U.S. patent application number 13/886477 was filed with the patent office on 2013-11-14 for insulated thermal interface material.
This patent application is currently assigned to NATIONAL TSING HUA UNIVERSITY. The applicant listed for this patent is NATIONAL TSING HUA UNIVERSITY. Invention is credited to YONG-CHIEN LING, JEN-YU LIU, CHIH-PING WANG.
Application Number | 20130299140 13/886477 |
Document ID | / |
Family ID | 49547730 |
Filed Date | 2013-11-14 |
United States Patent
Application |
20130299140 |
Kind Code |
A1 |
LING; YONG-CHIEN ; et
al. |
November 14, 2013 |
Insulated thermal interface material
Abstract
The present invention discloses an insulated thermal interface
material for applying between an electronic element and a thermal
dissipating element. The insulated thermal interface material at
least comprises a base, a first filler and a second filler. The
base is a polymer and the first filler is graphene. The first
filler and the second filler are dispersed in the base.
Inventors: |
LING; YONG-CHIEN; (HSINCHU,
TW) ; WANG; CHIH-PING; (TAIPEI, TW) ; LIU;
JEN-YU; (HSINCHU, TW) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NATIONAL TSING HUA UNIVERSITY |
Hsinchu |
|
TW |
|
|
Assignee: |
NATIONAL TSING HUA
UNIVERSITY
Hsinchu
TW
|
Family ID: |
49547730 |
Appl. No.: |
13/886477 |
Filed: |
May 3, 2013 |
Current U.S.
Class: |
165/135 |
Current CPC
Class: |
H01L 23/3737 20130101;
C08K 3/042 20170501; H01L 2924/0002 20130101; C08K 2201/011
20130101; C09K 5/14 20130101; C08K 3/04 20130101; C08K 5/14
20130101; C08K 3/36 20130101; F28F 3/00 20130101; C08K 5/34922
20130101; C08G 77/20 20130101; H01L 2924/0002 20130101; H01L
2924/00 20130101; C08K 3/04 20130101; C08L 83/04 20130101; C08K
5/34922 20130101; C08L 83/04 20130101; C08K 3/36 20130101; C08L
83/04 20130101; C08K 5/14 20130101; C08L 83/04 20130101; C08K 3/042
20170501; C08L 83/04 20130101; C08K 3/042 20170501; C08L 63/00
20130101 |
Class at
Publication: |
165/135 |
International
Class: |
F28F 3/00 20060101
F28F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 10, 2012 |
TW |
101116708 |
Claims
1. An insulated thermal interface material for applying between an
electronic element and a thermal dissipating element, the insulated
thermal interface material at least comprising: a base composing of
a polymer; and a first filler and a second filler dispersing in the
base, wherein the first filler includes a graphene.
2. The insulated thermal interface material according to claim 1,
wherein the first filler includes the graphene with a
length-to-thickness ratio or a width-to-thickness ratio of
50.about.10000 and selected from a group consisting of a graphene,
a graphene doped with nitrogen, a graphene doped with oxygen, a
graphene doped with both nitrogen and oxygen, multilayer graphene
stacking via van der Waals interaction, multilayer graphene doped
with nitrogen and stacking via van der Waals interaction,
multilayer graphene doped with oxygen stacking via van der Waals
interaction and multilayer graphene doped with both nitrogen and
oxygen stacking via van der Waals interaction.
3. The insulated thermal interface material according to claim 1,
wherein the second filler is a thermal conductive inorganic powder
and selected from a group consisting of aluminum oxide, magnesium
oxide, aluminum nitride, boron nitride, silicon carbide, tin oxide,
silicon nitride, aluminum oxide whisker, aluminum nitride whisker,
silicon carbide whisker, magnesium oxide whisker and silicon
nitride whisker.
4. The insulated thermal interface material according to claim 1,
wherein the base is a silicone rubber and at least contains an
organic polysiloxane compound, a curing agent and an adhesion
promoter, the weight percentage of the organic polysiloxane
compound, the curing agent, the adhesion promoter, the first filler
and the second filler are 91-99.55%, 0.1-5%, 0.1-3%, 0.0025-0.005%
and 0.25-0.5%, respectively.
5. The insulated thermal interface material according to claim 4,
wherein the second filler has an average granularity of 20.about.50
.mu.m.
6. The insulated thermal interface material according to claim 4,
wherein the organic polysiloxane compound has a degree of
polymerization of 200.about.12000 and is represented by the
following formula: R.sup.1.sub.aSiO.sub.(4-a)/2 Wherein R.sup.1 is
a single-valence C.sub.1.about.C.sub.10 hydrocarbon group and
selected from a group consisting of an alkyl group, a cycloalkyl
group, an aryl group, an aralkyl group, an alkyl group substituted
by halogen and an alkenyl group, and "a" further represents a
positive number of 1.9-2.05.
7. The insulated thermal interface material according to claim 4,
wherein the curing agent is an organic peroxide or a curing agent
applying in an alkylation reaction of silane.
8. The insulated thermal interface material according to claim 4,
wherein the adhesion promoter at least comprises a silicon compound
with a plurality of substitutes and the substitutes could be
selected from a group consisting of a cyclalkyl group, an alkoxyl
group, a methyl group, a vinyl group and a silane group.
9. The insulated thermal interface material according to claim 1,
wherein the base is a curing epoxy resin and selected from a group
consisting of a linear polyepoxide with epoxide as an end group, a
polyepoxide with epoxide at backbond and a polyepoxide with epoxide
as side chain.
10. The insulated thermal interface material according to claim 9
further comprising a particulate thermoplastic polymer, wherein the
weight percentage of the base, the particulate thermoplastic
polymer, the first filler and the second filler are 90.about.97%,
1.about.2%, 0.001.about.0.005% and 0.1.about.1%, respectively.
11. The insulated thermal interface material according to claim 10,
wherein the particulate thermoplastic polymer comprises a polymer
with a glass transition temperature of at least 60.degree. C.
12. The insulated thermal interface material according to claim 10,
wherein the particulate thermoplastic polymer comprises has an
average molecular weight higher than 7000.
13. The insulated thermal interface material according to claim 10,
wherein the particulate thermoplastic polymer is selected from a
group consisting of a poly(methyl methacrylate) and a methyl
methacrylate/methacrylic acid copolymer.
14. The insulated thermal interface material according to claim 10,
wherein the particulate thermoplastic polymer has an average
granularity of 0.25.about.250 .mu.m.
15. The insulated thermal interface material according to claim 9
further comprising a curing agent, and the curing agent contains a
dicyandiamide and its derivatives or a metal imidazole compound
represented by the following formula: ML.sub.m wherein M is a metal
and selected from a group consisting of Ag (I), Cu (I), Cu (II), Cd
(II), Zn (II), Hg (II), Ni (II) and Co (II), and L is a compound
represented by the following formula: ##STR00006## wherein R.sup.1,
R.sup.2and R.sup.3 could be selected from a group consisting of
hydrogen atom, alkyl group and aryl group, and m is the valence of
metal.
16. The insulated thermal interface material according to claim 1,
wherein the thermal conductivity of the insulated thermal interface
material is higher than 3 W/mK.
17. The insulated thermal interface material according to claim 1
further comprising an additive, and the additive could be selected
from a group consisting of coupling agent, lubricant, flow
controlling agent, thickener, accelerant, chain-extenders,
flexibilizer, dispersant and co-curing agent.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This Non-provisional application claims priority under 35
U.S.C. .sctn.119(a) on Patent Application No(s). [101116708] filed
in Taiwan, Republic of China [May 10, 2012], the entire contents of
which are hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] This invention relates to an insulated thermal interface
material, especially relates to an insulated thermal interface
material manufactured by dispersing graphene into a polymer to
enhance its conductivity and insulation.
BACKGROUND OF THE INVENTION
[0003] The electronic technique has been developed rapidly in
recent years. The high-frequency and high-speed of electronic
component, as well as the dense and microminiaturization of the
integrated circuit, results in an enormously increasing of the
heating value from unit volume of electronic component. It is an
urgent issue of cooling the electronic component to maintain the
performance of electronic parts. According to the abovementioned
problems, there is a need for a thermal dissipating element with
high thermal conductivity
[0004] Formerly, some solutions applied for improving the thermal
conductivity of the thermal dissipating element is to decrease the
thickness of the elements. However, it will cause problems because
of decreasing too much thickness, such as decreasing of the
strength, durability and/or electric insulating property of thermal
dissipating element. One of them is formation of the thermal
dissipating element into multilayer structure which composed of an
inner layer with great heat resistance and electric insulating
property, such as aromatic polyimide, polyamide, polyamideimide or
polyethylene naphthalate glycol, and an outer layer formed by
thermal interface material containing thermal conductive filler
with great heat and electric conductivity, such as silicon rubber.
However, the adhesion between outer and inner layers of those
multilayer insulating components are unstable, meaning the duration
of component is bad and peeling is inevitable as time goes by.
[0005] According to the abovementioned problems, another solution
is offered. That is, the thermal interface material, such as
silicon rubber, is used as an outer layer and the abovementioned
silicon rubber is obtained by curing an adhesion promoter which is
composed of silicon compounds. However, the thermal conductivity of
the inner layer formed by aromatic polyimides is obviously less
than that of the outer layer formed by silicon rubber, which
decreases the overall thermal conductivity of the complex.
[0006] Moreover, although the abovementioned thermal interface
material filled with conductive filler to increase the thermal
conductivity, such as silicon dioxide, aluminum oxide, aluminum,
silicon carbide, silicon nitride, magnesium oxide, magnesium
carbonate, zinc oxide and aluminum nitride which are often used as
thermal conductive filler in conductive subject of the thermal
interface material, there are disadvantages of the individual
thermal conductive filler listed as the following:
[0007] (1) High filling content is needed for silicon dioxide due
to low thermal conductivity. However, the hardness of conductive
subject of the thermal interface material is hard to be decreased
with high filling content, and molding could not be performed due
to excessive viscosity.
[0008] (2) Aluminum oxide and aluminum is amphoteric compound which
is easily affected by the inner impurities. When the conductive
subject of the thermal interface material is epoxy resin, it would
have bad influence on heat resistance and permanent deformation by
compression.
[0009] (3) Zinc oxide is usually precipitated and sedimented when
dispersing in the conductive subject of the thermal interface
material because it possesses high specific gravity of 5.7, and the
high hygroscopicity of zinc oxide powder is undesired.
[0010] (4) Silicon carbide also has high specific gravity. The
refining silicon carbide powder sold on the current market tends to
aggregate and sediment when dispersing in the conductive subject,
such as silicon rubber, of the thermal interface material. Silicon
carbide is hard to be re-dispersed and processed because it tends
to agglomerate.
[0011] (5) Silicon nitride and aluminum nitride is easily reacting
with water resulting in worst wet fastness.
[0012] (6) Magnesium oxide is optional high thermal conductive
filler, but it is similar to aluminum nitride which is easily
reacting with water resulting in worst wet fastness.
[0013] (7) Magnesium carbonate is not stable and tends to decompose
into magnesium oxide under high temperature.
SUMMARY OF THE INVENTION
[0014] According to the abovementioned disadvantages of the prior
art, such as the thermal conductive filler rises the cost of the
thermal interface material (eg. lots of thermal conductive filler
is needed), heat deterioration (eg. poor heat resistance), surface
seepage (eg. poor moisture tolerance) or some limitation between
the conductors (eg. epoxy resin) of the thermal interface material,
the present invention provides a thermal interface material filled
with graphene which could effectively conduct the heat generated by
an electronic element to the outside of the thermal dissipating
element, moreover, it possesses great electrical insulating
property which could be widely used in electric and electronic
area, for example, to be used as CPU and thermal dissipating
element of high-power transistor chip.
[0015] The present invention provides an insulated thermal
interface material for applying between an electronic element and a
thermal dissipating element. The abovementioned thermal dissipating
element at least comprises a base, a first filler and a second
filler. Wherein the base is a polymer, the first filler is a
graphene and the first filler and the second filler dispersed in
the base.
[0016] Preferably, the first filler is a graphene with a
length-to-thickness ratio or a width-to-thickness ratio of
50.about.10000 and selected from a group consisting of a graphene,
a graphene doped with nitrogen, a graphene doped with oxygen, a
graphene doped with both nitrogen and oxygen, multilayer graphene
stacking via van der Waals interaction, multilayer graphene doped
with nitrogen and stacking via van der Waals interaction,
multilayer graphene doped with oxygen stacking via van der Waals
interaction and multilayer graphene doped with both nitrogen and
oxygen stacking via van der Waals interaction.
[0017] Preferably, the second filler is a thermal conductive
inorganic powder and selected from a group consisting of aluminum
oxide, magnesium oxide, aluminum nitride, boron nitride, silicon
carbide, tin oxide, silicon nitride, aluminum oxide whisker,
aluminum nitride whisker, silicon carbide whisker, magnesium oxide
whisker and silicon nitride whisker.
[0018] Preferably, the base is a silicone rubber and at least
contains an organic polysiloxane compound, a curing agent and an
adhesion promoter, the weight percentage of the organic
polysiloxane compound, the curing agent, the adhesion promoter, the
first filler and the second filler are 91.about.99.55%,
0.1.about.5%, 0.1.about.3%, 0.0025.about.0.005% and
0.25.about.0.5%, respectively.
[0019] Preferably, the second filler has an average granularity of
20.about.50 .mu.m.
[0020] Preferably, the organic polysiloxane compound has a degree
of polymerization of 200.about.12000 and is represented by the
following formula:
R.sup.1.sub.aSiO.sub.(4-a)/2
Wherein R.sup.1 is a single-valence C.sub.1.about.C.sub.10
hydrocarbon group and selected from a group consisting of an alkyl
group, a cycloalkyl group, an aryl group, an aralkyl group, an
alkyl group substituted by halogen and an alkenyl group, and "a"
further represents a positive number of 1.9-2.05.
[0021] Preferably, the curing agent is an organic peroxide or a
curing agent applying in an alkylation reaction of silane.
[0022] Preferably, the adhesion promoter at least comprises a
silicon compound with a plurality of substitutes and the
substitutes could be selected from a group consisting of a
cycloalkyl group, an alkoxyl group, a methyl group, a vinyl group
and a silane group.
[0023] Preferably, the base is a curing epoxy resin and selected
from a group consisting of a linear polyepoxide with epoxide as an
end group, a polyepoxide with epoxide at backbond and a polyepoxide
with epoxide as side chain.
[0024] Preferably, the insulated thermal interface material further
comprising a particulate thermoplastic polymer, wherein the weight
percentage of the base, the particulate thermoplastic polymer, the
first filler and the second filler are 90.about.97%, 1.about.2%,
0.001.about.0.005% and 0.1.about.1%, respectively.
[0025] Preferably, the particulate thermoplastic polymer comprises
a polymer with a glass transition temperature of at least
60.degree. C.
[0026] Preferably, the particulate thermoplastic polymer comprises
has an average molecular weight higher than 7000.
[0027] Preferably, the particulate thermoplastic polymer is
selected from a group consisting of a poly(methyl methacrylate) and
a methyl methacrylate/methacrylic acid copolymer.
[0028] Preferably, the particulate thermoplastic polymer has an
average granularity of 0.25.about.250 .mu.m.
[0029] Preferably, the insulated thermal interface material further
comprising a curing agent, and the curing agent contains a
dicyandiamide and its derivatives or a metal imidazole compound
represented by the following formula:
ML.sub.m
wherein M is a metal and selected from a group consisting of Ag
(I), Cu (I), Cu (II), Cd (II), Zn (II), Hg (II), Ni (II) and Co
(II), and L is a compound represented by the following formula:
##STR00001##
wherein R.sup.1, R.sup.2and R.sup.3 could be selected from a group
consisting of hydrogen atom, alkyl group and aryl group, and m is
the valence of metal.
[0030] Preferably, the thermal conductivity of the insulated
thermal interface material is higher than 3 W/mK.
[0031] Preferably, the insulated thermal interface material further
comprising an additive, and the additive could be selected from a
group consisting of coupling agent, lubricant, flow controlling
agent, thickener, accelerant, chain-extenders, flexibilizer,
dispersant and co-curing agent.
[0032] The features and advantages of the present invention will be
understood and illustrated in the following specification and FIGS.
1A-2C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] FIG. 1A to FIG. 1C are diagrams showing the structure of an
insulated thermal interface material according to a first
embodiment of the present invention; and
[0034] FIG. 2A to FIG. 2C are diagrams showing the structure of an
insulated thermal interface material according to a second
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0035] Due to the difficulties suffered in the prior art, the
present invention provides an insulated thermal interface material
filled with graphene which could effectively conduct the heat
generated by an electronic element to the outside of a thermal
dissipating element by percentage collocated of the components,
moreover, it could further possesses great electrical insulating
property.
[0036] The present invention provides an insulated thermal
interface material which could be used between an electronic
element and a thermal dissipating element. Preferably, the
electronic element could be a power transistor, a metal oxide
semiconductor transistor, a field effect transistor, a thyristor, a
rectifier and a transformer, but the present invention is not
limited thereto.
[0037] The abovementioned insulated thermal interface material at
least comprises a base, a first filler and a second filler. The
base is a polymer, and the first filler is a graphene. And further,
the first filler and the second filler dispersed in the base.
[0038] Preferably, the first filler is a graphene with a
length-to-thickness ratio or a width-to-thickness ratio of
50.about.10000 and selected from a group consisting of a graphene,
a graphene doped with nitrogen, a graphene doped with oxygen, a
graphene doped with both nitrogen and oxygen, multilayer graphene
stacking via van der Waals interaction, multilayer graphene doped
with nitrogen stacking via van der Waals interaction, multilayer
graphene doped with oxygen stacking via van der Waals interaction
and multilayer graphene doped with both nitrogen and oxygen
stacking via van der Waals interaction.
[0039] Preferably, the second filler is a thermal conductive
inorganic powder and selected from a group consisting of aluminum
oxide, magnesium oxide, aluminum nitride, boron nitride, silicon
carbide, tin oxide, silicon nitride, aluminum oxide whisker,
aluminum nitride whisker, silicon carbide whisker, magnesium oxide
whisker and silicon nitride whisker. However, the second filler is
not limited thereto and could use any kind of powder which
possesses conductivity and insulativity and can be used to improve
the conductivity and insulativity of the insulated thermal
interface material. The thermal conductive powder could be used
alone or combined with two or more components.
[0040] Basically, the base is a silicone rubber or an epoxy resin.
The percentage of other components varies with different bases, but
the thermal interface material disclosed in the present invention
at least comprises the first filler and the second filler. The two
embodiments of the base will be illustrated as the following.
First Embodiment
[0041] In the first embodiment, the base is a silicone rubber and
at least contains an organic polysiloxane compound, a curing agent
and an adhesion promoter.
[0042] Preferably, the organic polysiloxane compound has a
polymerization degree of between 200.about.12000 and can be
represented by the following formula (I):
R.sup.1.sub.aSiO.sub.(4-a)/2 (I)
[0043] In the formula (I), R.sup.1 is a single-valence
C.sub.1.about.C.sub.10 hydrocarbon group and selected from a group
consisting of an alkyl group, a cycloalkyl group, an aryl group, an
aralkyl group, an alkyl group substituted by halogen and an alkenyl
group. Preferably, "a" further represents a positive number of
1.9-2.05.
[0044] Moreover, when R.sup.1 is an alkyl group, it could be
methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl
or decyl group. When R.sup.1 is a cycloalkyl group, it could be
cyclopentyl or cyclohexyl group. When R.sup.1 is an aryl group, it
could be phenyl, tolyl, xylyl or naphthyl group. When R.sup.1 is an
aralkyl group, it could be phenethyl or hydrocinnamyl group. When
R.sup.1 is a halogen substituted-alkyl group, it could be
3,3,3-trifluoropropyl or 3-chloropropyl group. When R.sup.1 is an
alkenyl group, it could be vinyl group, allyl group, butenyl group,
pentenyl group or hexenyl group. For example, the backbone of the
organic polysiloxane compound could be formed by a dimethysiloxane
unit or other similar units. And further, the methyl groups of the
organic polysiloxane compound can be partially substituted by vinyl
group, phenyl group or 3,3,3-trifluoropropyl group. Besides, the
terminal of the organic polysiloxane compound could be terminated
by tri-organic silyl group or hydrocarbon group. Preferably,
tri-organic silyl group comprises trimethylsilyl group,
dimethylvinylsilyl group or trivinylsilyl group.
[0045] According to the first embodiment of the present invention,
the curing agent is an alkylated silane or an organic peroxide.
When the curing agent is applied in an alkylation reaction of
silane, it is composed of catalysts based on platinum and
organicohydrogenpolysiloxane which in average of at least two
hydrogen atoms binding to a silicon atom within a single molecule.
Preferably, each molecular of the abovementioned organic
polysiloxane compound will have at least two or more alkenyl groups
bound on its silicon atom. The organohydrogenpolysiloxane of the
curing agent served as crosslinking agent and the addition reaction
occurs with the alkenyl group in organic polysiloxane compound. In
addition, the alkenyl group binding to the silicon atom is
preferably vinyl group, and the vinyl group could be at the
terminal, side chain or both. Preferably, at least one vinyl group
is binding on the silicon atom at the terminal of molecular
chain.
[0046] Preferably, the organic polysiloxane compound could be
selected from one or more combinations of the group listed below: a
copolymer of methylvinylsiloxane and dimethysiloxane terminated
with trimethylsiloxanes at both ends of the molecular chain, a
polymethylvinylsiloxane terminated with trimethylsiloxanes at both
ends of the molecular chain, a co-polymer of methylphenylsiloxane,
methylvinylsiloxane and dimethysiloxane terminated with
trimethylsiloxanes at both ends of the molecular chain, a
polydimethylsiloxane terminated with dimethylvinylsiloxanes at both
ends of the molecular chain, a polymethylvinylsiloxane terminated
with dimethylvinylsiloxanes at both ends of the molecular chain, a
co-polymer of methylvinylsiloxane and dimethysiloxane terminated
with dimethylvinylsiloxanes at both ends of the molecular chain, a
co-polymer of methylphenylsiloxane, methylvinylsiloxane and
dimethysiloxane terminated with dimethylvinylsiloxanes at both ends
of the molecular chain, and polydimethylsiloxane terminated with
trivinylsiloxanes at both ends of the molecular chain. However, the
present invention is not limited thereto.
[0047] As for the catalyst used to promote the curing of compound
is based on platinum and organohydrogenpolysiloxanes combinations,
and it could be chloroplatinic acid, alcohol solution of
chloroplatinic acid, olefin complex of platinum and vinylsiloxane
complex of platinum. There are no particular limitations of the
amount of catalyst based on platinum in the combinations, as long
as it reaches the effective catalytic amount.
[0048] When the curing agent is an organic peroxide, it could be
selected from a group consisting of benzoperoxide, dicumyl
peroxide, 2,5-dimethyl-2,5-bis(tert-butylperoxy)hexane,
ditert-butyl peroxide and benzenecarboperoxoic acid. Although there
are no specific limitations of the abovementioned organic
polysiloxane compound, preferably, each molecule at least comprises
two vinyl groups.
[0049] Under the circumstances, the organic polysiloxane compound
could be selected from one or more combinations of the group listed
below, but the present invention is not limited thereto: a
polydimethylsiloxane terminated with dimethylvinylsiloxanes at both
ends of the molecular chain, a polydimethylsiloxane terminated with
methylphenylvinylsiloxanes at both ends of the molecular chain, a
co-polymer of methylphenylsiloxane and dimethysiloxane terminated
with dimethylvinylsiloxanes at both ends of the molecular chain, a
co-polymer of methylvinylsiloxane and dimethysiloxane terminated
with dimethylvinylsiloxane at both ends of the molecular chain, a
co-polymer of methylvinylsiloxane and dimethysiloxane terminated
with trimethylsiloxanes at both ends of the molecular chain, a
poly[methyl(3,3,3-trifluoropropyl)siloxane] terminated with
dimethylvinylsiloxanes at both ends of the molecular chain, a
co-polymer of methylvinylsiloxane and dimethysiloxane terminated
with silanol groups at both ends of the molecular chain and a
co-polymer of methylphenylsiloxane, methylvinylsiloxane and
dimethysiloxane terminated with silanol groups at both ends of the
molecular chain.
[0050] According to the first embodiment of the present invention,
the addition of adhesion promoter could offer strong adhesiveness
between silicon rubber and further overcome the peeling problem
suffered in the prior art to get the abovementioned thermal
interface material with a long-term durability. Moreover, the
adhesion promoter at least comprises a silicon compound with a
plurality of substitutes, and the substitutes could be selected
from a group consisting of a cycloalkyl group, an alkoxyl group, a
methyl group, a vinyl group and a silane group. Preferably, the
silicon compound at least contains two abovementioned groups within
a molecule.
[0051] On the other hand, when the curing agent is applied in an
alkylation reaction of silane, preferably, the silicon compound of
the adhesion promoter contains vinyl group, silane group or both,
and epoxide group, alkoxyl group or both. When the curing agent is
the organic peroxide, the silicon compound of the adhesion promoter
contains methyl group, vinyl group or both, and epoxide group,
alkoxyl group or both. The silicon compound which comprises the
abovementioned groups is shown below, but the present invention is
not limited thereto.
##STR00002##
[0052] According to the first embodiment of the present invention,
the organic polysiloxane compound, the curing agent, the adhesion
promoter, the first filler and the second filler of the thermal
interface material has a weight percentage of 91-99.55%, 0.1-5%,
0.1-3%, 0.0025-0.005% and 0.25-0.5%, respectively. Basically, the
overall thermal conductivity of thermal interface material will
decrease if the addition amount of the first filler and the second
filler are too small. However, it will also be hard to mix and
affect the molding processing performance if the addition amount of
the first filler and the second filler are too much.
[0053] Preferably, the second filler has an average granularity of
about 20-50 .mu.m. Moreover, the thickness of each composite
material could be setup according to the anticipated structure and
application when producing the thermal interface material into thin
film. Although the present invention is not limited thereto, the
thermal conductivity decreases if the outer layer is too thin or
too thick. Therefore, the thickness is 30-800 .mu.m, preferably,
the thickness is in the range of 50-400 .mu.m.
[0054] Besides the abovementioned base, the first filler, the
second filler, the curing agent and the adhesion promoter, the
thermal interface material provided in the present invention
further comprising an additive, and it could be selected from a
group consisting of coupling agent, chain-extenders, flexibilizer,
dispersant and co-curing agent.
[0055] The preparation process of the thermal interface material
provided in the present invention is described as followed. First,
a mixing device is used, such as kneader, Banbury mixer,
planet-type mixer or Shinagawa mixer. If necessary, accompanying of
heating to about 100.degree. C. or higher could knead organic
polysiloxane compound, first filler and second filler together. In
the abovementioned kneading process, introducing and mixing of the
following compound, such as enhancing silicon dioxide including
pyrolysis of silicon dioxide or precipitation of silicon dioxide,
silicon oil or silicone wetting agent, flame retardant including
platinum, titanium oxide or benzotriazole, is applicable in
precondition of those addition does not affect the thermal
conductivity of outer layer
[0056] Cooling the mixture obtaining from kneading process to room
temperature, and filter through screening program. Then, adding
predetermined amount of adhesion promoter into the mixture to
perform second kneading using two-roll grinder or Shingawa mixer.
If needed, addition of the following agent, such as retarding agent
for addition reaction based on acetylene compound including
1-ethynyl-1-cyclohexanol, coloring agent including organic pigment
or inorganic pigment, or heat-resistance improvement agents
including iron oxide or cerium oxide, is applicable during the
second kneading process.
[0057] The thermal interface material after second kneading could
be used as outer layer coating agent. If needed, addition of
solvent including toluene is applicable, and the resulting mixture
is mixing in mixing device, such as planet-type mixer or kneader,
to form the outer layer coating agent, but the present invention is
not limited to single-layer structure. If needed, the
abovementioned inner layer (A) compounds including aromatic
polyimide could also be combined with thermal interface material
(B) into (B)/(A)/(B)/(A)/(B) five-layer structure, or it could also
includes isolating layer, such as glass-fiber fabric, graphite
flake or aluminum foil, into the structure, but the present
invention is not limited thereto.
[0058] After the illustration of the abovementioned structure,
property and component ratio of the thermal interface material, the
property, component ratio and tested result of two experimental
sets according to the first embodiment are presented below.
[0059] Formulation 1
[0060] (a) organic polysiloxane compound: a polydimethylsiloxane
terminated with dimethylvinylsiloxanes at both ends of the
molecular chain was used with 8000 average degree of
polymerization.
[0061] (b) graphene doped with 0.005% of nitrogen
[0062] (c) kneading between 0.5% dispersing assistant and 0.5% of
silicon oxide powder with 40 nm average granularity functionalized
with silane groups under room temperature. After filtering against
100 mesh filter, the abovementioned mixture and
[0063] (d) 1% adhesion promoter composed of silicon compound as
shown in formula (II)
##STR00003##
[0064] (e) 1.9% of bis(2-methyl benzoyl-yl)peroxide
[0065] (f) 0.4% of coloring agent were mixing, and further kneading
using two-roll grinder to obtain a mixture. Then, the mixture were
coating on the glass. This coated layer was processed into a
thickness of 62.5 .mu.m thermal interface material layer under
80.degree. C. dried temperature and 150.degree. C. curing
temperature.
[0066] Formulation 2
[0067] Besides the amount of the dispersing agent was changed from
0.5% to 1%, the manufacturing method of the thermal interface
material is the same as the formulation 1.
[0068] At last, the thermal conductivity and resistance of the
thermal interface material provided in the present invention are
shown in Table 1, and the thermal conductivity was measured with
laser flash method in heat-soaking device under 25.degree. C.:
TABLE-US-00001 TABLE 1 Thermal conductivity (W/mK) Resistance (Ohm
* cm) Formula 1 3.3167 4.7E+27 Formula 2 3.3167 5.7E+22
[0069] The larger of the abovementioned thermal conductivity, the
greater ability to spread and transfer the heat. As shown in Table
1, the thermal conductivity of thermal interface material provide
in the present invention is not lower than 3 W/mK, which is far
more better than the products currently sold in the market (about
0.5-0.6 W/mK). Besides, the electric material usually needs to
maintain insulation in order not to be burned due to the excess of
the current. Therefore, we also measured the resistance of this
thermal interface material and found that the resistance is
enormously large to reach basic demands of insulation for
electronic component.
[0070] Please refer to FIG 1A to FIG. 1C. FIG 1A to FIG. 1C are
diagrams showing the structure of the insulated thermal interface
material 10 according to the first embodiment of the present
invention. As shown in the FIG, collocation of first filler 11 and
second filler 12, the silicon rubber 13 could store and release
elastic energy E1 due to long backbone structure. Therefore, when
first filler 11 moves, rotates and vibrates under heating, it
compresses or elongates the spring-like silicon rubber 13 and
undergo transfer of thermal energy T and elastic energy F. In
addition, the thermal conductivity of continuity between the second
filler 12 and the first filler 11 results in a synergistic effect
of increasing thermal transfer and thermal insulation, which give
rise to a satisfying results of thermal conductivity and
resistance. Based on these reasons, the thermal interface material
10 provides in the present invention could be widely used as heat
conductive fins inserted between heating electronic device or
electric component and heat dissipating component. Moreover, the
abovementioned thermal interface material 10 displays great thermal
insulativity especially applied in heating apparatus. Meanwhile,
although not illustrated, the silicon rubber 13 further comprises
the adhesion promoter. Hence, strong interaction occurred when
combining this thermal interface material with the abovementioned
compounds including aromatic polyimide, that is the great duration
of the thermal interface material provides in the present
invention.
Second Embodiment
[0071] According to a second embodiment of the present invention,
the base is a curing epoxy resin and it could be selected from a
group consisting of a linear polyepoxide with epoxide as an end
group, a polyepoxide with epoxide at backbond and a polyepoxide
with epoxide as side chain. It can comprise the following compound
represented by the formula (III):
##STR00004##
[0072] In the formula (III), R' is an alkyl group, alkyl ether or
aryl group, n is an integer of 2-6. Preferably, the abovementioned
curing epoxy resin at least contains two epoxide groups within
every molecule and the average molecular weight is 150-10000.
[0073] The epoxy resin includes aromatic glycidyl ether (by
reacting of polyphenol with excess amount of epichlorohydrin),
cycloaliphatic glycidyl ether, hydrogenation of the glycidyl ether,
and their mixture. The polyphenols includes resorcinol,
pyrocatechol, hydroquinone and polycyclic phenol including
p,p'-dihydroxy benzyl, p,p'-dihydroxy biphenyl,
p,p'-dihydroxyphenyl sulfone, p,p'-hydroxy benzophenone,
2,2'-dihydroxy-1,1'-dinaphthylmethane and dihydroxy diphenyl
methane, dihydroxy diphenyl dimethyl methane,
dihydroxy-diphenyl-ethyl methyl methane, dimethyl phenyl methyl
propyl methane, dihydroxy-diphenyl-ethyl phenyl methane,
dihydroxy-diphenyl-propyl phenyl methane, dihydroxy-diphenyl-butyl
phenyl methane, dihydroxy-diphenyl-p-tolyl ethane,
dihydroxy-diphenyl-p-tolyl methyl methane,
dihydroxy-diphenyl-dicyclohexyl methane and the
2,2',2,3',2,4',3,3',3,4' and 4,4' isomers of
dihydroxy-phenyl-cyclohexane. Moreover, it further contains
condensation product of polyphenol formaldehyde and
multi-diglycidyl ether that only has epoxy or hydroxyl group as
active group.
[0074] According to the second embodiment of the present invention,
the abovementioned thermal interface material could chose to add
epoxy compound as reactive diluent which at least contains glycidyl
ether at the terminal, preferably a saturated or non-saturated ring
skeletons. There are several purposes of adding reactive diluents,
such as processing helper, toughening and compatible between
different materials. For example, reactive diluents could be
diglycidyl ether of cyclohexanedimethanol, diglycidyl ether of
resorcinol, p-tert-butyl phenyl glycidyl ether, hydroxymethyl
phenyl glycidyl ether, diglycidyl ether of neopentyl glycol,
trimethylol ethane triglycidyl ether, triglycidyl ether of
trimethylolpropane, N,N-diglycidyl-4-glycidyloxyaniline,
N,N-diglycidyl glyceryl aniline, N,N,N,N-tetraglycidyl
m-xylenedi-amine, multi-diglycidyl ether of vegetable oil, but the
present invention is not limited thereto.
[0075] Preferably, the insulated thermal interface material further
comprises a particulate thermoplastic polymer. the base, the
particulate thermoplastic polymer, the first filler and the second
filler has a weight percentage of 90-97%, 1-2%, 0.005-0.001% and
0.1-1%, respectively. The abovementioned particulate thermoplastic
polymer preferably contains a polymer with glass transition
temperature (T.sub.g) of at least 60.degree. C., the average
molecular weight is higher than 7000 and could be selected from a
group consisting of a poly(methyl methacrylate) and a methyl
methacrylate/methacrylic acid copolymer. In addition, the average
granularity of the particulate thermoplastic polymer is preferably
0.25-250 .mu.m.
[0076] Moreover, the thermal interface material further comprises a
curing agent, and the curing agent contains a dicyandiamide and its
derivatives or a metal imidazole compound represented by formula
(IV):
ML.sub.m (IV)
[0077] In formula (IV), M is a metal which could be selected from a
group consisting of Ag (I), Cu (I), Cu (II), Cd (II), Zn (II), Hg
(II), Ni (II) and Co (II). L is a compound shown by formula
(V):
##STR00005##
[0078] In formula (V), R.sup.1, R.sup.2, R.sup.3 could be selected
from a group consisting of hydrogen atom, alkyl group and aryl
group. m is the valence of metal. Preferably, the metal imidazole
compound is a green imidazole copper (II). In addition, the
equivalent weight of metal imidazole compound is based on a
criteria that it could cure epoxy resin, which preferably be
0.5-3%.
[0079] Preferably, the thermal interface material further comprises
an additive, and the additive could be selected from a group
consisting of coupling agent, lubricant, flow controlling agent,
thickener, accelerant, chain-extenders, flexibilizer, dispersant
and co-curing agent. And further, the flexibilizer helps to offer
the intensity of overlap shear and impact, and the composition is
different from the thermoplastic material. Flexibilizer is a
polymer which could react with epoxy resin and is cross-linkable.
Preferably, flexibilizer comprises a rubber-phase and a
thermoplastic-phase polymer or a material which could form
rubber-phase and a thermoplastic-phase compound with epoxy group.
Moreover, flexibilizer could be butadiene acrylonitrile terminated
with carboxyl group, a butadiene acrylonitrile terminated with
carboxyl group and core-shell polymer or the mixture, but the
present invention is not limited thereto. Furthermore, flow
controlling agent preferably includes pyrolysis of silicon dioxide
and un-pyrolysis silicon dioxide.
[0080] The adhesion promoter could be used to enhance the
attachment of binding agent and the base, and the composition of
the adhesion promoter could be varied with the target surface.
Adhesion promoter, such as dihydric phenol including catechol and
dithiobis phenol, is especially useful for the surface of ionic
lubricant used to pull the metal raw material during the
processing.
[0081] Moreover, the weight percentage of coupling agent could be
0.001-0.05%, and 1-2% for lubricant. Preferably, the coupling agent
could be selected from a group consisting of silane coupling agent,
titanate coupling agent or aluminate coupling agent, and the
lubricant could be selected from a group consisting of stearate,
stearic acid amines, low molecular weight polymer or paraffin.
[0082] Other additive such as filler (for example, aluminum powder,
carbon black, glass bulb, talc, clay, calcium carbonate, barium
sulfate, titanium dioxide, silicon dioxide, silicate, glass bead
and mica), flame retardant, antistatic agent, thermal conductive or
electric conductive granule and foaming agent (azodicaroxamide or
expandable polymer microsphere containing hydrocarbon liquid) etc.,
addition of the thermal interface material according to the
applicable field is choosable, but the present invention is not
limited thereto.
[0083] The preparation process of the thermal interface material
provides in the present invention is described below. First, one or
more epoxy resin was heated under 100-180.degree. C. to melt those
resin. Then, the resin was cooled to about 90-50.degree. C.
Addition of other epoxy resin, reactive diluents and flexibilizer
besides first filler and second filler under high shearing mixing.
If the mixture comprises the first filler and the second filler,
granules were added and mixed for 1 hour at most till the granules
are dispersed. Finally, the filler was added and mixed to obtain
the dispersed mixture. The mixture was cooled to below the glass
transition temperature of particulate thermoplastic, generally
50-100.degree. C. After that, the curing agent, the adhesion
promoter and the particulate thermoplastic were mixed in the epoxy
mixture. This epoxy mixture is flowable at this point and could be
poured into suitable container for further use.
[0084] Formulation 1
[0085] First, the melted epoxy mixture was cooled to about
50.degree. C. before addition of additives such as reactive
diluents and flexibilizer under high shearing mixing. Further
adding 0.005% of the first filler, such as graphene doped with
nitrogen, and 0.25% of the second filler, such as 50-200 mm sphere
aluminum oxide, and mixing for 1 hour till the granules are
dispersed. The mixture was further cooled to about 50.degree. C.
below the glass transition temperature of particulate
thermoplastic, before addition of the curing agent, the adhesion
promoter and the particulate thermoplastic into the epoxy
mixture.
[0086] Formulation 2
[0087] The only different between formulations 1 and 2 is to change
the percentage of the second filler from 0.005% to 0.5%.
[0088] Finally, the thermal conductivity and resistance of the
thermal interface material provided in the present invention are
shown in Table 2, and the thermal conductivity is then measured
with laser flash method in heat-soaking device under 25.degree.
C.:
TABLE-US-00002 TABLE 2 Thermal conductivity (W/mK) Resistance (Ohm
* cm) Formulation 1 0.6607 4.3E+22 Formulation 2 0.5826 2.8E+22
[0089] The larger of the abovementioned thermal conductivity, the
greater ability to spread and transfer the heat. As shown in Table
2, the thermal conductivity of the thermal interface material
provide in the present invention is far more better than the
products currently sold in the market (about 0.03-0.2 W/mK).
Besides, the electric material usually needs to maintain insulation
in order not to be burned due to the excess of the current.
Therefore, we also measured the resistance of this thermal
interface material and found that the resistance is enormously
large to reach basic demands of insulation for electronic
component.
[0090] Please refer to FIG. 2A to FIG. 2C. FIG. 2A to FIG. 2C are
diagrams showing the structure of the insulated thermal interface
material 10 according to the second embodiment of the present
invention. It is noted that the curing material, the first filler
11 and the second filler 12, is flowable below the curing
temperature and at least a part was diffused into the epoxy resin
14. Or the first filler 11 and the second filler 12 dispersed in
epoxy resin 14 and was separated by the epoxy resin 14. As shown in
the FIG, collocation of the first filler 11 and the second filler
12, the silicon rubber silicon resin 14 possesses similar structure
(benzene ring and epoxy group) comparing to the first filler 11.
Therefore, the thermal energy T could transmit through phonon and
the great connection between the first filler 11 and the second
filler 12, resulting in a synergistic effect of increasing thermal
transfer and thermal insulation.
[0091] Although the present invention has been described in terms
of specific exemplary embodiments and examples, it will be
appreciated that the embodiments disclosed herein are for
illustrative purposes only and various modifications and
alterations might be made by those skilled in the art without
departing from the spirit and scope of the invention as set forth
in the following claims.
* * * * *