JP2002088171A - Thermal conductive sheet, method for manufacturing the same, and heat dissipation device - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] Thermal conduction that is flexible and easy to compress, has good followability to uneven surfaces of components such as semiconductor elements, power supplies, and light sources used in electric products, and has a small thermal resistance value during mounting. Provided is a conductive sheet, a method for producing the same, and a heat dissipating device having excellent heat conductivity. A magnetic field is applied to a heat conductive polymer composition containing heat conductive fibers, and the magnetic sheet is perpendicular to the sheet thickness direction, ie, perpendicular to the sheet surface. A heat conductive sheet obtained by solidifying the composition after tilting the heat conductive fiber with respect to the direction, a method for manufacturing the same, and a heat radiating device having the sheet interposed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat conductive sheet having excellent heat conductivity, a method for manufacturing the same, and a heat radiating device. More specifically, a heat conductive sheet that is flexible and has a small heat resistance value at the time of mounting capable of effectively dissipating heat generated from components such as a semiconductor element, a power supply, and a light source used in an electric product, and a method of manufacturing the heat conductive sheet Also, the present invention relates to a heat radiating device having excellent thermal conductivity.

[0002]

2. Description of the Related Art Heretofore, a flexible heat conductive sheet such as silicone rubber has been used for the purpose of promoting heat transfer between a semiconductor element or electronic component that generates heat and a heat transfer member that dissipates heat.
These heat conductive sheets include metals, alloys, and compounds having high heat conductivity, such as silver, copper, gold, aluminum, and nickel, or aluminum oxide, magnesium oxide, silicon oxide, and nitride, in order to increase the heat conductivity. A powdery heat conductive filler such as boron, aluminum nitride, silicon nitride, silicon carbide, carbon black, graphite, and diamond is blended.

[0003] On the other hand, according to Japanese Patent Application Laid-Open No. H5-259671, a heat conductive filler is penetrated in a matrix resin in the thickness direction of a sheet, and the heat conductive filler is oriented upright or inclined to be oriented. A heat-dissipating sheet with improved properties and adhesion and a method for producing the same are disclosed.

Japanese Unexamined Patent Publication No. Hei 10-330502 discloses a heat radiation sheet in which rubber is filled with carbon fibers.
The thermal conductivity is improved by aligning the carbon fibers in the plane direction or the thickness direction of the sheet. Furthermore, the present inventors have proposed, in JP-A-2000-195998, a heat conductive sheet in which pitch-based carbon fibers coated with a ferromagnetic material are oriented in a certain direction in silicone rubber, and a manufacturing method. .

[0005]

However, Japanese Patent Application Laid-Open No. Hei 5-259671 discloses a method of orienting a particle-shaped thermally conductive filler such as aluminum nitride, boron nitride, gold, copper and aluminum. The thermal conductivity of the sheet does not always show sufficient performance, and the method of manufacturing a sheet with a tilted orientation structure is a method in which a block in which fillers are previously arranged is cut in a tilted manner, and the productivity is extremely low. Met. In addition, conventional thermal conductive sheets, in which carbon fibers and metal fibers are oriented in the thickness direction of the sheet, have extremely hard thermal conductive fibers aligned straight in the thickness direction of the sheet. Some flexibility is significantly impaired, and the resulting heat conductive sheet is difficult to compress even when pressurized, and has poor followability to uneven surfaces such as heating elements, resulting in a problem that thermal resistance does not decrease as a result. Was.

That is, a heat conductive sheet having good heat conduction properties in the thickness direction of the sheet, and being flexible, easily compressible, and excellent in performance at the time of mounting has not been developed, including a simple manufacturing method thereof. In addition, a large amount of heat generated from electronic components such as semiconductor elements cannot be dissipated, and various troubles that impair the reliability and life of the electronic components have occurred.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention can effectively dissipate heat generated from components such as a semiconductor element, a power supply, and a light source used in electric appliances. An object of the present invention is to provide a heat conductive sheet which is flexible, easy to compress, has good followability to an uneven surface, and has a small thermal resistance value during mounting, a method for manufacturing the same, and a heat dissipating device excellent in heat conductivity. That is, the present invention relates to a heat conductive sheet containing a heat conductive fiber in a polymer, wherein the heat conductive fiber is inclined and oriented with respect to the thickness direction of the sheet. is there.

Further, a magnetic field is applied to a heat conductive polymer composition containing at least one heat conductive fiber selected from graphitized carbon fibers, metal fibers, polybenzazole fibers, and ultra-high molecular weight polyethylene fibers, to form a sheet. The heat conductive sheet is characterized in that the heat conductive fibers are oriented at an angle to the thickness direction of the sheet, that is, the direction perpendicular to the sheet surface, that is, the composition is solidified after the inclined orientation. It is a manufacturing method of. Still another aspect of the present invention is a heat dissipating device characterized in that a heat conductive sheet in which heat conductive fibers are inclined with respect to the thickness direction of the sheet is interposed between the heat generating member and the heat transfer member.

The heat conductive fibers used in the present invention include:
The thermal conductivity in the fiber length direction is preferably 50 W / m · K or more, and at least one selected from graphitized carbon fibers, metal fibers, polybenzazole fibers, and ultrahigh molecular weight polyethylene fibers is suitable.

As the graphitized carbon fibers, pitch-based or mesophase-pitch-based materials are used rather than PAN-based materials, and after a processing step of melt spinning, infusibilization, carbonization, etc.
Pitch-based carbon fibers having a developed graphite structure and heat-treated at a high temperature exceeding 0 ° C. or 3000 ° C. are preferable because of their higher thermal conductivity in the fiber length direction. Further, graphitized carbon fibers, microcoiled graphitized carbon fibers, and nanotube-like graphitized carbon fibers obtained by a vapor phase growth method, an arc discharge method, or the like can also be used. The thermal conductivity in the fiber length direction of the graphitized carbon fiber is preferably 200 W / m · K or more,
More preferably, it is 400 W / m · K or more, more preferably 1000 W / m · K or more.

As the metal fibers, metal fibers such as gold, silver, copper, and aluminum having a thermal conductivity of 100 W / m · K or more, preferably 400 W / m · K or more are suitable. The polybenzazole fiber is an organic polymer fiber composed of a polybenzazole polymer, and preferably has a thermal conductivity in the fiber length direction of 40 W / m · K or more. Polybenzazole (PBZ) means polybenzoxazole homopolymer (PBO), polybenzothiazole homopolymer (PBT) and a random copolymer, sequential copolymer, block copolymer or graft copolymer of PBO and PBT. As such a polybenzazole fiber, for example, Zylon manufactured by Toyobo Co., Ltd. is commercially available.

The ultrahigh molecular weight polyethylene fiber is an organic polymer fiber composed of a polyolefin having a repeating monomer unit mainly composed of ethylene as a raw material polymer, and has a thermal conductivity in the fiber length direction of 40 W / m · K. The above are preferred. The viscosity average molecular weight of the ultrahigh molecular weight polyethylene as the raw material polymer is 500,000 or more, preferably 10
It is at least 100,000, more preferably at least 1.5 million. If the viscosity average molecular weight is less than 500,000, the resulting heat conductive sheet has a low thermal conductivity, which is not suitable.

In the present invention, a small amount of copolymerized monomers other than ethylene include α-olefins such as propylene and butene, acrylic acid and derivatives thereof, methacrylic acid and derivatives thereof, vinyl esters and derivatives thereof, vinyl ethers and derivatives thereof, Known copolymers with styrene and its derivatives, vinylsilane and its derivatives, and blends with a small amount of these polymers may be used. Although not affecting the constitution and effect of the present invention, the content of these copolymer monomers other than ethylene is preferably 5 mol% or less, and the content of the polymer different from ultrahigh molecular weight polyethylene is preferably 10 vol% or less. Such ultra-high molecular weight polyethylene fibers include:
For example, Dyneema SK60 manufactured by Toyobo Co., Ltd.
Dyneema SK71 and the like are commercially available.

The fiber length and fiber diameter of these heat conductive fibers are not specified. In the case of short fibers having a short length of heat conductive fibers, the average diameter of the fibers is 5 to 20 μm.
m and an average length in the range of 5 to 800 μm are preferable because the polymer can be easily filled and the heat conductivity of the obtained heat conductive sheet increases. When the average diameter is smaller than 5 μm or when the average length is longer than 800 μm, it is difficult to mix the polymer with the polymer at a high concentration. On the other hand, if the average diameter of the fibers exceeds 20 μm, the productivity of the fibers is undesirably reduced. For average length,
If it is shorter than 5 μm, the bulk specific gravity becomes small, which may cause problems in handling and workability during the manufacturing process, which is not preferable.

On the other hand, when the heat conductive fiber is a long fiber, the average diameter is not particularly limited, but is 5 to 20 μm.
The range is practical. In the case of long fibers, the fiber length may be selected in consideration of the fact that exposing the end faces of the fibers to the upper and lower surfaces of the sheet improves the thermal conductivity.

The heat conductive sheet of the present invention is characterized in that the heat conductive fibers are inclined with respect to the thickness direction of the sheet. An element or a heat transfer member that generates heat because the thermally conductive fibers that are oriented obliquely when the sheet is compressed are further inclined obliquely by stress when the sheet is compressed. And the actual thermal resistance can be reduced.

Although the angle of inclination is not limited, for example, when expressed in numerical values, when the thickness direction of the sheet is 90 degrees, the heat conductive fibers are 45 to 45 degrees.
89 degrees or 91 to 135 degrees, preferably 60 to 85
Means that it is oriented at an inclination angle of 95 degrees or 95 degrees to 120 degrees, is easily compressed, and can follow the uneven surface of the element that generates heat.

Regarding the fiber shape of the heat conductive fiber, a curved fiber other than a linear fiber can be used. In particular, in the case of hard and hard fibers, the fiber shape may be curved or bent in a U-shape, U-shape, S-shape, coil shape, spring shape, or the like.

The concentration of the heat conductive fiber contained in the heat conductive sheet is not limited, but may be 2 to 3.
A range of 80% by volume is preferred. If the content is less than 2% by volume, the heat conductivity of the obtained heat conductive sheet is small, and the heat radiation property is inferior. If it exceeds 80% by volume, the flexibility of the sheet is impaired and the viscosity of the composition before molding increases. It becomes difficult to disperse the heat conductive fibers uniformly, and
Incorporation of air bubbles is inevitable and is not preferred. A more preferred concentration of the thermally conductive fibers is in the range of 5-70% by volume.

The surface of the heat conductive fiber may be subjected to a known surface treatment in advance. For example, degreasing, washing, acid-alkali treatment, ultraviolet irradiation, corona discharge,
Plasma treatment, flame treatment, electrolytic oxidation, halogenation treatment,
In addition to coupling agent treatment, electroless plating, electrolytic plating, physical vapor deposition by vacuum vapor deposition or sputtering, chemical vapor deposition, painting, immersion, mechanochemical method of mechanically fixing fine particles, etc. Depending on the method, other metals, compounds, insulators and the like can be coated.

As the polymer used as the matrix of the heat conductive sheet of the present invention, ordinary thermoplastic resins, thermoplastic elastomers, thermosetting resins, and crosslinked rubbers can be used.

Examples of the thermoplastic resin or thermoplastic elastomer include polyethylene, polypropylene, ethylene-α-olefin copolymers such as ethylene-propylene copolymer, polymethylpentene, polyvinyl chloride, polyvinylidene chloride, polyvinyl acetate, and ethylene vinyl acetate. Copolymers, polyvinyl alcohol, polyacetal, fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene,
Polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polystyrene, polyacrylonitrile, styrene acrylonitrile copolymer, ABS resin, polyphenylene ether and modified P
PE resin, aliphatic and aromatic polyamides, polyimide, polyamide imide, polymethacrylic acid esters such as polymethacrylic acid and its methyl ester, polyacrylic acids, polycarbonate, polyphenylene sulfide, polysulfone, polyether sulfone, polyether nitrile , Polyether ketone, polyketone, liquid crystal polymer, thermoplastic resin such as silicone resin, ionomer, styrene butadiene or styrene isoprene block copolymer and its hydrogenated polymer, styrene thermoplastic elastomer, olefin thermoplastic elastomer, vinyl chloride Thermoplastic elastomers such as thermoplastic elastomer, polyester-based thermoplastic elastomer, polyurethane-based thermoplastic elastomer, and polyamide-based thermoplastic elastomer Etc. The. When repeatedly used for recycling, it is preferable to use a thermoplastic elastomer.

Examples of the thermosetting resin and crosslinked rubber include epoxy resin, polyimide resin, bismaleimide resin, benzocyclobutene resin, phenol resin, unsaturated polyester resin, diallyl phthalate resin, silicone resin, urethane resin, and thermosetting polyphenylene. Ether and modified PPE resin, natural rubber, butadiene rubber, isoprene rubber, styrene butadiene copolymer rubber, nitrile rubber,
Crosslinked rubbers such as hydrogenated nitrile rubber, chloroprene rubber, ethylene propylene rubber, chlorinated polyethylene, chlorosulfonated polyethylene, butyl rubber and halogenated butyl rubber, fluorine rubber, urethane rubber, silicone rubber and the like can be mentioned. Above all, when flexibility, electrical reliability and thermal reliability are required, it is most preferable to use silicone rubber.

The type of the silicone rubber is not particularly limited as long as it has a known organopolysiloxane skeleton. The curing method is also not limited, and includes an addition reaction type comprising an organopolysiloxane containing a vinyl group, an organopolysiloxane containing a hydrogen group at a silicon atom, and a platinum catalyst, a radical reaction type using an organic peroxide, and a condensation reaction. And a curing type using ultraviolet rays or electron beams. Among them, it is preferable to use a liquid addition reaction type organopolysiloxane that easily fills the thermally conductive fibers. Also, known reinforcing silica and flame retardants, coloring agents, heat resistance improvers,
Adhesion aids, tackifiers, oils, plasticizers, and the like can be appropriately compounded.

Further, the raw material composition of the heat conductive sheet of the present invention contains other metals and ceramics, specifically, silver,
Fillers with high thermal conductivity used in conventional thermal conductive sheets such as copper, gold, aluminum oxide, magnesium oxide, boron nitride, silicon nitride, aluminum nitride, silicon carbide, aluminum hydroxide and metal-coated resin It is also possible to use them together. The shape of these fillers is not limited, such as particle, scale, sphere, crush, needle, fiber, coil, and tube. Also,
In order to reduce the viscosity of the composition, it is effective to add a volatile organic solvent or a reactive plasticizer.

The thinner the heat conductive sheet is, the better the heat resistance is and the better. However, when mounting, it must be interposed in a fixed gap or a gap having irregularities, and requires a certain thickness. Moreover, if it is too thin, it becomes difficult to handle, so a thickness of 0.1 to 10 mm is preferable. More preferably, it is in the range of 0.2 to 4 mm.

Although the hardness of the heat conductive sheet may be determined according to the intended use, the softer the material, the more advantageous it is in terms of stress relaxation and followability during use. As a specific hardness, a low hardness product having a Shore A hardness of 70 or less, preferably 50 or less is suitable. Further, when used between a heat-transfer member and an electronic component that generates heat, such as a plurality of semiconductor packages having irregularities as shown in FIG. 9, a gel-like low-hardness product having an Asker C hardness of 30 or less is desirable.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION It is important that the heat conductive sheet of the present invention has heat conductive fibers inclined with respect to the thickness direction of the sheet, which is the heat transfer direction. By the heat conductive fibers being inclined and oriented in the thickness direction of the sheet,
When a sheet is sandwiched in the thickness direction between the heat-generating body and the heat-dissipating body, applying a compressive stress compresses the sheet in the thickness direction, improving the adhesion and contacting the inclined thermally conductive fibers. In addition, it works effectively for heat conduction, and has a small thermal resistance value and good thermal conductivity.

As a method for producing a heat conductive sheet using a heat conductive polymer composition containing heat conductive fibers and in which the heat conductive fibers are inclined and oriented with respect to the thickness direction of the sheet, the following method can be used. A method of diagonally cutting a molded body in which the thermally conductive fibers are oriented in a certain direction by molding, press molding, roll molding, calender molding, etc. <Production method> Utilizing the diamagnetic magnetic anisotropy of the thermally conductive fibers, Applying a magnetic field obliquely to the thermally conductive polymer composition,
Method for obliquely orienting thermally conductive fibers <Production method> Method for obliquely orienting a thermally conductive fiber containing a ferromagnetic substance by applying a magnetic field to a thermally conductive polymer composition in an oblique direction <Production method> High thermal conductivity Method of obliquely orienting a thermally conductive fiber by applying an electric field to the molecular composition in an oblique direction <Production method> Obliquely orienting the thermally conductive fiber by electrostatically implanting the thermally conductive fiber in an oblique direction and then impregnating a polymer. And the like.

Either method can produce a heat conductive sheet in which the heat conductive fibers are inclined and oriented with respect to the thickness direction of the sheet. An appropriate manufacturing method can be adopted according to the properties of the heat conductive fiber used and the required specifications of the target heat conductive sheet. Above all, a production method to which the above-mentioned <production method> and <production method> are applied is preferable. That is,
A magnetic field is applied to a thermally conductive polymer composition containing at least one kind of thermally conductive fiber selected from graphitized carbon fiber, metal fiber, polybenzazole fiber, and ultrahigh molecular weight polyethylene fiber, and the sheet thickness direction is The present invention is characterized by a production method in which the composition is solidified after the thermally conductive fibers are tilted and oriented.

According to the production method of the present invention, since a magnetic field is used, it is easy to select an arbitrary thickness and an arbitrary inclination angle, and a block oriented in a certain direction as in <Production method>. There is no need for a molding step, a diagonal cutting step, and equipment such as an electrode and an electrostatic flocking device as in <Production method> and <Production method>.

The heat radiating device of the present invention is characterized in that a heat conductive sheet in which heat conductive fibers are inclined with respect to the thickness direction of the sheet is interposed between the heat generating member and the heat transfer member. Heating members include microprocessors, drives, semiconductor devices such as memories, power supplies, light sources, motors, driving devices, etc.
Examples include a cooler, a heat sink, a heat spreader, a die pad, a printed circuit board, a cooling fan, a heat pipe, and a housing.

Specifically, the semiconductor elements 4 and 9 that generate heat, the printed circuit board 3, the radiator 6, the heat sink 7, and the housing 10
The heat conductive sheet 5 of the present invention can be interposed between them to manufacture the heat radiating device having excellent heat radiating properties of the present invention illustrated in FIGS. 5 to 7 and 9.

[0034]

[Example 1] <Production method> As a heat conductive fiber, a long fiber filament (manufactured by Amoco, USA) of a pitch-based graphitized carbon fiber having a heat conductivity of 1000 W / m · K and a diameter of 10 µm in the fiber length direction was reduced to 30% by volume. Then, 70% by volume of an addition type liquid silicone rubber raw material was impregnated and cured by heating to obtain a block-shaped composite material. This block-shaped composite material was sliced with a cutting blade to a thickness of 2 mm so that the long fibers of the graphitized carbon fibers were inclined with respect to the thickness direction. The resulting thermal conductive sheet has a Shore A hardness of 55 and a thermal conductivity in the thickness direction of 210 W
/ M · K, the long fiber filaments of the pitch-based graphitized carbon fibers in the heat conductive sheet were oriented at an inclination to the thickness direction of the sheet as shown in FIG.

The pitch-based graphitized carbon fiber produced between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG.
mm heat conductive sheet 3 and tightening torque 1k
The heat radiator was assembled by fixing at g · cm. As a result of measuring the thermal resistance value after 10 minutes from the energization, it was 0.05 ° C./W.

[0036]

Example 2 <Production Method> As a heat conductive fiber, a heat conductivity of 400 W / m · K in the fiber length direction, a copper wire having a diameter of 12 μm and a volume of 20% by volume were added to a liquid silicone rubber raw material 80 of an addition type.
By impregnation with volume% and heat curing, a block-like composite material was obtained. This block-like composite material was sliced to a thickness of 1 mm with a cutting blade so that the copper wire was oriented with inclination with respect to the thickness direction. The obtained thermal conductive sheet has a Shore A hardness of 40, a thermal conductivity in the thickness direction of 72.7 W / m · K, and a copper wire in the thermal conductive sheet with respect to the thickness direction of the sheet as shown in FIG. It was tilted and oriented.

A heat conductive sheet 3 having a thickness of 1 mm is arranged between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG. The heat radiator was assembled by fixing with a tightening torque of 1 kg · cm. As a result of measuring a thermal resistance value 10 minutes after energization, it was 0.09 ° C./W.

[0038]

Example 3 <Production Method> Pulverized graphitized carbon fiber (diameter: 9 μm, manufactured by Mitsubishi Chemical Corporation) having a thermal conductivity of 800 W / m · K in the fiber length direction (length: 80 μm) was used as the heat conductive fiber. ) 25% by volume, 5% by volume of spherical graphite (average particle size: 16 μm, manufactured by Osaka Gas Co., Ltd.) and 70% by volume of an additional liquid silicone rubber raw material were mixed and dispersed, and the thermally conductive polymer composition a which was degassed and vacuumed was used. Prepared. 5 (1) to 5 (2), 5 (2), 5 (1) to 5 (2) are filled with the prepared thermally conductive polymer composition a in a plate-shaped mold made of aluminum having a thickness of 0.5 mm, a length of 20 mm, and a width of 20 mm. As shown in 3), the graphitized carbon fiber is sufficiently inclined and oriented in a magnetic field atmosphere in which the N pole and the S pole having a magnetic flux density of 10 Tesla are opposed to each other while being inclined in the thickness direction, and then heat-cured to obtain an Asker C hardness of 40 and thickness. 0.
A 6 mm flexible heat conductive sheet was obtained. The thermal conductivity of the obtained thermally conductive sheet in the thickness direction is 7.6 W / m · K, and the graphitized carbon fibers in the thermally conductive sheet are inclined with respect to the thickness direction of the sheet as shown in FIG. It was oriented.

A pitch-based graphitized carbon fiber produced between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG. The sheet 3 was arranged and fixed with a tightening torque of 1 kg · cm to assemble a heat radiator. As a result of measuring the thermal resistance value 10 minutes after energization, 0.25 /
W.

[0040]

Example 4 <Production method> Polybenzazole staple fibers having a thermal conductivity of 100 W / m · K in the fiber length direction (Zylon HT manufactured by Toyobo Co., Ltd., 9 μm in diameter as thermal conductive fibers)
m, length 300 μm) and 95% by volume of an additional liquid silicone rubber raw material were mixed and dispersed to prepare a thermally conductive polymer composition b which was degassed under vacuum. A prepared heat conductive polymer composition b was filled in a plate-shaped mold made of aluminum having a thickness of 0.5 mm, a length of 20 mm, and a width of 20 mm, and was inclined in the thickness direction as shown in FIG. In a magnetic field atmosphere in which the N and S poles of Tesla face each other, the graphitized carbon fibers are sufficiently inclined and oriented, and then heat-cured to obtain an Asker C hardness of 18,
A 1 mm thick flexible heat conductive sheet was obtained. The thermal conductivity of the obtained thermal conductive sheet in the thickness direction is 2.2 W / m · K.
The polybenzazole short fibers in the heat conductive sheet are shown in FIG.
As shown in FIG.

The polybenzazole short fibers produced between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG.
mm heat conductive sheet 3 and tightening torque 1k
The heat radiator was assembled by fixing at g · cm. As a result of measuring a thermal resistance value 10 minutes after energization, it was 0.73 ° C./W.

[0042]

Fifth Embodiment <Production Method> A pitch-based graphitized carbon fiber having a thermal conductivity of 800 W / m · K (diameter: 9 μm, manufactured by Mitsubishi Chemical Corporation) having a thermal conductivity of 800 W / m · K as a heat conductive fiber (length: 80 μm) ) Was coated with ferromagnetic nickel at a thickness of 0.2 μm by electroless plating. 20% by volume of pitch-based graphitized carbon fiber coated with nickel
And spherical aluminum oxide powder (manufactured by Showa Denko KK)
A thermally conductive polymer composition c was prepared by mixing and dispersing 10% by volume (average particle size: 10 μm) and 70% by volume of an addition type liquid silicone rubber raw material and degassing in vacuo. An aluminum-made plate-shaped mold having a thickness of 0.5 mm, a length of 20 mm, and a width of 20 mm is filled with the prepared thermally conductive polymer composition c, and as shown in FIG. The graphitized carbon fiber was sufficiently inclined and oriented in a magnetic field atmosphere in which the N and S poles of .5 Tesla faced each other, and then heat-cured to obtain an Asker C hardness of 3.
7. A flexible heat conductive sheet having a thickness of 0.6 mm was obtained. The thermal conductivity of the obtained thermally conductive sheet in the thickness direction is 6.8 W.
/ M · K, the graphitized carbon fibers coated with nickel in the thermally conductive sheet were oriented obliquely to the thickness direction of the sheet as shown in FIG.

A nickel-coated graphitized carbon fiber prepared between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG. The conductive sheet 3 was arranged and fixed with a tightening torque of 1 kg · cm to assemble the heat radiator. As a result of measuring the thermal resistance value 10 minutes after energizing,
0.37 ° C / W.

[0044]

Comparative Example 1 As a heat conductive fiber, 30% by volume of a pitch-based graphitized carbon fiber long fiber filament (manufactured by Amoco USA) having a thermal conductivity in the fiber length direction of 1000 W / m · K and a diameter of 9 μm was added. Was impregnated with 70% by volume of a liquid silicone rubber raw material and cured by heating to obtain a block composite material. The block-shaped composite material is cut with a cutting blade to a thickness of 2 mm so that the long fibers of the graphitized carbon fibers are oriented straight in the thickness direction.
Sliced into. The resulting heat conductive sheet has a Shore A hardness of 78 and a heat conductivity in the thickness direction of 220 W / m · K.
The long fiber filaments of the pitch-based graphitized carbon fibers in the heat conductive sheet were oriented straight in the thickness direction of the sheet as shown in FIG.

A thermally conductive sheet having a thickness of 1 mm in which pitch-based graphitized carbon fibers produced between a semiconductor element 2 mounted on a printed circuit board 1 and a heat sink 5 shown in FIG. 3 was arranged and fixed with a tightening torque of 1 kg · cm to assemble a heat radiator. As a result of measuring the thermal resistance value 10 minutes after energizing, 0.15 ° C.
/ W.

[0046]

Comparative Example 2 As a heat conductive fiber, a copper wire having a heat conductivity of 400 W / m · K in a fiber length direction and a diameter of 12 μm was 20% by volume.
Then, 80% by volume of an addition type liquid silicone rubber raw material was impregnated and cured by heating to obtain a block composite material. This block-like composite material was sliced with a cutting blade to a thickness of 1 mm so that the copper wire was oriented straight in the thickness direction. The resulting thermal conductive sheet has a Shore A hardness of 57, a thermal conductivity in the thickness direction of 73.1 W / m · K, and a copper wire in the thermal conductive sheet with respect to the thickness direction of the sheet as shown in FIG. It was oriented straight.

A heat conductive sheet 3 having a thickness of 1 mm in which copper wires formed between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG. The fixing device was fixed with a tightening torque of 1 kg · cm to assemble the radiator. As a result of measuring a thermal resistance value 10 minutes after energization, it was 0.17 ° C./W.

[0048]

COMPARATIVE EXAMPLE 3 Pulverized graphitized carbon fiber (diameter: 9 μm, manufactured by Mitsubishi Chemical Corporation) having a thermal conductivity of 800 W / m · K in the fiber length direction as a heat conductive fiber (length: 80 μm)
m) 25% by volume of spherical graphite (average particle size: 16 μm, manufactured by Osaka Gas Co., Ltd.), 5% by volume, and 70% by volume of an additional liquid silicone rubber raw material were mixed and dispersed, and the thermally conductive polymer composition a was vacuum defoamed. Was prepared. A prepared metal mold having a thickness of 0.5 mm, a length of 20 mm, and a width of 20 mm is filled with the prepared heat conductive polymer composition a, and is inclined in the thickness direction as shown in FIG. The graphitized carbon fibers were sufficiently oriented in a magnetic field atmosphere where the N and S poles of Tesla faced each other, and then heat-cured to obtain a flexible heat conductive sheet having an Asker C hardness of 62 and a thickness of 0.6 mm. The thermal conductivity of the obtained thermally conductive sheet in the thickness direction is 7.8 W / m · K.
The graphitized carbon fibers in the heat conductive sheet were oriented straight in the thickness direction of the sheet as shown in FIG.

The heat conduction having a thickness of 0.6 mm in which the pitch-based graphitized carbon fibers produced between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG. The heat radiating device was assembled by disposing the conductive sheet 3 and fixing it with a tightening torque of 1 kg · cm. As a result of measuring the thermal resistance value after 10 minutes from the energization, it was found that the heat resistance value was 0.1%.
It was 48 ° C / W.

[0050]

Comparative Example 4 Polybenzazole short fibers having a thermal conductivity of 100 W / m · K in the fiber length direction (Zylon HT manufactured by Toyobo Co., Ltd., diameter 9 μm, length 30)
0 μm) 5% by volume and 95% by volume of an additional liquid silicone rubber raw material were mixed and dispersed to prepare a thermally conductive polymer composition b which was degassed in a vacuum. 0.5mm thick aluminum
A prepared heat conductive polymer composition b is filled in a plate-shaped mold having a length of 20 mm and a width of 20 mm, and the N pole and the S pole having a magnetic flux density of 10 Tesla face in parallel with the thickness direction as shown in FIG. After sufficiently orienting the polybenzazole short fiber in a magnetic field atmosphere, it is cured by heating, and has an Asker C hardness of 18, a thickness of 1 mm.
Of a flexible heat conductive sheet. The thermal conductivity of the obtained thermally conductive sheet in the thickness direction is 2.0 W / m · K, and the polybenzazole short fibers in the thermally conductive sheet are straight in the thickness direction of the sheet as shown in FIG. It was oriented.

A 1 mm thick heat conductive sheet 3 in which polybenzazole short fibers produced between the semiconductor element 2 mounted on the printed board 1 and the heat sink 5 shown in FIG. Was arranged and fixed with a tightening torque of 1 kg · cm to assemble a heat radiator. As a result of measuring the thermal resistance value after 10 minutes from the energization, 1.02 ° C.
/ W.

[0052]

[Comparative Example 5] Pulverized graphitized carbon fiber having a thermal conductivity of 800 W / m · K (diameter: 9 μm, manufactured by Mitsubishi Chemical Corporation) having a thermal conductivity of 800 W / m · K as a thermally conductive fiber (length: 80 μm)
m) was coated with nickel, which is a ferromagnetic substance, to a thickness of 0.2 μm by electroless plating. 20% by volume of the pitch-based graphitized carbon fibers coated with nickel and spherical aluminum oxide powder (average particle diameter 10 μm, manufactured by Showa Denko KK)
m) 10% by volume, addition type liquid silicone rubber raw material 70
A thermally conductive polymer composition (c) was prepared by mixing and dispersing by volume and degassing in a vacuum. Aluminum thickness 0.5mm, length 2
The prepared thermally conductive polymer composition c was filled in a plate-shaped mold having a thickness of 0 mm and a width of 20 mm, and the north pole and the south pole having a magnetic flux density of 0.5 Tesla faced in parallel with the thickness direction as shown in FIG. After the graphitized carbon fibers were sufficiently oriented in a magnetic field atmosphere, they were cured by heating to obtain a flexible thermally conductive sheet having an Asker C hardness of 41 and a thickness of 0.6 mm. The heat conductivity in the thickness direction of the obtained heat conductive sheet is 6.8 W / m · K, and the graphitized carbon fiber coated with nickel in the heat conductive sheet is in the thickness direction of the sheet as shown in FIG. It was oriented straight.

The nickel-coated graphitized carbon fiber prepared between the semiconductor element 2 mounted on the printed circuit board 1 and the heat sink 5 shown in FIG. The heat conductive sheet 3 was arranged and fixed with a tightening torque of 1 kg · cm to assemble a heat radiating device. As a result of measuring a thermal resistance value 10 minutes after energization, it was 0.54 ° C./W.

[0054]

Comparative Examples 1 and 2 are heat conductive sheets in which graphitized carbon and long copper fibers are oriented straight in the thickness direction of the sheet as the heat conductive fibers. In Comparative Examples 3, 4, and 5, graphitized carbon short fibers, polybenzazole short fibers, and nickel-coated graphitized carbon short fibers were respectively oriented as heat conductive fibers straight in the thickness direction of the sheet. FIG. In any case, the heat conductive sheet has good heat conductivity and flexibility. However, when interposed between the heat-generating element and the heat transfer member, the heat conductive fibers are oriented straight in the thickness direction. It can be seen that the thermal resistance value has increased without being able to sufficiently follow the surface.

The heat conductive sheets of Examples 1 to 5 of the present invention are graphitized coated with long graphitized carbon fiber, copper wire, graphitized carbon short fiber, polybenzazole short fiber, and nickel as the heat conductive fiber. A heat conductive sheet in which short carbon fibers or the like are inclined and oriented with respect to the thickness direction of the sheet, and have flexibility and high thermal conductivity. Also, unlike the comparative example, when the heat conductive fiber is interposed in the gap between the element that actually generates heat and the heat transfer member, the heat conductive fiber is inclined and oriented with respect to the thickness direction. It can be seen that when pressure is applied in the presence of a pressure, it is possible to follow the uneven surface very well, so that the thermal resistance value is reduced.

Further, Embodiments 3, 4, and 5
A magnetic field is applied to the heat conductive polymer composition containing the heat conductive fiber, and the composition is solidified after the heat conductive fiber is inclinedly oriented with respect to the thickness direction of the sheet. This is a production method, and a flexible, thermally conductive sheet of the present invention having good thermal conductivity can be easily obtained.

As described above, the heat conductive sheet of the present invention has good heat conduction properties in the thickness direction of the sheet, and is flexible, easily compressible, has excellent followability to uneven surfaces, and has a small heat resistance. It is a conductive sheet. Therefore, it is possible to provide a useful heat dissipation device having excellent heat dissipation characteristics by interposing the gap between the semiconductor element generating a large amount of heat and a radiator such as a heat sink or a housing or the gap between the semiconductor element and a printed board or a die pad. .

[Brief description of the drawings]

FIG. 1 is a heat conductive sheet of the present invention in which heat conductive fibers (long fibers) are obliquely oriented.

FIG. 2 is a heat conductive sheet of the present invention in which heat conductive fibers (short fibers) are obliquely oriented.

FIG. 3 shows a conventional heat conductive sheet in which heat conductive fibers (long fibers) are oriented straight.

FIG. 4 shows a conventional heat conductive sheet in which heat conductive fibers (short fibers) are oriented straight.

FIG. 5 shows an example of a heat radiator using the heat conductive sheet of the present invention (interposed in a gap between the ball grid array type semiconductor package 4 and the radiator 6).

FIG. 6 shows an example of a heat radiating device using the heat conductive sheet of the present invention (chip size semiconductor package 4 and printed circuit board 3).
Between the gaps)

FIG. 7 shows an example of a heat radiating device using the heat conductive sheet of the present invention (interposed between a pin grid array type semiconductor package 4 and a heat sink 7).

FIG. 8 shows an example of a heat dissipating device using a conventional heat conductive sheet (interposed between a pin grid array type semiconductor package 4 and a heat sink 7).

FIG. 9 shows an example of a heat radiating device using the heat conductive sheet of the present invention (intervening in a gap between a plurality of heat generating semiconductor elements 8 and a housing 9).

FIG. 10 shows an example of a heat dissipating device using a conventional heat conductive sheet (intervening in a gap between a plurality of heat generating semiconductor elements 8 and a housing 9).

FIG. 11 is an outline view showing an example of a method for producing a heat conductive sheet of the present invention.

FIG. 12 is a schematic view showing an example of a conventional method for producing a thermally conductive sheet.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 inclined thermally conductive fiber 2 straight oriented thermally conductive fiber 3 printed board 4 semiconductor element 5 thermally conductive sheet in which thermally conductive fiber of the present invention is inclined and oriented 6 radiator 7 heat sink 8 conventional Thermal conductive sheet in which thermal conductive fibers are oriented straight 9 Semiconductor element 10 Housing 11 Mold 12 Thermal conductive polymer composition containing thermal conductive fibers 13 Magnet 14 Magnetic lines of force

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 79/04 C08L 79/04 Z 101/00 101/00 H01L 23/36 H01L 23/36 DF term ( Reference) 4F071 AA15 AA67 AA69 AB03 AB06 AD01 AE22 AF44 AH19 BB13 BC01 BC02 BC12 4J002 AC001 BB031 BB032 BB051 BB061 BB121 BB151 BB171 BB231 BC031 BD031 BD101 BD141 BD151 BE021 BF021 CF01101 CF011 CB1011 001 CN031 CP031 DA026 DA066 DC006 FA042 FA046 FD202 FD206 GF00 GT00 5F036 AA01 BB21

Claims (7)

[Claims] 1. A thermally conductive sheet containing a thermally conductive fiber in a polymer, wherein the thermally conductive fiber is oriented obliquely with respect to the thickness direction of the sheet. 2. The heat conductive sheet according to claim 1, wherein the heat conductive fiber is at least one selected from graphitized carbon fiber, metal fiber, polybenzazole fiber, and ultrahigh molecular weight polyethylene fiber. 3. The polymer is silicone rubber and has a thickness of 0.1.
The heat conductive sheet according to claim 1 or 2, wherein Shore A hardness is 70 or less. 4. The thermal conductive fiber according to claim 1, wherein the heat conductive fiber has a linear shape or a curved or bent shape such as a U-shape, an S-shape, an arc shape, a coil shape or a spring shape. Conductive sheet 5. A sheet, comprising applying a magnetic field to a heat conductive polymer composition containing at least one heat conductive fiber selected from graphitized carbon fibers, metal fibers, polybenzazole fibers, and ultrahigh molecular weight polyethylene fibers. A method for producing a heat conductive sheet, comprising solidifying the composition after tilting the heat conductive fiber with respect to the thickness direction of the sheet. 6. A heat dissipating device characterized in that a heat conductive sheet in which heat conductive fibers are inclined with respect to the thickness direction of the sheet is interposed between the heat generating member and the heat transfer member. 7. The heat radiator according to claim 6, wherein the heat conductive fiber is at least one selected from graphitized carbon fiber, metal fiber, polybenzazole fiber, and ultrahigh molecular weight polyethylene fiber.