thickness with respect to a
predetermined plane configuration in a thickness direction
perpendicular to said predetermined plane configuration as
described with reference to FIG. 1, a contact probe, even of an
ultra fine structure, can be easily fabricated as an integral
object according to a fabrication method of a combination of
lithography and plating. Since each component does not have to be
machined or assembled in the fabrication method, reduction in the
size and complexity of the contact probe can be accommodated
sufficiently.
[0055] In contact probe 50, plunger unit 1 is supported at one end
of spring unit 2. Since spring unit 2 is formed of a combination of
leaf springs of unitary configuration, any force or impact applied
towards plunger unit 1 in the longitudinal direction of contact
probe 50 (vertical direction in FIG. 1) will cause spring unit 2 to
be deformed elastically as a whole to absorb that applied energy.
Therefore, as in a conventional contact probe, the stroke of
elastic deformation can be ensured sufficiently while the width of
the entire contact probe can be reduced compared to the
conventional case. For example, the width can be set to less than
0.1 mm with a stroke of at least 0.05 mm.
[0056] Even though the configuration is ultra fine, variation in
the spring constant can be set low enough. For example, assuming
that the range of the spring constant is 0.1 N/mm-10 N/mm,
variation in the spring constant is within .+-.35% in the case of
UV lithography and within .+-.10% in the case of X ray lithography.
Variation according to X ray lithography is smaller since the
resolution in lithography is superior due to the shorter wavelength
for X rays, which allows a leaf spring to be produced more precise
in thickness.
[0057] By covering the entire surface of the plunger or the surface
around the leading end of the plunger unit with a material such as
gold (Au) or rhodium (Rh) of a volume resistivity lower than that
of the material inside the plunger, the electrical contact
resistance when the plunger unit is brought into contact with the
under-test circuit can be reduced. Therefore, stable electrical
contact can be ensured.
[0058] The configuration of the contact probe is not limited to
that shown in FIG. 1. An enlargement of the periphery of plunger
unit 1 of contact probe 50 of FIG. 1 is shown in FIG. 9A. A plunger
unit 1a as shown in FIG. 9B or a plunger unit 1b as shown in FIG.
9C may be employed depending upon the configuration and property of
the circuit to be tested.
[0059] An enlarged perspective view of plunger unit 1a of FIG. 9A
is shown in FIG. 10A. Plunger unit 1a has a constant thickness.
More specifically, plunger unit 1a includes a top portion 4 as one
side and inclination portions 5 that are two planes sandwiching top
portion 4. The transverse sectional view of the configuration of
plunger unit 1a is as shown in FIG. 10B. More specifically,
inclination portions 5 are angled not more than 90.degree. with
respect to each other. The radius of curvature of the transverse
plane of top portion 4 is preferably not more than 5 .mu.m. This
provides the advantage that an insulating film such as a natural
oxide film formed at the surface of the under-test circuitry can be
easily broken to ensure electrical contact.
[0060] Although a leaf spring of unitary configuration that is
repeated for a plurality of times continuously as shown in FIG. 1
is desirable for the spring unit, a configuration other than that
shown in FIG. 1 can be employed. For example, a contact probe 51 as
shown in FIG. 11 may be provided, having a wave-like spring unit
2a. In the case of spring unit 2a, the S shaped portion formed of
the leaf spring can be regarded as the unitary configuration.
[0061] Second Embodiment
[0062] A structure of a contact probe 52 according to a second
embodiment of the present invention will be described with
reference to FIG. 12. Contact probe 52 includes a plunger unit 1 to
form contact with a circuit to be tested, a spring unit 2, a lead
wire connection unit 3, and a guide unit 6. The structural elements
other than the addition of guide unit 6 are similar to those of the
first embodiment shown in FIG. 1. Guide unit 6 is formed integrally
with the other components.
[0063] In comparison to the fabrication method described in the
first embodiment, an integral mask 31 shown in FIG. 13 is used
instead of integral mask 30 of FIG. 2. The remaining steps are
similar to those of the first embodiment.
[0064] The embodiment described with reference to FIG. 8 has
contact probe 50 arranged in guide hole 62 of insulating substrate
61. Therefore, a guide unit 6 was not required. However, in other
usages, some guide is required to prevent buckling of spring unit 2
and to maintain spring unit 2 at a constant posture. In the case of
contact probe 50 shown in FIG. 1, a guide unit had to be attached
afterwards. In the case of contact probe 52 shown in FIG. 12, no
attaching process is required since guide unit 6 is formed
integrally. Therefore, the labor in assembling can be alleviated.
Furthermore, guide unit 6 can be provided at the desired
relationship of position as long as integral mask 31 is properly
designed.
[0065] In the case guide unit 6 is provided, the configuration of
the spring unit is not limited to that of spring unit 2 in contact
probe 52 shown in FIG. 12. For example, contact probe 53 as shown
in FIG. 14 may have a spring unit 2a.
[0066] Also, a structure may be implemented in which a stopper 7 is
provided for each unitary configuration of spring unit 2 for
contact probe 52 to result in a contact probe 54 as shown in FIG.
15. Stopper unit 7 is a member to prevent the spring from sagging
excessively. This structure prevents the spring from exceeding the
elasticity limit to achieve plastic deformation and become
disabled.
[0067] The configuration of the stopper is not limited to that of
stopper 7. For example, a stopper 7a as shown in FIG. 16 of a
contact probe 55 can be provided. Any change in the configuration
of the stopper can be accommodated by just modifying the pattern
configuration of the integral mask. A contact probe can be formed
integrally according to a fabrication method employing lithography
and plating as described in the first embodiment.
[0068] Third Embodiment
[0069] A contact probe 56 according to a third embodiment of the
present invention is similar to contact probe 50 of FIG. 1 in the
configuration of the integrally formed portion. However, as shown
in FIG. 17A, the integrally formed portion is inserted inside a
cylindrical member 8, and plunger unit 1 protrudes from the other
end of cylindrical member 8, as shown in FIG. 17B. Cylindrical
member 8 is basically formed of a conductor having the inner wall
covered with an insulator. Furthermore, at a fixed portion 9 where
lead wire connection unit 3 and cylindrical member 8 overlap, lead
wire connection unit 3 and cylindrical portion 8 are preferably
fixed to each other.
[0070] Since plunger unit 1 protrudes from an end of cylindrical
member 8, plunger unit 1 can be brought into contact with the
circuit to be tested as in the conventional case. Furthermore,
since spring unit 2 is accommodated in cylindrical member 8, an
additional guide unit does not have to be provided to maintain the
posture of spring unit 2. Cylindrical member 8 plays the role of
the guide unit. Also, since cylindrical member 8 is basically
formed of a conductor, it also serves to shield spring unit 2.
Although cylindrical member 8 is formed of a conductor, contact
with spring unit 2 will not cause the current flowing through
spring unit 2 to short circuit since the inner wall is covered with
an insulator. Furthermore, the advantageous effects described
hereinafter are also obtained.
[0071] A specific example of the present embodiment will be
described. In the fabrication method of the first embodiment, a
contact probe 50 having a width of 0.056 mm was fabricated. A
bronze or stainless steel pipe having an outer diameter of 1.2 mm
and an inner diameter of 0.08 mm with the inner side coated with an
insulator such as Teflon (registered) or parylene was prepared as
cylindrical member 8. Alternatively, cylindrical member 8 may be a
glass pipe or a resin pipe of Teflon, Duracon (registered) and the
like instead of the above-described pipe, and may have the outer
side coated with metal. Furthermore, cylindrical member 8 is not
limited in its cylindrical configuration, and may have a cross
section other than a circle.
[0072] As shown in FIGS. 17A and 17B, contact probe 50 is inserted
in cylindrical member 8 and attached adhesively or caulked at fixed
portion 9.
[0073] Then, an electrode (not shown) is pulled out from each of
lead wire connection unit 3 and cylindrical member 8. By connecting
cylindrical member 8 to ground, spring unit 2 is shielded by
cylindrical member 8. Therefore, measurement at a high frequency of
approximately several GHz that generally causes crosstalk noise is
allowed.
[0074] In establishing contact with the circuit to be tested,
contact probe 56 is pushed forward until not only plunger unit 1
but also cylindrical member 8 forms contact with the same circuit
to be tested, and different potentials having a potential
difference of at least a predetermined level are applied across
plunger unit 1 and cylindrical member 8. Since contact probe 56 is
pushed forward, the contact of plunger unit 1 and cylindrical
member 8 with the circuit can be ensured. By applying a potential
difference of at least a predetermined level, electrical breakdown
occurs at the oxide film at the surface of the circuit to result in
current flow. Accordingly, the oxide film at the surface of the
circuit can be broken to obtain favorable electrical
conductance.
[0075] Since a contact probe can be fabricated as an integral
object according to the method employing lithography and plating,
the machining process for each component is unnecessary, and
assembly is no longer required. Therefore, reduction in the size
and increase of the number of contact probes can be accommodated
more easily. The provision of a cylindrical member allows the
spring portion to be shielded to prevent crosstalk noise.
[0076] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *