U.S. patent application number 12/981085 was filed with the patent office on 2011-04-28 for heat-conductive noise suppression sheet.
Invention is credited to Keiichi Araki, Satoshi Maruyama, Masao Matsui, Toshio Takahashi.
Application Number | 20110094827 12/981085 |
Document ID | / |
Family ID | 41507109 |
Filed Date | 2011-04-28 |
United States Patent
Application |
20110094827 |
Kind Code |
A1 |
Takahashi; Toshio ; et
al. |
April 28, 2011 |
HEAT-CONDUCTIVE NOISE SUPPRESSION SHEET
Abstract
A heat-conductive noise suppression sheet according to an
embodiment includes first ferrite particles, second ferrite
particles, a heat-conducting material, and a matrix material. The
first ferrite particles are spherical particles having an average
particle diameter in the range of 50 .mu.m to 150 .mu.m, the
content of the first ferrite particles with respect to the total
amount of solid components being in the range of 5 vol % to 25 vol
%. The second ferrite particles are irregularly shaped particles
having an average particle diameter in the range of 50 .mu.m or
less, the content of the second ferrite particles with respect the
total amount of solid components being in the range of 5 vol % to
45 vol %.
Inventors: |
Takahashi; Toshio;
(Miyagi-Ken, JP) ; Matsui; Masao; (Miyagi-Ken,
JP) ; Maruyama; Satoshi; (Miyagi-Ken, JP) ;
Araki; Keiichi; (Tokyo, JP) |
Family ID: |
41507109 |
Appl. No.: |
12/981085 |
Filed: |
December 29, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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PCT/JP2009/062377 |
Jul 7, 2009 |
|
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12981085 |
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Current U.S.
Class: |
181/294 |
Current CPC
Class: |
H01L 2224/73253
20130101; H01L 2924/01004 20130101; H01L 2924/01033 20130101; H01L
2224/2936 20130101; H01L 2924/00013 20130101; H01L 2924/01019
20130101; H01L 2924/0103 20130101; H01L 2924/01082 20130101; H01L
2924/00013 20130101; H01L 2924/3512 20130101; H01L 2924/00013
20130101; H01L 2924/01005 20130101; H01L 24/32 20130101; H01L
2924/01012 20130101; H01L 23/3736 20130101; H01L 2924/01078
20130101; H01L 2224/2936 20130101; H01L 23/3733 20130101; H01L
2924/01025 20130101; H01L 2924/00013 20130101; H01L 23/3737
20130101; H01L 2924/01006 20130101; H01L 2224/29299 20130101; H01L
2224/29299 20130101; H01L 2924/01013 20130101; H01L 2924/00014
20130101; H01L 2224/29199 20130101; H01L 2924/00014 20130101; H01L
2224/2929 20130101; H01L 2924/14 20130101; H01L 23/552 20130101;
H01L 2224/29299 20130101; H01L 2224/29 20130101; H01L 24/29
20130101; H01L 2924/01047 20130101; H01L 2924/00013 20130101; H01L
2924/01074 20130101; H01L 2224/29099 20130101; H01L 2924/00
20130101 |
Class at
Publication: |
181/294 |
International
Class: |
E04B 1/74 20060101
E04B001/74 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 10, 2008 |
JP |
2008-179664 |
Claims
1. A heat-conductive noise suppression sheet, comprising: first
ferrite particles that are spherical particles having an average
particle diameter in the range of 50 .mu.m to 150 .mu.m, the
content of the first ferrite particles with respect to the total
amount of solid components being in the range of 5 vol % to 25 vol
%; second ferrite particles that are irregularly shaped particles
having an average particle diameter in the range of 50 .mu.m or
less, the content of the second ferrite particles with respect the
total amount of solid components being in the range of 5 vol % to
45 vol %; a matrix material; and a heat-conducting material.
2. The heat-conductive noise suppression sheet according to claim
1, wherein the content of the first ferrite particles is 10 vol %
or more.
3. The heat-conductive noise suppression sheet according to claim
1, wherein the content of the first ferrite particles is 20 vol %
or more.
4. A heat-conductive noise suppression sheet, comprising: first
ferrite particles that are spherical particles having an average
particle diameter in the range of 50 .mu.m to 150 .mu.m, the
content of the first ferrite particles with respect to the total
amount of solid components being in the range of 20 vol % to 25 vol
%; second ferrite particles that are irregularly shaped particles
having an average particle diameter in the range of 50 .mu.m or
less, the content of the second ferrite particles with respect the
total amount of solid components being in the range of 20 vol % to
35 vol %; and a matrix material.
5. The heat-conductive noise suppression sheet according to claim
1, wherein the content of the second ferrite particles is 30 vol %
or more.
6. A heat-conductive noise suppression sheet, comprising: first
ferrite particles that are spherical particles having an average
particle diameter in the range of 50 .mu.m to 150 .mu.m, the
content of the first ferrite particles with respect to the total
amount of solid components being in the range of 20 vol % to 25 vol
%; second ferrite particles that are irregularly shaped particles
having an average particle diameter in the range of 50 .mu.m or
less, the content of the second ferrite particles with respect the
total amount of solid components being in the range of 10 vol % to
20 vol %; and a matrix material.
7. The heat-conductive noise suppression sheet according to claim
1, wherein the irregularly shaped particles are formed by crushing
the spherical particles.
8. The heat-conductive noise suppression sheet according to claim
4, further comprising a heat-conducting material.
9. The heat-conductive noise suppression sheet according to claim
8, wherein the heat-conducting material is aluminum oxide having an
average particle diameter in the range of 5 .mu.m to 25 .mu.m, and
the content of the heat-conducting material with respect to the
total amount of solid components is in the range of 2.5 vol % to 10
vol %.
10. The heat-conductive noise suppression sheet according to claim
1, wherein the matrix material is silicone gel, and the content of
the matrix material with respect to the total amount of solid
components is in the range of 30 vol % to 57.5 vol %.
Description
CLAIM OF PRIORITY
[0001] This application is a Continuation of International
Application No. PCT/JP2009/062377 filed on Jul. 7, 2009, which
claims benefit of Japanese Patent Application No. 2008-179664 filed
on Jul. 10, 2008. The entire contents of each application noted
above are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a heat-conductive noise
suppression sheet having a high noise suppression effect over a
wide frequency range from the hundred megahertz range to the
gigahertz range and high thermal conductivity.
[0004] 2. Description of the Related Art
[0005] As described in Japanese Unexamined Patent Application
Publication No. 2001-68312 and Japanese Unexamined Patent
Application Publication (Translation of PCT Application) No.
2006-504272, structures in which a heat-conductive noise
suppression sheet is interposed between a semiconductor component,
such as an IC, and a heat sink are known.
[0006] A heat-conductive noise suppression sheet for the
above-described use converts electromagnetic energy emitted from
the semiconductor component into thermal energy, and conducts the
thermal energy through the sheet so as to radiate heat to the heat
sink.
[0007] Japanese Unexamined Patent Application Publication No.
2001-68312 discloses a technique of increasing the noise
suppression effect by increasing the imaginary part .mu.'' of the
complex relative permeability.
[0008] However, it has been found that it is difficult to
effectively increase the noise suppression effect in both the
hundred megahertz range and the gigahertz range simply by adjusting
the imaginary part .mu.'' of the complex relative permeability.
[0009] In addition, it is necessary not only to increase the noise
suppression effect, but also to effectively increase the thermal
conductivity.
[0010] However, it has been found that even when the coefficient of
thermal conductivity is increased by increasing the content of
filler, the thermal conductivity cannot be effectively increased,
owing to a reduction in compressibility. The heat-conductive noise
suppression sheet is disposed between the semiconductor component,
such as an IC, and the heat sink in such a manner that the
heat-conductive noise suppression sheet is compressed. If the
compressibility of the sheet is low, the adhesion between the sheet
and the heat sink and the adhesion between the sheet and the
substrate decrease, which causes a reduction in thermal
conductivity.
SUMMARY OF THE INVENTION
[0011] The present invention has been made to solve the
above-described problem of the related art, and provides a
heat-conductive noise suppression sheet having a high noise
suppression effect over a wide frequency range from the hundred
megahertz range to the gigahertz range and high thermal
conductivity.
[0012] A heat-conductive noise suppression sheet according to an
aspect of the present invention includes first ferrite particles,
second ferrite particles, a heat-conducting material, and a matrix
material.
[0013] The first ferrite particles are spherical particles having
an average particle diameter in the range of 50 .mu.m to 150 .mu.m,
the content of the first ferrite particles with respect to the
total amount of solid components being in the range of 5 vol % to
25 vol %.
[0014] The second ferrite particles are irregularly shaped
particles having an average particle diameter in the range of 50
.mu.m or less, the content of the second ferrite particles with
respect the total amount of solid components being in the range of
5 vol % to 45 vol %.
[0015] According to the present invention, attention is focused not
only on the imaginary part .mu.'' of the complex relative
permeability but also on the imaginary part .epsilon.'' of the
complex relative permittivity to obtain a high noise suppression
effect over a wide frequency range from the hundred megahertz range
to the gigahertz range. More specifically, according to the present
invention, the imaginary part .mu.'' of the complex relative
permeability can be increased in the hundred megahertz range. Even
though the imaginary part .mu.'' of the complex relative
permeability is reduced in the gigahertz range, according to the
present invention, the imaginary part .epsilon.'' of the complex
relative permittivity can be reduced in the gigahertz range.
Therefore, a high noise suppression effect can be obtained over a
wide frequency range from the hundred megahertz range to the
gigahertz range.
[0016] According to the present invention, the first ferrite
particles, which are spherical particles having a larger average
particle diameter than that of the second ferrite particles, are
contained and the content of the first ferrite particles is
appropriately regulated. Therefore, the compressibility can be
increased while maintaining a high coefficient of thermal
conductivity. As a result, the thermal conductivity can be
effectively increased.
[0017] In the present invention, the content of the first ferrite
particles is preferably 10 vol % or more, and more preferably, 20
vol % or more.
[0018] According to another aspect of the present invention, a
heat-conductive noise suppression sheet includes first ferrite
particles, second ferrite particles, and a matrix material.
[0019] The first ferrite particles are spherical particles having
an average particle diameter in the range of 50 .mu.m to 150 .mu.m,
the content of the first ferrite particles with respect to the
total amount of solid components being in the range of 20 vol % to
25 vol %.
[0020] The second ferrite particles are irregularly shaped
particles having an average particle diameter in the range of 50
.mu.m or less, the content of the second ferrite particles with
respect the total amount of solid components being in the range of
20 vol % to 35 vol %.
[0021] In addition, in the present invention, the content of the
second ferrite particles is preferably 30 vol % or more.
[0022] According to another aspect of the present invention, a
heat-conductive noise suppression sheet includes first ferrite
particles, second ferrite particles, and a matrix material.
[0023] The first ferrite particles are spherical particles having
an average particle diameter in the range of 50 .mu.m to 150 .mu.m,
the content of the first ferrite particles with respect to the
total amount of solid components being in the range of 20 vol % to
25 vol %.
[0024] The second ferrite particles are irregularly shaped
particles having an average particle diameter in the range of 50
.mu.m or less, the content of the second ferrite particles with
respect the total amount of solid components being in the range of
10 vol % to 20 vol %.
[0025] According to the present invention, the content of the
second ferrite particles may be set to a relatively small value by
setting the content of the first ferrite particles to a relatively
large value. In such a case, even when the total filler content is
not very large, a high noise suppression effect can be obtained. In
addition, a high coefficient of thermal conductivity and high
compressibility can be obtained, so that high thermal conductivity
can be obtained.
[0026] In the present invention, the irregularly shaped particles
are preferably formed by crushing the spherical particles.
[0027] In the present invention, a heat-conducting material may be
additionally contained. More specifically, preferably, the
heat-conducting material is aluminum oxide having an average
particle diameter in the range of 5 .mu.m to 25 .mu.m, and the
content of the heat-conducting material with respect to the total
amount of solid components is in the range of 2.5 vol % to 10 vol
%.
[0028] In the present invention, preferably, the matrix material is
silicone gel, and the content of the matrix material with respect
to the total amount of solid components is in the range of 30 vol %
to 57.5 vol %.
[0029] According to the heat-conductive noise suppression sheet of
the present invention, a high noise suppression effect can be
obtained over a wide frequency range from the hundred megahertz
range to the gigahertz range. In addition, high thermal
conductivity can be obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a sectional view illustrating the manner in which
a heat-conductive noise suppression sheet according to an
embodiment is used;
[0031] FIG. 2 is a schematic diagram illustrating the inner
structure of the sheet according to the embodiment;
[0032] FIG. 3 is a graph showing the frequency characteristics of
the imaginary part .mu.'' of the complex relative permeability of
Example 1, Related-Art Example 1, and Comparative Example 1;
[0033] FIG. 4 is a graph showing the frequency characteristics of
the imaginary part .epsilon.'' of the complex relative permittivity
of Example 1, Related-Art Example 1, and Comparative Example 1;
[0034] FIG. 5 is a graph showing the frequency characteristics of
the amount of noise reduction in Example 1, Related-Art Example 1,
and Comparative Example 1;
[0035] FIG. 6 is a cross-sectional photograph (SEM photograph) of
Example 1;
[0036] FIG. 7 is a cross-sectional photograph (SEM photograph) of
Related-Art Example 1;
[0037] FIGS. 8A to 8D are schematic diagrams illustrating heat
distribution along cross sections of analysis models containing
different numbers of first ferrite particles (spherical particles);
and
[0038] FIG. 9 is a cross-sectional photograph (SEM photograph) of
Comparative Example 8.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0039] FIG. 1 is a sectional view illustrating the manner in which
a heat-conductive noise suppression sheet according to an
embodiment is used. FIG. 2 is a schematic diagram illustrating the
inner structure of the sheet.
[0040] Referring to FIG. 1, reference numeral 1 denotes a
semiconductor component, such as an IC, and reference numeral 2
denotes a heat sink. A heat-conductive noise suppression sheet 3
according to the present embodiment is provided between the
semiconductor component 1 and the heat sink 2. The heat-conductive
noise suppression sheet 3 and the semiconductor component 1 are in
close contact with each other, and the heat-conductive noise
suppression sheet 3 and the heat sink 2 are also in close contact
with each other.
[0041] The thickness H1 of the heat-conductive noise suppression
sheet 3 according to the present embodiment is about 1 mm to 5
mm.
[0042] As illustrated in FIG. 2, the heat-conductive noise
suppression sheet 3 contains first ferrite particles 4, second
ferrite particles 5, a heat-conducting material 6, and a matrix
material 7.
[0043] The first ferrite particles 4 are spherical particles having
an average particle diameter in the range of 50 .mu.m to 150 .mu.m,
and the content of the first ferrite particles 4 with respect to
the total amount of solid components is in the range of 5 vol % to
25 vol %. Here, "spherical particles" are particles that have no
corners on the surface and that have a degree of flatness (aspect
ratio) in the range of 1 to 2. In this specification, the "average
particle diameter" is the particle diameter corresponding to a
cumulative value of 50% (D50).
[0044] The content of the first ferrite particles 4 is preferably
in the range of 10 vol % to 25 vol %, and more preferably, in the
range of 20 vol % to 25 vol %.
[0045] The second ferrite particles 5 are irregularly shaped
particles having an average particle diameter in the range of 50
.mu.m or less, and the content of the second ferrite particles 5
with respect to the total amount of solid components is in the
range of 5 vol % to 45 vol %. The "irregularly shaped particles"
are particles other than spherical particles that have various
different shapes. The average particle diameter of the second
ferrite particles 5 is smaller than the average particle diameter
of the first ferrite particles 4.
[0046] The content of the second ferrite particles 5 is preferably
in the range of 30 vol % to 45 vol %.
[0047] The second ferrite particles 5, which are irregularly shaped
particles, are preferably formed by crushing the first ferrite
particles 4, which are spherical particles. Conformability to the
matrix material 7 can be increased by adding the second ferrite
particles 5.
[0048] Existing ferrites, such as Mn--Zn ferrite and Ni--Zn
ferrite, may be used as the first ferrite particles 4 and the
second ferrite particles 5.
[0049] The heat-conducting material 6 may be, for example, aluminum
oxide, magnesium oxide, zinc oxide, titanium oxide, aluminum
nitride, boron nitride, or silicon nitride. Preferably, the
heat-conducting material 6 is aluminum oxide. The heat-conducting
material 6 preferably has an average particle diameter in the range
of 5 .mu.m to 25 .mu.m, and the content of the heat-conducting
material 6 with respect to the total amount of solid components is
preferably in the range of 2.5 vol % to 10 vol %, and more
preferably, in the range of 5 vol % to 7 vol %.
[0050] The heat-conducting material 6 may be omitted. In such a
case, the sheet includes the first ferrite particles 4, the second
ferrite particles 5, and the matrix material 7.
[0051] Silicone gel is preferably used as the matrix material 7 to
increase the heat resistance and tackiness (adhesion) of the sheet.
The content of the matrix material 7 with respect to the total
amount of solid components is preferably in the range of 30 vol %
to 57.5 vol %, and more preferably, in the range of 35 vol % to 45
vol %.
[0052] According to the heat-conductive noise suppression sheet 3
of the present embodiment, the imaginary part .mu.'' of the complex
relative permeability can be increased in the hundred megahertz
range. More specifically, the imaginary part .mu.'' of the complex
relative permeability can be set to 3 or more. According to the
present embodiment, the imaginary part .epsilon.'' of the complex
relative permittivity can be reduced in the gigahertz range. More
specifically, the imaginary part .epsilon.'' of the complex
relative permittivity can be set to 0.2 or less.
[0053] In the present embodiment, a predetermined amount of first
ferrite particles 4, which are spherical particles, having a
predetermined particle diameter is added. The addition of the first
ferrite particles 4 is considered to contribute to the increase in
the imaginary part .mu.'' of the complex relative permeability in
the hundred megahertz range. In the present embodiment, similar to
the related art, the imaginary part .mu.'' of the complex relative
permeability tends to decrease in the gigahertz range. Accordingly,
in the present embodiment, to increase the noise suppression effect
in the gigahertz range even when the imaginary part .mu.'' of the
complex relative permeability is small, attention is focused on the
imaginary part .epsilon.'' of the complex relative
permittivity.
[0054] In the present embodiment, as described above, the imaginary
part .epsilon.'' of the complex relative permittivity is reduced in
the gigahertz range. The fact that the imaginary part .epsilon.''
of the complex relative permittivity is small means that the
insulation resistance is high.
[0055] In the present embodiment, the addition of a predetermined
amount of second ferrite particles 5, which are irregularly shaped
particles, having a predetermined particle diameter contributes to
the reduction in the imaginary part .epsilon.'' of the complex
relative permittivity in the gigahertz range. The second ferrite
particles 5, which are the irregularly shaped particles, added in
the present embodiment suppress deposition phenomenon and the like
of the first ferrite particles 4 in the manufacturing process.
Since the second ferrite particles 5, which are highly conformable
to the matrix material 7, are moderately dispersed between the
first ferrite particles 4, the ferrite particles do not easily come
into contact with each other, so that the insulation resistance is
increased. This is considered to be the reason why the imaginary
part .epsilon.'' of the complex relative permittivity is reduced.
The addition of the heat-conducting material 6, which is added to
increase the thermal conductivity, is considered to be another
reason for the reduction in the imaginary part .epsilon.'' of the
complex relative permittivity.
[0056] As described above, in the present embodiment, the imaginary
part .mu.'' of the complex relative permeability can be increased
in the hundred megahertz range. Even though the imaginary part
.mu.'' of the complex relative permeability is reduced in the
gigahertz range, in the present embodiment, the imaginary part
.epsilon.'' of the complex relative permittivity can be reduced in
the gigahertz range. Accordingly, electromagnetic energy can be
appropriately converted into thermal energy in a wide frequency
range from the hundred megahertz range to the gigahertz range, and
the thermal energy can be appropriately radiated from the inside of
the sheet to the outside, owing to the thermal conductivity.
Therefore, the heat-conductive noise suppression sheet 3 according
to the present embodiment provides a high noise suppression effect
over a wide frequency range from the hundred megahertz range to the
gigahertz range.
[0057] In addition, the heat-conductive noise suppression sheet 3
according to the present embodiment provides high thermal
conductivity.
[0058] To increase the thermal conductivity, it is essential to
increase the coefficient of thermal conductivity of the sheet 3
itself while increasing the compressibility thereof at the same
time. More specifically, even when the coefficient of thermal
conductivity is increased, the thermal conductivity is reduced if
the compressibility is low.
[0059] According to the present embodiment, the first ferrite
particles 4, which are spherical particles having a larger average
particle diameter than that of the second ferrite particles 5, are
contained. The coefficient of thermal conductivity can be increased
by adding the first ferrite particles 4. However, when the content
of the first ferrite particles 4 is excessively increased, the
compressibility decreases. As illustrated in FIG. 1, the
heat-conductive noise suppression sheet 3 is interposed between the
semiconductor component 1 and the heat sink 2. The thickness of the
heat-conductive noise suppression sheet 3 is reduced when the
heat-conductive noise suppression sheet 3 is pressed in the
thickness direction by, for example, a housing. At this time, if
the compressibility of the heat-conductive noise suppression sheet
3 is high, the adhesion between the heat-conductive noise
suppression sheet 3 and the semiconductor component 1 and the
adhesion between the heat-conductive noise suppression sheet 3 and
the heat sink 2 can be increased. As a result, the thermal
conductivity can be increased.
[0060] In the present embodiment, the first ferrite particles 4,
which are spherical particles, are contained and the content
thereof is in the range of 5 vol % to 25 vol %. In addition, an
amount of second ferrite particles 5 that is appropriate in
consideration of, for example, the noise suppression effect is also
contained. Therefore, a noise suppression effect and high thermal
conductivity can both be obtained.
[0061] In the present embodiment, the total content calculated by
adding the contents of the first ferrite particles 4, the second
ferrite particles 5, and the heat-conducting material 6 (the total
content of the ferrite particles 4 and 5 when the heat-conducting
material 6 is omitted) is preferably about 50 vol % to 60 vol %. In
such a case, high compressibility can be obtained, and high thermal
conductivity can be obtained accordingly.
[0062] If a sufficient amount, such as 20 vol % to 25 vol %, of
first ferrite particles 4 is contained, even when the content of
the second ferrite particles 5 or the sum of the contents of the
second ferrite particles 5 and the heat-conducting material 6 is
set to a small amount, such as 10 vol % to 20 vol %, a noise
suppression effect and high thermal conductivity can be obtained.
This embodiment is suitable for an application in which high
thermal conductivity is needed even if the noise suppression effect
is reduced as a result of reduction in the content of the second
ferrite particles 5.
[0063] In addition to the first ferrite particles 4, the second
ferrite particles 5, the heat-conducting material 6, and the matrix
material 7, the heat-conductive noise suppression sheet 3 according
to the present embodiment may further contain silane coupling
agent, platinum catalyst, flame retarder, etc., as necessary.
[0064] In the present embodiment, the first ferrite particles 4,
the second ferrite particles 5, and the heat-conducting material 6
are added to solution of the matrix material 7 and stirred so that
slurry is formed. As described above, the second ferrite particles
5, which are irregularly shaped particles, are preferably formed by
crushing the first ferrite particles 4, which are spherical
particles. The sheet-shaped heat-conductive noise suppression sheet
3 is formed by, for example, subjecting the slurry to a coating
process by a doctor blade method and a heating process. In the
present embodiment, instead of using the solution, the sheet may be
formed by, for example, hot-pressing a mixture of the matrix
material 7, the first ferrite particles 4, the second ferrite
particles 5, and the heat-conducting material 6.
EXAMPLES
[0065] The following samples (heat-conductive noise suppression
sheets) were prepared.
Example 1
[0066] (1) First Ferrite Particles (Spherical Particles): KNI-109GS
(Ni--Zn ferrite) manufactured by JFE Chemical Corporation was used.
The average particle diameter was 100 .mu.m. The content with
respect to the total amount of solid components was 20 vol %.
[0067] (2) Second Ferrite Particles (Irregularly shaped Particles):
KNI-109GSM (Ni--Zn ferrite) manufactured by JFE Chemical
Corporation was used. The average particle diameter was 40 .mu.m.
The content with respect to the total amount of solid components
was 35 vol %.
[0068] (3) Heat-Conducting Material: Aluminum oxide (AS-40
manufactured by Showa Denko K.K.) having an average particle
diameter of 12 .mu.m was used. The content with respect to the
total amount of solid components was 5 vol %.
[0069] (4) Matrix Material: Silicone gel (SE1896FR manufactured by
Toray Dow Corning Silicone Co. Ltd.) was used. The content with
respect to the total amount of solid components was 40 vol %.
[0070] FIG. 6 is a cross-sectional photograph (SEM photograph) of
the heat-conductive noise suppression sheet of Example 1. As is
clear from FIG. 6, the first ferrite particles, which are spherical
particles, are dispersed without clumping. The second ferrite
particles, which are irregularly shaped particles, the
heat-conducting material, and the matrix material are present
between the first ferrite particles. The matrix material is present
between the particles so as to fill the spaces between the
particles without leaving voids.
Related-Art Example 1
[0071] E7000K manufactured by Sony Chemical Corporation was used.
It was found by analysis that the heat-conductive noise suppression
sheet of Related-Art Example 1 contained Ni--Zn ferrite particles,
aluminum oxide particles, and silicone gel. FIG. 7 is a
cross-sectional photograph (SEM photograph) of the heat-conductive
noise suppression sheet according to Related-Art Example 1. It is
clear from FIG. 7 that the Ni--Zn ferrite particles are irregularly
shaped particles that correspond to the second ferrite particles
according to Example 1.
Comparative Example 1
[0072] (1) First Ferrite Particles (Spherical Particles): KNI-109GS
manufactured by JFE Chemical Corporation was used. The average
particle diameter was 100 .mu.m. The content with respect to the
total amount of solid components was 55 vol %.
[0073] (2) Heat-Conducting Material: Aluminum oxide (AS-40
manufactured by Showa Denko K.K.) having an average particle
diameter of 12 .mu.m was used. The content with respect to the
total amount of solid components was 5 vol %.
[0074] (3) Matrix Material: Silicone gel (SE1896FR manufactured by
Toray Dow Corning Silicone Co. Ltd.) was used. The content with
respect to the total amount of solid components was 40 vol %.
[0075] In the experiment, the frequency characteristics of the
imaginary part .mu.'' of the complex relative permeability, the
frequency characteristics of the imaginary part .epsilon.'' of the
complex relative permittivity, and the frequency characteristics of
the amount of noise reduction were measured for each sample.
[0076] FIG. 3 is a graph showing the frequency characteristics of
the imaginary part .mu.'' of the complex relative permeability of
each sample.
[0077] As is clear from FIG. 3, in the hundred megahertz frequency
range, the imaginary part .mu.'' of the complex relative
permeability of Example 1 is greater than that of Related-Art
Example 1, and is substantially equal to that of Comparative
Example 1.
[0078] FIG. 4 is a graph showing the frequency characteristics of
the imaginary part .epsilon.'' of the complex relative permittivity
of each sample.
[0079] As is clear from FIG. 4, in the frequency range of about 1
GHz or more, the imaginary part .epsilon.'' of the complex relative
permittivity of Example 1 is smaller than those of Related-Art
Example 1 and Comparative Example 1.
[0080] Thus, according to Example 1, the imaginary part .mu.'' of
the complex relative permeability can be effectively increased in
the frequency range of several hundred megahertz, and the imaginary
part .epsilon.'' of the complex relative permittivity can be
effectively reduced in the frequency range of 1 GHz or more.
[0081] FIG. 5 is a graph showing the frequency characteristics of
the amount of noise reduction in each sample. The amount of noise
reduction was measured by a spectrum analyzer with a tracking
generator (hereinafter referred to as TG). More specifically, a
measurement system which serves as a model of a noise propagation
path from the TG to the spectrum analyzer through the sample and a
radiating metal component was prepared. In this measurement system,
a signal intensity was measured in each of the case in which the
sample was present and the case in which the sample was absent, and
the noise reduction performance was determined from the difference
between the measured signal intensities.
[0082] The vertical axis in FIG. 5 shows the amount of noise
reduction. The amount of noise reduction of Related-Art Example 1
is defined as a reference value, and the amounts of noise reduction
of Example 1 and Comparative Example 1 are expressed as the
differences from the reference value. Therefore, in FIG. 5, if the
amount of reduction is positive, it means that the amount of noise
reduction is greater than that of Related-Art Example 1. If the
amount of reduction is negative, it means that the amount of noise
reduction is smaller than that of Related-Art Example 1.
[0083] As is clear from FIG. 5, the amount of noise reduction of
Example 1 in the hundred megahertz range is equivalent to that of
Comparative Example 1, and is greater than that of Related-Art
Example 1. In addition, the amount of noise reduction of Example 1
in the gigahertz range is greater than that of Comparative Example
1, and is equivalent to or greater than that of Related-Art Example
1.
[0084] According to Related-Art Example 1, in which the ferrite
particles are irregularly shaped particles, the noise suppression
effect is relatively high in the gigahertz range, but is low in the
hundred megahertz range.
[0085] According to Comparative Example 1, in which the ferrite
particles are spherical particles, the noise suppression effect is
high in the hundred megahertz range, but is low in the gigahertz
range.
[0086] In contrast, according to Example 1, in which both the first
ferrite particles, which are spherical particles, and the second
ferrite particles, which are irregularly shaped particles, are
added, a high noise suppression effect can be obtained over a wide
frequency range from the hundred megahertz range to the gigahertz
range.
[0087] Next, the following simulation regarding thermal
conductivity was performed.
[0088] In the experiment, simulation of thermal conductivity was
performed using analysis models in which the matrix material was
silicone gel and the filler content was 60 vol %.
[0089] The filler included the first ferrite particles, which were
spherical particles (Ni--Zn) with a diameter of 0.1 mm, the second
ferrite particles, which were irregularly shaped particles (Ni--Zn)
with an average particle diameter of 0.005 mm to 0.04 mm, and
alumina (heat-conducting material) with an average particle
diameter of 0.005 mm to 0.01 mm.
[0090] In the experiment, the number of first ferrite particles was
set to 2, 4, 6, and 11, and the temperature distribution between
the bottom surface and the top surface of each analysis model was
analyzed.
[0091] FIG. 8 illustrates the simulation results (schematic
diagrams) of the temperature distribution between the bottom
surface and the top surface along cross sections of analysis models
taken along the thickness direction.
[0092] In the diagrams in FIG. 8, the circles are the first ferrite
particles that appear in the cross sections. In the experiment, it
was assumed that the bottom surface was heated to 70.degree. C.
FIG. 8A shows the experiment result obtained when the number of
first ferrite particles was 2. FIG. 8B shows the experiment result
obtained when the number of first ferrite particles was 4. FIG. 8C
shows the experiment result obtained when the number of first
ferrite particles was 6. FIG. 8D shows the experiment result
obtained when the number of first ferrite particles was 11.
[0093] As is clear from FIG. 8, the thermal conductivity increased
as the number of first ferrite particles increased. In FIG. 8A, the
maximum temperature at the top surface of the analysis model was
64.6.degree. C. In FIG. 8B, the maximum temperature at the top
surface of the analysis model was 64.8.degree. C. In FIG. 8C, the
maximum temperature at the top surface of the analysis model was
65.1.degree. C. In FIG. 8D, the maximum temperature at the top
surface of the analysis model was 66.3.degree. C.
[0094] In the experiment, the content of the entire filler was
fixed at 60 vol %. Therefore, it was found from the experiment that
the first ferrite particles, which are spherical particles, largely
contribute to the thermal conductivity.
[0095] The coefficient of thermal conductivity can be increased by
increasing the content of the first ferrite particles. However, if
the content of the first ferrite particles is excessively
increased, the thermal conductivity will be reduced, owing to a
reduction in compressibility. Therefore, to determine the desirable
content, heat-conductive noise suppression sheets shown in Table 1
were produced.
TABLE-US-00001 TABLE 1 Heat- Coefficient Conducting Matrix of
Magnetic Powder Material Material Thermal Content (vol %) Content
Content Conduc- KNI- KNI- (vol %) (vol %) tivity 109GS 109GSM AS-40
SE1896FR (W/mk) Com- 55 5 40 0.994 parative Example 1 Com- 55 5 40
1.199 parative Example 2 Com- 35 20 5 40 1.324 parative Example 3
Example 1 20 35 5 40 1.243 Com- 50 7.5 42.5 1.116 parative Example
4 Example 2 25 25 7.5 42.5 1.273 Com- 50 5 45 1.097 parative
Example 5 Com- 50 50 0.8978 parative Example 6 Com- 50 50 0.8859
parative KNI- Example 7 106GSM Example 3 20 35 5 40 1.295 KNI-
106GSM Example 4 25 20 0.912
[0096] Example 1 and Comparative Example 1 shown in Table 1 are the
same as those used in the experiment described above with reference
to FIG. 5.
[0097] Referring to Table 1, sheet forming of Comparative Example
1, in which the volume percentage of the first ferrite particles
(KNI-109GS) was considerably large, was difficult. In Comparative
Example 1, although the volume percentage of the first ferrite
particles was large, conformability between resin and the filler
was low, and the air entered the structure. Therefore, the
coefficient of thermal conductivity was low. In addition, the
sample of Comparative Example 1 in the above-described state had a
low compressibility. As a result, the thermal conductivity was
extremely low.
[0098] In Comparative Example 3 shown in Table 1, the content of
the first ferrite particles (KNI-109GS) was 35 vol % and the
content of the second ferrite particles (KNI-109GSM) was 20 vol %.
In this example, a high coefficient of thermal conductivity was
obtained. However, in Comparative Example 3, sheet forming was
still difficult owing to the large content of the first ferrite
particles. Even when sheet forming of the heat-conductive noise
suppression sheet was successfully performed, the sheet was fragile
and easily damaged when the sheet was interposed between the
semiconductor component and the heat sink and compressed.
[0099] In Comparative Examples 2 and 4 to 7, the first ferrite
particles were not contained and the content of the second ferrite
particles (KNI-109GSM or KNI-106GSM) was set to a considerably
large amount, that is, to 50 vol % or 55 vol %. In each example,
the coefficient of thermal conductivity was not sufficient.
[0100] In contrast, in Examples 1 to 3, sheet forming was
successfully performed and high coefficients of thermal
conductivity were obtained. In Example 3, KNI-106GSM manufactured
by JEF Chemical Corporation was used as the second ferrite
particles. In Examples 1 to 3, not only the coefficient of thermal
conductivity but also the compressibility was high, as described
below, so that high thermal conductivity was obtained. In Example
4, the content of the first ferrite particles was larger than that
of the second ferrite particles. The coefficient of thermal
conductivity was lower than those in Examples 1 to 3. However, a
large amount of first ferrite particles, which largely contribute
to increasing the coefficient of thermal conductivity, was added.
Therefore, although the content of the filler is smaller than those
in Comparative Examples 6 and 7, the coefficient of thermal
conductivity is higher than those in Comparative Examples 6 and 7.
In Example 4, although no data is presented, the compressibility
can be further increased since the total content of filler
including the first and second ferrite particles is small.
Therefore, it can be expected that high thermal conductivity can be
obtained.
[0101] Next, a heat-conductive noise suppression sheet similar to
the sample of Example 1 except that the sheet contains 2.5 vol %
alumina and 42.5 vol % matrix material was manufactured.
[0102] In addition, a heat-conductive noise suppression sheet
(EGR-11F) manufactured by Fuji Polymer Co., Ltd. was used as
Comparative Example 8.
[0103] FIG. 9 is a cross-sectional photograph (SEM photograph) of
the heat-conductive noise suppression sheet of Comparative Example
8. It is clear from FIG. 9 that the ferrite particles are not
spherical particles, but are irregularly shaped particles that
correspond to the second ferrite particles according to the present
embodiment.
[0104] The above-described heat-conductive noise suppression sheets
were exposed to an environment with a temperature of 130.degree. C.
and a humidity of 85% for 20 hours. Then, the heat-conductive noise
suppression sheets were subjected to stress by performing 20 cycles
of 50% compression at 150.degree. C. for 30 minutes and 50%
compression at -65.degree. C. for 30 minutes.
[0105] After the above-described stress was applied, each
heat-conductive noise suppression sheet was placed on a heater, and
the temperature difference between the heater-side surface of the
heat-conductive noise suppression sheet and the surface opposite
the heater-side surface was measured while the heat-conductive
noise suppression sheet was compressed in the vertical
direction.
[0106] In the experiment, the temperature difference was measured
while the input to the heater was changed to 5 W, 10 W, and 15
W.
[0107] The experiment results are shown in Table 2.
TABLE-US-00002 TABLE 2 Output (Temperature Difference) High- Low-
Input Temperature Temperature Temperature [W] Side Side Difference
Comparative 5 51.2 34.7 16.5 Example 8 10 77.2 43.1 34.1 15 109.7
52.1 57.6 Example 1 5 47.7 32.8 14.9 (contains 2.5 vol % 10 75.1 42
33.1 alumina and 42.5 vol % matrix 15 98.2 49.3 48.9 material)
[0108] As is clear from Table 2, the temperature differences in
Example 1 was smaller than those in Comparative Example 8. Thus, it
was found that Example 1 has a high coefficient of thermal
conductivity and high compressibility, and therefore has higher
thermal conductivity.
* * * * *