U.S. patent application number 16/854267 was filed with the patent office on 2020-08-06 for thermally conductive sheet, production method for thermally conductive sheet, heat dissipation member, and semiconductor device.
The applicant listed for this patent is Dexerials Corporation. Invention is credited to Keisuke Aramaki, Hiroki Kanaya, Gupta Rishabh, Shinichi Uchida, Shunsuke Uchida.
Application Number | 20200251402 16/854267 |
Document ID | / |
Family ID | 1000004767980 |
Filed Date | 2020-08-06 |
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United States Patent
Application |
20200251402 |
Kind Code |
A1 |
Kanaya; Hiroki ; et
al. |
August 6, 2020 |
THERMALLY CONDUCTIVE SHEET, PRODUCTION METHOD FOR THERMALLY
CONDUCTIVE SHEET, HEAT DISSIPATION MEMBER, AND SEMICONDUCTOR
DEVICE
Abstract
A thermal conducting sheet, including: a binder resin;
insulating-coated carbon fibers; and a thermal conducting filler
other than the insulating-coated carbon fibers, wherein a mass
ratio (insulating-coated carbon fibers/binder resin) of the
insulating-coated carbon fibers to the binder resin is less than
1.30, and wherein the insulating-coated carbon fibers include
carbon fibers and a coating film over at least a part of a surface
of the carbon fibers, the coating film being formed of a cured
product of a polymerizable material.
Inventors: |
Kanaya; Hiroki; (Tokyo,
JP) ; Uchida; Shinichi; (Tokyo, JP) ; Uchida;
Shunsuke; (Tokyo, JP) ; Rishabh; Gupta;
(Tokyo, JP) ; Aramaki; Keisuke; (Tokyo,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Dexerials Corporation |
Tokyo |
|
JP |
|
|
Family ID: |
1000004767980 |
Appl. No.: |
16/854267 |
Filed: |
April 21, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16072671 |
Jul 25, 2018 |
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PCT/JP2017/001039 |
Jan 13, 2017 |
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16854267 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 23/367 20130101;
H01L 2924/16152 20130101; B29K 2101/10 20130101; C08K 2003/2227
20130101; H01L 23/42 20130101; C08K 9/04 20130101; B81B 3/0081
20130101; B29C 48/08 20190201; C08K 2003/282 20130101; B29C 48/022
20190201; C08G 77/20 20130101; C08K 3/22 20130101; C08K 2003/2296
20130101; C08K 9/00 20130101; B29C 48/0022 20190201; C08K 7/06
20130101; H01L 2224/73253 20130101; H01L 23/373 20130101; D04H
1/4242 20130101; C08L 101/00 20130101; H01L 2224/16225 20130101;
C08K 9/08 20130101; C08L 83/04 20130101; B29L 2031/18 20130101;
H01L 23/3672 20130101; H01L 23/3737 20130101; B29K 2509/02
20130101; B29C 39/003 20130101; B29K 2509/04 20130101; B29C 39/00
20130101; B29K 2105/243 20130101; B29K 2995/0007 20130101; C09D
183/04 20130101; C08K 3/28 20130101; B29K 2995/0013 20130101; C08K
3/00 20130101; B29K 2086/00 20130101; B29K 2105/16 20130101; B29K
2083/00 20130101; B29C 48/07 20190201; C08G 77/12 20130101 |
International
Class: |
H01L 23/373 20060101
H01L023/373; H01L 23/42 20060101 H01L023/42; C08L 101/00 20060101
C08L101/00; B29C 39/00 20060101 B29C039/00; C08K 3/22 20060101
C08K003/22; C08K 9/04 20060101 C08K009/04; B29C 48/00 20060101
B29C048/00; C08K 3/28 20060101 C08K003/28; C08L 83/04 20060101
C08L083/04; C08K 9/08 20060101 C08K009/08; C09D 183/04 20060101
C09D183/04; B29C 48/07 20060101 B29C048/07; C08K 9/00 20060101
C08K009/00; C08K 3/00 20060101 C08K003/00; H01L 23/367 20060101
H01L023/367; D04H 1/4242 20060101 D04H001/4242; C08K 7/06 20060101
C08K007/06; B29C 48/08 20060101 B29C048/08 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 26, 2016 |
JP |
2016-012672 |
Dec 27, 2016 |
JP |
2016-254263 |
Claims
1-12: (canceled)
13. A thermal conducting sheet, comprising: a binder resin;
insulating-coated carbon fibers; and a thermal conducting filler
other than the insulating-coated carbon fibers, wherein a mass
ratio (insulating-coated carbon fibers/binder resin) of the
insulating-coated carbon fibers to the binder resin is less than
1.30, wherein the insulating-coated carbon fibers include carbon
fibers and a coating film over at least a part of a surface of the
carbon fibers, the coating film being formed of a cured product of
a polymerizable material, and wherein an average thickness of the
coating film is 100 nm or greater but 1,000 nm or less.
14. The thermal conducting sheet according to claim 13, wherein an
amount of the thermal conducting filler is from 48% by volume
through 75% by volume.
15. The thermal conducting sheet according to claim 13, wherein
compressibility of the thermal conducting sheet at a load of 0.5
kgf/cm.sup.2 is 3% or more.
16. The thermal conducting sheet according to claim 13, wherein the
average thickness of the coating film is 200 nm or greater but
1,000 nm or less.
17. The thermal conducting sheet according to claim 13, wherein the
thermal conducting filler includes at least one selected from the
group consisting of aluminum oxide, aluminum nitride, and zinc
oxide.
18. The thermal conducting sheet according to claim 13, wherein the
binder resin is a silicone resin.
19. A method for producing the thermal conducting sheet according
to claim 13, the method comprising: obtaining a molded body of a
thermal conducting resin composition containing the binder resin,
the insulating-coated carbon fibers, and the thermal conducting
filler by molding the thermal conducting resin composition into a
predetermined shape and curing the thermal conducting resin
composition; and obtaining a molded body sheet by cutting the
molded body so as to have a sheet shape.
20. The method for producing the thermal conducting sheet according
to claim 19, further comprising: obtaining the insulating-coated
carbon fibers by applying energy to a mixture obtained by mixing
the polymerizable material, the carbon fibers, a polymerization
initiator, and a solvent to activate the polymerization initiator,
and form a coating film over at least a part of a surface of the
carbon fibers, the coating film being formed of a cured product of
the polymerizable material.
21. A heat dissipation member, comprising: a heat spreader
configured to dissipate heat generated by an electronic part; and
the thermal conducting sheet according to claim 13 provided on the
heat spreader and interposed between the heat spreader and the
electronic part.
22. A semiconductor device, comprising: an electronic part; a heat
spreader configured to dissipate heat generated by the electronic
part; and the thermal conducting sheet according to claim 13
provided on the heat spreader and interposed between the heat
spreader and the electronic part.
23. The semiconductor device according to claim 22, further
comprising: a heat sink, wherein the thermal conducting sheet
according to claim 13 is interposed between the heat spreader and
the heat sink.
Description
TECHNICAL FIELD
[0001] The present invention relates to a thermal conducting sheet
disposed between a heat generator such as a semiconductor element
and a heat dissipator such as a heat sink, a method for producing a
thermal conducting sheet, and a heat dissipation member and a
semiconductor device including the thermal conducting sheet.
BACKGROUND ART
[0002] Hitherto, various cooling measures have been employed in
semiconductor is elements mounted on various electrical appliances
such as personal computers and other devices, because if heat
generated as a result of driving is accumulated, driving of the
semiconductor elements and peripheral devices may be adversely
affected. As a method for cooling electronic parts such as
semiconductor elements, there are known, for example, a method for
mounting the device with a fan to cool the air in the device
housing, and a method for mounting the semiconductor element to be
cooled with a heat sink such as a heat dissipation fin and a heat
dissipation plate.
[0003] When a heat sink is mounted on the aforementioned
semiconductor element to perform cooling, a thermal conducting
sheet is provided between the semiconductor element and the heat
sink in order to efficiently dissipate heat in the semiconductor
element. As this thermal conducting sheet, a sheet obtained by
adding a filler such as a thermal conducting filler in a dispersed
state in a silicone resin is widely used. As one example of the
thermal conducting filler, carbon fibers are favorably employed
(for example, see PTLs 1 to 4).
[0004] However, the thermal conducting sheet containing the carbon
fibers is excellent in thermal conductivity, but has a problem that
electrical conductivity easily becomes high.
[0005] Therefore, for the purpose of increasing an insulating
property of the thermal conducting sheet, a thermal conducting
sheet including thermal conducting fibers in which an electrically
insulating material is coated on the surfaces of
electrically-conductive, thermally-conductive fibers has been
proposed (see, PTL 5).
[0006] However, this proposed technique is insufficient because an
excellent thermal conductivity and an excellent insulating property
that have been demanded in recent years cannot be achieved.
CITATION LIST
Patent Literature
[0007] PTL 1: Japanese Patent (JP-B) No. 5671266
[0008] PTL 2: Japanese Patent Application Laid-Open (JP-A) No.
2005-54094
[0009] PTL 3: JP-B No. 5660324
[0010] PTL 4: JP-B No. 4791146
[0011] PTL 5: JP-A No. 2003-174127
SUMMARY OF INVENTION
Technical Problem
[0012] The present invention aims to solve the various problems in
the related art and achieve an object described below. That is, the
present invention has an object to provide a thermal conducting
sheet that can achieve an excellent thermal conductivity and an
excellent insulating property at the same time, a method for
producing the thermal conducting sheet, and a heat dissipation
member and a semiconductor device using the thermal conducting
sheet.
Solution to Problem
[0013] Means for solving the above problems are as follows. That
is,
<1> A thermal conducting sheet, including: a binder resin;
insulating-coated carbon fibers; and a thermal conducting filler
other than the insulating-coated carbon fibers,
[0014] wherein a mass ratio (insulating-coated carbon fibers/binder
resin) of the insulating-coated carbon fibers to the binder resin
is less than 1.30, and
[0015] wherein the insulating-coated carbon fibers include carbon
fibers and a coating film over at least a part of a surface of the
carbon fibers, the coating film being formed of a cured product of
a polymerizable material.
<2> The thermal conducting sheet according to <1>,
[0016] wherein an amount of the thermal conducting filler is from
48% by volume through 75% by volume.
<3> The thermal conducting sheet according to <1> or
<2>,
[0017] wherein compressibility of the thermal conducting sheet at a
load of 0.5 kgf/cm.sup.2 is 3% or more.
<4> The thermal conducting sheet according to any one of
<1> to <3>,
[0018] wherein the polymerizable material includes a compound
including two or more radically polymerizable double bonds.
<5> The thermal conducting sheet according to any one of
<1> to <4>,
[0019] wherein the thermal conducting filler includes at least one
selected from the group consisting of aluminum oxide, aluminum
nitride, and zinc oxide.
<6> The thermal conducting sheet according to any one of
<1> to <5>,
[0020] wherein the binder resin is a silicone resin.
<7> A method for producing the thermal conducting sheet
according to any one of <1> to <6>, the method
including: obtaining a molded body of a thermal conducting resin
composition containing the binder resin, the insulating-coated
carbon fibers, and the thermal conducting filler by molding the
thermal conducting resin composition into a predetermined shape and
curing the thermal conducting resin composition; and obtaining a
molded body sheet by cutting the molded body so as to have a sheet
shape. <8> The method for producing the thermal conducting
sheet according to <7>,
[0021] wherein the polymerizable material is a radically
polymerizable material.
<9> The method for producing the thermal conducting sheet
according to <7> or <8>, further including: obtaining
the insulating-coated carbon fibers by applying energy to a mixture
obtained by mixing the polymerizable material, the carbon fibers, a
polymerization initiator, and a solvent to activate the
polymerization initiator, and form a coating film over at least a
part of a surface of the carbon fibers, the coating film being
formed of a cured product of the polymerizable material. <10>
A heat dissipation member, including:
[0022] a heat spreader configured to dissipate heat generated by an
electronic part; and
[0023] the thermal conducting sheet according to any one of
<1> to <6> provided on the heat spreader and interposed
between the heat spreader and the electronic part.
<11> A semiconductor device, including:
[0024] an electronic part;
[0025] a heat spreader configured to dissipate heat generated by
the electronic part; and
[0026] the thermal conducting sheet according to any one of
<1> to <6> provided on the heat spreader and interposed
between the heat spreader and the electronic part.
<12> The semiconductor device according to <11>,
further including:
[0027] a heat sink,
[0028] wherein the thermal conducting sheet according to any one of
<1> to <6> is interposed between the heat spreader and
the heat sink.
Advantageous Effects of Invention
[0029] The present invention can solve the various problems in the
related art, achieve the object described above, and provide a
thermal conducting sheet that can achieve an excellent thermal
conductivity and an excellent insulating property at the same time,
a method for producing the thermal conducting sheet, and a heat
dissipation member and a semiconductor device using the thermal
conducting sheet.
BRIEF DESCRIPTION OF DRAWINGS
[0030] FIG. 1 is a cross-sectional view illustrating a thermal
conducting sheet, a heat dissipation member, and a semiconductor
device to which the present invention is applied.
DESCRIPTION OF EMBODIMENTS
(Thermal Conducting Sheet)
[0031] A thermal conducting sheet of the present invention includes
at least a binder resin, insulating-coated carbon fibers, and a
thermal conducting filler, and further includes other components if
necessary.
<Binder Resin>
[0032] The binder resin is not particularly limited and may be
appropriately selected depending on the intended purpose. Examples
of the binder resin include thermosetting polymers.
[0033] Examples of the thermosetting polymers include cross-linked
rubbers, epoxy resins, polyimide resins, bismaleimide resins,
benzocyclobutene resins, phenol resins, unsaturated polyester,
diallyl phthalate resins, silicone resins, polyurethane, polyimide
silicone, thermosetting polyphenylene ether, and thermosetting
modified polyphenylene ether. These may be used alone or in
combination.
[0034] Examples of the cross-linked rubbers include natural
rubbers, butadiene rubber, isoprene rubber, nitrile rubber,
hydrogenated nitrile rubber, chloroprene rubber, ethylene propylene
rubber, chlorinated polyethylene, chlorosulfonated polyethylene,
butyl rubber, halogenated butyl rubber, fluororubber, urethane
rubber, acrylic rubber, polyisobutylene rubber, and silicone
rubber. These may be used alone or in combination.
[0035] Among these examples, the thermosetting polymer is
particularly preferably a silicone resin, because of an excellent
molding processability and an excellent weatherability and in terms
of close adhesiveness and conformity with an electronic part.
[0036] The silicone resin is not particularly limited and may be
appropriately selected depending on the intended purpose. It is
preferable that the silicone resin contain a main agent formed of a
liquid silicone gel, and a curing agent. Examples of such a
silicone resin include addition-reactive silicone resins and
thermally-vulcanizable millable silicone resins to be vulcanized
with peroxides. Among these silicone resins, addition-reactive
silicone resins are particularly preferable because the thermal
conducting sheet needs to have close adhesiveness with a heat
generating surface of an electronic part and with a heat sink
surface.
[0037] As the addition-reactive silicone resin, a two-pack
addition-reactive silicone resin containing vinyl group-containing
polyorganosiloxane as a main agent and Si--H group-containing
polyorganosiloxane as a curing agent is preferable.
[0038] The blending ratio between the main agent and the curing
agent in the combination of the main agent of the liquid silicone
gel and the curing agent is not particularly limited and may be
appropriately selected depending on the intended purpose.
[0039] The amount of the binder resin is not particularly limited
and may be appropriately selected depending on the intended
purpose. The amount of the binder resin is preferably from 10% by
volume through 40% by volume, more preferably from 15% by volume
through 40% by volume, particularly preferably from 20% by volume
through 40% by volume.
[0040] In the present specification, a numerical range presented
using "through" means such a range that the numeral described
before the "through" is included in the numerical range as the
minimum value and the numeral described after the "through" is
included in the numerical range as the maximum value.
<Insulating-Coated Carbon Fibers>
[0041] The insulating-coated carbon fibers include at least carbon
fibers and a coating film provided over at least a part of a
surface of the carbon fibers, and further include other components
if necessary.
[0042] The coating film is formed of a cured product of a
polymerizable material.
--Carbon Fibers--
[0043] The carbon fibers are not particularly limited and may be
appropriately selected depending on the intended purpose. Examples
of the carbon fibers include pitch-based to carbon fibers,
PAN-based carbon fibers, carbon fibers formed of graphitized PBO
fibers, and carbon fibers synthesized by, for example, an arc
discharge method, a laser evaporation method, a CVD method
(chemical vapor deposition method), and a CCVD method (catalytic
chemical vapor deposition method). Among these carbon fibers,
carbon fibers formed of graphitized PBO fibers and pitch-based
carbon fibers are particularly preferable in terms of thermal
conductivity.
[0044] The carbon fibers can be used in a state that a part or the
whole of each carbon fiber is surface-treated, in order to have a
high close adhesiveness with the coating film. Examples of the
surface treatment include an oxidation treatment, a nitriding
treatment, nitration, and sulfonation, or a treatment for attaching
or bonding, for example, a metal, a metal compound, and an organic
compound to a functional group introduced into the surface by these
treatments or to the surface of the carbon fibers. Examples of the
functional group include a hydroxyl group, a carboxyl group, a
carbonyl group, a nitro group, and an amino group.
[0045] An average fiber length (average longer-axis length) of the
carbon fibers is not particularly limited and may be appropriately
selected depending on the intended purpose. The average fiber
length of the carbon fibers is preferably from 50 .mu.m through 250
.mu.m, more preferably from 75 .mu.m through 200 .mu.m,
particularly preferably from 90 .mu.m through 170 .mu.m.
[0046] An average fiber diameter (average shorter-axis length) of
the carbon fibers is not particularly limited and may be
appropriately selected depending on the intended purpose. The
average fiber diameter of the carbon fibers is preferably from 4
.mu.m through 20 .mu.m, more preferably from 5 .mu.m through 14
.mu.m.
[0047] An aspect ratio (average longer-axis length/average
shorter-axis length) of the carbon fibers is not particularly
limited and may be appropriately selected depending on the intended
purpose. The aspect ratio of the carbon fibers is preferably 8 or
more, more preferably from 9 through 30. When the aspect ratio is
less than 8, the thermal conductivity may be poor because the fiber
length (longer-axis length) of the carbon fibers is short.
[0048] Here, the average longer-axis length and the average
shorter-axis length of the carbon fibers can be measured with, for
example, a microscope and a scanning electron microscope (SEM).
--Cured Product of Polymerizable Material--
[0049] A cured product of the polymerizable material is obtained by
curing a polymerizable material. In other words, the cured product
is also a polymer of the polymerizable material.
[0050] The polymerizable material is not particularly limited and
may be appropriately selected depending on the intended purpose, so
long as it is an organic material having a polymerizable property.
Examples of the polymerizable material include organic compounds
having a polymerizable property and resins having a polymerizable
property.
[0051] Polymerization caused by the polymerizable material is, for
example, radical polymerization, cationic polymerization, and
anionic polymerization. Among them, radical polymerization is
preferable because the kind of applicable polymerizable materials,
the kind of applicable polymerization initiators, and the kind of
applicable solvents are abundant and various cured products can be
obtained.
[0052] That is, the polymerizable material is preferably a
radically polymerizable material.
----Radically Polymerizable Material----
[0053] The radically polymerizable material is not particularly
limited and may be appropriately selected depending on the intended
purpose, so long as it is a material that uses energy to cause
radical polemerization. Examples of the radically polymerizable
material include compounds including a radically polymerizable
double bond.
[0054] Examples of the radically polymerizable double bond include
a vinyl group, an acryloyl group, and a methacryloyl group.
[0055] The number of the radically polymerizable double bonds in
the compound including the radically polymerizable double bond is
preferably two or more in terms of strength of the coating film
such as thermal resistance and solvent resistance. That is, the
compound including the radically polymerizable double bond
preferably includes at least one or more kinds of the compounds
including two or more radically polymerizable double bonds.
[0056] Examples of the compounds including two or more radically
polymerizable double bonds include divinylbenzene and compounds
including two or more (meth)acryloyl groups.
[0057] Examples of the compounds including two or more
(meth)acryloyl groups include ethylene glycol di(meth)acrylate,
(poly)ethylene glycol di(meth)acrylate, propylene glycol
di(meth)acrylate, (poly)propylene glycol di(meth)acrylate,
pentaerythritol tetra(meth)acrylate, pentaerythritol
tri(meth)acrylate, pentaerythritol di(meth)acrylate,
trimethylolpropane tri(meth)acrylate, dipentaerythritol
hexa(meth)acrylate, dipentaerythritol penta(meth)acrylate, glycerol
tri(meth)acrylate, glycerol di(meth)acrylate, 1,6-hexanediol
di(meth)acrylate, neopentylglycol di(meth)acrylate,
tetramethylolmethane tri(meth)acrylate, tetramethylolpropane
tetra(meth)acrylate, tricyclodecane dimethanol di(meth)acrylate,
and (poly)ethoxylated bisphenol A di(meth)acrylate.
[0058] Here, the (meth)acryloyl group is a generic name of acryloyl
groups and methacryloyl groups. The (meth)acrylate is a generic
name of acrylates and methcrylates.
[0059] The radically polymerizable material may be used alone or in
combination.
[0060] A molecular weight of the radically polymerizable material
is not particularly limited and may be appropriately selected
depending on the intended purpose. The molecular weight of the
radically polymerizable material is preferably from 50 through
500.
[0061] The amount of a constitutional unit originated from the
polymerizable material in the cured product and the coating film is
not particularly limited and may be appropriately selected
depending on the intended purpose. The amount of the constitutional
unit is preferably 50% by mass or more, more preferably 90% by mass
or more.
[0062] An average thickness of the coating film of the
insulating-coated carbon fibers is not particularly limited and may
be appropriately selected depending on the intended purpose. The
average thickness of the coating film is preferably 50 nm or more,
more preferably 100 nm or more, particularly preferably 200 nm or
more, in order to achieve a high insulating property. An upper
limit of the average thickness is not particularly limited and may
be appropriately selected depending on the intended purpose. For
example, the upper limit of the average thickness is preferably
1,000 nm or less, more preferably 500 nm or less.
[0063] The average thickness can be measured through observation
using a transmission electron microscope (TEM).
[0064] In the thermal conducting sheet, the insulating-coated
carbon fibers need not have the coating film on the ends thereof in
the longer direction. Particularly, there may be a case where the
thermal conducting sheet is produced by slicing a block-shaped
molded body. Therefore, in the surfaces of the thermal conducting
sheet, the insulating-coated carbon fibers need not have the
coating film on the ends thereof in the longer direction.
[0065] The amount of the insulating-coated carbon fibers is not
particularly limited and may be appropriately selected depending on
the intended purpose. The amount of the insulating-coated carbon
fibers is preferably from 2% by volume through 20% by volume, more
preferably from 10% by volume through 20% by volume. When the
amount of the insulating-coated carbon fibers is less than 2% by
volume, the thermal conducting sheet may be insufficient in thermal
characteristics (particularly, thermal conductivity). When the
amount of the insulating-coated carbon fibers is more than 20% by
volume, the thermal conducting sheet may be insufficient in an
insulating property.
[0066] A mass ratio (insulating-coated carbon fibers/binder resin)
of the insulating-coated carbon fibers to the binder resin is less
than 1.30, preferably 0.10 or more but less than 1.30, more
preferably 0.30 or more but less than 1.30, still more preferably
0.50 or more but less than 1.30, particularly preferably 0.60 or
more but 1.20 or less. When the mass ratio is 1.30 or more, an
insulating property of the thermal conducting sheet becomes
insufficient.
[0067] Here, the thermal conducting sheet contains the
insulating-coated carbon fibers. That is, it is obvious that a
lower limit of the mass ratio (insulating-coated carbon
fibers/binder resin) of the insulating-coated carbon fibers to the
binder resin is not 0.00 (the mass ratio is more than 0.00).
[0068] A method for producing the insulating-coated carbon fibers
is not particularly limited and may be appropriately selected
depending on the intended purpose. For example, examples of the
method include an insulating-coated carbon fiber producing step
that will be described hereinafter.
<Thermal Conducting Filler>
[0069] The thermal conducting filler is not particularly limited
and may be appropriately selected depending on the intended purpose
so long as the thermal conducting filler is a thermal conducting
filler other than the insulating-coated carbon fibers. Examples of
the thermal conducting filler include inorganic fillers.
[0070] For example, a shape, a material, and an average particle
diameter of the inorganic filler are not particularly limited and
may be appropriately selected depending on the intended purpose.
The shape of the inorganic filler is not particularly limited and
may be appropriately selected depending on the intended purpose.
Examples of the shape include a spherical shape, an ellipsoidal
shape, a block shape, a grainy shape, a flat shape, and an acicular
shape. Among these shapes, a spherical shape and an ellipsoidal
shape are preferable in terms of fillability and a spherical shape
is particularly preferable.
[0071] In the present specification, the inorganic filler is
different from the insulating-coated carbon fibers and the carbon
fibers.
[0072] Examples of the inorganic filler include aluminum nitride
(AlN), silica, aluminum oxide (alumina), boron nitride, titania,
glass, zinc oxide, silicon carbide, silicon, silicon oxide,
aluminum oxide, and metal particles. These may be used alone or in
combination. Among these inorganic fillers, aluminum oxide, boron
nitride, aluminum nitride, zinc oxide, and silica are preferable,
and in terms of thermal conductivity, aluminum oxide, aluminum
nitride, and zinc oxide are particularly preferable.
[0073] The inorganic filler may be surface-treated. When the
inorganic filler is to treated with a coupling agent as the surface
treatment, the inorganic filler is improved in dispersibility and
the thermal conducting sheet has an improved flexibility.
[0074] An average particle diameter of the inorganic filler is not
particularly limited and may be appropriately selected depending on
the intended purpose.
[0075] When the inorganic filler is alumina, the average particle
diameter thereof is preferably from 1 .mu.m through 10 .mu.m, more
preferably from 1 .mu.m through 5 .mu.m, particularly preferably
from 3 .mu.m through 5 .mu.m. When the average particle diameter of
the alumina is less than 1 .mu.m, the inorganic filler may have a
high viscosity and may not mix well. When the average particle
diameter of the alumina is more than 10 .mu.m, the thermal
conducting sheet may have a high thermal resistance.
[0076] When the inorganic filler is aluminum nitride, the average
particle diameter thereof is preferably from 0.3 .mu.m through 6.0
.mu.m, more preferably from 0.3 .mu.m through 2.0 .mu.m,
particularly preferably from 0.5 .mu.m through 1.5 .mu.m. When the
average particle diameter of the aluminum nitride is less than 0.3
.mu.m, the inorganic filler may have a high viscosity and may not
mix well. When the average particle diameter of the aluminum
nitride is more than 6.0 .mu.m, the thermal conducting sheet may
have a high thermal resistance.
[0077] The average particle diameter of the inorganic filler can be
measured with, for example, a particle size distribution meter and
a scanning electron microscope (SEM).
[0078] The amount of the thermal conducting filler is not
particularly limited and may be appropriately selected depending on
the intended purpose. The amount of the thermal conducting filler
is preferably from 45% by volume through 75% by volume, more
preferably from 48% by volume through 75% by volume, particularly
preferably from 48% by volume through 70% by volume. When the
amount of the thermal conducting filler is less than 45% by volume,
thermal resistance of the thermal conducting sheet may become high.
When the amount of the thermal conducting filler is more than 75%
by volume, flexibility of the thermal conducting sheet may become
low.
<Other Components>
[0079] The other components are not particularly limited and may be
appropriately selected depending on the intended purpose. Examples
of the other components include a thixotropic nature imparting
agent, a dispersant, a curing accelerator, a retarder, a slight
adhesiveness imparting agent, a plasticizer, a flame retardant, an
antioxidant, a stabilizer, and a colorant.
[0080] An average thickness of the thermal conducting sheet is not
particularly limited and may be appropriately selected depending on
the intended purpose. The average thickness of the thermal
conducting sheet is preferably from 0.05 mm through 5.00 mm, more
preferably from 0.07 mm through 4.00 mm, particularly preferably
from 0.10 mm through 3.00 mm.
[0081] It is preferable that the surface of the thermal conducting
sheet be coated with a bled-out component that has bled out from
the thermal conducting sheet conformally to the bossed shapes of
the insulating-coated carbon fibers that are protruding.
[0082] The method for obtaining this state of the surface of the
thermal conducting sheet can be performed through, for example, a
surface coating step which will be described hereinafter.
[0083] A volume resistivity of the thermal conducting sheet under
application of voltage of 1,000 V is preferably 1.0.times.10.sup.10
.OMEGA.cm or more, in order to prevent short circuit of an electric
circuit around a semiconductor element to be used. The volume
resistivity can be measured according to, for example, the JIS
K-6911.
[0084] An upper limit of the volume resistivity is not particularly
limited and may be appropriately selected depending on the intended
purpose. For example, the volume resistivity is 1.0.times.10.sup.18
.OMEGA.cm or less.
[0085] The compressibility of the thermal conducting sheet at a
load of 0.5 kgf/cm.sup.2 is preferably 3% or more, more preferably
5% or more in terms of close adhesiveness with an electronic part
and with a heat sink.
[0086] An upper limit of the compressibility of the thermal
conducting sheet is not particularly limited and may be
appropriately selected depending on the intended purpose. The
compressibility of the thermal conducting sheet is preferably 30%
or less.
(Method for Producing Thermal Conducting Sheet)
[0087] A method for producing the thermal conducting sheet of the
present invention includes at least a molded body producing step
and a molded body sheet producing step, preferably includes an
insulating-coated carbon fiber producing step and a surface coating
step, and further includes other steps if necessary.
[0088] A method for producing the thermal conducting sheet is a
method for producing the thermal conducting sheet of the present
invention.
<Molded Body Producing Step>
[0089] The molded body producing step is not particularly limited
and may be appropriately selected depending on the intended
purpose, so long as the molded body producing step is a step of
obtaining a molded body of a thermal conducting resin composition
containing the binder resin, the insulating-coated carbon fibers,
and the thermal conducting filler by molding the thermal conducting
resin composition into a predetermined shape and curing the thermal
conducting resin composition.
--Thermal Conducting Resin Composition--
[0090] The thermal conducting resin composition includes at least a
binder resin, insulating-coated carbon fibers, and a thermal
conducting filler and further includes other components if
necessary.
[0091] Examples of the binder resin include the binder resin
exemplified in the description of the thermal conducting sheet.
[0092] Examples of the insulating-coated carbon fibers include the
insulating-coated carbon fibers exemplified in the description of
the thermal conducting sheet.
[0093] Examples of the thermal conducting filler include the
thermal conducting filler exemplified in the description of the
thermal conducting sheet.
[0094] The method for molding the thermal conducting resin
composition into a predetermined shape in the molded body producing
step is not particularly limited and may be appropriately selected
depending on the intended purpose. Examples of the method include
an extrusion molding method and a die molding method.
[0095] It is preferable to perform the molded body producing step
by filling a hollow die with the thermal conducting resin
composition and thermally curing the thermal conducting resin
composition, because random orientation of the insulating-coated
carbon fibers can be obtained in the thermal conducting sheet to be
obtained.
[0096] Because of the random orientation of the insulating-coated
carbon fibers in the thermal conducting sheet obtained, there is a
lot of mutual intertwining of the insulating-coated carbon fibers,
leading to a higher thermal conductivity than when the
insulating-coated carbon fibers are oriented in a constant
direction. Further, because of the random orientation of the
insulating-coated carbon fibers, there are also a lot of contact
points between the insulating-coated carbon fibers with the thermal
conducting filler (for example, an inorganic filler) in addition to
the mutual intertwining of the insulating-coated carbon fibers,
leading to an even higher thermal conductivity than when the
insulating-coated carbon fibers are oriented in a constant
direction.
[0097] The extrusion molding method and the die molding method are
not particularly limited and may be appropriately employed from
various types of known extrusion molding methods and die molding
methods depending on the viscosity of the thermal conducting resin
composition and the properties required of the thermal conducting
sheet to be obtained.
[0098] When the thermal conducting resin composition is extruded
from a die in the extrusion molding method or when the thermal
conducting resin composition is pressed into a die in the die
molding method, for example, the binder resin fluidizes to cause
some of the insulating-coated carbon fibers to be oriented along
the fluidizing direction. However, many of the insulating-coated
carbon fibers are randomly oriented.
[0099] When a slit is attached to the leading end of the die, there
is a tendency that the insulating-coated carbon fibers are
uniformly oriented in the width-direction center of the extruded
molded block. On the other hand, there is a tendency that the
insulating-coated carbon fibers are randomly oriented in the
width-direction peripheries of the molded block due to the effect
of the slit wall.
[0100] A size and a shape of the molded body (a block-shaped molded
body) can be determined depending on the required size of the
thermal conducting sheet. Examples of the size and shape include a
rectangular parallelepiped having a cross-section in which the
vertical size is from 0.5 cm through 15 cm and the horizontal size
is from 0.5 cm through 15 cm. The length of the rectangular
parallelepiped may be determined if necessary.
[0101] Curing of the thermal conducting resin composition in the
molded body producing step is preferably thermal curing. A curing
temperature in the thermal curing is not particularly limited and
may be appropriately selected depending on the intended purpose.
The curing temperature is preferably from 60.degree. C. through
120.degree. C. when, for example, the binder resin contains a
liquid silicone gel main agent and a curing agent. A curing time in
the thermal curing is not particularly limited and may be
appropriately selected depending on the intended purpose. The time
is, for example, from 0.5 hours through 10 hours.
<Molded Body Sheet Producing Step>
[0102] The molded body sheet producing step is not particularly
limited and may be appropriately selected depending on the intended
purpose so long as the molded body sheet producing step is a step
of cutting the molded body into a sheet shape to obtain a molded
body sheet. For example, the molded body sheet producing step can
be performed with a slicing device.
[0103] In the molded body sheet producing step, the molded body is
cut into a sheet shape, to obtain a molded body sheet. The
insulating-coated carbon fibers are protruding on the surface of
the obtained molded body sheet. This is considered due to that in
cutting of the molded body into a sheet shape with, for example,
the slicing device, the cured component of the binder resin is
drawn and elongated by the cutting member of, for example, the
slicing device due to the hardness difference between the cured
component of the binder resin and the insulating-coated carbon
fibers, so the cured component of the binder resin is removed from
the surface of the insulating-coated carbon fibers in the surface
of the molded body sheet.
[0104] The slicing device is not particularly limited and may be
appropriately selected depending on the intended purpose. Examples
of the slicing device include an ultrasonic cutter and a plane. The
cutting direction along which the molded body is cut is preferably
from 60 degrees through 120 degrees, more preferably from 70
degrees through 100 degrees, particularly preferably 90 degrees
(vertically) with respect to the extruding direction because there
are components that are oriented in the extruding direction when
the molding method is the extrusion molding method.
[0105] An average thickness of the molded body sheet is not
particularly limited and may be appropriately selected depending on
the intended purpose. The average thickness of the molded body
sheet is preferably from 0.06 mm through 5.01 mm, more preferably
from 0.08 mm through 4.01 mm, particularly preferably from 0.11 mm
through 3.01 mm.
<Surface Coating Step>
[0106] The surface coating step is not particularly limited and may
be appropriately selected depending on the intended purpose so long
as the surface coating step is a step of coating the surface of the
molded body sheet with a bled-out component that bleeds out from
the molded body sheet conformally to the bossed shapes of the
insulating-coated carbon fibers that are protruding. Examples of
the surface coating step include a press treatment and a treatment
for leaving the molded body sheet standing.
[0107] Here, the "bled-out component" is a component that has been
contained in the thermal conducting resin composition but has not
contributed to the curing, and refers to, for example, a
non-curable component and an uncured component of the binder
resin.
--Press Treatment--
[0108] The press treatment is not particularly limited and may be
appropriately selected depending on the intended purpose so long as
the press treatment is a treatment for pressing the molded body
sheet to coat the surface of the molded body sheet with a bled-out
component that bleeds out from the molded body sheet conformally to
the bossed shapes of the insulating-coated carbon fibers that are
protruding.
[0109] The press can be performed with, for example, a pair of
press devices formed of a platen and a press head having a flat
surface. The press may also be performed with a pinch roll.
[0110] A press pressure is not particularly limited and may be
appropriately selected depending on the intended purpose. The press
pressure is preferably from 0.1 MPa through 100 MPa, more
preferably from 0.5 MPa through 95 MPa. This is because there is a
tendency that when the pressure is too low, thermal resistance
results in the same level as when the press is not performed, and
because there is a tendency that when the pressure is too high, the
sheet is elongated.
[0111] The press time is not particularly limited and may be
appropriately selected depending on, for example, the component of
the binder resin, the press pressure, the area of the sheet, and
the bleeding amount of the bled-out component.
[0112] In order to even more promote the effects of bleeding of the
bled-out component and coating of the surface of the molded body
sheet, the press treatment may be performed under heating using a
press head including a built-in heater. In order to enhance these
effects, the heating temperature is preferably higher than or equal
to the glass transition temperature of the binder resin. This can
shorten the press time.
[0113] In the press treatment, the molded body sheet is pressed in
order to cause the bled-out component to bleed out from the molded
body sheet and coat the surface with the bled-out component.
Therefore, the thermal conducting sheet to be obtained can have a
better conformity and a better close adhesiveness with the surface
of an electronic part and of a heat spreader and can have a lower
thermal resistance. When the coating with the bled-out component
has a thickness of a level that reflects the shape of the
insulating-coated carbon fibers on the surface of the thermal
conducting sheet, thermal resistance rise can be avoided.
[0114] With the press, the molded body sheet is compressed in the
thickness direction and can be increased in the frequency of mutual
contacts of the insulating-coated carbon fibers and of the thermal
conducting filler. This can reduce the thermal resistance of the
thermal conducting sheet.
[0115] It is preferable to perform the press treatment with the use
of a spacer for compressing the molded body sheet to have a
predetermined thickness. That is, for example, by the molded body
sheet being pressed with the spacer placed on a placing surface
that faces the press head, the thermal conducting sheet can be
formed to have a predetermined sheet thickness corresponding to the
height of the spacer.
--Treatment for Leaving Molded Body Sheet Standing--
[0116] The treatment for leaving the molded body sheet standing is
not particularly limited and may be appropriately selected
depending on the intended purpose so long as it is a treatment for
leaving the molded body sheet standing to let the surface of the
molded body sheet be coated with the bled-out component that has
bled out from the molded body sheet.
[0117] The treatment for coating the surface of the molded body
sheet and the insulating-coated carbon fibers exposed on the
surface of the molded body sheet with the bled-out component of the
binder resin that has bled out from the molded body sheet may be
the treatment for leaving the molded body sheet standing, instead
of the press treatment. Also in this case, the thermal conducting
sheet to be obtained can have a better conformity and a better
close adhesiveness with the surface of an electronic part and of a
heat spreader and can have a lower thermal resistance, as in the
case of the press treatment. Further, when the coating with the
bled-out component has a thickness of a level that reflects the
shape of the insulating-coated carbon fibers on the surface of the
thermal conducting sheet, thermal resistance rise can be
avoided.
[0118] The standing time is not particularly limited and may be
appropriately selected depending on the intended purpose.
<Insulating-Coated Carbon Fiber Producing Step>
[0119] The insulating-coated carbon fiber producing step is a step
of obtaining the insulating-coated carbon fibers by applying energy
to a mixture to activate a polymerization initiator and form a
coating film over at least a part of a surface of the carbon
fibers, the coating film being formed of a cured product of a
polymerizable material.
[0120] The mixture is obtained by mixing the polymerizable
material, the carbon fibers, the polymerization initiator, and the
solvent.
[0121] It is preferable that the mixture be being stirred when the
energy is applied to the mixture.
[0122] By applying the energy to the mixture and activating the
polymerization initiator, it is possible to form an insulating
coating film having a desired thickness over the carbon fibers
without causing mutual aggregation of the carbon fibers. Because a
coating film having a better insulating property than that of
existing coating films can be formed, the obtained
insulating-coated carbon fibers can have a greatly improved
insulating property while maintaining a high thermal
conductivity.
--Polymerization Initiator--
[0123] The polymerization initiator is not particularly limited and
may be appropriately selected depending on the intended purpose so
long as the polymerization initiator can generate active species
upon application of the energy and allow the polymerizable material
to undergo polymerization.
[0124] When the polymerizable material is a radically polymerizable
material, examples of the polymerization initiator include thermal
polymerization initiators such as azo-compounds and organic
peroxides, and ultraviolet polymerization initiators such as
alkylphenone types and acylphosphine oxide types.
[0125] Examples of the energy include a thermal energy and a light
energy.
[0126] That is, in the case of using a thermal energy as the
energy, for example, the mixture is heated to equal to or higher
than a thermal decomposition temperature of the thermal
polymerization initiator, to thereby activate the thermal
polymerization initiator and allow the polymerizable material to
undergo polymerization. The thermal energy is applied to the
mixture through, for example, heat transfer by thermal
conduction.
[0127] In the case of using a light energy as the energy, for
example, the mixture is irradiated with ultraviolet rays, to
thereby activate the ultraviolet polymerization initiator and allow
the polymerizable material to undergo polymerization.
[0128] Examples of the solvent include an organic solvent and
water.
[0129] Examples of the organic solvent include hexane, cyclohexane,
diethyl ether, polyether (glyme), .gamma.-butyrolactone,
N-methylpyrrolidone, acetonitrile, tetrahydrofuran, ethyl acetate,
xylene, toluene, benzene, dimethyl sulfoxide, acetone, methyl ethyl
ketone, isopropyl alcohol, ethanol, and methanol.
[0130] Among these organic solvents, ethanol or a mixture of
ethanol and isopropyl alcohol is preferably used when
divinylbenzene is used as the radically polymerizable material.
Ethanol or a mixture of ethanol and toluene is preferably used when
a compound containing two or more (meth)acryloyl groups is used as
the radically polymerizable material.
--Deaeration--
[0131] In the production of the insulating-coated carbon fibers,
the mixture may be deaerated. This is for promoting surface
wettability of the carbon fibers. The deaeration method is not
particularly limited, and examples of the deaeration method include
a method through depressurization and a method using ultrasonic
waves.
--Inerting--
[0132] In the production of the insulating-coated carbon fibers,
inerting may be performed.
[0133] The inerting refers to a treatment for reducing the oxygen
concentration.
[0134] This is for preventing a polymerization reaction described
below from being inhibited by oxygen. The inerting method is not
particularly limited and may be appropriately selected depending on
the intended purpose. Examples of the inerting method include a
method of supplying an inert gas such as nitrogen by bubbling while
the mixture is being stirred, and a method of substituting nitrogen
in a container by depressurization and nitrogen purge.
--Polymerization Reaction--
[0135] In the production of the insulating-coated carbon fibers,
for example, a coating film formed of a cured product of the
polymerizable material is formed over at least a part of the carbon
fibers by, for example, applying energy while the mixture is being
stirred.
[0136] When the energy is a thermal energy, the temperature of the
mixture during polymerization is preferably from 0.degree. C.
through 200.degree. C., more preferably from 25.degree. C. through
150.degree. C., particularly preferably from 50.degree. C. through
100.degree. C. This is because the coating film can be formed
without fail and the insulating-coated carbon fibers having a high
insulating property can be obtained.
[0137] In the insulating-coated carbon fiber producing step, it is
preferable to lower the temperature (slow cooling) to room
temperature after the polymerization reaction. This is for lowering
the temperature of the solvent to precipitate the polymerized
product dissolved in a trace amount in the solvent as the coating
film. The slow cooling method is not particularly limited, and
examples of the slow cooling method include a method of immersing
the reaction container in a cooling tank with temperature
management.
[0138] In the insulating-coated carbon fiber producing step, for
example, before the polymerization reaction, the carbon fibers and
the polymerizable material (monomer) are present in a
dispersed/dissolved state in the solvent under stirring. After
energy application, the monomer undergoes polymerization in the
solution. After polymerization has progressed to the critical chain
length for precipitation in the solvent, a polymer precipitates
over the surface of the carbon fibers that serve as triggers
(nuclei) for precipitation. In this case, the formed polymer, when
seen on the whole, is insoluble in the solvent or, if soluble, very
scarcely soluble. When a polymerizable group has remained in the
precipitated polymer, the monomer is expected to undergo reaction
and further cause precipitation and is expected to form a
physically or chemically laminated layer. Subsequently, slow
cooling is performed, which lowers the temperature in the reaction
tank and reduces the solubility to the solvent, allowing an
assumption that the polymer dissolved in a trace amount in the
solvent also contributes to the polymer film thickness. By making
the contribution mild, it is possible to reduce the risk of
coalescing. The insulating-coated carbon fiber producing step
enables formation of a more uniform coating film having a higher
selectivity to the surface of the carbon fibers, compared with
emulsion polymerization that results in an embedded state by a
random phase separation. The formed insulating coating film has a
higher insulating property than that of existing insulating coating
films.
[0139] The polymerization reaction is a reaction for precipitating
an insulating coating film formed of a polymerized product (cured
product) over the carbon fibers, and is a reaction similar to
precipitation polymerization. However, the polymerization reaction
is different from the typical precipitation polymerization in that
the polymerization reaction is not a mechanism that is mainly based
on electrostatic pulling force/adsorption, absorption of the
monomer and the initiator component, and binding by a functional
group on the surface.
[0140] Further, in the insulating-coated carbon fiber producing
step, after the slow cooling, the obtained insulating-coated carbon
fibers may be settled.
[0141] Settling of the obtained insulating-coated carbon fibers
facilitates separation from the solvent. Settling can be performed
by leaving the reaction container standing still for a certain time
after the slow cooling.
(Heat Dissipation Member)
[0142] A heat dissipation member of the present invention includes
at least a heat spreader and a thermal conducting sheet, and
further includes other members if necessary.
(Semiconductor Device)
[0143] A semiconductor device of the present invention includes at
least an electronic part, a heat spreader, and a thermal conducting
sheet, and further includes other members if necessary.
[0144] The electronic part is not particularly limited and may be
appropriately selected depending on the intended purpose. Examples
of the electronic part include a CPU, an MPU, and a graphic
computing element.
[0145] The heat spreader is not particularly limited and may be
appropriately selected depending on the intended purpose so long as
the heat spreader is a member configured to dissipate heat
generated by the electronic part.
[0146] The thermal conducting sheet is the thermal conducting sheet
of the present invention, and is disposed on the heat spreader and
interposed between the heat spreader and the electronic part.
[0147] An example of the semiconductor device of the present
invention will be described with reference to the drawing.
[0148] FIG. 1 is a schematic cross-sectional view of an example of
the semiconductor device of the present invention. A thermal
conducting sheet 1 of the present invention is configured to
dissipate heat generated by an electronic part 3 such as a
semiconductor element. As illustrated in FIG. 1, the thermal
conducting sheet 1 is fixed on a principal surface 2a of a heat
spreader 2 facing the electronic part 3 and is interposed between
the electronic part 3 and the heat spreader 2. The thermal
conducting sheet 1 is also interposed between the heat spreader 2
and a heat sink 5. Together with the heat spreader 2, the thermal
conducting sheet 1 constitutes a heat dissipation member configured
to dissipate heat of the electronic part 3.
[0149] The heat spreader 2 is formed in, for example, a square
plate shape, and includes the principal surface 2a facing the
electronic part 3 and a side wall 2b formed upright along the
circumference of the principal surface 2a. In the heat spreader 2,
the thermal conducting sheet 1 is provided on the principal surface
2a surrounded by the side wall 2b, and the heat sink 5 is provided
on the other surface 2c opposite to the principal surface 2a with
the thermal conducting sheet 1 interposed between the heat sink and
the other surface. The head spreader 2 may be formed of; for
example, copper or aluminum having a good thermal conductivity,
because a higher thermal conductivity ensures a lower thermal
resistance and a more efficient absorption of heat from the
electronic part 3 such as a semiconductor element.
[0150] The electronic part 3 is, for example, a semiconductor
element such as BGA, and is mounted on a wiring board 6. The end
surface of the side wall 2b of the heat spreader 2 is also mounted
on the wiring board 6. In this way, the electronic part 3 is
surrounded by the side wall 2b with a predetermined distance
secured.
[0151] Then, with the thermal conducting sheet 1 bonded to the
principal surface 2a of the heat spreader 2, a heat dissipation
member configured to absorb heat generated by the electronic part 3
and dissipate the heat through the heat sink 5 is formed. The heat
spreader 2 and the thermal conducting sheet 1 may be bonded to each
other by the own adhesive force of the thermal conducting sheet 1,
but an adhesive may be appropriately used. As the adhesive, known
heat dissipating resins or heat dissipating adhesive films that
serve bonding and thermal conduction of the thermal conducting
sheet 1 to the heat spreader 2 may be used.
EXAMPLES
[0152] Next, Examples of the present invention will be described.
In the present Examples, samples of thermal conducting sheets were
prepared. Then, various evaluations of each of the samples were
performed.
[0153] Note that, the present invention is not limited to these
Examples.
Production Example 1
<Production of Insulating-Coated Carbon Fibers>
[0154] Pitch-based carbon fibers having an average fiber diameter
of 9 .mu.m and an average fiber length of 100 .mu.m (product name:
XN-100-10M, manufactured by Nippon Graphite Fiber Co., Ltd.) (100
g) and ethanol (450 g) were charged into a glass container and
mixed with a stirring blade, to obtain a slurry liquid. While
inerting was performed by adding nitrogen to the slurry liquid at a
flow rate of 160 mL/min, divinylbenzene (93% divinylbenzene,
manufactured by Wako Pure Chemical Industries, Ltd.) (25 g) was
added to the slurry.
[0155] Ten minutes after addition of divinylbenzene, a
polymerization initiator (product name: V-65, an oil-soluble
azo-polymerization initiator, manufactured by Wako Pure Chemical
Industries, Ltd.) (0.500 g) previously dissolved in ethanol (50 g)
was charged into the slurry liquid. After feeding, the resultant
was stirred for 5 minutes and then inerting by nitrogen was
stopped.
[0156] Subsequently, the resultant was subjected to temperature
increase under stirring, retained at a temperature of 70.degree.
C., and then subjected to temperature decrease to 40.degree. C. The
reaction time was from the start of temperature increase to the
start of temperature decrease. After temperature decrease, the
resultant was left to stand still for 15 minutes, to settle the
solids dispersed in the slurry liquid. After settling, the
supernatant was removed by decantation, and the resultant was
stirred for 15 minutes with an additional solvent (750 g) to wash
the solids.
[0157] After washing, the solids were collected by suction
filtration, and the collected solids were dried at 100.degree. C.
for 6 hours, to obtain insulating-coated carbon fibers.
Production Examples 2 to 8
<Production of Insulating-Coated Carbon Fibers>
[0158] Insulating-coated carbon fibers were obtained in the same
manner as in Production Example 1, except that the formulation was
changed as presented in Table 2-1 and Table 2-2.
Comparative Production Example 1
<Production of Insulating-Coated Carbon Fibers>
[0159] Pitch-based carbon fibers having an average fiber diameter
of 9 .mu.m and an average fiber length of 100 .mu.m (product name:
XN-100-10M, manufactured by Nippon Graphite Fiber Co., Ltd.) (100
g), tetraethoxysilane (TEOS) (200 g), and ethanol (900 g) were
charged into a polyethylene container and mixed with a stirring
blade.
[0160] While the resultant was warmed to 50.degree. C., a reaction
initiator (10% ammonia water) (176 g) was charged into the
resultant for 5 minutes. The resultant was stirred for 3 hours from
the time at which solvent charging was completed (0 minutes).
[0161] After stirring was completed, the resultant was subjected to
temperature decrease and solids were collected by suction
filtration. Then, the solids were washed with water and ethanol and
were subjected to suction filtration again to collect solids.
[0162] The collected solids were dried at 100.degree. C. for 2
hours and further fired at 200.degree. C. for 8 hours, to obtain
insulating-coated carbon fibers.
(Evaluation)
[0163] The insulating-coated carbon fibers obtained in Production
Examples 1 to 8 and Comparative Production Example 1 were evaluated
in the manners described below. The following carbon fibers that
were not insulating-coated were also evaluated for resistance.
Evaluation results are presented in Tables 2-1 and 2-2.
Comparative Sample 1
[0164] Pitch-based carbon fibers having an average fiber diameter
of 9 .mu.m and an average fiber length of 100 .mu.m (product name:
XN-100-10M: manufactured by Nippon Graphite Fiber Co., Ltd.)
Comparative Sample 2
[0165] Pitch-based carbon fibers having an average fiber diameter
of 9 .mu.m and an average fiber length of 120 .mu.m (product name:
XN-100-12M: manufactured by Nippon Graphite Fiber Corporation)
Comparative Sample 3
[0166] Pitch-based carbon fibers having an average fiber diameter
of 9 .mu.m and an average fiber length of 150 .mu.m (product name:
XN-100-15M: manufactured by Nippon Graphite Fiber Corporation)
(1) Yield
[0167] The mass of each sample of the insulating-coated carbon
fibers was measured.
[0168] Then, the mass was divided by the mass of the carbon fibers
used, to thereby calculate the yield. As the calculated yield was
higher, it can be understood that the coating amount was
higher.
(2) Film Thickness of Coating Film
[0169] Each sample of the insulating-coated carbon fibers was cut
with a focused ion beam (FIB) and the cross-section was observed
with a transmission electron microscope (TEM). Then, an average
film thickness of the coating was measured.
(3) Resistance of Coated Carbon Fibers
[0170] After each sample of the insulating-coated carbon fibers was
charged into a tubular container (with a diameter of 9 mm and a
length of 15 mm) at a filling density of 0.750 g/cm.sup.3,
resistance of the sample with respect to applied voltage variation
was measured by a two-terminal method, using a high resistance
measuring instrument. Note that, resistance of the carbon fibers
that were not insulating-coated was measured in an applied voltage
range in which the maximum was 10 Vby a four-terminal method, using
a low resistance measuring instrument.
[0171] A sample having a very high resistance value that exceeded
the measurement range (see Table 1) was indicated in Table 2-1 and
Table 2-2 as "Over Range".
[0172] Measurable ranges when the high resistance measuring
instrument was used to are as follows.
TABLE-US-00001 TABLE 1 Measurable range Resistance Measurement 1.0
.times. 10.sup.3 or more but (.OMEGA.) voltage 1 V less than 1.0
.times. 10.sup.11 Measurement 1.0 .times. 10.sup.3 or more but
voltage 10 V less than 1.0 .times. 10.sup.11 Measurement 1.0
.times. 10.sup.6 or more but voltage 50 V less than 1.0 .times.
10.sup.12 Measurement 1.0 .times. 10.sup.6 or more but voltage 100
V less than 1.0 .times. 10.sup.12 Measurement 1.0 .times. 10.sup.6
or more but voltage 250 V less than 1.0 .times. 10.sup.12
Measurement 1.0 .times. 10.sup.7 or more but voltage 500 V less
than 1.0 .times. 10.sup.13 Measurement 1.0 .times. 10.sup.8 or more
but voltage 1000 V less than 1.0 .times. 10.sup.15
TABLE-US-00002 TABLE 2-1 Comparative Production Comparative
Production Example Example sample 1 2 3 4 5 1 1 2 3 Formu- Carbon
XN-100-10M 100 100 XN- XN- XN- lation fibers XN-100-12M 100 100 100
100- 100- 100- (g) XN-100-15M 100 10M 12M 15M Monomer
Divinylbenzene 25 25 25 15 LIGHT ESTER 18.75 EG TEOS 200 Initiator
V-65 0.500 0.500 0.500 0.400 0.375 Aqueous 10% 176 NH3 solution
Solvent Ethanol 500 500 500 500 500 900 Reaction Temperature 70 70
70 70 70 50 -- -- -- condition (.degree. C.) Time (hr) 4 4 4 4 4 4
-- -- -- Evaluation Yield 107% 108% 107% 105% 109% 107% -- -- --
TEM film thickness 213 nm 261 nm 253 nm 120 nm 300 nm 70 nm -- --
-- (N = 2 Ave.) Aggregation None None None None None None None None
None Resistance 10 V OverRange 1.03E+10 3.98E-01 5.70E-02 1.56E-02
.OMEGA. 100 V OverRange 7.31E+09 -- 500 V OverRange 1.65E+09 --
1000 V 6.08E+13 2.74E+14 1.33E+12 2.70E+12 1.10E+14 6.02E+08 --
TABLE-US-00003 TABLE 2-2 Production Production Production Example 6
Example 7 Example 8 Formulation Carbon .chi.N100-10M (g) fibers
.chi.N100-12M 100 100 100 .chi.N100-15M Mono- Divinyl- 25 25 25 mer
benzene LIGHT ESTER G TEOS Initiator V-65 0.5 0.5 0.5 Aqueous 10%
NH3 solution Solvent Ethanol 500 500 500 Reaction condition
Tempera- 70 70 70 ture (.degree. C.) Time (hr) 4.5 5 5.5 Evaluation
Yield 108% 109% 108% TEM film thickness 302 325 396 (nm)
Aggregation None None None Resis- 10 V Over Range tance 100 V Over
Range .OMEGA. 500 V Over Range 1000 V 3.03E+13 4.62E+13
3.61E+14
[0173] In Tables 2-1 and 2-2, "E" denotes "exponent of 10". That
is, "1E+3" denotes "1000" and "1E-1" denotes "0.1". The same is
applicable to Tables 4-1 to 4-5.
[0174] XN-100-10M: Pitch-based carbon fibers having an average
fiber diameter of 9 .mu.m and an average fiber length of 100 .mu.m,
Nippon Graphite Fiber Corporation
[0175] XN-100-12M: Pitch-based carbon fibers having an average
fiber diameter of 9 .mu.m and an average fiber length of 120 .mu.m,
Nippon Graphite Fiber Corporation
[0176] XN-100-15M: Pitch-based carbon fibers having an average
fiber diameter of 9 .mu.m and an average fiber length of 150 .mu.m,
Nippon Graphite Fiber Corporation LIGHT ESTER EG: Ethylene glycol
dimethacrylate, Kyoeisha Chemical Co., Ltd.
Examples 1
[0177] Materials were mixed in the following formulation to prepare
a silicone resin composition (thermal conducting resin
composition).
--Formulation--
TABLE-US-00004 [0178] --Composition 1 (Total 100% by volume)--
Insulating-coated carbon fibers of 12.43% by volume Production
Example 1 Alumina (product name: DAW03, average 54.23% by volume
particle diameter 4 .mu.m, Denka Company Limited) Silicone resin
33.34% by volume Note that, the silicone resin is as follows.
--Silicone resin-- Silicone resin A (product name: 527 (A), 55% by
mass Dow Corning Toray Co., Ltd.) Silicone resin B (product name:
527 (B), 45% by mass Dow Corning Toray Co., Ltd.)
[0179] The silicone resin composition obtained was extruded into a
rectangular parallelepiped die (42 mm.times.42 mm) the inside wall
of which had been provided with a PET film subjected to a release
treatment, to thereby mold a silicone molded body. The silicone
molded body obtained was cured in an oven at 100.degree. C. for 6
hours, to obtain a silicone cured product.
[0180] The silicone cured product obtained was heated for 1 hour at
100.degree. C. in an oven and was cut using an ultrasonic cutter to
thereby obtain a molded body sheet having a thickness of 2.05 mm. A
slicing speed of the ultrasonic cutter was 50 mm per second. An
ultrasonic vibration applied to the ultrasonic cutter was 20.5 kHz
as an oscillating frequency and 60 .mu.m as an amplitude.
[0181] The obtained molded body sheet was sandwiched between PET
films that had been subjected to a release treatment and was
pressed with spacers having a thickness of 1.98 mm being inserted,
to thereby obtain a thermal conducting sheet sample having a
thickness of 2.00 mm. The press conditions were 50.degree. C., 0.5
MPa, and 3 minutes. The filler found on the surface immediately
after the slicing was not coated with the binder. By the press, the
filler was pressed against the sheet and indented into the sheet,
to cause the binder component to be exposed to the surface.
Therefore, the filler was coated with the binder by reflecting the
filler shape on the sheet surface. After the press, the binder
component was found on the surface of the release-treatment PET
that had contacted the sheet.
<Evaluation>
[0182] The following evaluations were performed. Results are
presented in Table 4-1.
Thermal Characteristics (Effective Thermal Conductivity, Thermal
Resistance, and Compressibility)
[0183] Measurement of thermal characteristics was performed using a
thermal resistance measuring instrument (manufactured by Dexerials
Corporation) compliant with ASTM-D5470.
[0184] Effective thermal conductivity was a thermal conductivity in
a thickness direction.
[0185] Each characteristic was measured under a load of 0.5
kgf/cm.sup.2.
Electric Characteristics (Volume Resistivity and Dielectric
Breakdown Voltage)
--Volume Resistivity--
[0186] Volume resistivity with respect to applied voltage variation
was measured with a resistance measuring instrument (manufactured
by Mitsubishi Chemical Analytech Co., Ltd., HIRESTA-UX).
[0187] A sample having a considerably high resistance value that
exceeded the measurement range (see Table 1) was indicated in Table
4-1 to Table 4-5 as "Over Range" or "O.R.". A sample having a
considerably low resistance value that fell below the measurement
range (see Table 1) was indicated in Table 4-3 as "Under
Range".
[0188] Because the measurement range of volume resistivity was
based on the measurement range of a resistance value, the unit of
the measurement range in Table 1 was .OMEGA..
--Dielectric Breakdown Voltage--
[0189] A dielectric breakdown voltage was measured with an
ultrahigh-voltage breakdown voltage tester (manufactured by Keisoku
Giken Co., Ltd., 7473) at a voltage increasing rate of 0.05
kV/second at room temperature. The voltage at which dielectric
breakdown occurred was the dielectric breakdown voltage (kV or
kV/mm).
Examples 2 to 10 and Comparative Examples 1 to 6
[0190] A thermal conducting sheet was prepared in the same manner
as in Example 1 except that each formulation of the compositions
was changed as described in Table 3-1 or 3-2 and Table 4-1 to
4-3.
[0191] The thermal conducting sheets obtained were evaluated in the
same manner as in Example 1. Results are presented in Tables 4-1 to
4-3.
Examples 11 to 19
[0192] A thermal conducting sheet was obtained in the same manner
as in Example 1 except that the formulation of each composition and
the thickness of each sheet were changed as presented in Table 3-3,
and Table 4-4 to Table 4-5.
[0193] The thermal conducting sheets obtained were evaluated in the
same manner as in Example 1. Results are presented in Table 4-4 to
Table 4-5.
TABLE-US-00005 TABLE 3-1 Example Silicone resin 1 2 3 4 5 6 7 8 9
10 527 (A) % by 55 55 0 0 0 0 0 55 0 0 527 (B) mass 45 45 0 0 0 0 0
45 0 0 CY52-276 (A) 0 0 55 55 55 55 55 0 55 55 CY52-276 (B) 0 0 45
45 45 45 45 0 45 45
TABLE-US-00006 TABLE 3-2 Comparative Example Silicone resin 1 2 3 4
5 6 527 (A) % by 56 57 57 50 59 56 527 (B) mass 44 43 43 50 41 44
CY52-276 (A) 0 0 0 0 0 0 CY52-276 (B) 0 0 0 0 0 0
TABLE-US-00007 TABLE 3-3 Example Silicone resin 11 12 13 14 15 16
17 18 19 527 (A) % by 55 55 55 55 55 55 55 55 55 527 (B) mass 45 45
45 45 45 45 45 45 45
[0194] 527 (A): Silicone resin, Dow Corning Toray Co., Ltd.
[0195] 527 (B): Silicone resin, Dow Corning Toray Co., Ltd.
[0196] CY52-276 (A): Silicone resin, Dow Corning Toray Co.,
Ltd.
[0197] CY52-276 (B): Silicone resin, Dow Corning Toray Co.,
Ltd.
TABLE-US-00008 TABLE 4-1 Examples 1 2 3 4 5 Compounding ratio
Carbon Production Example 1 12.43 (% by volume) fibers Production
Example 2 12.43 10.06 13.18 13.82 Production Example 3 Production
Example 4 Production Example 5 Comparative Production Example 1
XN-100-10M XN-100-12M XN-100-15M Alumina DAW03 54.23 54.23 37.62
26.00 25.84 Aluminum nitride H1 JC 25.32 33.16 33.13 Silicone resin
33.34 33.34 26.99 27.67 27.20 Total (% by volume) 100.00 100.00
100.00 100.00 100.00 Amount of thermal conducting filler (% by
volume) 54.23 54.23 62.94 59.16 58.97 Carbon fibers (C)-silicone
resin (S) ratio C/S (mass ratio) 0.85 0.85 0.85 1.09 1.16 Thermal
Effective thermal conductivity [W/mK] 8.96 9.90 9.91 11.93 12.80
characteristics Thermal resistance [.degree. C. cm.sup.2/W] 1.99
1.82 1.78 1.49 1.42 Compressibility [%] 10.73 10.09 11.66 10.84
9.05 Electric Volume resistivity 1 V Over Range characteristics
[(.OMEGA. cm] 10 V Over Range 50 V Over Range 100 V Over Range 250
V Over Range 500 V O.R. 6.51E+12 Over Range 1000 V 2.94E+13 1.1E+13
3.32E+13 3.73E+13 9.48E+12 Dielectric breakdown voltage [kV] 1.93
1.84 2.24 2.13 1.90 [kV/mm] 0.97 0.92 1.12 1.07 0.95
TABLE-US-00009 TABLE 4-2 Examples 6 7 8 9 10 Compounding ratio
Carbon fibers Production Example 1 (% by volume) Production Example
2 8.57 6.82 12.76 Production Example 3 Production Example 4 13.34
8.57 Production Example 5 8.57 Comparative Production Example 1
XN-100-10M XN-100-12M XN-100-15M Alumina DAW03 30.43 31.30 53.01
30.43 30.43 Aluminum nitride H1 JC 35.12 36.12 35.12 35.12 Silicone
resin 25.88 25.76 34.23 25.88 25.88 Total (% by volume) 100.00
100.00 100.00 100.00 100.00 Amount of thermal conducting filler (%
by volume) 65.55 67.42 53.01 65.55 65.55 Carbon fibers (C)-silicone
resin (S) ratio C/S (mass ratio) 0.76 0.61 0.85 0.76 0.76 Thermal
Effective thermal conductivity [W/mK] 10.06 9.05 12.84 11.23 9.60
characteristics Thermal resistance [.degree. C. cm.sup.2/W] 1.80
1.96 1.34 1.63 1.84 Compressibility [%] 9.35 11.49 13.80 8.42 11.84
Electric Volume resistivity 1 V Over Range characteristics
[(.OMEGA. cm] 10 V Over Range 50 V Over Range 100 V Over Range 250
V Over Range 500 V Over Range 4.53E+12 1000 V 4.19E+13 3.98E+13
8.48E+12 1.93E+13 8.09E+12 Dielectric breakdown voltage [kV] 2.67
2.94 1.82 2.23 3.80 [kV/mm] 1.34 1.47 0.91 1.12 1.90
TABLE-US-00010 TABLE 4-3 Comparative Example 1 2 3 4 5 6
Compounding ratio Carbon fibers Production Example 1 (% by volume)
Production Example 2 Production Example 3 Production Example 4
23.07 Production Example 5 Comparative Produc- 12.48 tion Example 1
XN-100-10M 22.34 23.07 XN-100-12M 19.63 XN-100-15M 23.07 Alumina
DAW03 20.66 42.68 42.68 6.05 54.44 42.69 Aluminum nitride H1 23.84
JC 41.90 Silicone resin 33.16 34.25 34.25 32.42 33.08 34.24 Total
(% by volume) 100.00 100.00 100.00 100.00 100.00 100.00 Amount of
thermal conducting filler (% by volume) 44.50 42.68 42.68 47.95
54.44 42.69 Carbon fibers (C)-silicone resin (S) ratio C/S (mass
ratio) 1.54 1.54 0.86 0.70 0.86 1.54 Heat characteristics Effective
thermal conductivity [W/mK] 17.21 11.54 15.30 22.80 8.78 12.79
Thermal resistance [.degree. C. cm.sup.2/W] 0.85 1.17 0.83 0.78
1.82 1.36 Compressibility [%] 27.14 32.47 36.38 10.80 20.26 12.79
Electric characteristics Volume resistivity 1 V 4.40E+04 2.51E+04
1.20E+03 1.80E+03 Over Range [(.OMEGA. cm] 10 V Under Range Over
Range 50 V Under Range Over Range 100 V Under Range Over Range 250
V Under Range Over Range 500 V Under Range 8.37E+12 O.R. 1000 V
Under Range 4.29E+11 4.53E+11 Dielectric breakdown voltage [kV]
0.04 0.04 0.04 0.04 1.61 1.30 [kV/mm] 0.02 0.02 0.02 0.02 0.805
0.65
TABLE-US-00011 TABLE 4-4 Examples 11 12 13 14 15 Compounding ratio
Carbon fibers Production Example 6 12.43 (% by volume) Production
Example 7 12.43 Production Example 8 12.43 12.43 12.43 Alumina
DAW03 54.23 54.23 54.23 54.23 54.23 Silicone resin 33.34 33.34
33.34 33.34 33.34 Total (% by volume) 100.00 100.00 100.00 100.00
100.00 Ratio of thermal conducting filler amount (% by volume)
66.66 66.66 66.66 66.66 66.66 Sheet thickness [mm] 2.0 2.0 1.0 1.5
2.0 Carbon fibers-silicone resin ratio C/S (mass ratio) 0.37 0.37
0.37 0.37 0.37 Thermal characteristics Effective thermal
conductivity [W/m k] 8.22 8.25 5.72 6.76 7.86 Thermal resistance
[.degree. C. cm2/W] 1.58 1.92 1.66 2.05 2.39 Compressibility [%]
15.4 21.4 6.64 5.12 6.1 Electric characteristics Volume resistivity
1 V Over Range .OMEGA. cm 10 V Over Range 50 V Over Range 100 V
Over Range 250 V Over Range 500 V Over Range 1000 V 2.21E+13
3.11E+13 1.09E+13 3.89E+13 3.77E+13 Dielectric breakdown voltage
[kV] 2.11 2.23 1.11 1.89 2.51 [kV/mm] 1.06 1.12 1.11 1.26 1.26
TABLE-US-00012 TABLE 4-5 Examples 16 17 18 19 Compounding ratio
Carbon fibers Production Example 6 (% by volume) Production Example
7 Production Example 8 12.43 12.43 12.43 3.22 Alumina DAW03 54.23
54.23 54.23 53.7 Silicone resin 33.34 33.34 33.34 43.08 Total (% by
volume) 100.00 100.00 100.00 100.00 Ratio of thermal conducting
filler amount (% by volume) 66.66 66.66 66.66 56.92 Sheet thickness
[mm] 2.5 3.0 3.5 0.44 Carbon fibers-silicone resin ratio C/S (mass
ratio) 0.37 0.37 0.37 0.075 Thermal characteristics Effective
thermal conductivity [W/m k] 8.29 8.7 8.84 1.07 Thermal resistance
[.degree. C. cm2/W] 2.81 3.31 3.73 3.43 Compressibility [%] 6.1
6.45 6.42 16.3 Electric characteristics Volume resistivity 1 V Over
Range .OMEGA. cm 10 V Over Range 50 V Over Range 100 V Over Range
250 V Over Range 500 V Over Range 1000 V 3.49E+13 3.28E+13 2.88E+13
1.23E+12 Dielectric breakdown voltage [kV] 3.07 3.44 3.80 0.60
[kV/mm] 1.23 1.15 1.09 1.36
[0198] H1: Aluminum nitride, average particle diameter 1 .mu.m,
Tokuyama Corporation [0199] JC: Aluminum nitride, average particle
diameter 1.2 .mu.m, Toyo Aluminium K.K.
[0200] Here, a specific gravity of each component is as
follows.
[0201] Silicone resin: 0.97
[0202] Carbon fibers: 2.22
[0203] Alumina: 3.75
[0204] Aluminum nitride: 3.25
[0205] In Examples 1 to 19, both an excellent thermal conductivity
and an excellent insulating property could be achieved.
[0206] In addition, even when a thickness of the insulating coating
on the carbon fibers and a thickness of the sheet were changed,
favorable characteristics were exhibited.
[0207] In Comparative Examples 1 to 4, the insulating-coated carbon
fibers were not used. Therefore, each insulating property was
insufficient.
[0208] In Comparative Example 5, the insulating-coated carbon
fibers obtained in Comparative Production Example 1 were used.
However, the thermal conducting sheet of Comparative Example 5 did
not have as favorable an insulating property as the thermal
conducting sheet of the present invention.
[0209] The thermal conducting sheet of Comparative Example 6 having
a mass ratio (insulating-coated carbon fibers/binder resin) of 1.30
or more did not have as favorable an insulating property as the
thermal conducting sheet of the present invention.
REFERENCE SIGNS LIST
[0210] 1: thermal conducting sheet [0211] 2: heat spreader [0212]
2a: principal surface [0213] 3: electronic part [0214] 3a: upper
surface [0215] 5: heat sink [0216] 6: wiring board
* * * * *