U.S. patent application number 17/612398 was filed with the patent office on 2022-07-14 for conductive adhesive sheet.
The applicant listed for this patent is Tatsuta Electric Wire & Cable Co., Ltd.. Invention is credited to Kenji AOKI, Yuusuke HARUNA, Sougo ISHIOKA, Hiroshi TAJIMA.
Application Number | 20220220346 17/612398 |
Document ID | / |
Family ID | 1000006260149 |
Filed Date | 2022-07-14 |
United States Patent
Application |
20220220346 |
Kind Code |
A1 |
HARUNA; Yuusuke ; et
al. |
July 14, 2022 |
Conductive Adhesive Sheet
Abstract
Provided is a conductive adhesive sheet that has excellent
connection stability even containing conductive particles in a
small proportion. The inventive conductive adhesive sheet contains
a binder component and conductive particles. The conductive
particles are distributively arranged. Assume that all the
conductive particles are regularly arranged; and that an optional
region of the conductive adhesive sheet is viewed in plan view so
that a distribution number Np of the distributed conductive
particles be 9 to 25, a condition: 1.5X.ltoreq.Y.ltoreq.100X is
met, where X represents the average of equivalent circle diameters
of the distributed conductive particles; and Y represents the
center-to-center distance between adjacent two of the distributed
conductive particles, which are regularly arranged in the plan
view. The ratio N/Np is 1.0 to 100.0, where N represents the number
of the primary particles in the optional region. When optional
three unique regions including the optional region are viewed in
plan view so that the distribution number Np in each region be 9 to
25, the ratio Ng/Np is 0.8 to 1.0, where Ng represents the
distribution number of conductive particles present in two or more
of the three regions.
Inventors: |
HARUNA; Yuusuke;
(Kizugawa-shi, Kyoto, JP) ; AOKI; Kenji;
(Kizugawa-shi, Kyoto, JP) ; TAJIMA; Hiroshi;
(Kizugawa-shi, Kyoto, JP) ; ISHIOKA; Sougo;
(Kizugawa-shi, Kyoto, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tatsuta Electric Wire & Cable Co., Ltd. |
Osaka |
|
JP |
|
|
Family ID: |
1000006260149 |
Appl. No.: |
17/612398 |
Filed: |
May 20, 2020 |
PCT Filed: |
May 20, 2020 |
PCT NO: |
PCT/JP2020/019842 |
371 Date: |
November 18, 2021 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C09J 2301/314 20200801;
C09J 2301/408 20200801; C09J 2203/326 20130101; C09J 11/04
20130101; C09J 9/02 20130101; C09J 7/10 20180101; Y10T 428/28
20150115; C09J 11/08 20130101 |
International
Class: |
C09J 9/02 20060101
C09J009/02; C09J 7/10 20060101 C09J007/10; C09J 11/04 20060101
C09J011/04; C09J 11/08 20060101 C09J011/08 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2019 |
JP |
2019-094741 |
Claims
1. A conductive adhesive sheet comprising: a binder component; and
conductive particles, wherein the conductive particles are
distributively arranged each as a primary particle or an aggregate
of primary particles, wherein, with the assumption that all the
conductive particles are regularly arranged; and that an optional
region of the conductive adhesive sheet is viewed in plan view so
that a distribution number Np of the distributively arranged
conductive particles be 9 to 25, a condition:
1.5X.ltoreq.Y.ltoreq.100X is met, where X represents an average of
equivalent circle diameters of the distributively arranged
conductive particles; and Y represents a center-to-center distance
between adjacent two of the distributively arranged conductive
particles which are regularly arranged in the plan view, wherein a
ratio N/Np is 1.0 to 100.0, where N represents a number of the
primary particles in the optional region, wherein, when optional
three unique regions including the optional region are viewed in
plan view so that the distribution number Np in each region be 9 to
25, a ratio Ng/Np is 0.8 to 1.0, where Ng represents a distribution
number of conductive particles present in two or more of the three
regions, and wherein the center-center-distance Y is 100 to 1000
.mu.m.
2. The conductive adhesive sheet according to claim 1, wherein the
ratio N/Np is from 1.05 to 50.0.
3. The conductive adhesive sheet according to claim 1, wherein the
center-to-center distance Y has a coefficient of variation of 0.5
or less.
4. The conductive adhesive sheet according to claim 1, wherein the
conductive adhesive sheet comprises a thermosetting resin as the
binder component.
5. The conductive adhesive sheet according to claim 1, wherein the
conductive adhesive sheet contains the conductive particles in a
proportion of 10 to 60 mass percent of the totality, 100 mass
percent, of the conductive adhesive sheet.
6. The conductive adhesive sheet according to claim 1, wherein, at
least in an area of the conductive adhesive sheet, a portion in
which the conductive particles are distributively arranged has a
large thickness as compared with a portion in which no conductive
particle is distributively arranged.
7. The conductive adhesive sheet according to claim 1, wherein the
average X of the equivalent circle diameters is 2 to 120 .mu.m.
8. An electromagnetic shielding film comprising the conductive
adhesive sheet according to claim 1.
9. A ground connector comprising the conductive adhesive sheet
according to claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to conductive adhesive
sheets.
BACKGROUND ART
[0002] Electroconductive adhesives (conductive adhesives) are
heavily used in printed circuit boards. An example is a conductive
adhesive sheet (conductive bonding film) typically for electrically
connecting an electromagnetic shielding film disposed on a printed
circuit board to an external ground for circuit grounding or to a
stiffener (reinforcing member).
[0003] A known exemplary conductive adhesive sheet for use in
printed circuit boards is a conductive sheet having a conductive
layer including a thermosetting resin and dendritic conductive fine
particles. In the conductive sheet, the conductive layer has a
thickness that meets a specific condition. The dendritic conductive
fine particles have an average particle diameter D50 of from 3
.mu.m to 50 .mu.m and are present in the conductive layer in a
proportion of from 50 weight percent to 90 weight percent (see PTL
1).
CITATION LIST
Patent Literature
[0004] PTL 1: PCT International Publication Number
WO2012/164925
SUMMARY OF INVENTION
Technical Problem
[0005] In economic terms, the amount of conductive particles to be
used in such a conductive adhesive sheet is preferably minimized.
However, with a decreasing amount of the conductive particles, the
conductive adhesive sheet tends to have lower conductivity and
lower connection stability.
[0006] The present invention has been made under these
circumstances and has an object to provide a conductive adhesive
sheet that has excellent connection stability even when containing
conductive particles in a small proportion.
Solution to Problem
[0007] After intensive investigations to achieve the object, the
inventors of the present invention have found that a specific
conductive adhesive sheet has excellent connection stability even
when containing conductive particles in a small proportion. In the
conductive adhesive sheet, the relationship between the diameters
of distributively arranged conductive particles and the distance or
spacing between the distributively arranged conductive particles is
controlled to be specific, and the arrangement of the conductive
particles are regulated. The present invention has been made on the
basis of these findings.
[0008] Specifically, the present invention provides, in an aspect,
a conductive adhesive sheet containing a binder component and
conductive particles. The conductive particles are distributively
arranged each as a primary particle or an aggregate of primary
particles. Assume that all the conductive particles are regularly
arranged, and that an optional region of the conductive adhesive
sheet is viewed in plan view so that a distribution number Np of
the distributively arranged conductive particles be 9 to 25, the
condition: 1.5X.ltoreq.Y.ltoreq.100X is met, where X represents an
average of equivalent circle diameters of the distributively
arranged conductive particles; and Y represents a center-to-center
distance between adjacent two of the distributively arranged
conductive particles which are regularly arranged in the plan view.
The ratio N/Np of the primary particles in the optional region to
the distribution number Np is 1.0 to 100.0. When optional three
unique regions including the optional region are viewed in plan
view so that the distribution number Np in each region be 9 to 25,
the ratio Ng/Np of the distribution number Ng of conductive
particles present in two or more of the three regions to the
distribution number Np is from 0.8 to 1.0.
[0009] In the conductive adhesive sheet according to the present
invention, the conductive particles are distributively arranged as
a primary particle or an aggregate of primary particles. As is
described above, in a predetermined region (namely, in an optional
region of the conductive adhesive sheet in such a plan view that a
distribution number Np of the distributively arranged conductive
particles be 9 to 25 with the assumption that all the conductive
particles are regularly arranged), the center-to-center distance
(Y) of adjacent distributively arranged conductive particles
(aggregate units when the conductive particles are aggregates),
which are regularly arranged in the plan view, and the average (X)
of equivalent circle diameters of the distributively arranged
conductive particles have a relationship that meets the condition:
1.5X.ltoreq.Y.ltoreq.100X. As the relationship meets the condition:
1.5X.ltoreq.Y, the conductive particles disperse appropriately all
around the conductive adhesive sheet, because adjacent conductive
particles are sufficiently largely spaced. Thus, the conductive
adhesive sheet exhibits good adhesion to an adherend. As the
relation meets the condition: Y.ltoreq.100X, the conductive
adhesive sheet has excellent connection stability, because the
spacing between the distributively arranged conductive particles is
not too large.
[0010] The conductive adhesive sheet according to the present
invention satisfies the following condition regarding the
distributively arranged conductive particles (distributed
conductive particles) in the predetermined region, as is described
above. Specifically, the number (N) of primary particles of the
distributed conductive particles and the number (Np) of the
conductive particles with the assumption that all the conductive
particles are regularly arranged have a relationship that meets the
condition: N/Np=1.0 to 100.0. As the ratio N/Np is 1.0 or more, the
conductive adhesive sheet has good connection stability while
keeping the amount of the conductive particles small, because the
conductive particles are arranged sufficiently at positions to be
arranged, or the conductive particles are present in a sufficient
number in a specific region or area. As the ratio N/Np is 100.0 or
less, the conductive adhesive sheet has good adhesion to an
adherend, because excessive aggregation of the conductive particles
is restrained to some extent.
[0011] The conductive adhesive sheet according to the present
invention also satisfies the following condition regarding the
distributed conductive particles in the predetermined region, as is
described above. When optional three unique regions including the
optional region are viewed in plan view so that the distribution
number Np in each region be 9 to 25, the ratio Ng/Np of the
distribution number Ng of conductive particles present in two or
more of the three regions to the distribution number Np is from 0.8
to 1.0. As the ratio Ng/Np is 0.8 or more, the conductive adhesive
sheet has good connection stability and good adhesion to an
adherend, because the conductive adhesive sheet has less
proportions of missing arrangement of conductive particles in an
ideal arrangement and of conductive particles that are arranged at
positions out of the ideal arrangement.
[0012] The conductive adhesive sheet according to the present
invention preferably has a ratio N/Np of 1.05 to 50.0. When the
ratio N/Np is 1.05 or more, the conductive adhesive sheet has
better connection stability, because the distributed conductive
particles in the conductive adhesive sheet contain aggregates
appropriately. When the ratio N/Np is 50.0 or less, the conductive
adhesive sheet has better adhesion to an adherend, because the
conductive particles are more restrained from excessive
aggregation.
[0013] The conductive adhesive sheet according to the present
invention preferably has a coefficient of variation of the
center-to-center distance Y of 0.5 or less. The conductive adhesive
sheet, when having such a configuration, has better adhesion to an
adherend and better connection stability.
[0014] The conductive adhesive sheet according to the present
invention preferably includes a thermosetting resin as the binder
component. When having the configuration as above, the binder
component can be cured after the conductive adhesive sheet
according to the present invention is placed and receives
pressurization and heating to fluidize the adhesive.
[0015] The conductive adhesive sheet according to the present
invention preferably includes the conductive particles in a
proportion of 10 to 60 mass percent of the totality (100 mass
percent) of the conductive adhesive sheet. The conductive adhesive
sheet according to the present invention, even when containing the
conductive particles in such a small proportion as compared with
conductive particles in conventional conductive bonding films,
exhibits good connection stability when used as a conductive
bonding film. The conductive adhesive sheet according to the
present invention, when having such a configuration, is
advantageously usable for conductive bonding film use.
[0016] The conductive adhesive sheet according to the present
invention preferably has an area where a portion in which the
conductive particles are distributively arranged has a large
thickness as compared with a portion in which no conductive
particle is distributively arranged. The conductive adhesive sheet
according to the present invention, when having the configuration
as above, has such a configuration that the area bearing or
including the conductive particles protrudes as compared with the
adhesive surface. The conductive adhesive sheet therefore has
better connection stability with higher contact frequency of the
conductive particles to an adherend.
[0017] The conductive adhesive sheet according to the present
invention preferably has an average of the equivalent circle
diameters of 15 to 100 .mu.m. The conductive adhesive sheet
according to the present invention, when having the configuration
as above, has good connection stability as compared with
conventional anisotropic conductive films. The conductive adhesive
sheet according to the present invention, when having the
configuration, is advantageously usable for conductive bonding film
use.
[0018] The present invention provides, in another aspect, an
electromagnetic shielding film including the conductive adhesive
sheet.
[0019] The present invention provides, in still another aspect, a
ground connector including the conductive adhesive sheet.
Advantageous Effects of Invention
[0020] The conductive adhesive sheet according to the present
invention exhibits excellent connection stability even when
containing conductive particles in a small proportion. The
conductive adhesive sheet can therefore surely economically have
connection stability as compared with conventional conductive
bonding films.
BRIEF DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is an enlarged top view of a conductive adhesive
sheet according to an embodiment of the present invention;
[0022] FIG. 2 is an enlarged top view of a conductive adhesive
sheet according to another embodiment of the present invention;
[0023] FIG. 3 is an enlarged top view of a conductive adhesive
sheet according to still another embodiment of the present
invention;
[0024] FIG. 4 is an enlarged top view of a conductive adhesive
sheet according to another embodiment of the present invention;
[0025] FIG. 5 is a schematic cross-sectional view of a conductive
adhesive sheet according to an embodiment of the present invention;
and
[0026] FIG. 6 is a schematic cross-sectional view of an exemplary
printed circuit board formed using a conductive adhesive sheet
according to an embodiment of the present invention.
DESCRIPTION OF EMBODIMENTS
Conductive Adhesive Sheet
[0027] The conductive adhesive sheet according to the present
invention contains a binder component and conductive particles. The
conductive particles are distributively arranged each as a primary
particle or an aggregate (such as a secondary particle) derived
from primary particles. The distributed conductive particles are
approximately regularly arranged in rows or lines in a planar
direction in plan view of the conductive adhesive sheet. Assume
that all the conductive particles are regularly arranged; and that
an optional or arbitrary region of the conductive adhesive sheet is
viewed in plan view so that a distribution number Np of the
distributed conductive particles be 9 to 25, the conductive
adhesive sheet satisfies the condition: 1.5X.ltoreq.Y.ltoreq.100X,
where X represents an average of equivalent circle diameters of the
distributed conductive particles; and Y represents a
center-to-center distance between adjacent two of the distributed
conductive particles which are regularly arranged in the plan view.
The ratio N/Np of the number of the primary particles in the
optional region to the distribution number Np is 1.0 to 100.0. When
optional three unique regions including the optional region are
viewed in plan view so that the distribution number Np in each
region be 9 to 25, the ratio Ng/Np of a distribution number of
conductive particles present in two or more of the three regions to
the distribution number Np is 0.8 to 1.0.
[0028] An embodiment of the conductive adhesive sheet according to
the present invention will be illustrated below. FIG. 1 is an
enlarged top view of a conductive adhesive sheet according to an
embodiment of the present invention.
[0029] As illustrated in FIG. 1, in the inventive conductive
adhesive sheet 1, conductive particles 11 are distributively
arranged in a binder component 12 in a region R in a planar
direction of the conductive adhesive sheet 1. The conductive
particles 11 are distributively arranged in units of primary
particles when such a conductive particle is a primary particle
11a, and are distributively arranged in units of aggregates when
such a conductive particle is an aggregate 11b. Hereinafter, the
term "conductive particle", unless otherwise specified, refers to a
distributively arranged conductive particle unit; specifically,
refers to a primary particle when the conductive particle is
distributively arranged as a primary particle; and refers to an
aggregate when such conductive particles are distributively
arranged in units of aggregates. In the region R, the distribution
number of the distributed conductive particles is 9, with the
assumption that all the conductive particles are regularly
arranged. The distributed conductive particles 11 are regularly
arranged in rows. Specifically, in other words, the conductive
particles 11 are regularly arranged in a first arrangement
direction L1, and in a second arrangement direction L2 that forms
an angle .alpha. of 90.degree. with the first arrangement direction
L1. In the first arrangement direction L1, conductive particles 11
are arranged at approximately uniform spacing; and, two or more of
such a row of the conductive particles are arranged in columns at
approximately uniform spacing in the second arrangement direction
L2 that forms an angle .alpha. of 90.degree. with the first
arrangement direction L1. The term "first arrangement direction L1"
refers to a direction in which an adjacent conductive particle is
arranged at the shortest distance from an optional conductive
particle 11 (for example, distance d1 in FIG. 1). The term "second
arrangement direction L2" refers to an arrangement direction
different from the first arrangement direction L1, in which an
adjacent conductive particle is arranged at the second shortest
distance next to d1, or at a distance equal to D1, from the
optional conductive particle 11 (for example, distance d2 in FIG.
1). Hereinafter, the term "third arrangement direction" refers to
an arrangement direction different from the first arrangement
direction L1 and the second arrangement direction L2, in which an
adjacent conductive particle is arranged at the third shortest
distance next to D2 or at a distance equal to D2 from the optional
conductive particle 11 (for example, distance d3 in FIG. 1).
[0030] In FIG. 1, all the conductive particles 11 are regularly
arranged in the region R. However, the conductive particles 11 in
the present invention have only to be arranged approximately
regularly. Examples of such approximately regular arrangements
include an arrangement where some conductive particles 11 are
slightly misaligned from the rows or columns, as illustrated in
FIG. 2; and an arrangement where some conductive particles 11 are
not arranged (are missing) at some positions in which the
conductive particles are to be arranged, as illustrated in FIG. 3.
Such misalignment and missing in arrangement may be within ranges
not adversely affecting advantageous effects of the present
invention.
[0031] The angle .alpha. which the first arrangement direction L1
forms with the second arrangement direction L2 is a smaller angle
when two angles which the first arrangement direction L1 forms with
the second arrangement direction L2 are different. The angle
.alpha. is not limited and can be appropriately selected within the
range of 0.degree. to 90.degree.. An exemplary arrangement where
the angle .alpha. is an acute angle is an arrangement as
illustrated in FIG. 4. Among them, the conductive adhesive sheet
according to the present invention preferably has an arrangement
where the angle .alpha. is 90.degree., as illustrated in FIGS. 1 to
3 (a lattice form), or an arrangement where the angle .alpha. is
45.degree. (a hound's-tooth check form). When the conductive
particles are arranged in a lattice form, the conductive adhesive
sheet may have better adhesion to an adherend and better connection
stability.
[0032] In the conductive adhesive sheet according to the present
invention, the center-to-center distance Y (d1, d2, or d3 in FIG.
1) of distributed conductive particles that are adjacent in a
planar direction, and the average X of equivalent circle diameters
of the distributed conductive particles have a relationship that
meets the condition: 1.5.ltoreq.Y.ltoreq.100X. As the condition:
1.5X.ltoreq.Y is met, the conductive adhesive sheet has good
adhesion to an adherend. This is because conductive particles
adjacent in the planar direction are sufficiently largely spaced,
and the conductive particles appropriately disperse all around the
conductive adhesive sheet. As the condition: Y.ltoreq.100X is met,
the conductive adhesive sheet has excellent connection stability,
because the conductive particles are distributively arranged at
spacing that is not too large.
[0033] The lower limit of the center-to-center distance Y is
preferably 3X, more preferably 5X, and still more preferably 7X.
The upper limit of the center-to-center distance Y is preferably
50X, more preferably 30X, and still more preferably 15X. In the
conductive adhesive sheet according to the present invention, the
center-to-center distance d1, the center-to-center distance d2, and
center-to-center distance d3 each meet the condition:
1.5X.ltoreq.Y.ltoreq.100X.
[0034] The term "equivalent circle diameter" of a conductive
particle refers to the equivalent circle diameter of a primary
particle when the distributively arranged conductive particle is
the primary particle; and refers to the equivalent circle diameter
of an aggregate, such as a secondary particle, when the
distributively arranged conductive particle is the aggregate. The
equivalent circle diameter is calculated typically by image
analysis of an optical photomicrograph in an optional region in
which the distribution number Np is 9 to 25 (for example, 9 in the
region R in FIG. 1) with the assumption that all the conductive
particles are regularly arranged (in a perfect arrangement).
Specifically, the equivalent circle diameter can be calculated
after taking the image of an optical photomicrograph into a
personal computer (PC), where the photomicrograph has been taken at
such a magnification that a 1-mm square region falls within the
photomicrograph, and subjecting the image to image processing. The
distribution number Np in the optional region is preferably 9, 16,
or 25 in which the conductive particles are distributively arranged
in an equal number both in the first arrangement direction L1 and
the second arrangement direction L2.
[0035] The average X of equivalent circle diameters of the
conductive particles is preferably 2 to 120 .mu.m, more preferably
15 to 100 .mu.m, and still more preferably 25 to 80 .mu.m, although
the conductive adhesive sheet may have any other average X. The
conductive adhesive sheet according to the present invention, when
having an average X of the equivalent circle diameters within the
range, exhibits good connection stability as compared with
conventional anisotropic conductive films. When having the
configuration as above, the conductive adhesive sheet according to
the present invention is advantageously usable for conductive
bonding film use.
[0036] The center-to-center distance Y is determined typically as a
center-to-center distance (distance between the conductive
particles) Y of two conductive particles that are regularly
arranged in the region R for determination of the center-to-center
distance Y and are adjacent to each other in the same arrangement
direction. When the distributed conductive particle in question is
an aggregate, the "center" refers to the center of the equivalent
circle of the aggregate.
[0037] The coefficient of variation of the center-to-center
distances Ys is preferably 0.5 or less, and more preferably 0.3 or
less, although the coefficient of variation is not limited. The
coefficient of variation of the center-to-center distances Ys works
as a measure or scale for degree of regular arrangement of the
distributed conductive particles. The coefficient of variation of
the center-to-center distances Ys of conductive particles is a
value determined by dividing the standard deviation of the
center-to-center distances of the conductive particles by the
average of the center-to-center distances. When the coefficient of
variation is 0.5 or less, the conductive adhesive sheet has
connection stability and adhesion to an adherend in better balance,
because the distributed conductive particles are arranged highly
regularly.
[0038] The center-to-center distance d1 from a conductive particle
adjacent in the first arrangement direction L1, the
center-to-center distance d2 from a conductive particle adjacent in
the second arrangement direction L2, and the center-to-center
distance d3 from a conductive particle adjacent in the third
arrangement direction may be different from one another, or two or
more of them may be identical, or all of them may be identical.
[0039] The center-to-center distances d1, d2, and d3 are each
preferably 100 to 1000 .mu.m, more preferably 150 to 800 .mu.m, and
still more preferably 200 to 600 .mu.m. The conductive adhesive
sheet, when having center-to-center distances within the range, has
adhesion to an adherend and connection stability both at better
levels.
[0040] In the conductive adhesive sheet according to the present
invention, the number (N) of primary particles of the conductive
particles and the number (Np) of conductive particles with the
assumption that all the conductive particles are regularly arranged
(in a perfect arrangement) have a relationship meeting the
condition: N/Np=1.0 to 100.0. As the ratio N/Np is 1.0 or more, the
conductive adhesive sheet has good connection stability, because
conductive particles are arranged sufficiently at positions to be
arranged, or conductive particles are present in a sufficient
number in a specific region (area). As the ratio N/Np is 100.0 or
less, the conductive adhesive sheet exhibits good adhesion to an
adherend with a smaller amount of conductive particles to be used,
because excessive aggregation of the conductive particles is
restrained to some extent. The ratio N/Np is determined in the
optional region defined for the determination of the
center-to-center distance Y.
[0041] The ratio N/Np is preferably 1.05 to 50.0, more preferably
1.2 to 30.0, and still more preferably 1.5 to 10.0. When the ratio
N/Np is 1.05 or more, the conductive adhesive sheet has better
connection stability, because the distributed conductive particles
in the conductive adhesive sheet include aggregates appropriately.
When the ratio N/Np is 50.0 or less, the conductive adhesive sheet
has better adhesion to an adherend, because excessive aggregation
of conductive particles is more restrained.
[0042] For example, in the conductive adhesive sheets 1 illustrated
in FIGS. 1 to 3, the distribution numbers Np in the region R are
each 9. The number N in FIG. 1 is 32 (N/Np=3.6), the number N in
FIG. 2 is 35 (N/Np=3.9), and the number N in FIG. 3 is 39
(N/Np=4.3).
[0043] In the conductive adhesive sheet according to the present
invention, when optional three unique regions including the
optional region are viewed in plan view so that the distribution
number Np in each region be 9 to 25, the ratio Ng/Np of the
distribution number Ng of conductive particles present in two or
more of the three regions to the distribution number Np is 0.8 to
1.0, preferably 0.85 to 1.0, and more preferably 0.9 to 1.0. As the
ratio Ng/Np is 0.8 or more, the conductive adhesive sheet has good
connection stability and good adhesion to an adherend, because the
conductive adhesive sheet has less proportions of missing
arrangement of conductive particles in ideal arrangement and of
conductive particles that are arranged at positions out of the
ideal arrangement. The conductive adhesive sheet desirably has a
higher ratio Ng/Np, and the ratio Ng/Np is most preferably 1.0. Of
the three regions defined for the determination of the ratio Ng/Np,
one region is the optional region defined for the determination of
the center-to-center distance Y, and the other two regions are
regions that do not include the conductive particles present in the
optional region, and do not include any of conductive particles
that overlap each other. The three regions to be selected are
regions having an identical Np.
[0044] Specifically, typically on the assumption that FIGS. 1 to 3
are enlarged views of different regions in one conductive adhesive
sheet according to the present invention, the three regions defined
for the determination of the ratio Ng/Np in the conductive adhesive
sheet according to the present invention are the region R in FIG.
1, the region R in FIG. 2, and the region R in FIG. 3. However,
there is no conductive particle that overlaps in each of the three
regions Rs in FIGS. 1 to 3. When FIGS. 1 to 3 are superimposed, the
distribution number of conductive particles that are present in two
or more regions is 9, because, of Np=9 in the three regions, the
distribution number where no conductive particle is present is 0;
the distribution number of conductive particles that are present
only in one region is 0; the distribution number of conductive
particles that are present in two regions is 1; and the
distribution number of conductive particles that are present in
three regions is 8. In this case, the ratio Ng/Np is 1.0.
[0045] Preferably, in an area or areas of the conductive adhesive
sheet according to the present invention, a portion where the
conductive particles are arranged has a thickness (for example, h1
given in FIG. 5) larger than the thickness (for example, h2 in FIG.
5) of a portion where no conductive particle is arranged. The
conductive adhesive sheet according to the present invention, when
having the configuration as above, has such a configuration that a
portion where conductive particles are arranged protrudes from the
adhesion face. Thus, the conductive adhesive sheet has high contact
frequency of the conductive particles to an adherend and has still
better connection stability. FIG. 5 is a schematic cross-sectional
view of a conductive adhesive sheet according to an embodiment of
the present invention.
[0046] The conductive adhesive sheet according to the present
invention has a thickness appropriately selectable according to the
intended use, and has a thickness of typically 1 to 50 .mu.m, and
preferably 5 to 25 .mu.m. The conductive adhesive sheet, when
having a thickness of 1 .mu.m or more, can be more satisfactorily
embedded in an opening disposed in an electromagnetic shielding
assembly of a printed circuit board. The conductive adhesive sheet,
when having a thickness of 50 .mu.m or less, can meet demands for
thinning. The conductive adhesive sheet according to the present
invention, when to be suitably used as a bonding film, may have a
thickness of typically 10 to 70 .mu.m, and preferably 30 to 65
.mu.m.
[0047] The conductive adhesive sheet according to the present
invention has a number of conductive particles (primary particles)
per unit area of preferably 10 to 1000 per square millimeter, more
preferably 20 to 800 per square millimeter, and still more
preferably 30 to 600 per square millimeter, although the conductive
adhesive sheet may have any other number per unit area. The
conductive adhesive sheet, when having a number per unit area
within the range, has connection stability and adhesion to an
adherend in better balance.
[0048] The conductive adhesive sheet according to the present
invention has an electric resistance of preferably 1 n or less, and
more preferably 0.5.OMEGA. or less, as measured after heating and
pressurization at 170.degree. C. and 3.0 MPa.
[0049] Non-limiting examples of the binder component include
thermoplastic resins, thermosetting resins, and actinic
radiation-curable compounds. The conductive adhesive sheet may
include each of different binder components alone or in
combination.
[0050] Non-limiting examples of the thermoplastic resins include
polystyrene resins, vinyl acetate resins, polyester resins,
polyolefin resins (such as polyethylene resins and polypropylene
resin compositions), polyimide resins, and acrylic resins. The
binder component may include each of different thermoplastic resins
alone or in combination.
[0051] Examples of the thermosetting resins include both resins
having thermosetting property (thermosetting resins) and resins
resulting from curing of the thermosetting resins. Non-limiting
examples of the thermosetting resins include phenolic resins, epoxy
resins, urethane resins, melamine resins, and alkyd resins. The
binder component may include each of different thermosetting resins
alone or in combination.
[0052] Non-limiting examples of the epoxy resins include bisphenol
epoxy resins, spirocyclic epoxy resins, naphthalene epoxy resins,
biphenyl epoxy resins, terpene epoxy resins, glycidyl ether epoxy
resins, glycidylamine epoxy resins, and novolac epoxy resins.
[0053] Non-limiting examples of the bisphenol epoxy resins include
bisphenol-A epoxy resins, bisphenol-F epoxy resins, bisphenol-S
epoxy resins, and tetrabromobisphenol-A epoxy resins. Non-limiting
examples of the glycidyl ether epoxy resins include
tris(glycidyloxyphenyl)methane and tetrakis
(glycidyloxyphenyl)ethane. A non-limiting example of the
glycidylamine epoxy resins is tetraglycidyldiaminodiphenylmethane.
Non-limiting examples of the novolac epoxy resins include epoxy
cresol novolac resins, epoxy phenol novolac resins,
.alpha.-naphthol novolac epoxy resins, and brominated epoxy phenol
novolac resins.
[0054] Examples of the actinic radiation-curable compounds include
both actinic radiation-curable compounds, which are compounds
curable by actinic radiation irradiation; and compounds resulting
from curing of the actinic radiation-curable compounds.
Non-limiting examples of the actinic radiation-curable compounds
include polymerizable compounds having at least two radically
reactive groups (such as (meth)acryloyl groups) in the molecule.
The binder component may include each of different actinic
radiation-curable compounds alone or in combination.
[0055] Among them, the binder component preferably includes a
thermosetting resin. In this case, the binder component can be
cured after the conductive adhesive sheet according to the present
invention is placed and receives pressurization and heating to
fluidize the adhesive.
[0056] The binder component, when including a thermosetting resin,
may include a curing agent for promoting heat cure reaction, as a
component constituting the binder component. The curing agent can
be appropriately selected according to the type of the
thermosetting resin. The binder component may include each of
different curing agents alone or in combination.
[0057] The conductive adhesive sheet according to the present
invention includes the binder component in a proportion of
preferably 40 to 90 mass percent, more preferably 45 to 85 mass
percent, and still more preferably 50 to 80 mass percent, of the
totality (100 mass percent) of the conductive adhesive sheet. The
conductive adhesive sheet, when containing the binder component in
a proportion of 40 mass percent or more, exhibits better adhesion
to an adherend and better fluidity upon pressurization-heating. The
conductive adhesive sheet, when containing the binder component in
a proportion of 90 mass percent or less, can include the conductive
particles in a sufficient amount.
[0058] Non-limiting examples of the conductive particles include
metal particles, metal-coated resin particles, and carbon fillers.
The conductive adhesive sheet may include each of different types
of conductive particles alone or in combination.
[0059] Non-limiting examples of metals constituting the metal
particles and constituting the coating layer of the metal-coated
resin particles include gold, silver, copper, nickel, zinc, tin,
bismuth, and indium. The conductive particles may include or bear
each of different metals alone or in combination.
[0060] Specifically, non-limiting examples of the metal particles
include copper particles, silver particles, nickel particles,
silver-coated copper particles, gold-coated copper particles,
silver-coated nickel particles, gold-coated nickel particles,
silver-coated alloy particles, tin-coated copper particles,
tin-coated nickel particles, and solder particles. Non-limiting
examples of the silver-coated alloy particles include silver-coated
copper alloy particles including copper-containing alloy particles
(such as copper alloy particles made of an alloy among copper,
nickel, and zinc) coated with silver. The metal particles can be
prepared typically by electrolytic process, atomization, or
reducing process.
[0061] Among them, the metal particles preferably include any of
silver particles, silver-coated copper particles, silver-coated
copper alloy particles, tin-coated copper particles, tin-coated
nickel particles, and solder particles. Of these, silver particles,
silver-coated copper particles, and silver-coated copper alloy
particles are preferred, and silver-coated copper particles and
silver-coated copper alloy particles are particularly preferred,
from the viewpoints of excellent conductivity, restrainment of
oxidation and aggregation of metal particles, and lower cost of the
metal particles. Tin-coated copper particles, tin-coated nickel
particles, and solder particles are also preferred, from the
viewpoint of forming an alloy with the circuit or grounding member
of the printed circuit board and establishing firm connection
thereto.
[0062] Non-limiting examples of the shape or form of the conductive
particles include spherical, flaky (scaly), dendritic, fibrous, and
amorphous (polyhedral) forms. Among them, the conductive particles
preferably have a spherical, dendritic, or amorphous (polyhedral)
form, for providing lower electric resistance of the conductive
adhesive sheet.
[0063] The conductive particles have a median diameter (D50) of
preferably 15 to 100 .mu.m, and more preferably 25 to 80 .mu.m,
although the conductive particles may have any other median
diameter (D50). The conductive adhesive sheet according to the
present invention, when having a median diameter D50 of the
conductive particles within the range, exhibits satisfactory
connection stability as compared with conventional anisotropic
conductive films. The conductive adhesive sheet according to the
present invention, when having the configuration as above, is
advantageously usable for conductive bonding film use. The term
"median diameter D50" refers to a particle size at an integrated
value of 50% in a particle size distribution determined by laser
diffraction scattering technique.
[0064] The conductive adhesive sheet according to the present
invention contains the conductive particles in a proportion of
preferably 10 to 60 mass percent, more preferably 15 to 55 mass
percent, and still more preferably 20 to 50 mass percent, of the
totality (100 mass percent) of the conductive adhesive sheet,
although the proportion is not limited. The conductive adhesive
sheet, when containing the conductive particles in a proportion of
10 mass percent or more, may exhibit better connection stability.
The conductive adhesive sheet, when containing the conductive
particles in a proportion of 60 mass percent or less, may have
better adhesion to an adherend. The conductive adhesive sheet
according to the present invention, when used as a conductive
bonding film, exhibits good connection stability even when
containing the conductive particles in such a small proportion as
above, as compared with the proportion of conductive particles in
conventional conductive bonding films. The conductive adhesive
sheet according to the present invention, when having the
configuration as above, is advantageously usable for conductive
bonding film use.
[0065] The conductive adhesive sheet according to the present
invention may further include one or more components other than the
above-mentioned components, within ranges not adversely affecting
the advantageous effects of the present invention. Examples of the
other components include components contained in known or common
conductive adhesive sheets. Non-limiting examples of the other
components include flame retardants, plasticizers, antifoaming
agents, viscosity modifiers, antioxidants, diluents, antisettling
agents, fillers, colorants, leveling agents, coupling agents, and
tackifier resins. The conductive adhesive sheet may include each of
different other components alone or in combination.
[0066] The conductive adhesive sheet according to the present
invention can be produced by a known or common production method.
For example, the conductive adhesive sheet may be produced by
applying an adhesive composition for the formation of a conductive
adhesive sheet onto a temporary substrate such as a separate film,
or onto a substrate, and as needed, subjecting the coated layer to
desolvation and/or partial curing. To arrange conductive particles
in an arrangement specified in the present invention, the
conductive adhesive sheet may be produced by applying an adhesive
composition containing no conductive particle, and then embedding
the conductive particles at desired positions in the adhesive
composition. Alternatively, the conductive adhesive sheet may be
produced by arraying the conductive particles on a temporary
substrate or a substrate in an arrangement specified in the present
invention, thereafter applying an adhesive composition containing
no conductive particle, and then, as needed, subjecting the applied
composition to desolvation and/or partial curing.
[0067] The adhesive composition may further include, for example, a
solvent (solventing medium), in addition to the components to be
contained in the conductive adhesive sheet. Non-limiting examples
of the solvent include toluene, acetone, methyl ethyl ketone,
methanol, ethanol, propanol, and dimethylformamide. The solids
concentration of the adhesive composition is appropriately set
according typically to the thickness of the conductive adhesive
sheet to be formed.
[0068] The adhesive composition may be applied by a known coating
technique. For example, the adhesive composition may be applied
using a coater such as a rotogravure roll coater, reverse roll
coater, kiss-contact roll coater, lip coater, dip roll coater, bar
coater, knife coater, spray coater, comma coater, direct coater, or
slot die coater.
[0069] The conductive adhesive sheet according to the present
invention is preferably used for printed circuit board use, and
particularly preferably used for conductive bonding film use, from
the viewpoints of adhesion to an adherend and connection stability.
Non-limiting examples of the printed circuit board use include a
conductive bonding film, as well as a conductive adhesive sheet
constituting an electromagnetic shielding assembly (for example, a
conductive adhesive sheet disposed on an insulating protective
layer which covers a circuit pattern of a printed circuit board).
Non-limiting examples of the conductive bonding film include
adhesives for FGFs, bonding films for bonding between a stiffener
and a printed circuit board, and bonding films for bonding between
an external ground for circuit grounding and a printed circuit
board.
[0070] FIG. 6 illustrates a conductive adhesive sheet according to
an exemplary embodiment of the present invention when used as a
conductive bonding film between a stiffener and a printed circuit
board. A shielded printed circuit board 2 in FIG. 6 includes a
printed circuit board 20; an electromagnetic shielding assembly 30
disposed on the printed circuit board 20; a conductive adhesive
layer 40 charged in a through hole 33 provided in the
electromagnetic shielding assembly 30; and a stiffener 50 bonded
through the conductive adhesive layer 40. The conductive adhesive
layer 40 is made of or from the conductive adhesive sheet according
to the present invention.
[0071] The printed circuit board 20 includes a base 21; a circuit
pattern 23 disposed partially on the base 21; an insulating
protective layer (cover lay) 24 that covers and insulatively
protects the circuit pattern 23; and an adhesive layer 22 that
covers the circuit pattern 23 and bonds the circuit pattern 23 and
the base 21 to the insulating protective layer 24. The circuit
pattern 23 includes signal circuits.
[0072] The electromagnetic shielding assembly 30 includes a
conductive adhesive layer 31 and an insulating layer 32 disposed in
this sequence on the printed circuit board 20, more specifically,
on the insulating protective layer 24 of the printed circuit board
20. The conductive adhesive layer 31 and the insulating layer 32
have a through hole 33 that penetrates these layers in a thickness
direction (namely, the surface of the printed circuit board 20 is
exposed). The presence of the through hole 33 allows the conductive
adhesive sheet according to the present invention to flow into the
through hole 33 by pressurization and heating to form the
conductive adhesive layer 40 and to be electrically connected to
the conductive adhesive layer 31. The printed circuit board 20,
more specifically, the insulating protective layer 24 defines the
bottom of the through hole 33. Specifically, the through hole 33 is
defined by the side of the insulating layer 32, the side of the
conductive adhesive layer 31, and the surface of the printed
circuit board 20 (in particular, of the insulating protective layer
24). The conductive adhesive layer 31 may be the conductive
adhesive sheet according to the present invention, or a layer
formed from the conductive adhesive sheet according to the present
invention (for example, one formed by thermocompression
bonding).
[0073] The electromagnetic shielding assembly 30 can be prepared
using an electromagnetic shielding film. The electromagnetic
shielding film may be a shielding film including the conductive
adhesive sheet according to the present invention (electromagnetic
shielding film according to the present invention). The
electromagnetic shielding film typically includes a transfer film,
an insulating layer (protective layer), the conductive adhesive
sheet according to the present invention (conductive bonding
layer), and a separate film disposed in the specified sequence.
Upon use, the separate film is removed to expose the surface of the
electromagnetic shielding film, the exposed surface is applied to
the printed circuit board 20, and then the transfer film is
removed.
[0074] Functionally, the conductive adhesive layer 40 is disposed
on the electromagnetic shielding assembly 30, fills the through
hole 33 with itself, and is electrically connected through the
through hole 33 to the conductive adhesive layer 31. The stiffener
50 is secured through the conductive adhesive layer 31 to the
printed circuit board 20 and the electromagnetic shielding assembly
30.
[0075] When the stiffener 50 works as a grounding component, the
conductive adhesive layer 40 functions as a ground connector. As
the ground connector, the conductive adhesive sheet according to
the present invention can be used. The ground connector is a ground
connector having the conductive adhesive sheet according to the
present invention (ground connector according to the present
invention). The ground connector may include a conductor such as a
metal layer disposed on the conductive adhesive sheet according to
the present invention.
[0076] The conductive adhesive layer 40 is not in contact with
(does not reach) the circuit pattern. This configuration can
eliminate or minimize insufficient charging of the adhesive to form
the conductive adhesive layer 40 into the through hole, and
resulting entry of air bubbles into the through hole, because the
adhesive has only to flow into the through hole in a small
dimension. This can restrain interfacial delamination typically in
reflow process and give stable connection reliability.
[0077] The presence of the stiffener 50 in the shielded printed
circuit board 2 allows the printed circuit board 20 to retain its
shape. When the shielded printed circuit board is bent, such a
stiffener having a certain area laminated on the top of the
electromagnetic shielding assembly can restrain the resilience of
the resulting multilayer assembly and maintains the shape as being
bent. The shielded printed circuit board is therefore preferably a
flexible printed circuit board (FPC).
[0078] The shielded printed circuit board can be produced by a
production method typically including a stiffener stacking step and
a thermocompression bonding step. The stiffener stacking step is
the step of stacking a stiffener including an electromagnetic
bonding film, which is the conductive adhesive sheet according to
the present invention, on the top of the through hole, so as to
bring the electromagnetic bonding film into contact with the
electromagnetic shielding assembly. The thermocompression bonding
step is the step of conducting thermocompression bonding to allow
the electromagnetic bonding film to flow into the through hole to
form a conductive adhesive layer and to allow the conductive
adhesive layer derived from the electromagnetic bonding film to
come into contact with the conductive adhesive layer of the
electromagnetic shielding assembly.
[0079] Specifically, in the stiffener stacking step, the conductive
bonding film, which is the conductive adhesive sheet according to
the present invention, and the stiffener 50 are laminated on each
other, the laminate is cut to an optional size, and is arranged on
the insulating layer 32 so that the surface of the conductive
bonding film closes or plugs the opening of the through hole 33. In
the thermocompression bonding step, the conductive bonding film
softens and is fluidized by pressurization and heating, and flows
into and fills the through hole 33 by the action of the pressure
upon pressurization. The charged conductive bonding film is then
cured by subsequent cooling or thermal polymerization and forms the
conductive adhesive layer 40. Thus, the conductive bonding film
fluidizes by thermocompression bonding and comes into contact with
the conductive adhesive layer 31.
REFERENCE SIGNS LIST
[0080] 1 conductive adhesive sheet according to the present
invention [0081] 11 conductive particle [0082] 11a conductive
particle (primary particle) [0083] 11b conductive particle
(aggregate) [0084] 12 binder component [0085] R region [0086] L1
first arrangement direction [0087] L2 second arrangement direction
[0088] .alpha. angle formed by the first arrangement direction L1
and the first arrangement direction L2 [0089] d1 center-to-center
distance between adjacent conductive particles in the first
arrangement direction [0090] d2 center-to-center distance between
adjacent conductive particles in the second arrangement direction
[0091] d3 center-to-center distance between adjacent conductive
particles in the third arrangement direction [0092] h1 thickness of
a portion where a conductive particle is arranged [0093] h2
thickness of a portion where no conductive particle is arranged
[0094] 2 shielded printed circuit board [0095] 20 printed circuit
board [0096] 21 base [0097] 22 adhesive layer [0098] 23 circuit
pattern (trace) [0099] 24 insulating protective layer (cover lay)
[0100] 30 electromagnetic shielding assembly [0101] 31 conductive
adhesive layer [0102] 32 insulating layer [0103] 33 through hole
[0104] 40 conductive adhesive layer [0105] 50 stiffener
* * * * *