U.S. patent application number 09/733559 was filed with the patent office on 2001-06-21 for heat conductive mold and manufacturing method thereof.
Invention is credited to Kimura, Tsunehisa, Tateda, Shinya, Tobita, Masayuki, Yamato, Masahumi.
Application Number | 20010004546 09/733559 |
Document ID | / |
Family ID | 18460395 |
Filed Date | 2001-06-21 |
United States Patent
Application |
20010004546 |
Kind Code |
A1 |
Tobita, Masayuki ; et
al. |
June 21, 2001 |
Heat conductive mold and manufacturing method thereof
Abstract
A heat conductive mold is provided in which boron nitride powder
has a magnetic field which is oriented in a fixed direction within
a polymer. The polymer is preferably at least one selected from
silicon rubber, epoxy, Polyimide and polyurethane. The content of
the boron nitride powder is from twenty-two 400 weight parts to 100
weight parts ofpolymer. A method is also provided in which a heat
conductive mold of excellent heat conductivity is provided. The
method includes impressing a magnetic field to the polymer
composition containing boron nitride powder. The magnetic field
impressed on the boron nitride powder, in the composition is
impressed to have a fixed direction. The field is set after the
direction is established. As an alternative, the method may include
pressing the magnetic field to the polymer composition including
the boron nitride powder and also a solvent.
Inventors: |
Tobita, Masayuki; (Tokyo,
JP) ; Tateda, Shinya; (Tokyo, JP) ; Kimura,
Tsunehisa; (Tokyo, JP) ; Yamato, Masahumi;
(Tokyo, JP) |
Correspondence
Address: |
McGLEW AND TUTTLE, P.C.
SCARBOROUGH STATION
SCARBOROUGH
NY
10510-0827
US
|
Family ID: |
18460395 |
Appl. No.: |
09/733559 |
Filed: |
December 8, 2000 |
Current U.S.
Class: |
438/519 ;
257/E23.09; 257/E23.107 |
Current CPC
Class: |
H01L 2924/01012
20130101; H01L 2224/73253 20130101; H01L 2224/16 20130101; H01L
21/4871 20130101; H01L 2924/01019 20130101; H01L 2224/29386
20130101; H01L 23/433 20130101; H01L 2224/29499 20130101; H01L
2224/2929 20130101; H01L 2224/2929 20130101; H01L 23/3737 20130101;
H01L 2924/0665 20130101; H01L 2924/16195 20130101 |
Class at
Publication: |
438/519 |
International
Class: |
H01L 021/265 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 17, 1999 |
JP |
11-358646 |
Claims
1. A heat conductive mold, wherein boron nitride powder is magnetic
field oriented to a fixed direction in a polymer.
2. The heat conductive mold of claim 1, wherein the polymer is at
least one selected from silicon rubber, epoxy, polyimide and
polyurethane.
3. The heat conductive mold of claim 1 or 2, wherein the content of
boron nitride powder is 20 to 400 weight parts to 100 weight parts
of polymer.
4. A manufacturing method of heat conductive mold of excellent heat
conductivity, by impressing magnetic field to the polymer
composition containing boron nitride powder, field orienting boron
nitride powder in the composition to a fixed direction, and then
setting the same.
5. A manufacturing method of heat conductive mold of excellent heat
conductivity, by impressing magnetic field to the polymer
composition containing boron nitride powder and solvent, field
orienting boron nitride powder in the composition to a fixed
direction, and then setting the same after having removed the
solvent.
Description
FIELD OF THE INVENTION
[0001] The present invention concerns a heat conductive mold of
good heat conductivity and manufacturing method thereof.
PRIOR ARTS
[0002] Recently, measures against the heat generated from
electronic apparatuses are becoming an important issue by the high
density implementation of semi-conductor package or higher
integration and speed-up of LSI, following the performance
enhancement, miniaturization, and weight reduction of electronic
apparatuses. Ordinarily, in order to dissipate heat from heating
devices, method to use printed circuit boards made of good heat
conductive metals or ceramics, method to form a thermal veer hole
to radiate heat in the substrate, method to use good heat
conductive metals, ceramics or resins as semiconductor package
material, method to interpose highly heat conductive grease or
flexible heat conductive rubber sheet for the purpose of reducing
the contact heat resistance between the heat source and the
radiator, or between the heat source and the metallic heat
conductive plate, method to use cooling fan, heat pipe or heat
dissipation plate, or others are publicly known.
[0003] As such heat conductive mold requiring good thermal
conductivity, molds filled with highly heat conductive aluminum
oxide, boron nitride, aluminum nitride, magnesium oxide, zinc
oxide, silicon carbide, quartz, aluminum hydroxide or other metal
oxides, metal nitrides, metal carbides, metal hydroxides or other
electric insulation fillers are used in practice.
[0004] However, flake form boron nitride powder could not deploy
enough its heat conductivity in case of sheet-shaped mold where
boron nitride power is simply diffused in polymer, because its heat
conductivity in the flake thickness direction is lower than the
heat conductivity in the surface direction, and the flake is filled
with its surface direction in parallel with the sheet thickness
direction. Therefore, various methods have been proposed to orient
flake form boron nitride powder vertically in the thickness
direction of the sheet-shaped mold.
[0005] To be more specific, the heat conductive insulation sheet
disclosed in the Japanese Patent Publication SHOU 62-154410 is a
heat conductive insulation sheet made of organo-poly-siloxane and
boron nitride powder specifying X-ray diffraction characteristics
in the sheet thickness direction, and realized by a method using
specific boron nitride powder and a manufacturing method applying a
composition including boron nitride powder by ultrasonic
commotion.
[0006] The Japanese Patent Publication HEI 3-151658 is a heat
radiation sheet where boron nitride powder is oriented upright in
the thickness direction of the sheet, manufactured by a method for
thrusting the extruded sheet, or the compression orientation
method.
[0007] The Japanese Patent Publication HEI 8-244094 discloses a
manufacturing method for charging flake-shaped particles vertically
in the thickness direction of the sheet by the extrusion molding
method, the Japanese Patent Publication HEI 11-77795 and the
Japanese Patent Publication HEI11-156914 a continuous manufacturing
method of rubber sheet for charging boron nitride powder vertically
in the thickness direction of the sheet by the extrusion molding
method using a die of particular structure.
[0008] However, the manufacturing method illustrated in the
Japanese Patent Publication SHOU 62-154410 requires ultrasonic
commotion machine or other special equipment or treatment
processes, or use of specific boron nitride powder making the
method inconvenient.
[0009] All of methods disclosed in the Japanese Patent Publication
HEI 3-151 658, Japanese Patent Publication HEI 8-244094, Japanese
Patent Publication HEI 11-77795 and Japanese Patent Publication HEI
11-156 914 use flake form boron nitride powder or the like, require
dies of complicated structure or extrusion molding equipment and
complicated processing operations, and they were not necessarily
simple manufacturing methods.
[0010] On the other hand, the Japanese Patent Publication Laid-Open
No. HEI 11-87483 by the Applicant orients diamagnetic filler of
20Weight/m.multidot.K or more in thermal conductivity in a constant
direction in polymer; however, boron nitride powder was not taken
into account as diamagnetic material.
SUMMARY OF THE INVENTION
[0011] To solve these problems, we have studied seriously and found
that a heat conductive mold characterized by that boron nitride
powder is field oriented in a constant direction in polymer
presents a good heat conductivity, a method to manufacture easily a
heat conductive mold of good thermal conductivity applying the
nature of boron nitride powder to orient along the magnetic power
line in a magnetic field, and attained the present invention.
[0012] Namely, the present invention concerns a heat conductive
mold characterized by that boron nitride powder is field oriented
in a constant direction in polymer, a manufacturing method of heat
conductive mold characterized by that boron nitride powder is field
oriented in a constant direction in a composition by impressing
magnetic field to a polymer component including boron nitride
powder, and a manufacturing method of heat conductive mold
characterized by that boron nitride powder is field oriented in a
constant direction in a composition by impressing magnetic field to
a liquid polymer component including boron nitride powder and
solvent, and set after having removed the solvent.
[0013] Boron nitride powder used in the present invention is not
particularly specified as for the kind of crystalline system, shape
or size of powder particle, aggregation rate of powder particle, or
their distribution. Concerning the crystalline system, boron
nitride powder of hexagonal system, cubic system or other
structures can be used. Particularly, highly crystalline boron
nitride powder of hexagonal system or cubic system is preferable,
because of its excellent thermal conductivity.
[0014] The particle form of boron nitride powder is not limited to
flake form or flat form, but also various other forms of boron
nitride powder, such as granular, massive, spherical, fiber,
whisker form boron nitride powder, or ground product thereof can be
used. The particle diameter of boron nitride powder is not
specified; however, individual average primary diameter in the
range of 0.01.about.100 .mu.m, and more preferably, in the range of
1.about.50 .mu.m can be used. Under 0.01 .mu.m, it is difficult to
charge in quantity, and boron nitride powder larger than 100 .mu.m
is difficult to produce, and disadvantageous in terms of price. As
for the flake form boron nitride powder, it is practical to use
within the range of 1.about.1 60 .mu.m in its maximum diameter,
because it can easily be blended with polymer and field oriented.
Further, boron nitride powder having a structure where primary
particles are aggregated can be used.
[0015] In particular, the present invention is basically different
from a conventional manufacturing method of mechanical orientation
using boron nitride powder an-isotropic shape and is hardly
influenced by the boron nitride powder shape, because it can be
field oriented in a way to increase the heat conductivity using the
magnetic anisotropy proper to the boron nitride powder.
[0016] The quantity of boron nitride powder to be contained in
polymer is preferably 20.about.400 weight parts to 100 weight parts
of polymer. Less than 20 weight parts, the improvement effect of
heat conductivity is small, while the content more than 400 weight
parts increases the composition viscosity, reduces the fluidity,
making the molding difficult and bubble inclusion inevitable, so it
is not appropriate. More preferably, boron nitride powder is added
by 30.about.300 weight parts, and still preferably, by 40.about.250
weight parts. Higher concentrations may also be obtained by using
boron nitride powders of different particle diameter, or by surface
treatment.
[0017] The kind of polymer used for the present invention is not
particularly limited. According to the shape, hardness, mechanical
nature, thermal nature, electric nature, durability, reliability or
other required performances, thermoplastic resins, thermoplastic
elastomers, setting resins, reticulated rubbers, or the like can be
selected. Polymer used for charging boron nitride powder at a high
concentration, polymers and polymer precursors presenting low
viscosity in liquid or melt state. Also, it is preferable to reduce
the viscosity of polymers or polymer precursors by dissolving with
solvent, in order to increase the concentration of boron nitride
powder, or to accelerate the field orientation of boron nitride
powder in the magnetic field atmosphere.
[0018] Thermoplastic resins or thermoplastic elastomers used as
polymer include polyethylene, polypropylene, ethylene propylene
copolymer or other ethyleneaolefin copolymer, polymethylpentene,
PVC, polyvinylidene chloride, polyvinyl acetate, ethylene
vinylacetate copolymer, polyvinyl alcohol, polyvinylacetal,
polyvinylidene fluoride and polytetrafluoroethylene or other
fluoric resins, polyethylene terephthalate, polystyrene,
polyacrylonitrile, styrene acrylonitrile copolymer, ABS resin,
polyphenylene ether and degenerated PPE resin, aliphatic and
aromatic polyamides, polyimide, polyamide-imide, polymethacrylic
acid and its methylester or other polymethacrylic acid esters,
polyacrylic acids, polycarbonate, polyphenylene sulfide,
plysulfone, polyether sulfone, polyether nitrile, polyether ketone,
plyketone, liquid crystal polymer, silicone resin, ionomer or other
thermoplastic resins, styrene butadiene or styrene isoprene bloc
copolymer and their hydrogenated polymer and styrene base
thermoplastic elastomers, olefin base thermoplastic elastomers, PVC
base thermoplastic elastomers, polyester base thermoplastic
elastomers, polyurethane base thermoplastic elastomers, polyamide
base thermoplastic elastomers, or other thermoplastic
elastomers.
[0019] Thermosetting resins and reticulated rubbers include epoxy,
polyimide, bismuth imide, benzocyclo butene, phenol, unsaturated
polyester, diallyl phtalate, silicone, polyurethane, polyimide
silicone, thermosetting type polyphenylene, ether resin and
degenerated PPE resin, natural rubber, butadiene rubber, isoprene
rubber, styrene butadiene copolymer rubber, nitrile rubber,
hydrogenated nitrile rubber, chloroprene, ethylene propylene
rubber, chlorinated polyethylene, chlorosulphonated polyethylene,
butyl rubber and butyl rubber halide, fluoric rubber, urethane
rubber, silicone rubber or other reticulated rubber.
[0020] The heat conductive mold of the present invention uses
preferably, at least one of these polymers selected from silicone
rubber, epoxy, polyurethane, unsaturated polyester, polyimide,
bismuth imide, benzocyclobutene, fluoric resin, and polyphenylene
ether resin, and more preferably, at least one of these polymers
selected from silicone rubber, epoxy, polyimide and polyurethane in
terms of heat resistance, and electric reliability. Moreover, these
polymers can be a low viscosity liquid for blending with boron
nitride powder and can reduce the viscosity when heat melted, and
when magnetic field is impressed, boron nitride powder is oriented
easily.
[0021] For wiring board application or the like requiring low
dielectric constant, dielectric tangent and characteristics in high
frequency range, fluoric resin or thermosetting type polyphenylene
ether resin or degenerated PPE resin, polyolefin base resin are
preferable. Further, polymer alloy made of a plurality of polymers
selected from these polymers may also be used. The reticulation
method of thermosetting resin or reticulated rubber is not limited
to thermosetting, but polymers by publicly known reticulation
methods such as photo-setting, hygro-setting, or the like may also
be used.
[0022] The heat conductive mold of the present invention may be
used with a small amount of other heat conductive filler of
spherical, powder, fiber, needle, flake or whisker form filler made
of highly conductive aluminum oxide, aluminum nitride, zinc oxide,
silicon carbide, aluminum hydroxide or other metal oxides, metal
nitrides, metal carbides, metal hydroxides or metals, alloys,
carbon, graphite, and diamond.
PREFERRED EMBODIMENTS OF THE INVENTION
[0023] The manufacturing method of heat conductive mold of the
present invention characterized by that boron nitride powder is
field oriented in a constant direction in a polymer is
characterized by that boron nitride powder in a composition is
oriented and set in a constant direction in a composition by
impressing magnetic field to a polymer component including boron
nitride powder. Further, it is characterized by that boron nitride
powder in the composition is oriented in a constant direction in a
composition by impressing magnetic field to a polymer component
including boron nitride powder and solvent, and set after having
removed the solvent.
[0024] It is possible to orient boron nitride powder in a polymer
composition in a fixed direction along the magnetic power line, by
impressing exterior magnetic field to the composition, using the
anisotropy of magnetic susceptibility of boron nitride powder, and
to obtain a heat conductive mold whose heat conductivity in the
fixed direction is extremely enhanced. For example, in order to
align boron nitride powder in the thickness direction of
sheet-shaped heat conductive mold, N pole and S pole of permanent
magnet or electromagnet are opposed in the thickness direction, and
disposed so that the magnetic power line corresponds to the desired
orientation direction of boron nitride powder (FIG. 5). On the
other hand, in order to enhance the heat conductivity in a fixed
direction in the vertical direction and in the transversal
direction or in the vertical and transversal horizontal directions
in a plane of sheet-shaped heat conductive mold, boron nitride
powder can be oriented aligned in the direction in the plane by
opposing the magnet N pole and S pole vertically to the thickness
direction (FIG. 6). Otherwise, boron nitride powder can also be
aligned in the direction in the plane by opposing the magnet N pole
and N pole, or S pole and S pole in the thickness direction.
Besides, the magnetic power line is not required to be straight
line, but it may be a curve, a rectangle, or two directions or
more. For the sheet-shaped mold, it is also possible place the
magnetic power line slant to the sheet thickness, to field orient
the flake form boron nitride powder in the slant direction.
[0025] The boron nitride powder magnetic field orientation method
of the present invention is essentially different from the
mechanical orientation method of boron nitride powder using fluid
field or shearing filed of extrusion molding or press molding
proposed in the prior art. In other words, it is possible to obtain
a high heat conductivity by orienting boron nitride powder in an
arbitrary fixed direction corresponding to the magnetic power line
direction. In addition, magnets are not required to be opposed at
both sides, but it is possible to field orient boron nitride powder
in the raw material composition by a magnet disposed only on one
side.
[0026] Magnetic field generation means user as exterior magnetic
field may be a permanent magnet, electromagnet or coil, and a flux
density range from 0.05 to 30 tesla can achieve a practical
orientation of boron nitride powder. As the present invention used
a very weak an-isotropic magnetization rate of boron nitride
powder, it is necessary to orient boron nitride powder sufficiently
in a stronger magnetic filed atmosphere, and to set matrix polymer
by thermosetting reaction or cooling. Preferable magnetic flux
density for orientation is 0.5 tesla or more, and more preferably,
1 tesla or more.
[0027] In order to improve wetness or adhesivity between boron
nitride powder and polymer, preliminary degreasing or cleaning of
the boron nitride powder surface, or surface treatment by silane
base, titane base, aluminum bas or other ordinary coupling agents
facilitate further the diffusion a blending of a quantity of boron
nitride powder, and the obtained mold will have a higher heat
conductivity.
[0028] The heat conductive mold of the present invention can be
applied to radiation plate, radiation rubber sheet, semiconductor
package component, heat sink, heat spreader, case, belt, roller,
tube, tape base material, cap, profile or the like requiring a high
heat conductivity. As boron nitride powder is excellent in electric
insulation, the heat conductive mold of the present invention may
also be applied to the wiring substrate.
BRIEF EXPLANATION OF THE DRAWINGS
[0029] FIG. 1 shows an example of utilization of the heat
conductive mold of the present invention (disposed in a gap between
a ball grid array type semiconductor package 2 and a radiator
4);
[0030] FIG. 2 shows an example of utilization of the heat
conductive mold of the present invention (disposed in a gap between
a chip size type semiconductor package 2 and a printed circuit
board 1);
[0031] FIG. 3 shows an example of utilization of the heat
conductive mold of the present invention (disposed in a gap between
a pin grid array type semiconductor package 2 and a heat sink
5);
[0032] FIG. 4 shows an example of utilization of the rubber sheet
shape heat conductive mold of a first embodiment of the present
invention (disposed in a gap between a plurality of heating
semiconductor device 6 and a case 7);
[0033] FIG. 5 shows an example of manufacturing method of the heat
conductive mold of the present invention;
[0034] FIG. 6 shows another example of manufacturing method of the
heat conductive mold of the present invention;
[0035] FIG. 1.about.FIG. 4 show examples wherein the heat
conductive mold 3 obtained by the present invention is interposed
between heating semiconductor device 2, 6 and head conductive
members, such as radiator 4, print circuit board 1, heat sink 5, or
case 7.
[0036] Now, the present invention will be described more in detail
based on examples. In the following examples and comparison
examples, the heat conductivity was evaluated through the
measurement of heat resistance value using a transistor (made by
Toshiba Corp. TO-220).
EXAMPLE 1
[0037] A composition is prepared by blending 100 weight parts of
added type liquid silicon rubber (made by GE Toshiba Silicon,
TSE3070), 80 weight parts of hexagonal crystalline system flake
form boron nitride powder (Denki Kagaku Kogyo K.K., SGP average
particle diameter 19 .mu.m) and 100 weight parts of hexane as
solvent. The composition is charged into a plate shape die of 15 mm
in thickness, 20 mm in length and 20 mm in width, boron nitride
powder is oriented sufficiently under the magnetic field atmosphere
where N pole and S pole of 2 tesla in flux density are opposed in
the thickness direction, then heat dried to remove solvent hexane,
and heat set, to obtain rubber sheet shape heat conductive mold of
1.5 mm in thickness. The heat resistance value of the obtained heat
conductive mold was 0.26.degree. C./W.
COMPARISON EXAMPLE 1
[0038] A composition is prepared by blending 100 weight parts of
added type liquid silicon rubber (made by GE Toshiba Silicon,
TSE3070), and 80 weight parts of hexagonal crystalline system flake
form boron nitride powder (Denki Kagaku Kogyo K.K., S G P average
particle diameter 19 .mu.m). The composition is charged into a
plate shape die of 15 mm in thickness, 20 mm in length and 20 mm in
width and heat set, to obtain rubber sheet shape heat conductive
mold. The heat resistance value of the obtained heat conductive
mold was 0.38.degree. C./W.
EXAMPLE 2
[0039] A composition is prepared by blending 100 weight parts of
liquid epoxy resin (made by Three Bond Co., Ltd. TB2280C) and 180
weight parts of hexagonal crystalline system granular boron nitride
powder (Showa Denko Co., Ltd. UHP-EX average particle diameter 35
.mu.m). The composition is charged into a plate shape die of 15 mm
in thickness, 20 mm in length and 20 mm in width, boron nitride
powder is oriented sufficiently under the magnetic field atmosphere
where N pole and S pole of 6 tesla in flux density are opposed in
the thickness direction, and heat set, to obtain a hard plate shape
heat conductive mold as shown in FIG. 5(1), FIG. 5(2) and FIG.
5(3). The heat resistance value of the obtained heat conductive
mold was 0.21.degree. C./W.
COMPARISON EXAMPLE 2
[0040] A composition is prepared by blending 100 weight parts of
liquid epoxy resin (made by Three Bond Co., Ltd. TB2280C) and 180
weight parts of hexagonal crystalline system granular boron nitride
powder (Showa Denko Co., Ltd. UHP-EX average particle diameter 35
.mu.m). The composition is charged into a plate shape die of 15 mm
in thickness, 20 mm in length and 20 mm in width, and heat set, to
obtain a hard plate shape heat conductive mold. The heat resistance
value of the obtained heat conductive mold was 0.32.degree.
C./W.
EXAMPLE 3
[0041] A composition is prepared by blending 100 weight parts of
solid portion of polyimide varnish containing N methyl pyrrolidone
as solvent (made by Ube Kosan Co., Ltd., Yupifine ST, concentration
of solid portion 18.5%) and 60 weight parts of hexagonal
crystalline system flake form boron nitride powder (made by Showa
Denko Co., Ltd. UHP-S1 average particle diameter 1 to 2 .mu.m). The
composition is charged into a box die of 20 mm in length, 20 mm in
width and 40 mm in depth, boron nitride powder is oriented
sufficiently under the magnetic field atmosphere where N pole and S
pole of 6 tesla in flux density are opposed in the thickness
direction, and heat set after having removed solvent N methyl
pyrrolidone, to obtain a film shape heat conductive mold of 120
.mu.m in thickness. The heat resistance value of the obtained heat
conductive mold was 0.18.degree. C./W.
COMPARISON EXAMPLE 3
[0042] A composition is prepared by blending 100 weight parts of
solid portion of polyimide varnish containing N methyl pyrrolidone
as solvent (made by Ube Kosan Co., Ltd., Yupifine ST, concentration
of solid portion 18.5%) and 60 weight parts of hexagonal
crystalline system flake form boron nitride powder (made by Showa
Denko Co., Ltd. UHP-S1 average particle diameter 1 to 2 .mu.m). The
composition is charged into a box die of 20 mm in length, 20 mm in
width and 40 mm in depth, and heat set after having removed solvent
N methyl pyrrolidone, to obtain a film shape heat conductive mold
of 120 .mu.m in thickness. The heat resistance value of the
obtained heat conductive mold was 0.27.degree. C./W.
[0043] Comparison Example 1 Comparison Example 3 are conventional
molds wherein flake form boron nitride powder is charged into
polymer, and Comparison Example 2 is the one wherein granular boron
nitride powder is charged, and they present a high heat resistance
value. The heat conductive mold of Example 1 Example 2, Example 3
of the present invention are obtained by impressing magnetic field
to the polymer composition containing the same amount of flake form
boron nitride powder or granular boron nitride powder as the
corresponding Comparison Example, field orienting boron nitride
powder in the composition, and then heat setting, and it presents
smaller heat resistance value and better heat conductivity than the
Comparison Example.
[0044] As described above, the present invention allows to produce
a heat conductive mold of excellent heat conductivity, by
impressing magnetic field to the polymer composition containing
flake form boron nitride powder or granular boron nitride powder,
field orienting boron nitride powder in the composition to a fixed
direction, and then heat setting.
[0045] Using the heat conductive mold of the present invention,
various radiation components requiring a high heat conductivity
such as high heat value CPU (central processing unit) or other
semiconductors, power source, light source, plasma display, printed
circuit board or the like can be supplied.
* * * * *