U.S. patent application number 13/016726 was filed with the patent office on 2011-10-27 for thermal conductive sheet.
This patent application is currently assigned to NITTO DENKO CORPORATION. Invention is credited to Takahiro FUKUOKA, Kazutaka HARA, Hitotsugu HIRANO, Seiji IZUTANI, Hisae UCHIYAMA.
Application Number | 20110259568 13/016726 |
Document ID | / |
Family ID | 44408130 |
Filed Date | 2011-10-27 |
United States Patent
Application |
20110259568 |
Kind Code |
A1 |
IZUTANI; Seiji ; et
al. |
October 27, 2011 |
THERMAL CONDUCTIVE SHEET
Abstract
A thermal conductive sheet containing a plate-like boron nitride
particle, wherein the thermal conductivity in a direction
perpendicular to the thickness direction of the thermal conductive
sheet is 4 W/mK or more, and a glass transition point determined as
the peak value of tan.delta. obtained by measuring a dynamic
viscoelasticity of the thermal conductive sheet at a frequency of
10 Hz is 125.degree. C. or more.
Inventors: |
IZUTANI; Seiji; (Osaka,
JP) ; UCHIYAMA; Hisae; (Osaka, JP) ; FUKUOKA;
Takahiro; (Osaka, JP) ; HARA; Kazutaka;
(Osaka, JP) ; HIRANO; Hitotsugu; (Osaka,
JP) |
Assignee: |
NITTO DENKO CORPORATION
Osaka
JP
|
Family ID: |
44408130 |
Appl. No.: |
13/016726 |
Filed: |
January 28, 2011 |
Current U.S.
Class: |
165/185 |
Current CPC
Class: |
C09K 5/14 20130101 |
Class at
Publication: |
165/185 |
International
Class: |
F28F 7/00 20060101
F28F007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 29, 2010 |
JP |
2010-018256 |
Apr 9, 2010 |
JP |
2010-090908 |
Jul 16, 2010 |
JP |
2010-161853 |
Claims
1. A thermal conductive sheet comprising a plate-like boron nitride
particle, wherein the thermal conductivity in a direction
perpendicular to the thickness direction of the thermal conductive
sheet is 4 W/mK or more, and a glass transition point determined as
the peak value of tan.delta. obtained by measuring a dynamic
viscoelasticity of the thermal conductive sheet at a frequency of
10 Hz is 125.degree. C. or more.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] The present application claims priority from Japanese Patent
Application No. 2010-018256 filed on Jan. 29, 2010; No. 2010-090908
filed on Apr. 9, 2010; and No. 2010-161853 filed on Jul. 16, 2010,
the contents of which are hereby incorporated by reference into
this application.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a thermal conductive sheet,
to be specific, to a thermal conductive sheet for use in power
electronics technology.
[0004] 2. Description of Related Art
[0005] In recent years, power electronics technology which uses
semiconductor elements to convert and control electric power is
applied in hybrid devices, high-brightness LED devices, and
electromagnetic induction heating devices. In power electronics
technology, a high current is converted to, for example, heat, and
therefore materials that are disposed near the semiconductor
element are required to have excellent heat dissipation
characteristics (excellent heat conductivity).
[0006] For example, Japanese Unexamined Patent Publication No.
2008-280496 has proposed a thermal conductive sheet containing a
plate-like boron nitride powder and an acrylic ester copolymer
resin.
[0007] In the thermal conductive sheet of Japanese Unexamined
Patent Publication No. 2008-280496, the boron nitride powder is
oriented so as to orient its major axis direction (direction
perpendicular to the plate thickness of the boron nitride powder)
in the thickness direction of the sheet, and thermal conductivity
in the thickness direction of the thermal conductive sheet is
improved in this way.
SUMMARY OF THE INVENTION
[0008] However, there are cases where the thermal conductive sheet
is required to have a high thermal conductivity in a direction
(plane direction) perpendicular to the thickness direction
depending on its use and purpose. In such a case, the thermal
conductive sheet of Japanese Unexamined Patent Publication No.
2008-280496 is disadvantageous in that the major axis direction of
the boron nitride powder is perpendicular to (crossing) the plane
direction, and therefore the thermal conductivity in the plane
direction is insufficient.
[0009] Furthermore, when such a thermal conductive sheet is used,
for example, the thermal conductive sheet is bonded to various
devices for conducting (dissipating) heat generated from the
devices, and therefore excellent heat resistance (resistance to
deformation) is required so as not to be deformed by the heat and
not to be peeled off from the devices.
[0010] An object of the present invention is to provide a thermal
conductive sheet that is excellent in thermal conductivity in the
plane direction, and also excellent in heat resistance.
[0011] A thermal conductive sheet of the present invention contains
a plate-like boron nitride particle, wherein the thermal
conductivity in a direction perpendicular to the thickness
direction of the thermal conductive sheet is 4 W/mK or more, and a
glass transition point determined as the peak value of tan.delta.
obtained by measuring a dynamic viscoelasticity of the thermal
conductive sheet at a frequency of 10 Hz is 125.degree. C. or
more.
[0012] The thermal conductive sheet of the present invention is
excellent in thermal conductivity in the plane direction that is
perpendicular to the thickness direction, and also excellent in
heat resistance.
[0013] Therefore, the thermal conductive sheet of the present
invention can be applied to various heat dissipation uses as a
thermal conductive sheet that allows decrease in deformation under
high temperature, that suppresses peeling off, that is excellent in
handleability, and that is excellent in thermal conductivity in the
plane direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows a perspective view of an embodiment of a
thermal conductive sheet of the present invention.
[0015] FIG. 2 shows process drawings for describing a method for
producing the thermal conductive sheet shown in FIG. 1:
[0016] (a) illustrating a step of hot pressing a mixture or a
laminated sheet,
[0017] (b) illustrating a step of dividing the pressed sheet into a
plurality of pieces, and
[0018] (c) illustrating a step of laminating the divided
sheets.
[0019] FIG. 3 shows a perspective view of a test device (Type I,
before bend test) of a bend test.
[0020] FIG. 4 shows a perspective view of a test device (Type I,
during bend test) of a bend test.
DETAILED DESCRIPTION OF THE INVENTION
[0021] A thermal conductive sheet of the present invention contains
boron nitride particles.
[0022] To be specific, the thermal conductive sheet contains boron
nitride (BN) particles as an essential component, and further
contains, for example, a resin component.
[0023] The boron nitride particles are formed into a plate-like (or
flake-like) shape, and are dispersed so as to be orientated in a
predetermined direction (described later) in the thermal conductive
sheet.
[0024] The boron nitride particles have an average length in the
longitudinal direction (maximum length in the direction
perpendicular to the plate thickness direction) of, for example, 1
to 100 .mu.m, or preferably 3 to 90 .mu.m. The boron nitride
particles have an average length in the longitudinal direction of,
5 .mu.m or more, preferably 10 .mu.m or more, more preferably 20
.mu.m or more, even more preferably 30 .mu.m or more, or most
preferably 40 .mu.m or more, and usually has an average length in
the longitudinal direction of, for example, 100 .mu.m or less, or
preferably 90 .mu.m or less.
[0025] The average thickness (the length in the thickness direction
of the plate, that is, the length in the short-side direction of
the particles) of the boron nitride particles is, for example, 0.01
to 20 .mu.m, or preferably 0.1 to 15 .mu.m.
[0026] The aspect ratio (length in the longitudinal
direction/thickness) of the boron nitride particles is, for
example, 2 to 10000, or preferably 10 to 5000.
[0027] The average particle size of the boron nitride particles as
measured by a light scattering method is, for example, 5 .mu.m or
more, preferably 10 .mu.m or more, more preferably 20 .mu.m or
more, particularly preferably 30 .mu.m or more, or most preferably
40 .mu.m or more, and usually is 100 .mu.m or less.
[0028] The average particle size as measured by the light
scattering method is a volume average particle size measured with a
dynamic light scattering type particle size distribution
analyzer.
[0029] When the average particle size of the boron nitride
particles as measured by the light scattering method is below the
above-described range, the thermal conductive sheet may become
fragile, and handleability may be reduced.
[0030] The bulk density (JIS K 5101, apparent density) of the boron
nitride particles is, for example, 0.3 to 1.5 g/cm.sup.3, or
preferably 0.5 to 1.0 g/cm.sup.3.
[0031] As the boron nitride particles, a commercially available
product or processed goods thereof can be used. Examples of
commercially available products of the boron nitride particles
include the "PT" series (for example, "PT-110") manufactured by
Momentive Performance Materials Inc., and the "SHOBN.RTM.UHP"
series (for example, "SHOBN.RTM.UHP-1") manufactured by Showa Denko
K.K.
[0032] The resin component is a component that is capable of
dispersing the boron nitride particles, i.e., a dispersion medium
(matrix) in which the boron nitride particles are dispersed,
including, for example, resin components such as a thermosetting
resin component and a thermoplastic resin component.
[0033] Examples of the thermosetting resin component include epoxy
resin, thermosetting polyimide, phenol resin, urea resin, melamine
resin, unsaturated polyester resin, diallyl phthalate resin,
silicone resin, and thermosetting urethane resin.
[0034] Examples of the thermoplastic resin component include
polyolefin (for example, polyethylene, polypropylene, and
ethylene-propylene copolymer), acrylic resin (for example,
polymethyl methacrylate), polyvinyl acetate, ethylene-vinyl acetate
copolymer, polyvinyl chloride, polystyrene, polyacrylonitrile,
polyamide (Nylon.RTM.), polycarbonate, polyacetal, polyethylene
terephthalate, polyphenylene oxide, polyphenylene sulfide,
polysulfone, polyether sulfone, poly ether ether ketone, polyallyl
sulfone, thermoplastic polyimide, thermoplastic urethane resin,
polyamino-bismaleimide, polyamide-imide, polyether-imide,
bismaleimide-triazine resin, polymethylpentene, fluorine resin,
liquid crystal polymer, olefin-vinyl alcohol copolymer, ionomer,
polyarylate, acrylonitrile-ethylene-styrene copolymer,
acrylonitrile-butadiene-styrene copolymer, and
acrylonitrile-styrene copolymer.
[0035] These resin components can be used alone or in combination
of two or more.
[0036] Of the thermosetting resin components, preferably, an epoxy
resin is used.
[0037] The epoxy resin is in a state of liquid, semi-solid, or
solid under normal temperature.
[0038] To be specific, examples of the epoxy resin include aromatic
epoxy resins such as bisphenol epoxy resin (for example, bisphenol
A epoxy resin, bisphenol F epoxy resin, bisphenol S epoxy resin,
hydrogenated bisphenol A epoxy resin, dimer acid-modified bisphenol
epoxy resin, and the like), novolak epoxy resin (for example,
phenol novolak epoxy resin, cresol novolak epoxy resin, biphenyl
epoxy resin, and the like), naphthalene epoxy resin, fluorene epoxy
resin (for example, bisaryl fluorene epoxy resin and the like), and
triphenylmethane epoxy resin (for example, trishydroxyphenylmethane
epoxy resin and the like); nitrogen-containing-cyclic epoxy resins
such as triepoxypropyl isocyanurate (triglycidyl isocyanurate) and
hydantoin epoxy resin; aliphatic epoxy resin; alicyclic epoxy resin
(for example, dicyclo ring-type epoxy resin and the like);
glycidylether epoxy resin; and glycidylamine epoxy resin.
[0039] These epoxy resins can be used alone or in combination of
two or more.
[0040] The epoxy resin has an epoxy equivalent of, for example, 100
to 1000 g/eqiv., or preferably 180 to 700 g/eqiv., and has a
softening temperature (ring and ball test) of, for example,
80.degree. C. or less (to be specific, 20 to 80.degree. C.), or
preferably 70.degree. C. or less (to be specific, 35 to 70.degree.
C.).
[0041] The epoxy resin has a melt viscosity at 80.degree. C. of,
for example, 10 to 20,000 mPas, or preferably 50 to 10,000 mPas.
When two or more epoxy resins are used in combination, the melt
viscosity of the mixture of these epoxy resins is set within the
above-described range.
[0042] When two or more epoxy resins are used in combination, for
example, a combination of a liquid epoxy resin and a solid epoxy
resin is used, or more preferably, a combination of a liquid
aromatic epoxy resin and a solid aromatic epoxy resin is used.
Examples of such a combination include, to be more specific, a
combination of a liquid bisphenol epoxy resin and a solid
triphenylmethane epoxy resin, and a combination of a liquid
bisphenol epoxy resin and a solid bisphenol epoxy resin.
[0043] Preferably, a semi-solid epoxy resin is used alone, or more
preferably, a semi-solid aromatic epoxy resin is used alone.
Examples of those epoxy resins include, in particular, a semi-solid
fluorene epoxy resin.
[0044] A combination of a liquid epoxy resin and a solid epoxy
resin, or a semi-solid epoxy resin can improve conformability to
irregularities (described later) of the thermal conductive
sheet.
[0045] Furthermore, by combining a plurality of epoxy resins having
different properties and condition, the glass transition point can
be set to a desired range.
[0046] Furthermore, when two or more epoxy resins are used in
combination, for example, a first epoxy resin having a softening
temperature of, for example, below 45.degree. C., or preferably
35.degree. C. or less, and a second epoxy resin having a softening
temperature of, for example, 45.degree. C. or more, or preferably
55.degree. C. or more are used in combination. In this way, the
kinetic viscosity (in conformity with JIS K 7233, described later)
of the resin component (mixture) can be set to a desired range, and
also, conformability to irregularities of the thermal conductive
sheet can be improved.
[0047] The epoxy resin can also be prepared as an epoxy resin
composition containing, for example, an epoxy resin, a curing
agent, and a curing accelerator.
[0048] The curing agent is a latent curing agent (epoxy resin
curing agent) that can cure the epoxy resin by heating, and
examples thereof include an imidazole compound, an amine compound,
an acid anhydride compound, an amide compound, a hydrazide
compound, and an imidazoline compound. In addition to the
above-described compounds, a phenol compound, a urea compound, and
a polysulfide compound can also be used.
[0049] Examples of the imidazole compound include 2-phenyl
imidazole, 2-methyl imidazole, 2-ethyl-4-methyl imidazole, and
2-phenyl-4-methyl-5-hydroxymethyl imidazole.
[0050] Examples of the amine compound include aliphatic polyamines
such as ethylene diamine, propylene diamine, diethylene triamine,
and triethylene tetramine; and aromatic polyamines such as metha
phenylenediamine, diaminodiphenyl methane, and diaminodiphenyl
sulfone.
[0051] Examples of the acid anhydride compound include phthalic
anhydride, maleic anhydride, tetrahydrophthalic anhydride,
hexahydrophthalic anhydride, 4-methyl-hexahydrophthalic anhydride,
methyl nadic anhydride, pyromelletic anhydride, dodecenylsuccinic
anhydride, dichloro succinic anhydride, benzophenone
tetracarboxylic anhydride, and chlorendic anhydride.
[0052] Examples of the amide compound include dicyandiamide and
polyamide.
[0053] An example of the hydrazide compound includes adipic acid
dihydrazide.
[0054] Examples of the imidazoline compound include
methylimidazoline, 2-ethyl-4-methylimidazoline, ethylimidazoline,
isopropylimidazoline, 2,4-dimethylimidazoline, phenylimidazoline,
undecylimidazoline, heptadecylimidazoline, and
2-phenyl-4-methylimidazoline.
[0055] These curing agents can be used alone or in combination of
two or more.
[0056] A preferable example of the curing agent is an imidazole
compound.
[0057] Examples of the curing accelerator include tertiary amine
compounds such as triethylenediamine and
tri-2,4,6-dimethylaminomethylphenol; phosphorus compounds such as
triphenylphosphine, tetraphenylphosphonium tetraphenylborate, and
tetra-n-butylphosphonium-o,o-diethylphosphorodithioate; a
quaternary ammonium salt compound; an organic metal salt compound;
and derivatives thereof. These curing accelerators can be used
alone or in combination of two or more.
[0058] In the epoxy resin composition, the mixing ratio of the
curing agent is, for example, 0.5 to 50 parts by mass, or
preferably 1 to 10 parts by mass per 100 parts by mass of the epoxy
resin, and the mixing ratio of the curing accelerator is, for
example, 0.1 to 10 parts by mass, or preferably 0.2 to 5 parts by
mass per 100 parts by mass of the epoxy resin.
[0059] The above-described curing agent, and/or the curing
accelerator can be prepared and used, as necessary, as a solution,
i.e., the curing agent and/or the curing accelerator dissolved in a
solvent; and/or as a dispersion liquid, i.e., the curing agent
and/or the curing accelerator dispersed in a solvent.
[0060] Examples of the solvent include organic solvents including
ketones such as acetone and methyl ethyl ketone, ester such as
ethyl acetate, and amide such as N,N-dimethylformamide; and
water-based solvents including water, and alcohols such as
methanol, ethanol, propanol, and isopropanol. A preferable example
is an organic solvent, more preferable examples are ketones and
amides.
[0061] Of the thermoplastic resin components, preferably,
polyolefin is used.
[0062] Preferable examples of polyolefin are polyethylene and
ethylene-propylene copolymer.
[0063] Examples of polyethylene include a low density polyethylene
and a high density polyethylene.
[0064] Examples of ethylene-propylene copolymer include a random
copolymer, a block copolymer, or a graft copolymer of ethylene and
propylene.
[0065] These polyolefins can be used alone or in combination of two
or more.
[0066] The polyolefins have a weight average molecular weight
and/or a number average molecular weight of, for example, 1000 to
10000.
[0067] The polyolefin can be used alone, or can be used in
combination.
[0068] Of the resin components, preferably, a thermosetting resin
component is used, or more preferably, an epoxy resin is used.
[0069] The resin component has a kinetic viscosity as measured in
conformity with the kinetic viscosity test of JIS K 7233 (bubble
viscometer method) (temperature: 25.degree. C..+-.0.5.degree. C.,
solvent: butyl carbitol, resin component (solid content)
concentration: 40 mass %) of, for example, 0.22.times.10.sup.-4 to
2.00.times.10.sup.-4 m.sup.2/s, preferably 0.3.times.10.sup.-4 to
1.9.times.10.sup.-4 m.sup.2/s, or more preferably
0.4.times.10.sup.-4 to 1.8.times.10.sup.-4 m.sup.2/s. The
above-described kinetic viscosity can also be set to, for example,
0.22.times.10.sup.-4 to 1.00.times.10.sup.-4 m.sup.2/s, preferably
0.3.times.10.sup.-4 to 0.9.times.10.sup.-4 m.sup.2/s, or more
preferably 0.4.times.10.sup.-4 to 0.8.times.10.sup.-4
m.sup.2/s.
[0070] When the kinetic viscosity of the resin component exceeds
the above-described range, excellent flexibility and conformability
to irregularities (described later) may not be given to the thermal
conductive sheet. On the other hand, when the kinetic viscosity of
the resin component is below the above-described range, boron
nitride particles may not be oriented in a predetermined
direction.
[0071] In the kinetic viscosity test in conformity with JIS K 7233
(bubble viscometer method), the kinetic viscosity of the resin
component is measured by comparing the bubble rising speed of a
resin component sample with the bubble rising speed of criterion
samples (having a known kinetic viscosity), and determining the
kinetic viscosity of the criterion sample having a matching rising
speed to be the kinetic viscosity of the resin component.
[0072] In the thermal conductive sheet, the proportion of the
volume-based boron nitride particle content (solid content, that
is, the volume percentage of boron nitride particles relative to a
total volume of the resin component and the boron nitride
particles) is, for example, 35 vol % or more, preferably 60 vol %
or more, or more preferably 75 vol % or more, and usually, for
example, 95 vol % or less, or preferably 90 vol % or less.
[0073] When the proportion of the volume-based boron nitride
particle content is below the above-described range, the boron
nitride particles may not be oriented in a predetermined direction
in the thermal conductive sheet. On the other hand, when the
proportion of the volume-based boron nitride particle content
exceeds the above-described range, the thermal conductive sheet may
become fragile, and handleability and conformability to
irregularities may be reduced.
[0074] The mass-based mixing ratio of the boron nitride particles
relative to 100 parts by mass of the total amount (total solid
content) of the components (boron nitride particles and resin
component) forming the thermal conductive sheet is, for example, 40
to 95 parts by mass, or preferably 65 to 90 parts by mass, and the
mass-based mixing ratio of the resin component relative to 100
parts by mass of the total amount of the components forming the
thermal conductive sheet is, for example, 5 to 60 parts by mass, or
preferably 10 to 35 parts by mass. The mass-based mixing ratio of
the boron nitride particles relative to 100 parts by mass of the
resin component is, for example, 60 to 1900 parts by mass, or
preferably 185 to 900 parts by mass.
[0075] When two epoxy resins (a first epoxy resin and a second
epoxy resin) are used in combination, the mass ratio (mass of the
first epoxy resin/mass of the second epoxy resin) of the first
epoxy resin relative to the second epoxy resin can be set
appropriately in accordance with the softening temperature and the
like of the epoxy resins (the first epoxy resin and the second
epoxy resin). For example, the mass ratio of the first epoxy resin
relative to the second epoxy resin is 1/99 to 99/1, or preferably
10/90 to 90/10.
[0076] In the resin component, in addition to the above-described
components (polymer), for example, a polymer precursor (for
example, a low molecular weight polymer including oligomer), and/or
a monomer are contained.
[0077] FIG. 1 shows a perspective view of an embodiment of a
thermal conductive sheet of the present invention, and FIG. 2 shows
process drawings for describing a method for producing the thermal
conductive sheet shown in FIG. 1.
[0078] Next, a method for producing a thermal conductive sheet as
an embodiment of the present invention is described with reference
to FIG. 1 and FIG. 2.
[0079] In this method, first, the above-described components are
blended at the above-described mixing ratio and are stirred and
mixed, thereby preparing a mixture.
[0080] In the stirring and mixing, in order to mix the components
efficiently, for example, the solvent may be blended therein with
the above-described components, or, for example, the resin
component (preferably, the thermoplastic resin component) can be
melted by heating.
[0081] Examples of the solvent include the above-described organic
solvents. When the above-described curing agent and/or the curing
accelerator are prepared as a solvent solution and/or a solvent
dispersion liquid, the solvent of the solvent solution and/or the
solvent dispersion liquid can also serve as a mixing solvent for
the stirring and mixing without adding a solvent during the
stirring and mixing. Alternatively, in the stirring and mixing, a
solvent can be further added as a mixing solvent.
[0082] In the case when the stirring and mixing is performed using
a solvent, the solvent is removed after the stirring and
mixing.
[0083] To remove the solvent, for example, the mixture is allowed
to stand at room temperature for 1 to 48 hours; heated at 40 to
100.degree. C. for 0.5 to 3 hours; or heated under a reduced
pressure atmosphere of, for example, 0.001 to 50 kPa, at 20 to
60.degree. C., for 0.5 to 3 hours.
[0084] When the resin component (preferably, a thermoplastic resin
component) is to be melted by heating, the heating temperature is,
for example, a temperature in the neighborhood of or exceeding the
softening temperature of the resin component, to be specific, 40 to
150.degree. C., or preferably 70 to 140.degree. C.
[0085] Next, in this method, the obtained mixture is
hot-pressed.
[0086] To be specific, as shown in FIG. 2 (a), as necessary, for
example, the mixture is hot-pressed with two releasing films 4
sandwiching the mixture, thereby producing a pressed sheet 1A.
Conditions for the hot-pressing are as follows: a temperature of,
for example, 50 to 150.degree. C., or preferably 60 to 140.degree.
C.; a pressure of, for example, 1 to 100 MPa, or preferably 5 to 50
MPa; and a duration of, for example, 0.1 to 100 minutes, or
preferably 1 to 30 minutes.
[0087] More preferably, the mixture is hot-pressed under vacuum.
The degree of vacuum in the vacuum hot-pressing is, for example, 1
to 100 Pa, or preferably 5 to 50 Pa, and the temperature, the
pressure, and the duration are the same as those described above
for the hot-pressing.
[0088] When the temperature, the pressure, and/or the duration in
the hot-pressing is outside the above-described range, there is a
case where a porosity P (described later) of the thermal conductive
sheet 1 cannot be adjusted to a desired value.
[0089] The pressed sheet 1A obtained by the hot-pressing has a
thickness of, for example, 50 to 1000 .mu.m, or preferably 100 to
800 .mu.m.
[0090] Next, in this method, as shown in FIG. 2 (b), the pressed
sheet 1A is divided into a plurality of pieces (for example, four
pieces), thereby producing a divided sheet 1B (dividing step). In
the division of the pressed sheet 1A, the pressed sheet 1A is cut
along the thickness direction so that the pressed sheet 1A is
divided into a plurality of pieces when the pressed sheet 1A is
projected in the thickness direction. The pressed sheet 1A is cut
so that the respective divided sheets 1B have the same shape when
the divided sheets 1B are projected in the thickness direction.
[0091] Next, in this method, as shown in FIG. 2 (c), the respective
divided sheets 1B are laminated in the thickness direction, thereby
producing a laminated sheet 1C (laminating step).
[0092] Thereafter, in this method, as shown in FIG. 2 (a), the
laminated sheet 1C is hot-pressed (preferably hot-pressed under
vacuum) (hot-pressing step). The conditions for the hot-pressing
are the same as the conditions for the hot-pressing of the
above-described mixture.
[0093] The thickness of the hot-pressed laminated sheet 1C is, for
example, 1 mm or less, or preferably 0.8 mm or less, and usually
is, for example, 0.05 mm or more, or preferably 0.1 mm or more.
[0094] Thereafter, the series of the steps of the above-described
dividing step (FIG. 2 (b)), laminating step (FIG. 2 (c)), and
hot-pressing step (FIG. 2 (a)) are performed repeatedly, so as to
allow boron nitride particles 2 to be efficiently oriented in a
predetermined direction in the resin component 3 in the thermal
conductive sheet 1. The number of the repetition is not
particularly limited, and can be set appropriately according to the
charging state of the boron nitride particles. The number of the
repetition is, for example, 1 to 10 times, or preferably 2 to 7
times.
[0095] The thermal conductive sheet 1 can be obtained in this
manner.
[0096] The thickness of the obtained thermal conductive sheet 1 is,
for example, 1 mm or less, or preferably 0.8 mm or less, and
usually, for example, 0.05 mm or more, or preferably 0.1 mm or
more.
[0097] In the thermal conductive sheet 1, the proportion of the
volume-based boron nitride particle content (solid content, that
is, volume percentage of boron nitride particles relative to the
total volume of the resin component and the boron nitride
particles) is, as described above, for example, 35 vol % or more
(preferably 60 vol % or more, or more preferably 75 vol % or more),
and usually 95 vol % or less (preferably 90 vol % or less).
[0098] When the proportion of the boron nitride particle content is
below the above-described range, the boron nitride particles may
not be oriented in a predetermined direction in the thermal
conductive sheet.
[0099] When the resin component 3 is the thermosetting resin
component, for example, the series of the steps of the
above-described dividing step (FIG. 2 (b)), laminating step (FIG. 2
(c)), and hot-pressing step (FIG. 2 (a)) are performed repeatedly
for an uncured thermal conductive sheet 1, and then the uncured (or
semi-cured (in B-stage)) thermal conductive sheet 1 is cured by
heat after the hot-pressing step (FIG. 2 (a)), i.e., after the
final step, thereby producing a cured thermal conductive sheet
1.
[0100] To cure the thermal conductive sheet 1 by heat, the
above-described hot press or a dryer is used. Preferably, a dryer
is used. Conditions for the curing by heat are as follows: a
heating temperature of, for example, 60 to 250.degree. C., or
preferably 80 to 200.degree. C., and a pressure of, for example,
100 MPa or less, or preferably 50 MPa or less.
[0101] In the thus obtained thermal conductive sheet 1, as shown in
FIG. 1 and its partially enlarged schematic view, the longitudinal
direction LD of the boron nitride particle 2 is oriented along a
plane (surface) direction SD that crosses (is perpendicular to) the
thickness direction TD of the thermal conductive sheet 1.
[0102] The calculated average of the angle formed between the
longitudinal direction LD of the boron nitride particle 2 and the
plane direction SD of the thermal conductive sheet 1 (orientation
angle .alpha. of the boron nitride particles 2 relative to the
thermal conductive sheet 1) is, for example, 25 degrees or less, or
preferably 20 degrees or less, and usually 0 degree or more.
[0103] The orientation angle .alpha. of the boron nitride particle
2 relative to the thermal conductive sheet 1 is obtained as
follows: the thermal conductive sheet 1 is cut along the thickness
direction with a cross section polisher (CP); the cross section
thus appeared is photographed with a scanning electron microscope
(SEM) at a magnification that enables observation of 200 or more
boron nitride particles 2 in the field of view; a tilt angle
.alpha. between the longitudinal direction LD of the boron nitride
particle 2 and the plane direction SD (direction perpendicular to
the thickness direction TD) of the thermal conductive sheet 1 is
obtained from the obtained SEM photograph; and the average value of
the tilt angles .alpha. is calculated.
[0104] The thus obtained thermal conductivity in the plane
direction SD of the thermal conductive sheet 1 is 4 W/mK or more,
preferably 5 W/mK or more, more preferably 10 W/mK or more, even
more preferably 15 W/mK or more, or particularly preferably 25 W/mK
or more, and usually 200 W/mK or less.
[0105] The thermal conductivity in the plane direction SD of the
thermal conductive sheet 1 is substantially the same before and
after the curing by heat when the resin component 3 is the
thermosetting resin component.
[0106] When the thermal conductivity in the plane direction SD of
the thermal conductive sheet 1 is below the above-described range,
thermal conductivity in the plane direction SD is insufficient, and
therefore there is a case where the thermal conductive sheet 1
cannot be used for heat dissipation that requires thermal
conductivity in such a plane direction SD.
[0107] The thermal conductivity in the plane direction SD of the
thermal conductive sheet 1 is measured by a pulse heating method.
In the pulse heating method, the xenonflash analyzer "LFA-447"
(manufactured by Erich NETZSCH GmbH & Co. Holding KG) is
used.
[0108] The thermal conductivity in the thickness direction TD of
the thermal conductive sheet 1 is, for example, 0.5 to 15 W/mK, or
preferably 1 to 10 W/mK.
[0109] The thermal conductivity in the thickness direction TD of
the thermal conductive sheet 1 is measured by a pulse heating
method, a laser flash method, or a TWA method. In the pulse heating
method, the above-described device is used, in the laser flash
method, "TC-9000" (manufactured by Ulvac, Inc.) is used, and in the
TWA method, "ai-Phase mobile" (manufactured by ai-Phase Co., Ltd)
is used.
[0110] Thus, the ratio of the thermal conductivity in the plane
direction SD of the thermal conductive sheet 1 relative to the
thermal conductivity in the thickness direction TD of the thermal
conductive sheet 1 (thermal conductivity in the plane direction
SD/thermal conductivity in the thickness direction TD) is, for
example, 1.5 or more, preferably 3 or more, or more preferably 4 or
more, and usually 20 or less.
[0111] Although not shown in FIG. 1, for example, pores (gaps) are
formed in the thermal conductive sheet 1.
[0112] The proportion of the pores in the thermal conductive sheet
1, that is, a porosity P, can be adjusted by setting the proportion
of the boron nitride particle 2 content (volume-based), and further
setting the temperature, the pressure, and/or the duration at the
time of hot pressing the mixture of the boron nitride particle 2
and the resin component 3 (FIG. 2 (a)). To be specific, the
porosity P can be adjusted by setting the temperature, the
pressure, and/or the duration of the hot pressing (FIG. 2 (a))
within the above-described range.
[0113] The porosity P of the thermal conductive sheet 1 is, for
example, 30 vol % or less, or preferably 10 vol % or less.
[0114] The porosity P is measured by, for example, as follows: the
thermal conductive sheet 1 is cut along the thickness direction
with a cross section polisher (CP); the cross section thus appeared
is observed with a scanning electron microscope (SEM) at a
magnification of 200 to obtain an image; the obtained image is
binarized based on the pore portion and the non-pore portion; and
the area ratio, i.e., the ratio of the pore portion area to the
total area of the cross section of the thermal conductive sheet 1
is determined by calculation.
[0115] The thermal conductive sheet 1 has a porosity P2 after
curing of, relative to a porosity P1 before curing, for example,
100% or less, or preferably 50% or less.
[0116] For the measurement of the porosity P(P1), when the resin
component 3 is a thermosetting resin component, the thermal
conductive sheet 1 before being cured by heat is used.
[0117] When the porosity P of the thermal conductive sheet 1 is
within the above-described range, the conformability to
irregularities (described later) of the thermal conductive sheet 1
can be improved.
[0118] The glass transition point of the thermal conductive sheet 1
is 125.degree. C. or more, preferably 130.degree. C. or more, more
preferably 140.degree. C. or more, more preferably 150.degree. C.
or more, more preferably 170.degree. C. or more, more preferably
190.degree. C. or more, or more preferably 210.degree. C. or more,
and usually 300.degree. C. or less.
[0119] When the glass transition point is the above-described lower
limit or more, a thermal conductive sheet with excellent heat
resistance can be ensured, and therefore deformation under high
temperature can be reduced, and peeling off can be suppressed.
[0120] That is, when the thermal conductive sheet 1 is bonded to a
device of various types and the temperature of the device rises to
exceed the glass transition point of the thermal conductive sheet
1, the thermal conductive sheet 1 may be peeled off from the device
depending on the changes in the linear expansion coefficient.
However, because the glass transition point of this thermal
conductive sheet 1 is equal to or more than the above-described
upper limit, even if the device temperature rises, the temperature
can be prevented from exceeding the glass transition point of the
thermal conductive sheet 1, and as a result, deformation of the
thermal conductive sheet 1 can be reduced, and the peeling off can
be suppressed.
[0121] The glass transition point is obtained by measuring a
dynamic viscoelasticity at a frequency of 10 Hz, and determining
the peak value of tan.delta. (loss tangent).
[0122] When the thermal conductive sheet 1 is evaluated in the bend
test in conformity with the cylindrical mandrel method of JIS K
5600-5-1 under the test conditions shown below, preferably, no
fracture is observed.
Test Conditions:
[0123] Test Device: Type I
[0124] Mandrel: diameter 10 mm
[0125] Bending Angle: 90 degrees or more
[0126] Thickness of the thermal conductive sheet 1: 0.3 mm
[0127] FIGS. 3 and 4 show perspective views of the Type I test
device. In the following, the Type I test device is described.
[0128] In FIGS. 3 and 4, a Type I test device 10 includes a first
flat plate 11; a second flat plate 12 disposed in parallel with the
first flat plate 11; and a mandrel (rotation axis) 13 provided for
allowing the first flat plate 11 and the second flat plate 12 to
rotate relatively.
[0129] The first flat plate 11 is formed into a generally
rectangular flat plate. A stopper 14 is provided at one end portion
(free end portion) of the first flat plate 11. The stopper 14 is
formed on the surface of the second flat plate 12 so as to extend
along the one end portion of the second flat plate 12.
[0130] The second flat plate 12 is formed into a generally
rectangular flat plate, and one side thereof is disposed so as to
be adjacent to one side (the other end portion (proximal end
portion) that is opposite to the one end portion where the stopper
14 is provided) of the first flat plate 11.
[0131] The mandrel 13 is formed so as to extend along one side of
the first flat plate 11 and one side of the second flat plate 12
that are adjacent to each other.
[0132] In the Type I test device 10, as shown in FIG. 3, the
surface of the first flat plate 11 is flush with the surface of the
second flat plate 12 before the start of the bend test.
[0133] To perform the bend test, the thermal conductive sheet 1 is
placed on the surface of the first flat plate 11 and the surface of
the second flat plate 12. The thermal conductive sheet 1 is placed
so that one side of the thermal conductive sheet 1 is in contact
with the stopper 14.
[0134] Then, as shown in FIG. 4, the first flat plate 11 and the
second flat plate 12 are rotated relatively. In particular, the
free end portion of the first flat plate 11 and the free end
portion of the second flat plate 12 are rotated to a predetermined
angle with the mandrel 13 as the center. To be specific, the first
flat plate 11 and the second flat plate 12 are rotated so as to
bring the surface of the free end portions thereof closer (oppose
each other).
[0135] In this way, the thermal conductive sheet 1 is bent with the
mandrel 13 as the center, conforming to the rotation of the first
flat plate 11 and the second flat plate 12.
[0136] More preferably, no fracture is observed in the thermal
conductive sheet 1 even when the bending angle is set to 180
degrees under the above-described test conditions.
[0137] When the resin component 3 is the thermosetting resin
component, a semi-cured (in B-stage) thermal conductive sheet 1
(that is, the thermal conductive sheet 1 before being cured by
heat) is tested in the bend test.
[0138] When the fracture is observed in the bend test at the above
bending angle in the thermal conductive sheet 1, there is a case
where excellent flexibility cannot be given to the thermal
conductive sheet 1.
[0139] Furthermore, for example, when the thermal conductive sheet
1 is evaluated in the 3-point bending test in conformity with JIS K
7171 (2008) under the test conditions shown below, no fracture is
observed.
Test Conditions:
[0140] Test piece: size 20 mm.times.15 mm
[0141] Distance between supporting points: 5 mm
[0142] Testing speed: 20 mm/min (indenter depressing speed)
[0143] Bending angle: 120 degrees
[0144] Evaluation method: Presence or absence of fracture such as
cracks at the center of the test piece is observed visually when
tested under the above-described test conditions.
[0145] In the 3-point bending test, when the resin component 3 is a
thermosetting resin component, the thermal conductive sheet 1
before being cured by heat is used.
[0146] Thus, the thermal conductive sheet 1 is excellent in
conformability to irregularities because no fracture is observed in
the above-described 3-point bending test. The conformability to
irregularities is, when the thermal conductive sheet 1 is provided
on an object with irregularities, a property of the thermal
conductive sheet 1 that conforms to be in close contact with the
irregularities.
[0147] A mark such as, for example, letters and symbols can be
given to the thermal conductive sheet 1. That is, the thermal
conductive sheet 1 is excellent in mark adhesion. The mark adhesion
is a property of the thermal conductive sheet 1 that allows
reliable adhesion of the above-described mark thereon.
[0148] The mark can be adhered (applied, fixed, or firmly fixed) to
the thermal conductive sheet 1, to be specific, by printing,
engraving, or the like.
[0149] Examples of printing include, for example, inkjet printing,
relief printing, intaglio printing, and laser printing.
[0150] When the mark is to be printed by inkjet printing, relief
printing, or intaglio printing, for example, an ink fixing layer
for improving mark's fixed state can be provided on the surface
(printing side) of the thermal conductive sheet 1.
[0151] When the mark is to be printed by laser printing, for
example, a toner fixing layer for improving mark's fixed state can
be provided on the surface (printing side) of the thermal
conductive sheet 1.
[0152] Examples of engraving include laser engraving and
punching.
[0153] The thermal conductive sheet 1 is excellent in thermal
conductivity in the plane direction that is perpendicular to the
thickness direction, and also excellent in heat resistance.
[0154] Thus, as a thermal conductive sheet that allows decrease in
deformation under high temperature, that suppresses peeling off,
that is excellent in handleability, and that has excellent thermal
conductivity in the plane direction, the thermal conductive sheet
can be used for various heat dissipation applications, to be
specific, as a thermal conductive sheet applied in power
electronics technology, to be more specific, as a thermal
conductive sheet used, for example, as an LED heat dissipation
substrate, or as a heat dissipation material for batteries.
[0155] In the above-described hot-pressing step (FIG. 2 (a)), for
example, a plurality of calendering rolls and the like can also be
used for rolling the mixture and the laminated sheet 1C.
[0156] When the resin component 3 is the thermosetting resin
component, without curing by heat as described above, the thermal
conductive sheet of the present invention can also be obtained as
the uncured thermal conductive sheet 1.
[0157] That is, with the thermal conductive sheet of the present
invention, when the resin component is the thermosetting resin
component, there is no particular limitation as to whether or not
curing by heat is carried out or when curing by heat is carried
out. For example, the curing by heat can be performed after the
laminating step (FIG. 2 (c)) as described above, or can be
performed after the elapse of a predetermined period from the
above-described hot-pressing step (FIG. 2 (a), hot-pressing of the
mixture but the hot-pressing does not allow curing by heat). To be
specific, the curing by heat can be performed at the time when the
sheet is applied in power electronics technology, or after the
elapse of a predetermined period after such application.
EXAMPLES
[0158] Hereinafter, the present invention is described in further
detail with reference to Examples. However, the present invention
is not limited to Examples.
Example 1
[0159] The components described below were blended, stirred, and
allowed to stand at room temperature (23.degree. C.) for one night,
thereby allowing methyl ethyl ketone (dispersion medium for the
curing agent) to volatilize, and preparing a semi-solid mixture.
The details of the components are as follows: 13.42 g of PT-110
(trade name, plate-like boron nitride particles, average particle
size (light scattering method) 45 .mu.m, manufactured by Momentive
Performance Materials Inc.), 1.0 g of jER.RTM.828 (trade name,
bisphenol A epoxy resin, liquid, epoxy equivalent 184 to 194
g/eqiv., softening temperature (ring and ball method) below
25.degree. C., melt viscosity (80.degree. C.) 70 mPas, manufactured
by Japan Epoxy Resins Co., Ltd.), 2.0 g of EPPN-501HY (trade name,
triphenylmethane epoxy resin, solid, epoxy equivalent 163 to 175
g/eqiv., softening temperature (ring and ball method) 57 to
63.degree. C., manufactured by NIPPON KAYAKU Co., Ltd), and 3.0 g
(solid content 0.15 g) (5 mass % per total amount of epoxy resins
of jER.RTM.828 and EPPN-501HY) of a curing agent (a solution of 5
mass % Curezol.RTM. 2PZ (trade name, manufactured by Shikoku
Chemicals Corporation.) in methyl ethyl ketone).
[0160] In the above-described blending, the volume percentage (vol
%) of the boron nitride particles relative to the total volume of
the solid content excluding the curing agent (that is, solid
content of the boron nitride particle and epoxy resin) was 70 vol
%.
[0161] Then, the obtained mixture was sandwiched by two
silicone-treated releasing films, and then these were hot-pressed
with a vacuum hot-press at 80.degree. C. under an atmosphere
(vacuum atmosphere) of 10 Pa with a load of 5 tons (20 MPa) for 2
minutes. A pressed sheet having a thickness of 0.3 mm was thus
obtained (ref: FIG. 2 (a)).
[0162] Thereafter, the obtained pressed sheet was cut so as to be
divided into a plurality of pieces when projected in the thickness
direction of the pressed sheet. Divided sheets were thus obtained
(ref: FIG. 2 (b)). Next, the divided sheets were laminated in the
thickness direction. A laminated sheet was thus obtained (ref: FIG.
2 (c)).
[0163] Then, the obtained laminated sheet was hot-pressed under the
same conditions as described above with the above-described vacuum
hot-press (ref: FIG. 2 (a)).
[0164] Then, a series of the above-described operations of cutting,
laminating, and hot-pressing (ref: FIG. 2) was repeated four times.
A thermal conductive sheet (in B-stage) having a thickness of 0.3
mm was thus obtained.
[0165] Thereafter, the obtained thermal conductive sheet was
introduced into a dryer, and heated at 150.degree. C. for 120
minutes so as to be cured by heat.
Examples 2 to 14
[0166] Thermal conductive sheets were obtained in the same manner
as in Example 1 in accordance with the mixing formulation and
production conditions of Tables 1 to 3.
(Evaluation)
1. Thermal Conductivity
[0167] The thermal conductivity of the thermal conductive sheets
obtained in Examples 1 to 14 was measured.
[0168] That is, the thermal conductivity in the plane direction
(SD) was measured by a pulse heating method using a xenon flash
analyzer "LFA-447" (manufactured by Erich NETZSCH GmbH & Co.
Holding KG).
[0169] The results are shown in Tables 1 to 3.
2. Glass Transition Point
[0170] The glass transition point of the thermal conductive sheets
obtained in Examples 1 to 14 was measured.
[0171] That is, the thermal conductive sheet was measured with a
temperature rising speed of 1.degree. C./min and a frequency of 10
Hz using a dynamic viscoelasticity measuring apparatus (model
number: DMS 6100, manufactured by Seiko Instruments Inc.).
[0172] The glass transition point was determined by the obtained
data, i.e., the peak value of tan.delta..
[0173] The results are shown in Tables 1 to 3.
3. Porosity (P)
[0174] The porosity (P1) of the thermal conductive sheets before
being cured by heat in Examples 1 to 14 was measured by the
following measurement method.
[0175] Measurement method of porosity: The thermal conductive sheet
was cut along the thickness direction with a cross section polisher
(CP); and the cross section thus appeared was observed with a
scanning electron microscope (SEM) at a magnification of 200. The
obtained image was binarized based on the pore portion and the
non-pore portion; and the area ratio, i.e., the ratio of the pore
portion area to the total area of the cross section of the thermal
conductive sheet was calculated.
[0176] The results are shown in Tables 1 to 3.
4. Conformability to Irregularities (3-Point Bending Test)
[0177] The 3-point bending test in conformity with JIS K 7171
(2010) was carried out for the thermal conductive sheets before
being cured by heat of Examples 1 to 14 with the following test
conditions, thus evaluating conformability to irregularities with
the following evaluation criteria. The results are shown in Tables
1 to 3.
Test Conditions:
[0178] Test Piece: size 20 mm.times.15 mm
[0179] Distance Between Supporting Points: 5 mm
[0180] Testing Speed: 20 mm/min (indenter depressing speed)
[0181] Bending Angle: 120 degrees
(Evaluation Criteria)
[0182] Excellent: No fracture was observed.
[0183] Good: Almost no fracture was observed.
[0184] Bad: Fracture was clearly observed.
5. Printed Mark Visibility (Mark Adhesion by Printing: Mark
Adhesion by Inkjet Printing or Laser Printing)
[0185] Marks were printed on the thermal conductive sheets of
Examples 1 to 14 by inkjet printing and laser printing, and the
marks were observed.
[0186] As a result, it was confirmed that the marks were
excellently visible in both cases of inkjet printing and laser
printing, and that mark adhesion by printing was excellent in any
of the thermal conductive sheets of Examples 1 to 14.
TABLE-US-00001 TABLE 1 Average Particle Size Example (.mu.m) Ex. 1
Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Mixing Boron Nitride PT-110*.sup.1 45
13.42 3.83 5.75 12.22 23 -- Formulation Particle/g*.sup.A/ [70]
[40] [50] [68] [80] of [vol %]*.sup.B/ [69] [38.8] [48.8] [66.9]
[79.2] Components [vol %]*.sup.C UHP-1*.sup.2 9 -- -- -- -- --
12.22 [68] [66.9] Polymer Thermosetting Epoxy Resin Epoxy Resin
A*.sup.3 -- 3 3 3 3 3 Resin Composition (Semi-solid) Epoxy Resin
B*.sup.4 1 -- -- -- -- -- (Liquid) Epoxy Resin C*.sup.5 -- -- -- --
-- -- (Solid) Epoxy Resin ID*.sup.6 2 -- -- -- -- -- (Solid) Curing
Agent*.sup.7 -- 3 3 3 3 3 (Solid Content in (0.15) (0.15) (0.15)
(0.15) (0.15) Grams) Curing Agent*.sup.8 3 -- -- -- -- -- (Solid
Content (0.15) in Grams) Production Hot-pressing Temperature
(.degree. C.) 80 80 80 80 80 80 Conditions Number of Time
(times)*.sup.D 5 5 5 5 5 5 Load (MPa)/(tons) 20/5 20/5 20/5 20/5
20/5 20/5 Evaluation Thermal Thermal Conductivity Plane Direction
30 4.5 6.0 30.0 32.5 17.0 Conductive (W/m K) (SD) Sheet Thickness
Direction 2.0 1.3 3.3 5.0 5.5 5.8 (TD) Ratio 15.0 3.5 1.8 6.0 5.9
2.9 (SD/TD) Glass Transition Point (.degree. C.) 216 139 140 139
138 140 Porosity (vol %) 4 0 0 5 12 6 Conformability to
Irregularities/3-point bending test Good Good Good Good Good Good
JIS K 7171 (2008) Boron Nitride Orientation Angle
(.alpha.)(degrees) 18 18 18 15 13 20 Particle g*.sup.A: Blended
Weight [vol %]*.sup.B: Percentage relative to the total volume of
the thermal conductive sheet (excluding curing agent) [vol
%]*.sup.C: Percentage relative to the total volume of the thermal
conductive sheet Number of Time*.sup.D: Number of times of
hot-pressing of laminated sheet
TABLE-US-00002 TABLE 2 Average Particle Size Example (.mu.m) Ex. 7
Ex. 8 Ex. 9 Mixing Boron Nitride PT-110*.sup.1 45 12.22 12.22 13.42
Formulation Particle/g*.sup.A/ [68] [68] [70] of [vol %]*.sup.B/
[66.9] [66.9] [69] Components [vol %]*.sup.C UHP-1*.sup.2 9 -- --
-- Polymer Thermosetting Epoxy Resin Epoxy Resin A*.sup.3 -- -- --
Resin Composition (Semi-solid) Epoxy Resin B*.sup.4 1.5 3 --
(Liquid) Epoxy Resin C*.sup.5 1.5 -- -- (Solid) Epoxy Resin
D*.sup.6 -- -- 3 (Solid) Curing Agent*.sup.7 3 3 3 (Solid Content
in (0.15) (0.15) (0.15) Grams) Curing Agent*.sup.8 -- -- -- (Solid
Content in Grams) Production Hot-pressing Temperature (.degree. C.)
80 80 80 Conditions Number of Time (times)*.sup.D 5 5 5 Load
(MPa)/(tons) 20/5 20/5 20/5 Evaluation Thermal Thermal Conductivity
Plane Direction (SD) 30.0 30.0 24.5 Conductive (W/m K) Thickness
Direction 5.0 5.0 2.1 Sheet (TD) Ratio 6.0 6.0 11.7 (SD/TD) Glass
Transition Point (.degree. C.) 130 168 217 Porosity (vol %) 4 2 10
Conformability to Irregularities/3-point bending test Good Good Bad
JIS K 7171 (2008) Boron Nitride Orientation Angle
(.alpha.)(degrees) 15 16 16 Particle g*.sup.A: Blended Weight [vol
%]*.sup.B: Percentage relative to the total volume of the thermal
conductive sheet (excluding curing agent) [vo l%]*.sup.C:
Percentage relative to the total volume of the thermal conductive
sheet Number of Time*.sup.D: Number of times of hot-pressing of
laminated sheet
TABLE-US-00003 TABLE 3 Average Particle Size Example (.mu.m) Ex. 10
Ex. 11 Ex. 12 Ex. 13 Ex. 14 Mixing Boron Nitride PT-110*.sup.1 45
3.83 13.42 13.42 13.42 13.42 Formulation Particle/g*.sup.A/ [40]
[70] [70] [70] [70] of [vol %]*.sup.B/ [37.7] [69] [69] [69] [69]
Components [vol %]*.sup.C UHP-1*.sup.2 9 -- -- -- -- -- Polymer
Thermosetting Epoxy Resin Epoxy Resin A*.sup.3 3 3 3 3 3 Resin
Composition (Semi-solid) Epoxy Resin B*.sup.4 -- -- -- -- --
(Liquid) Epoxy Resin C*.sup.5 -- -- -- -- -- (Solid) Epoxy Resin
D*.sup.6 -- -- -- -- -- (Solid) Curing Agent*.sup.7 6 3 3 3 3
(Solid Content in (0.3) (0.15) (0.15) (0.15) (0.15) Grams) Curing
Agent*.sup.8 -- -- -- -- -- (Solid Content in Grams) Production
Hot-pressing Temperature (.degree. C.) 80 60 70 80 80 Conditions
Number of Time (times)*.sup.D 5 5 5 5 5 Load (MPa)/(tons) 20/5 20/5
20/5 20/5 40/10 Evaluation Thermal Thermal Conductivity Plane
Direction (SD) 4.1 10.5 11.2 32.5 50.7 Conductive (W/m K) Thickness
Direction 1.1 2.2 3.0 5.5 7.3 Sheet (TD) Ratio 3.7 4.8 3.7 5.9 6.9
(SD/TD) Glass Transition Point (.degree. C.) 145 138 138 139 139
Porosity (vol %) 0 29 26 8 3 Conformability to
Irregularities/3-point bending test Excellent Excellent Excellent
Excellent Good JIS K 7171 (2008) Boron Nitride Orientation Angle
(.alpha.)(degrees) 20 17 15 15 13 Particle g*.sup.A: Blended Weight
[vol %]*.sup.B: Percentage relative to the total volume of the
thermal conductive sheet (excluding curing agent) [vol %]*.sup.C:
Percentage relative to the total volume of the thermal conductive
sheet Number of Time*.sup.D: Number of times of hot-pressing of
laminated sheet
[0187] In Tables 1 to 3, values for the components are in grams
unless otherwise specified.
[0188] In the rows of "boron nitride particles" in Tables 1 to 3,
values on the top represent the Blended Weight (g) of the boron
nitride particles; values in the middle represent the volume
percentage (vol %) of the boron nitride particles relative to the
total volume of the solid content excluding the curing agent in the
thermal conductive sheet (that is, solid content of the boron
nitride particles and epoxy resin); and values at the bottom
represent the volume percentage (vol %) of the boron nitride
particles relative to the total volume of the solid content in the
thermal conductive sheet (that is, solid content of boron nitride
particles, epoxy resin, and curing agent).
[0189] For the components with "*" added in Tables 1 to 3, details
are given below.
PT-110*.sup.1: trade name, plate-like boron nitride particles,
average particle size (light scattering method) 45 .mu.m,
manufactured by Momentive Performance Materials Inc. UHP-1*.sup.2:
trade name: SHOBN.RTM.UHP-1, plate-like boron nitride particles,
average particle size (light scattering method) 9 .mu.m,
manufactured by Showa Denko K. K. Epoxy Resin A*.sup.3: OGSOL EG
(trade name), bisarylfluorene epoxy resin, semi-solid, epoxy
equivalent 294 g/eqiv., softening temperature (ring and ball test)
47.degree. C., melt viscosity (80.degree. C.)1360 mPas,
manufactured by Osaka Gas Chemicals Co., Ltd. Epoxy Resin B*.sup.4:
jER.RTM. 828 (trade name), bisphenol A epoxy resin, liquid, epoxy
equivalent 184 to 194 g/eqiv., softening temperature (ring and ball
test) below 25.degree. C., melt viscosity (80.degree. C.) 70 mPas,
manufactured by Japan Epoxy Resins Co., Ltd. Epoxy Resin C*.sup.5:
jER.RTM. 1002 (trade name), bisphenol A epoxy resin, solid, epoxy
equivalent 600 to 700 g/eqiv., softening temperature (ring and ball
test) 78.degree. C., melt viscosity (80.degree. C.) 10000 mPas or
more (measurement limit or more), manufactured by Japan Epoxy
Resins Co., Ltd. Epoxy Resin D*.sup.6: EPPN-501HY (trade name),
triphenylmethane epoxy resin, solid, epoxy equivalent 163 to 175
g/eqiv., softening temperature (ring and ball test) 57 to
63.degree. C., manufactured by NIPPON KAYAKU Co., Ltd. Curing
Agent*.sup.7: a solution of 5 mass % Curezol.RTM. 2PZ (trade name,
manufactured by Shikoku Chemicals Corporation) in methyl ethyl
ketone. Curing Agent*.sup.8: a dispersion liquid of 5 mass %
Curezol.RTM. 2P4 MHZ-PW (trade name, manufactured by Shikoku
Chemicals Corporation) in methyl ethyl ketone.
[0190] While the illustrative embodiments of the present invention
are provided in the above description, such is for illustrative
purpose only and it is not to be construed as limiting the scope of
the present invention. Modification and variation of the present
invention that will be obvious to those skilled in the art is to be
covered by the following claims.
* * * * *