 |
Description  |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an electric inspection unit using an
anisotropically electroconductive sheet and a process for producing the
anisotropically electroconductive sheet.
2. Discussion of the Background
Anisotropically electroconductive sheets are useful as materials for
achieving electrical connection in various applications because of their
structural characteristics.
However, in the inspection of a base board for a printed wiring board or
the like, pin probes have heretofore been used as materials for achieving
electric connection.
The pin probes are, however, difficult to miniaturize because of their
structural restriction. Accordingly, they are inappropriate for electric
inspection of a base board which now tends to be made as fine as possible.
Moreover, when the electrode in a portion to be inspected is a surface
electrode, a point contact is formed, and therefore, a bad contact tends
to be caused. In particular, pin probes are quite inadequate for electric
inspection of a base board for surface-mounting technology (referred to
hereinafter as the SMT base board) which is now being widely used.
On the other hand, anisotropically electroconductive sheets have no such
structural limitations as in the case of pin probes in the electric
inspection of a base board, and can be produced in such a form as to be
applicable to a conduction-insulation test of printed wiring having high
mounting density, a representative of which is the SMT base board.
Anisotropically electroconductive sheets which have heretofore been known
are those having the following structures:
(1) Structure in which plural insulating rubber sheets are alternately
laminated to plural electroconductive rubber sheets filled with
electroconductive carbon particles (see Japanese Patent Application Kokoku
No. 56-48,951).
(2) Structure in which metal particles are uniformly dispersed in an
elastomer sheet (see Japanese Patent Application Kokai No. 51-93,393).
(3) Structure in which electroconductive magnetic particles are
non-uniformly distributed in an elastomer sheet (see Japanese Patent
Application Kokai Nos. 53-147,772 and 54-146,873).
However, anisotropically electroconductive sheets having the above
structures (1) to (3) are all flat, and hence, it is necessary to apply a
large pressure thereto for forming effective electric paths. In addition,
in the case of miniaturized printed wiring boards and the like, there are
many points to be inspected, and the total necessary pressure becomes
considerably large and there is such a problem that the pressing mechanism
of inspecting unit must be unusually strong.
Under such circumstances, a proposal has been made of an anisotropically
electroconductive sheet structure so that a difference in height is formed
between the surface of an electroconductive portion and the surface of an
insulating portion (see Japanese Patent Application Kokai No. 61-250,906).
When an anisotropically electroconductive sheet having a structure in which
such a difference in height is formed is used, the total necessary
pressure can be reduced.
However, the above anisotropically electroconductive sheet is prepared by a
press-molding in the prior art; therefore, a press mold to be used in the
press-molding must be prepared in conformity with the shape and size of an
anisotropically electroconductive sheet each time. Also, the mold must
have a structure which can withstand press-molding. Moreover, when the
above anisotropically electroconductive sheet is formed by press-molding,
it is difficult to release from the mold because the sheet has a structure
in which such a difference in height is formed.
On the other hand, conventional electric inspection unit in which an
anisotropically electroconductive sheet is used adopts a so-called
intermediary pin system as shown in FIG. 7 in the accompanying drawings.
In FIG. 7, 91 refers to an inspection head provided with many inspection
electrodes 96, 92 to an intermediary pin system, 93 to an off-glid
adaptor, 94 to a printed wiring board and 95 to a back side adaptor.
The intermediary pin system 92 consists of an anisotropically
electroconductive sheet 92A, an intermediary pin 92B and another
anisotropically electroconductive sheet 92C and has a function of
absorbing errors in dimension in the direction vertical to the surface to
be inspected of the printed wiring board 94 and a function of preventing
electric current from spreading in the transverse direction in the
interiors of the anisotropically electroconductive sheets 92A and 92C by
the intermediary pin 92B per se to keep the point-to-point correspondence
between the inspection electrodes 96 and the portions to be inspected.
However, an electric inspection unit in which such an intermediary pin
system is adopted is complicated in structure, has a difficulty in
production, and in addition, is so heavy in weight that its handling is
not easy. Moreover, the unit has many points at which electric current
flows upon contact, and hence, is inferior in reliability.
SUMMARY OF THE INVENTION
Therefore, the first object of this invention is to provide an electric
inspection unit which has a simple structure and is lightweight and by
which the inspection of a base board having many portions to be inspected
can be conducted with a high reliability.
The second object of this invention is to provide a process for producing
an anisotropically electroconductive sheet which can be released easily
from a mold using a mold having small pressure-resistance and a simple
structure.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Other objects and advantages of this invention will become apparent from
the following description and the accompanying drawings, in which:
FIGS. 1 and 2 are, respectively, a vertically cross-sectional front view
and a plan view of a part of an anisotropically electroconductive sheet to
be used in the electric inspection unit of this invention,
FIG. 3 is a diagrammatic view showing an example of an apparatus for
producing an anisotropically electroconductive sheet,
FIG. 4 is a perspective view of an example of the molding surface of an
upper mold,
FIG. 5 is an exploded view of the electric inspection unit of this
invention,
FIG. 6 is a graph showing the experimental results in Example 4 and
Comparative Example 2, and
FIG. 7 is an exploded view of an electric inspection unit in which a
conventional intermediary pin system is adopted.
In these figures, 10 refers to electroconductive portions, 11 to a
projecting portions, 12 to a high-molecular-weight substance, 13 to
electroconductive particles, 15 to insulating portions, 20 to the upper
mold, 30 to the lower mold, 21 and 31 to base boards, 22 and 32 to
ferromagnetic substance portions, 23 and 33 to non-magnetic portions, 24
to a plate of ferromagnetic substance, 40 to a mixture sheet, 50 to a
space, 61 to inspection heads, 62 to anisotropically electroconductive
sheets, 63 to off-glid adaptors, 64 to a printed wiring board, 65 to an
inspection electrode, 64A to portions to be inspected, 91 to an inspection
head, 92 to an intermediary pin system, 93 to off-glid adaptors, 94 to a
printed wiring board, 95 to a back side adaptor, 96 to inspection
electrodes, 92A and 92C to anisotropically electroconductive sheets, and
92B to an intermediary pin system.
According to this invention, there is provided an electric inspection unit
comprising many inspection electrodes and an anisotropically
electroconductive sheet which is placed so as to be present between the
electrodes and a base board to be inserted into the unit when the base
board is electrically inspected, characterized in that the anisotropically
electroconductive sheet has a plurality of electroconductive portions
extending in the direction of thickness of the sheet, which portions are
arranged so as to be insulated from one another by insulating portions
consisting of an insulating, elastic, high-molecular-weight substance,
each of the electroconductive portions being formed in a portion
projecting from the surface of the insulating portion by filling the
insulating portions densely with electroconductive particles.
This invention further provides a process for producing an anisotropically
electroconductive sheet which comprises forming a layer of a molding
material consisting of a mixture of electroconductive particles having
magnetism and a high-molecular-weight substance in the cavity of a mold
consisting of a pair of upper and lower molds, the molding surfaces of
each of which is flat or has much smaller concaves and convexes than the
height of projecting portions of the anisotropically electroconductive
sheet to be produced; applying a magnetic field having an intensity
distribution to the molding material layer in the direction of thickness
of the layer in the state that a space is present between the molding
surface of the upper mold and the upper surface of the molding material
layer, to fluidize the molding material while transferring the
electroconductive particles by magnetic force, thereby changing the
external shape of the molding material layer; and then curing the molding
material layer.
Referring to the accompanying drawings, this invention is specifically
explained below.
FIGS. 1 and 2 show embodiments of structure of an anisotropically
electroconductive sheet to be used in the electric inspection unit of this
invention, in which a plurality of electroconductive portions 10 extending
in the direction of thickness of the sheet are densely arranged in the
form of a matrix in the state that they are separated from one another by
insulating portions 15, and each electroconductive portion 10 is formed in
a portion projecting from the surface of the insulating portion 15 on one
side of the sheet. Incidentally, each electroconductive portion 10 may
project on the other side of the sheet.
Each electroconductive portion 10 is formed by filling an insulating,
elastic, high-molecular-weight substance 12 densely with electroconductive
particles 13, and has such a pressure-sensitive electroconductivity that
the resistivity is reduced upon applying pressure. The degree of filling
with the electroconductive particles 13 in the electroconductivity portion
10 is preferably 20% by volume or more, particularly preferably more than
40% by volume. Incidentally, when the degree of filling with the
electroconductive particles 13 is low, the resistivity of the
anisotropically electroconductive sheet is not reduced even when a
pressure is applied to the sheet, and hence, highly reliable electric
connection becomes difficult.
Incidentally, in the anisotropically electroconductive sheet to be used in
the electric inspection unit of this invention, electroconductive portions
are formed in the projecting portions; however, an insulating portion
having a thickness of about 0.5 mm may be formed around the
electroconductive portion in the projecting portion.
The thickness D of the electroconductive portion 10 is determined taking
into consideration the projection height h of the projecting portion 11
and the thickness d of the insulating portion. However, when the thickness
D of the electroconductive portion 10 is too large, the resistivity in the
conductive state is increased, so that the upper limit thereof is
preferably about 5 mm, practically 1-5 mm, and particularly preferably 2-4
mm. When the thickness D of the electroconductive portion 10 is in this
range, an effective conductivity is surely obtained even when a small
pressure is applied.
In addition, the thickness d of the insulating portion 15 is preferably
0.1-0.8 mm in practice. When the thickness d of the insulating portion 15
is in this range, a sufficient insulation is obtained, and at the same
time, the projection height h of the electroconductive portion 10 can be
set at an adequate value without making the thickness D of the
electroconductive portion 10 too large. Incidentally, when the thickness d
of the insulating portion 15 is too small, the strength as a sheet becomes
low and hence the handling thereof becomes inconvenient. On the contrary,
when the thickness d is too large, the projection height h of the
electroconductive portion 10 becomes too large, so that the resistivity in
the conductive state tends to be increased.
It is preferable that the outer diameter (or the longer side in the case of
quadrangle) R of the projecting portion and the shortest distance r
between the adjacent projecting portions 11 satisfy the following
relation:
0.1.ltoreq.r/R.
When this relation is satisfied, the displacement in the transverse
direction is easily tolerated when the projecting portion 11 is deformed
by applying a pressure thereto in the thickness direction. Simultaneously,
it is possible to sufficiently avoid the possibility that the adjacent
projecting portions 11 are electrically contacted with each other.
In the unit area S effective to the electric connection of an
anisotropically electroconductive sheet, it is preferable that the sum
total S.sub.10 of areas of the projecting portions 11 and the sum total
S.sub.20 of areas of the insulating portions 15 satisfy the following
relation when the maximum displacement which can be considered in practice
is assumed as .epsilon.:
##EQU1##
The number of electroconductive portions 10 per unit area, namely density
of electroconductive portions, is preferably 10-70 portions/cm.sup.2 in
order that the portions 10 can correspond to the miniaturized printed
wiring board and the like.
The shape of the projecting portion 11 in the plan view (in other words,
the shape observed from the surface from which the portion projects) may
be not only circle but also quadrangle or any other shape.
The electroconductive particles which are a constituent of the
electroconductive portion 10 include, for example, particles of metals
having magnetism such as nickel, iron, cobalt and the like or their
alloys; these particles plated with gold, silver, palladium, rhodium or
the like; particles of non-magnetic metals plated with an
electroconductive magnetic substance such as nickel, cobalt or the like;
inorganic particles such as glass beads and the like plated with an
electroconductive magnetic substance such as nickel, cobalt or the like;
and polymer particles plated with an electroconductive magnetic substance
such as nickel, cobalt or the like; etc. In view of reducing the
production cost, particles of nickel, iron or their alloys are
particularly preferable. In view of such electric characteristics that the
contact resistance is small, gold-plated particles are preferably used.
The particle diameters of the electroconductive particles are preferably
10-400 .mu.m, more preferably 40-100 .mu.m viewpoint of making the
electric contact of the electroconductive particles with one another
sufficient in the electroconductive portion 10 and facilitating the
displacement upon applying pressure in the electroconductive portion 10.
The insulating, elastic high-molecular-weight substance which is another
constituent of the electroconductive portion 10 is preferably a
high-molecular-weight substance having a crosslinked structure, and
uncrosslinked high polymer materials which can be used to obtain such
high-molecular-weight substance having a crosslinked structure, include
silicone rubber, polybutadiene, natural rubber, polyisoprene,
styrene-butadiene copolymer rubber, acrylonitrile-butadiene copolymer
rubber, ethylene-propylene copolymer rubber, urethane rubber, polyester
rubber, chloroprene rubber, epichlorohydrin rubber and the like.
The material constituting the insulating portion 15 is generally the same
high-molecular-weight substance as that constituting the electroconductive
portion.
An explanation is made below of the present process for producing an
anisotropically electroconductive sheet.
In the present production process, a pair of upper and lower molds are
used, the molding surface of each of which is flat or has much smaller
concaves and convexes than the height of the projecting portion of the
anisotropically electroconductive sheet.
When molding is effected, a layer of a molding material consisting of a
mixture of electroconductive particles having magnetism and a high polymer
material (referred to hereinafter as the mixture sheet) is in the cavity
of the mold. The mixture sheet has a thickness of 0.1-3 mm in view of
practical use.
Subsequently, a magnetic field having an intensity distribution is applied
to the mixture sheet in the direction of the thickness of the sheet in the
state that a space is formed between the molding surface of the upper mold
and the upper surface of the mixture sheet, and the molding material is
fluidized while the electroconductive particles are transferred by the
magnetic force to change the exterior shape of the mixture sheet, and then
the molding material is cured, whereby an anisotropically
electroconductive sheet is produced. In this case, the distance between
the molding surface of the upper mold and the molding surface of the lower
mold is required to be greater than the thickness of the mixture sheet;
however, it is preferably 1-5 mm and particularly preferably 2-4 mm.
Since a space is thus present between the molding surface of the upper mold
and the upper surface of the mixture sheet in the cavity of the mold, it
follows that the electroconductive particles protrude together with the
high polymer material by the action of magnetic field having an intensity
distribution applied to the mixture sheet.
The means for curing the mixture sheet after changing the exterior shape of
the mixture sheet is generally crosslinking.
A more detail explanation is made hereinafter. The mold is composed of a
pair of corresponding upper and lower molds, each of these molds having a
substantially flat plate-like shape as a whole, and it is preferable that
the upper and lower molds be constructed so as to be mountable on an
electromagnet or constructed integrally with an electromagnet, whereby the
mixture sheet can be heat-cured while a magnetic field is applied to the
mixture sheet.
In order to form projections which become the electroconductive portions in
appropriate positions by applying a magnetic field to the mixture sheet,
it is preferable that at least the upper mold, preferably both the upper
mold and the lower mold, are so constructed that a base plate consisting
of a ferromagnetic substance such as iron, nickel or the like has a layer
consisting of portions of a ferromagnetic substance such as iron, nickel
or the like for generating an intensity distribution in the magnetic field
in the mold and portions of a non-magnetic substance such as a
non-magnetic metal, e.g. copper or the like, a heat-resistant resin such
as polyimide or the like, air, or the like which are arranged in the form
of a mosaic (said layer is referred to hereinafter as the mosaic layer).
The molding surface of each of the upper and lower molds is flat or may
have formed thereon much smaller concaves and convexes than the projection
height of the projecting portions, for example, concaves and convexes of
0.5 mm or less in height or depth. When such concaves and convexes are
formed on the molding surface of the lower mold, the corresponding
concaves and convexes are formed on the lower surface of an
anisotropically electroconductive sheet.
The thickness of each of the upper and lower molds is preferably 3 mm-5 cm,
particularly preferably 5 mm-1 cm. When the upper and lower molds are
thin, the strength of the mold is insufficient and hence the mold per se
is deformed during the handling. On the contrary, when the upper and lower
molds are thick, they become heavy and the handling of the molds becomes
difficult.
The area, exterior shape and the like of each of the upper and lower molds
are not critical, and it is necessary that a magnetic field having an
intensity distribution can be formed by the action of electromagnet on the
whole molding surface of at least the mixture sheet.
The thickness of the mosaic layer of the mold is preferably 0.1-1 mm in
view of practical use. When the mosaic layer is thin, the intensity
distribution of magnetic field becomes insufficient, and it becomes
difficult to produce an anisotropically electroconductive sheet. On the
contrary, when the mosaic layer is thick it takes too much time and labor
for the preparation of a mold.
The arrangement, shape and the like of each of the ferromagnetic substance
portion and the non-magnetic substance portion in the mosaic layer are
determined based on the anisotropically electroconductive sheet to be
prepared. That is, it is essential that the ferromagnetic substance
portion be arranged in places corresponding to the electroconductive
portions of the anisotropically electroconductive sheet, and the shape of
the said ferromagnetic substance portion be adapted to the shape of the
cross-section of the electroconductive portion.
The above-mentioned mold can be produced, for example, by the following
method:
(1) From a ferromagnetic substance base plate are cut off portions at which
non-magnetic substance portions are to be formed, by a method such as
cutting, etching or the like, and thereafter, the cut portions are filled
with a non-magnetic substance by a method of pouring a resin into the cut
portions or plating the cut portions with copper to form the mosaic layer,
thereby producing a mold.
(2) A non-magnetic substance plate is perforated at the portions at which
ferromagnetic substance portions are to be formed, a ferromagnetic
substance molded into the necessary shape is fixed in the resulting holes,
and the resulting mosaic layer is attached to the ferromagnetic substance
base plate to produce a mold.
The ferromagnetic substance constituting the mosaic layer of ferromagnetic
substance portion and non-magnetic substance portion in a mold is not
always identical in material with the ferromagnetic substance plate which
becomes a base plate. A thin non-magnetic substance layer may be present
between the two ferromagnetic substances. That is, it is sufficient that
the two ferromagnetic substances be magnetically connected intimately to
each other to form a series of magnetic circuit, thereby forming a
sufficient magnetic field distribution in the mold. It is not always
necessary that the two ferromagnetic substances be directly contacted with
each other.
On the molding surface of the mold, it is not always necessary that the
mosaic layer consisting of ferromagnetic substance portion and
non-magnetic substance portion be bare and, for example, the mosaic layer
may be covered with a layer of a non-magnetic resin if it is sufficiently
thin.
In the mosaic layer consisting of ferromagnetic substance portions and
non-magnetic substance portions, it is non always necessary that the
non-magnetic substance portions be fixed in. A gas such as air may be
present in the non-magnetic portions as far as such problems as
insufficient strength of mold and the like are not raised. In this case,
the molding surface of the mold can be made flat by attaching a sheet of a
resin or the like to the surface of the ferromagnetic substance portion.
FIG. 3 shows an example of apparatus for producing an anisotropically
electroconductive sheet, and in this figure, 1A refers to electromagnet,
20 and 30 to the upper mold and the lower mold, respectively, which
constitute a mold, and 40 to a mixture sheet composed of a molding
material, namely, an electroconductive particles having magnetism and an
uncrosslinked, high polymer material.
In the upper mold 20 and the lower mold 30 of a mold, 21 and 31 refer to
base plates each composed of a ferromagnetic substance, 22 and 32 to
ferromagnetic substance portions for forming the electroconductive
portions, 23 and 33 to non-magnetic substance portions, and the above
mosaic layer of the upper mold 20 is composed of the ferromagnetic
substance portions 22 and the non-magnetic substance portions 23 and the
mosaic layer of the lower mold 30 is composed of the ferromagnetic
substance portions 32 and the non-magnetic substance portions 33.
The example of FIG. 3 has such a structure that the upper mold 20 and the
lower mold 30 can be separated from electromagnets 1A and 1B; however, it
may be such a structure that magnetic electrodes of electromagnet can be
as such used as the mold too.
FIG. 4 shows an example of the molding surface of the upper mold 20, in
which many grooves are crosswise formed on one side of a plate 24 made of
a ferromagnetic substance and the grooves enable the formation of the
non-magnetic substance portions 23 and the magnetic substance around the
groove forms the ferromagnetic substance portions 22.
Next, an explanation is made of a specific process for producing the
anisotropically electroconductive sheet.
First of all, on the upper surface, namely, the molding surface, of the
lower mold 30 which is placed horizontally is coated a mixture of
electroconductive particles having magnetism and uncrosslinked high
polymer material, in a uniform thickness to form the mixture sheet 40.
The thickness of the mixture sheet 40 is preferably 0.1-3 mm as stated
above, and the volume fraction of electroconductive particles is
preferably about 5-50% by volume, provided that from the viewpoint of
enhancing the performance of the anisotropically electroconductive sheet,
it is important to collectively consider and optimalize the shape of the
electroconductive portion of anisotropically electroconductive sheet, the
volume fraction of electroconductive particles, the whole shape of the
anisotropically electroconductive sheet, etc.
Subsequently, the upper mold 20 is put above the mixture sheet 40 in a
face-to-face relation through the space 50. This space 50 is put for the
purpose that when a magnetic field is applied to the mixture sheet 40, the
electroconductive particles in the mixture sheet 40 can be transferred and
the molding material forming the mixture sheet 40 is fluidized to change
the exterior shape thereof, thereby enabling the electroconductive
portions and the insulating portions to be formed. Incidentally, the
distance from the molding surface of the lower mold 30 to the molding
surface of the upper mold 20 becomes the thickness D of the finished
anisotropically electroconductive sheet.
The upper mold 20 and the lower mold 30 which are in the above-mentioned
state are set, respectively, on the electromagnets 1A and 1B, and the
electromagnets 1A and 1B are worked to apply a magnetic field having an
intensity distribution to the mixture sheet 40 in the direction of the
thickness of the mixture sheet through the upper mold 20 and the lower
mold 30, thereby protruding the electroconductive portions, and thereafter
or while the magnetic field is applied, the uncrosslinked high polymer
material is crosslinked. Thus, the electroconductive portions 10 and the
insulating portions 15 are formed at one time.
When the structure used is such that the distance between the upper mold 20
and the lower mold 30 can be changed in the state that the magnetic field
is applied, such an operation is possible that the upper mold 20 is placed
just above the mixture sheet 40 at the beginning, the distance between the
upper mold 20 and the lower mold 30 is gradually broadened while the
magnetic field is applied and when the necessary distance has been reached
the crosslinking is conducted.
The intensity of the magnetic field to be applied to the mixture sheet 40
is usually 200-20,000 gauss on the average in the cavity of the mold. The
crosslinking temperature and time in the crosslinking reaction can be
appropriately varied depending upon the type of uncrosslinked high polymer
material, the period of time for which the electroconductive particles can
be concentratedly transferred to the electroconductive portions, etc.
However, when a room temperature-curing type silicone rubber is used, the
crosslinking time is about 24 hours at room temperature, about 2 hours at
40.degree. C. or about 30 minutes at 80.degree. C.
In order to facilitate the concentrated transfer of the electroconductive
particles to the electroconductive portions, the viscosity of the mixture
sheet before the crosslinking reaction starts should preferably be
10.sup.4 -10.sup.7 poise under such conditions that the strain rate is
10.sup.1 sec.sup.-1 at 25.degree. C.
Next, the electric inspection unit of this invention is explained. FIG. 5
is a diagrammatic view illustrating explodedly an example of the electric
inspection unit of this invention. In FIG. 5, 61 refers to an inspection
head, 62 to an anisotropically electroconductive sheet, 63 to an off-glid
adaptor, 64 to a printed circuit base board.
The unit of this example is a so-called both side inspection type unit
which can inspect both sides of a printed wiring board 64 at the same
time, and a set of the inspection head 61, the anisotropically
electroconductive sheet 62 and the off-glid adaptor 63 is arranged on each
of the sides of the printed wiring board 64. Incidentally, the
anisotropically electroconductive sheet 62 is supported by a carrier board
(not shown in the figure) perforated at places corresponding to the
projecting portions of the sheet.
The inspection head 61 has pin-like inspection electrodes 65 arranged at
the positions corresponding to the electroconductive portions 10 of the
anisotropically electroconductive sheet 62.
The off-glid adaptor 63 is used for allowing the arrangement pattern of
each portion to be inspected 64A of the printed wiring board 64 to
correspond to the arrangement pattern of the inspection electrode 65.
Incidentally, this off-glid adaptor 63 is selectively used according to
the arrangement pattern of each portion to be inspected 64A of the printed
wiring board 64, and when the arrangement pattern of each portion to be
inspected 64A is identical with that of the inspection electrodes 65, the
off-glid can be omitted.
In this unit, an anisotropically electroconductive sheet is interposed
between many inspection electrodes 65 and the printed wiring board 64, and
in this state, the electric inspection of the printed wiring board 64 is
conducted.
That is, upon applying a pressure by a pressure-applying means (not shown
in FIG. 5) to the inspection electrodes 65, the anisotropically
electroconductive sheet 62 and the off-glid adaptors 63 which are arranged
on both sides of the printed wiring board 64 as shown in FIG. 5 so that
the printed wiring board is pressed from both sides thereof, the
electroconductive portions 10 of the anisotropically electroconductive
sheet 62 are pressed to exhibit effective electroconduction, whereby it
becomes possible to inspect whether the electrical continuity or
insulation of each electrode to be inspected of the printed wiring board
is good or not.
The pressure-applying means is usually provided on the back side of the
inspection head 61; however, an electric circuit necessary for the
inspection is provided on the back side of the inspection head 61.
Therefore, it is important to protect the electric circuit from dynamic
stress.
In the anisotropically electroconductive sheet used in the electric
inspection unit of this i | | |
