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BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an inspection electrode unit for printed wiring
board, inspection apparatus comprising the inspection electrode unit and a
process for inspecting a printed wiring board using the same.
2. Discussion of Background
With respect to printed wiring boards having fabricated therein integrated
circuits and the like, in generally, it is necessary to inspect the
electric characteristics of the printed wiring boards before fabricating
integrated circuits and the like in order to check whether the wiring
patterns of the printed wiring boards have the desired performance.
Heretofore, in order to carry out the inspection of printed wiring boards,
there has been used, basically, an inspection electrode unit of the
individually responding type in which inspection electrodes are arranged
correspondingly to the patterns of electrodes to be inspected of a printed
wiring board and in which the inspection electrodes are electrically
connected to the inspection circuits of a tester by means of wirings.
Alternatively, a so-called universal type inspection electrode unit in
which inspection electrodes are placed at the standard grids arranged
crosswise has been used in combination with a connector for connecting the
electrodes to be inspected of a printed wiring board to the inspection
electrodes of the inspection electrode unit.
Recently, in the field of a printed wiring board, there has been a tendency
that the degree of integration of element and the pattern density are
being heightened more and more, and as a result, the inspection electrode
density of an inspection electrode unit is also being heightened. However,
the inspection electrode unit of the individually responding type is
required to have inspection electrodes of a pattern corresponding to the
electrodes to be inspected of a printed wiring board, and hence, it is
finally required that inspection electrodes must be formed at a density as
high as in electrodes to be inspected using spring probes though said
inspection electrode unit has an advantage that the individually
responding type enables the inspection circuit to be utilized more
effectively than the universal type. Accordingly, there has been the
problem that it is difficult to produce the inspection electrode unit and
the cost becomes very high.
In the case of the universal type inspection electrode unit, the distance
between adjacent electrodes in pairs to the inspection circuit of a tester
is constant, and hence, it is sufficient that a part of the electrodes to
be inspected are electrically connected to the inspection electrodes of
the unit nearest to the electrodes to be inspected. However, another part
of the electrodes to be inspected is often required to be electrically
connected to inspection electrodes placed in considerably distant
positions. This is because the density of electrodes to be inspected is
considerably higher than that of the inspection electrodes. As a result,
it becomes necessary to increase the wiring density in connector; however,
there is a limit in heightening the density. In fact, there remain many
inspection electrodes which cannot effectively be used, and hence, there
is the problem that they are inferior in efficiency and have useless
parts.
As discussed above, it is difficult for conventional inspection electrode
units for printed wiring board to respond well to the desired heightening
of the density of electrodes to be inspected. As a result, the
construction of inspection electrode unit becomes complicated and it is
difficult to sufficiently heighten the density of wiring pattern in a
connector for achieving electrical connection. Hence, it is impossible to
carry out highly reliable inspection.
SUMMARY OF THE INVENTION
An object of this invention is to provide an inspection electrode unit for
printed wiring board having a high electrode density which unit makes it
possible to easily achieve highly efficient electrical connection between
the electrodes to be inspected of the printed wiring board and the
inspection circuit of a tester for checking electric conduction in the
printed wiring board and also makes it possible to achieve the necessary
inspection of the printed wiring board with high reliability.
Another object of this invention is to provide inspection apparatus for
printed wiring board having a high electrode density in which the
above-mentioned inspection electrode unit is included and which is
basically of the individually responding type and, nevertheless, makes it
possible to easily achieve electrical connection to the inspection circuit
of a tester with high efficiency and also makes it possible to carry out,
with sufficiently high reliability, inspection of a printed wiring board
having a high electrode density.
A further object of this invention is to provide inspection apparatus for
printed wiring board in which the above-mentioned inspection electrode
unit is included and which can easily achieve electrical connection to the
inspection circuit of a tester with high efficiency even if the printed
wiring board has electrodes to be inspected on both sides and makes it
possible to carry out sufficiently reliable inspection of a high density
printed wiring board.
A still further object of this invention is to provide an inspection
apparatus for printed wiring board in which an inspection mechanism having
a different system of electrical connection to the electrodes to be
inspected of a printed wiring board can easily be substituted.
A still another object of this invention is to provide a method for
inspecting a printed wiring board using the above-mentioned inspection
electrode unit.
BRIEF DESCRIPTION OF THE DRAWINGS
Other objects and advantages of this invention will become apparent from
the following description and the accompanying drawings in which FIG. 1 is
a diagrammatical cross-sectional view of the construction of the
inspection electrode element in an example of the inspection electrode
unit for printed wiring board of this invention; FIG. 2 is a view for
explaining the inspection method of this invention; FIG. 3 is a
diagrammatical cross-sectional view of the construction of a connector
which can be used in this invention; FIG. 4 is a diagrammatical
cross-sectional view of the construction of another connector which can be
used in this invention; FIG. 5 is a diagrammatical view of the inspection
electrode element of an example of the inspection electrode unit of this
invention in which the region of electrodes to be inspected is the same in
size as the functional region of the inspection electrode element; FIG. 6
is a view for explaining the average inspection electrode density on the
inspection electrode element of FIG. 5; FIG. 7 is a diagrammatical view of
the inspection electrode element of an example of the present inspection
electrode unit in which the region of electrodes to be inspected is larger
in size than the functional region of the inspection electrode element;
FIG. 8 is a view for explaining the average inspection electrode density
on the inspection electrode element of FIG. 7; FIG. 9 is a diagrammatical
view of the construction of an inspection electrode element which can be
used in the present inspection apparatus; FIG. 10 is a diagrammatical view
of the construction of an inspection electrode element which can be used
in the present inspection apparatus; and FIG. 11 is a diagrammatical view
of the construction of an individually responding type inspection
mechanism which can be used in the present inspection apparatus.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to this invention, there is provided an inspection electrode unit
for printed wiring board, which consists essentially of an insulating
substrate; an inspection electrode element set up on one side of the
substrate in which inspection electrodes are formed at the standard grids
crosswise arranged and which element has a plurality of functional regions
each having the same inspection electrode arrangement; and a connecting
material for electrically connecting the inspection electrodes to one
another which are placed in the corresponding positions of the plural
functional regions, to form commonized electrodes.
According to this invention, there is also provided a method for inspecting
a printed wiring board which comprises using the above-mentioned
inspection electrode unit for printed wiring board; placing, on the
inspection electrode side of the unit, a printed wiring board to be
inspected having a region of electrodes to be inspected larger in size
than each of the functional regions of the inspection electrode element in
the unit on the electrode side of the unit through a connector so that the
electrodes to be connected face the electrodes side of the unit; and
connecting each of the electrodes to be inspected of the printed wiring
board to one of the commonized electrodes of the inspection electrode
element by means of the connector, and checking the electric conduction in
the printed wiring board in this state by means of the commonized
electrodes.
According to this invention, there is still further provided an inspection
apparatus for printed wiring board which comprises an off-grid adaptor to
be placed on a printed wiring board to be inspected and an inspection head
arranged above the off-grid adaptor, characterized in that the off-grid
adaptor consists of a pitch-converting board having, on its surface side,
surface electrodes corresponding to the electrodes to be inspected of the
printed wiring board and, on its back side, back electrodes arranged at
grids and electrically connected to the surface electrodes, and an
anisotropically electroconductive sheet (referred to hereinafter as the
first anisotropically electroconductive sheet); and said inspection head
comprises the abovementioned inspection electrode unit for printed wiring
board and another anisotropically electroconductive sheet (referred to
hereinafter as the second anisotropically electroconductive sheet), the
inspection electrodes of the unit being connected to the back electrodes
of the pitch-converting board through the second anisotropically
electroconductive sheet and arranged in the grid form.
This invention is illustrated below referring to the accompanying drawings.
First of all, the inspection electrode unit for printing wiring board of
this invention is explained.
In FIG. 1, on the inspection electrode element provided on one side of a
rectangular, plate-like, insulating substrate, inspection electrodes p are
formed at the standard grids arranged crosswise according to the so-called
universal arrangement. The whole surface region of this inspection
electrode element 11 is divided into two in each of the longitudinal and
transverse directions to form 4 functional regions A, B, C and D which are
the same rectangles (in FIG. 1, they correspond, respectively, to upper
left, upper right, lower left and lower right). Each of the functional
regions A to D has inspection electrodes p which are crosswise placed in
the same arrangement.
Now, in order to indicate a specific electrode among the inspection
electrodes p arranged crosswise in m lines and n columns, the address of a
specific inspection electrode p placed in the mth line and the nth column
is indicated as (m,n) hereinafter and when one of the functional regions
is indicated simultaneously, one of the symbols A to D is added to the top
of the address. For example, the inspection electrode placed in the first
line and the first column of the functional region A is indicated as
A(l,l).
The inspection electrodes p at the corresponding positions in the
functional regions A to D of the inspection electrode element 11 are
electrically connected to one another through a connecting material. That
is to say, an inspection electrode p having the same address (m,n) is
present in each of the functional regions A to D and the total number
thereof is 4. The 4 inspection electrodes p having the same address are
electrically connected to one another. The inspection electrodes
electrically connected to one another are called a "commonized electrode"
and expressed as P(m,n) herein. Accordingly, a certain commonized
electrode P(m, n) consists of inspection electrodes A(m,n), B(m,n), C(m,n)
and D(m,n) which are electrically connected, and act as 4 branched
terminals.
The electrical connection of the inspection electrodes having the same
address may be achieved by an appropriate connecting material, and is not
restricted to any specific construction or means. For example, a
multi-layer wiring circuit can be formed in the insulating substrate on
which the inspection electrode element 11 is provided, and used as a
connecting material. Also, the connecting material may be composed of an
appropriate lead wire.
As shown in FIG. 2, using the inspection electrode unit consisting of the
inspection electrode element 11 and the connecting material as mentioned
above, inspection of a printed wiring board 30 to be inspected is
conducted. That is, the printed wiring board 30 to be inspected is
arranged through a connector 20 on the inspection electrode element 11. In
this case, the connector 20 has a size capable of covering the whole
surface of the inspection electrode element 11, and has, on its side
facing the printed wiring board 30 (the upper side in FIG. 2), connection
terminals (referred to hereinafter as the first connection terminals) of a
pattern corresponding to the electrodes to be inspected of the printed
wiring board 30, and on the opposite side, connection terminals (referred
to hereinafter as the second connection terminals) to be individually
connected to the commonized electrodes of the inspection electrode element
11. In addition, said connector 20 has a connection through which the
first connection terminals are electrically connected to the second
connection terminals. By placing this connector 20 between the printed
wiring board 30 and the inspection electrode element 11, the electrodes to
be inspected of the printed wiring board 30 are individually connected to
the commonized electrodes of the inspection electrode element 11, and
simultaneously, a state is achieved that plural electrodes to be inspected
are not commonly connected to one commonized electrode.
A more detailed explanation is made. As shown in, for example, in FIG. 3,
the connector 20 is composed of an electroconductive-pin-supporting plate
21 having a size capable of covering the whole surface of the inspection
electrode element 11 and many electroconductive pins 22 supported by the
electroconductive-pin-supporting plate 21. The
electroconductive-pin-supporting plate 21 has an upper plate 21A and a
lower plate 21B facing the upper plate 21A through a spacer 21B. The upper
plate 21A has through holes at positions corresponding to the electrodes
to be inspected of the printed wiring board 30 and at the same time the
lower plate 21C has through holes at positions corresponding to the
inspection electrodes p commonized in the inspection electrode element 11.
The electroconductive pins 22 are free to elongate and shorten elastically
by means of built-in springs, and project upward and downward through the
through holes formed in the upper plate 21A and the lower plate 21C of the
electroconductive-pin-supporting plate 21, for example, in the inclined
state and are kept by means of the springs 23 placed in a space between
the upper plate 21A and the lower plate 21C so that the pins can move
upward and downward resisting to the elastic force of the springs 23.
According to the connector 20 having such a construction, a state is
achieved in which the lower end of the electroconductive pin 22 contacts
elastically the inspection electrode p and the upper end thereof contacts
elastically the electrode 31 to be inspected, whereby electrical
connection is achieved between the electrodes 31 to be inspected placed in
the inherent pattern of the printed wiring board 30 and the inspection
electrodes p placed at standard grids of the inspection electrode element
11. That is to say, the upper and lower ends of each electroconductive pin
22 act as the first and second connection terminals, respectively, in the
connector 20.
FIG. 4 shows another example. In this example, the connector 20 is composed
of a pitch-converting board 25 having a size capable of covering the whole
surface of the inspection electrode element 11; a first anisotropically
electroconductive elastomer sheet 26 placed between the pitch-converting
board 25 and the printed wiring board 30 to be inspected; and a second
anisotropically electroconductive elastomer sheet 27 placed between the
pitch-converting board 25 and the inspection electrode element 11.
The pitch-converting board 25 has upper side electrodes 25A arranged on its
upper side in the same pattern as the electrodes 31 to be inspected of the
printed wiring board 30; lower side electrodes 25B arranged on its lower
side at the same standard grids as those of the inspection electrodes p of
the inspection electrode element 11; and wirings-in-layer 25C for
electrically connecting the upper side electrodes 25A to the lower side
electrodes 25B. Also, each of the first anisotropically electroconductive
elastomer sheet 26 and the second anisotropically electroconductive sheet
27 has electroconductive path-forming portions in the direction of
thickness of the elastomer sheet.
By pressing such a connector 20 between the inspection electrode element 11
and the printed wiring board 30, the electrodes 31 to be inspected of the
printed wiring board 30 are electrically connected to the upper side
electrodes 25A of the pitch-converting board 25 through the first
anisotropically electroconductive elastomer sheet 26, and simultaneously,
the inspection electrodes p of the inspection electrode element 11 are
electrically connected to the lower side electrodes 25B of the
pitch-converting board 25 through the second anisotropically
electroconductive elastomer sheet 27. As a result, electrical connection
is achieved between the electrodes 31 to be inspected and the inspection
electrodes p. That is, in the connector 20, the upper side electrodes 25A
and the lower side electrodes 25B act as the first connection terminals
and the second connection terminals, respectively.
In the above-mentioned state, the printed wiring board 30 is inspected by
means of the commonized electrodes of the inspection electrode element 11.
As explained below, when the region in which electrodes to be inspected of
the printed wiring board 30 are present is larger in size than each of the
functional regions of the inspection electrode element 11, the excellent
effect of this invention is actually exhibited.
For an explanation, a case is assumed where the region of electrodes to be
inspected of the printed wiring board 30 is the same rectangular as each
functional region of the inspection electrode element 11, namely, the
dimension of the region of electrodes to be inspected is 1/2 of the
inspection electrode element 11 in both longitudinal and transverse
directions, and hence, the size of the region of electrodes to be
inspected is 1/4 of the inspection electrode element 11. When the printed
wiring board 30 is placed at the center of the inspection electrode
element 11, as is clear from FIG. 5, the region of electrodes to be
inspected of the printed wiring board 30 is divided into two in each of
the longitudinal and transverse directions by the boundary lines of the
functional regions A to D (dot-and-dash lines in FIG. 5) to form 4
functional regions. These 4 region portions are called inspection region
portions, and the upper left portion, upper right portion, lower left
portion and lower right portion are expressed as a, b, c and d,
respectively. That is, the upper left inspection region portion is
indicated as "inspection region portion a".
Assuming that each of the functional regions A to D is divided into two in
each of the longitudinal and transverse directions to form 4 region
sections (the division is shown by broken lines in FIG. 5), the 4 region
sections are called functional region sections, and the upper left, upper
right, lower left and lower right region sections are expressed as LU, RU,
LD and RD, respectively. Moreover, when the functional regions are to be
specified simultaneously, symbols A to D for expressing the functional
regions are put in front thereof. For example, the upper left section in
the functional region A is expressed as "functional region section ALU,
and the lower right section in the functional region D as "functional
region section DRD".
Under the above-mentioned conditions, FIG. 5 is explained below. In the
above-mentioned state, the inspection region portion a is positioned in
the functional region section ARD, the inspection region portion b in the
functional region section BLD, the inspection region portion c in the
functional region section CRU, and the inspection region portion d in the
functional region section DLU. However, in each of the functional regions
A to D, the inspection electrodes p are electrically connected to one
another, and hence, the functional region sections LU in all the
functional regions A to D, namely 4 functional region sections ALU, BLU,
CLU and DLU, are equivalent to one another. The same is applied to the
functional region sections RU, LD and RD in all the functional regions A
to D.
The above-mentioned state is the state that assuming the average inspection
electrode density in the region of electrodes to be inspected of the
printed wiring board 30 as .alpha., the average inspection electrode
density in the whole of the inspection electrode element 11 in which the
electrical connection state is considered becomes an equimultiple thereof,
namely 1.alpha.. FIG. 6 shows the state of this average inspection
electrode density. The numerals shown in each region portion indicate a
multiple of .alpha.. As can be seen from FIG. 6, in this state, in all the
regions, the average inspection electrode density is 1.alpha., and this is
completely equal to the state that the region of electrodes to be
inspected of the printed wiring board is connected correspondingly to one
functional region only of the inspection electrode element 11, and
accordingly, in this case, the advantage of this invention does not appear
as an actual effect.
However, when the region of electrodes to be inspected of the printed
wiring board 30 is larger in size than each functional region as shown in
FIG. 7, it follows that the region of electrodes to be inspected is also
present in the functional region sections surrounding the basic region 40
(the region surrounded by thick broken lines in FIG. 7 and this is equal
to the region of electrodes to be inspected of the printed wiring board 30
in FIG. 5) occupied by the 4 functional region sections ARD, BLD, CRU and
DLU which belong to the functional regions A to D and positioned at the
center.
The state of average inspection electrode density in this case is, as shown
in FIG. 8, the state that there are the central portion 51 surrounded by
solid lines in which the average inspection electrode density is 1.alpha.,
the intermediate flame portion 52 highlighted by netlike points in which
the average inspection electrode density is 2.alpha. or 4.alpha., and the
peripheral portion 53 positioned on the outer side of the intermediate
flame portion 52 in which the average inspection electrode density is
1.alpha. or 2.alpha.. The central portion 51 is smaller in size than the
basic region 40.
The average inspection electrode density is explained in more detail below.
In FIG. 8, each of the functional regions A to D is divided into 3 in each
of the longitudinal and transverse directions. In this case, in common to
the functional regions A to D, each of the divided regions in the
longitudinal direction are expressed as "top", "middle" and "bottom" in
order from the top, and each of the divided regions in the transverse
direction are expressed as "left", "center" and "right" in order from the
left side. In the total 4 top left sections of each of the functional
regions A to D, the region of electrodes to be inspected is directly
placed in only the functional region D. Accordingly, the average
inspection electrode density in the total 4 top left sections is 1.alpha.
in each of the functional regions A to D. Similarly, in the total 4 top
right sections, the region of electrodes to be inspected is directly in
only the functional region C, and in the total 4 bottom left sections, the
region of electrodes to be inspected is directly placed in only the
functional region B. In the total 4 bottom right sections, the region of
electrodes to be inspected is directly placed in only the functional
region A. Accordingly, the average inspection electrode density in each of
these sections becomes 1.alpha..
The total 4 top center sections in each of the functional regions A to D,
the region of electrodes to be inspected is directly placed in the
functional regions C and D, and accordingly, the average inspection
density of the 4 top center sections is 2.alpha. in each of the functional
regions A to D. Similarly, in the total 4 bottom center sections, the
region of electrodes to be inspected is directly placed in the functional
regions A and B, and in the total 4 middle left sections, the region of
electrodes to be inspected is directly placed in the functional regions B
and D. In the total 4 middle right sections, the region of electrodes to
be inspected is directly placed in the functional regions A and C. Hence,
the average inspection electrode densities in these sections are all
2.alpha..
On the other hand, in the total 4 middle center sections, the region of
electrodes to be inspected is directly placed in all the functional
regions A to D, and the average inspection electrode densities in the
middle center sections are all 4.alpha.. Thus, the distribution of average
inspection electrode density in each of the functional regions A to D
becomes the same.
The average inspection electrode density state in the above-mentioned
inspection electrode element 11 is such that when the longitudinal and
transverse dimensions of the region of electrodes to be inspected of the
printed wiring board are increased, the width of each of the longitudinal
and transverse peripheral portions 53 becomes correspondingly small and
simultaneously the crosswise dimensions of the central portion 51 become
small, while the width of each of the longitudinal and transverse
intermediate flame portions 52 becomes correspondingly large. In this
case, in the intermediate flame portion 52, the crosswise dimensions of
each of the 4 middle center portions in which the average inspection
electrode density is 4.alpha. become large, and when the crosswise
dimensions of the region of electrodes to be inspected of the printed
wiring board 30 becomes the same as those of the inspection electrode
element 11, it follows that the middle center section in each of the
functional regions A to D occupies the whole of the corresponding
functional region, and as a result, the average inspection electrode
density in the whole region becomes 4.alpha..
When the region of electrodes to be inspected of the printed wiring board
30 is smaller in size than the whole of the inspection electrode element
11 but larger in size than each of the functional regions as mentioned
above, the central portion 51 having a low average inspection electrode
density and the peripheral portion 53 having a relatively low average
inspection electrode density are necessarily formed through the
intermediate flame portion 52 having a relatively high average inspection
electrode density on the inspection electrode element 11. Accordingly, by
use of the inspection electrodes positioned in the central portion 51
having a low average inspection electrode density and the peripheral
portion 53, the electrodes to be inspected can be electrically connected
individually to the commonized electrodes of the inspection electrode
element 11 in a great degree of freedom and with ease. That is to say,
since it follows that the region of electrodes to be inspected of the
printed wiring board 30 is arranged so that it overlaps simultaneously
with each of the 4 functional regions A to D, it is sufficient that the
commonized electrode which is nearest to the electrode to be inspected or
relatively near but easy to electrically connect is selected and the
electrode to be inspected is electrically connected to the selected
commonized electrode. In particular, the commonized electrode P(m,n)
consists of inspection electrodes A(m,n), B(m,n), C(m,n) and D(m,n) which
act as equivalent terminals, and hence, any of the inspection electrodes
may be utilized for electrical connection. Therefore, a very great degree
of freedom can be obtained. Since the utilization efficiency of the whole
inspection electrodes p becomes high so that the number of the useless
inspection electrodes is greatly reduced and the inspection can be
effected in a very high efficiency.
An example of the inspection electrode unit of this invention is explained
above referring to an inspection electrode unit having an inspection
electrode element having 4 functional regions which are adjacent to one
another on the upper, lower, left and right sides. The number of the
functional regions, however, is not critical in this invention, and any
plural number of functional regions may be used. However, it can be said
to be ideal that the number of the functional regions is 4.sup.n (n is an
integer of 1 or more) as in the abovementioned example, because the
printed wiring board is usually rectangular and when the number of
functional regions is increased the connecting material for electrically
connecting the corresponding inspection electrodes in each functional
region is required to have a complicated construction. However, the
inspection electrode element has the same effect even if it has two
functional regions which are arranged longitudinally or transversely or
three functional regions in each of the longitudinal and transverse
directions. When the printed wiring board has electrodes to be inspected
on both sides, it is possible to apply the inspection electrode unit of
this invention to both sides of the printed wiring board, and the
inspection electrode elements of the two inspection electrode units
applied to both sides of the printed wiring board can be handled similarly
as commonized electrodes.
Next, the inspection apparatus for printed wiring board of this invention
is explained. The inspection apparatus comprises an off-grid adaptor to be
placed on a printed wiring bard to be inspected and an inspection head
placed on the off-grid adaptor.
The off-grid adaptor consists essentially of a pitch-converting board
having, on its surface side, surface electrodes of a pattern corresponding
to the electrodes to be inspected of the printed wiring board and, on its
back side, back electrodes which are placed at the grids and electrically
connected to the surface electrodes, and an anisotropically
electroconductive sheet (referred to hereinafter as the first
anisotropically electroconductive sheet) to be placed between the
pitch-converting board and the printed wiring board to be inspected.
The above inspection head comprises an anisotropically electroconductive
sheet (referred to hereinafter as the second anisotropically
electroconductive sheet) and the above-mentioned inspection electrode unit
having inspection electrodes which are placed in a grid arrangement and
electrically connected to the back electrodes of the pitch-converting
board through the second anisotropically electroconductive sheet.
When a printed wiring board having electrodes to be inspected is intended
to be inspected by the inspection apparatus for printed wiring board of
this invention, this apparatus can be provided with two sets of the
off-grid adaptor and the inspection head correspondingly to both sides of
the printed wiring board to be inspected. The commonized electrode in the
inspection electrode unit for the inspection head facing one side of the
printed wiring board is electrically connected to the commonized electrode
in the inspection electrode unit for the inspection head facing the other
side of the printed wiring board, and the inspection electrodes for the
two commonized electrodes which are electrically connected to each other
are placed in an area in one of the inspection electrode units and an area
in the other, these areas being in such a relation that they do not
overlap each other.
If the inspection apparatus is constructed as mentioned above, an
inspection electrode electrically connected to a certain electrode to be
inspected of a printed wiring board is present in all the plural
functional regions of the inspection electrode unit, and hence, the
electrical connection between the electrode to be inspected and the
inspection circuit of a tester can be carried out in a very great degree
of freedom. Simultaneously, the number of terminals to be connected to the
inspection circuit of the tester is greatly reduced and the utilization
efficiency of the whole inspection electrodes can be enhanced by
commonizing the inspection electrodes in each functional region.
Also, by electrically connecting the inspection electrodes constituting the
commonized electrodes placed in areas of the two inspection electrode
units placed on both sides of a printed wiring board to be inspected, said
areas being in such a relating that they do not overlap each other, a
greater degree of freedom can be given the electrical connection between
one of the inspection electrode units and the inspection circuit of
tester, and the number of connections to the inspection circuit can be
reduced.
Moreover, when the above-mentioned inspection head is mounted on a pressing
mechanism so as to be free to mount and demount, the inspection head and
the off-grid adaptor can be demounted, and hence, another inspection
mechanism different in electrical connection system to electrodes to be
inspected of a printed wiring board can be easily substituted therefor.
Next, the inspection apparatus of this invention is explained in more
detail referring to the accompanying drawings.
FIG. 9 is an explanatory cross-sectional view of the construction of the
essential portion in an example of the inspection apparatus for printed
wiring board of this invention. In FIG. 9, 61 is a printed wiring board to
be inspected which has electrodes 62 to be inspected on both sides. On the
upper and lower sides of the printed circuit board 61, inspection heads 68
and 68' are placed through off-grid adaptors 63 and 63', respectively.
The off-grid adaptor 63 or 63' is composed, respectively, of a
pitch-converting board 66 or 66' and an anisotropically electroconductive
sheet 67 or 67' (referred to hereinafter as the inner anisotropically
electroconductive sheet) placed between the pitch-converting board 66 or
66' and the printed wiring board 61. The pitch-converting board 66 or 66'
has, on its surface side facing the printed wiring board 61, surface
electrodes 64 or 64', respectively, having a pattern corresponding to the
electrodes 62 or 62', respectively, of the printed wiring board 61. Also,
the pitch-converting board 66 or 66' has back electrodes 65 or 65'
electrically connected, respectively, to the surface electrodes 64 or 64'
in the state that the back electrodes are arranged on the grids.
The inspection head 68 or 68' is composed, respectively, of an inspection
electrode unit 70 or 70' and an anisotropically electroconductive sheet 71
or 71' (referred to hereinafter as the outer anisotropically
electroconductive sheet) placed between the inspection electrode unit 70
or 70' and the pitch-converting board 66 or 66', respectively, and the
inspection electrode unit 70 or 70' has, on its surface side, inspection
electrodes 69 or 69' formed in a grid arrangement matching to the back
electrodes 65 or 65', respectively, of the pitch-converting board 66 or
66', namely in an arrangement in which the electrodes are placed on all
grids. In each of the inspection electrode units 70 and 70', a wiring
circuit 74 or 74' having a multilayer structure is formed, respectively,
for commonizing the inspection electrodes 69 or 69' in order to reduce the
number of inspection points correspondingly to the number of electrodes of
the inspection circuit of a tester as described hereinafter, and
simultaneously, a lead terminal portion 75 or 75' is formed at one end of
the inspection electrode unit 70 or 70', respectively, by means of a part
of the wiring circuit 74 or 74', and the terminal of the lead terminal
portion 75 or 75' is connected to the inspection circuit 76 of a tester by
means of a connector 73 or 73', respectively, which connector is connected
free to mount and demount.
77 is a press plate for pressing the inspection electrode unit 70 of the
upper side inspection head 68 downward, and is mounted free to mount and
demount on a pressing mechanism which is not shown in the figure. Also,
the press plate 77 is mounted so that the base level in the pressing
direction (downward in FIG. 9), namely the base level before starting the
pressing operation, can be controlled. An accepting plate 78 consisting of
an elastic cushion is placed below the lower side of the inspection
electrode unit 70' of the lower side inspection head 68'.
Each of the inspection electrode units 70 and 70' of the inspection heads
68 and 68' has an inspection electrode element 11 as illustrated
hereinbefore referring to FIGS. 1, 5, 6, 7 and 8. The inspection electrode
element 11 has, on its surface, inspection electrodes p which are formed
on the crosswise arranged standard grids according to the so-called
universal arrangement. The inspection electrode element 11 has 4
functional regions A, B, C and D (upper left, upper right, lower left and
lower right in FIG. 1) which are the same rectangles, formed by dividing
the whole surface region of the inspection electrode element into two in
each of the longitudinal and transverse directions as shown by
dot-and-dash lines in FIG. 1. Each of the functional regions A to D has
inspection electrodes p which are arranged crosswise in the same
arrangement as one another.
Now, in each of the functional regions A to D, in order to indicate a
specific electrode among the inspection electrodes p arranged crosswise in
m lines and n columns, the address of a specific inspect | | |
