JP2000191998A - Thermally conductive adhesive, method of adhesion and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a semiconductor device that can effectively dissipate the heat generated from the device by filling carbon fibers coated with a ferromagnetic substance on their surfaces with an adhesive polymer and intervening the thermally conductive adhesive between the substrates so that the carbon fibers are oriented in a certain direction. SOLUTION: Carbon fibers having an average diameter of 5-20 μ, an average length of 20-800 μm and a thermal conductivity of >=200 W/mk in the fiber- length direction are coated with at least one ferromagnetic particles selected from nickel, iron, ferrite, chromium, cobalt, manganese or rare earth in a layer thickness of 0.01-5 μm, and filled with at least one of adhesive polymer selected from the group consisting of epoxy, polyimide, acryl, urethane, vinyl and silicone polymers to prepare the objective thermally conductive adhesive. The resultant adhesive (3) is intervened between the semiconductor chips 8 and the substrates such as die pads 7 or the like, thus the carbon fibers are oriented in a certain direction by action of the external magnetic field and adhered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat conductive adhesive which is required to have a high heat conductivity for effectively dissipating heat generated from components such as semiconductor elements, power supplies and light sources used in electric products. The present invention relates to a bonding method and a semiconductor device having excellent heat dissipation.

[0002]

2. Description of the Related Art Conventionally, a heat conductive adhesive having an adhesive polymer as a matrix has been used to join a semiconductor element or electronic component that generates heat with a heat transfer member that dissipates heat generated from the semiconductor element or electronic component. I have. These adhesives include silver, copper, gold, aluminum, nickel and other metals or alloys with high thermal conductivity, compounds, or aluminum oxide, magnesium oxide, silicon oxide, boron nitride, etc. A powdery ceramic filler such as aluminum nitride, silicon nitride, and silicon carbide, and a powdery or fibrous heat conductive filler such as carbon black and diamond are compounded.

[0003] A heat conductive adhesive is known in which carbon fiber is blended with an adhesive polymer as a heat conductive filler. For example, Japanese Patent Application Laid-Open No. 63-305520 proposes a die bond material filled with carbon-based fine powder or carbon fiber. JP-A-6-212137 discloses an adhesive material filled with carbon fibers having a specific structure, that is, carbon fibers having a three-dimensional structure using a mesophase pitch as a base material, for the purpose of improving the heat conduction characteristics. Further, Japanese Unexamined Patent Publication No.
Japanese Patent Application Laid-Open No. 324127 discloses a die bonding material for a semiconductor element using a graphite material obtained by heat-treating a specific polymer material.

Further, Japanese Patent Application Laid-Open No. 5-209157,
According to Japanese Patent Application Laid-Open No. 6-299129, for an electronic device, the heat radiation characteristics are further improved by specifying the structure of the carbon fiber or metal fiber to be contained in a lump-like or thread-like shape, or a woven or non-woven fabric. Adhesives have been proposed. On the other hand, according to JP-A-62-194653 and JP-A-63-62762, an adhesive containing a magnetic substance powder such as nickel is oriented in a thickness direction in a magnetic field to improve thermal conductivity. A method is disclosed.

[0005]

However, the amount of heat generated by recent high-density and high-performance electronic components such as semiconductor devices and electric appliances tends to increase remarkably. An adhesive having sufficiently high heat conduction properties could not be obtained by the conventional improvement method using a heat conductive filler. The conventional method of orienting an adhesive containing a magnetic substance powder in a thickness direction in a magnetic field is based on a conventional powdery or needle-like nickel-based or iron-based material that has a thermal conductivity of 100 W / mK or less. Therefore, it was not possible to develop a sufficiently high thermal conductivity as an adhesive even if the film was oriented by a magnetic field.

That is, since an adhesive having even higher heat conduction properties has not been developed, electrochemical migration is accelerated due to a large amount of heat generated from electronic components such as semiconductor elements, and the formation of wiring and pad portions is accelerated. Corrosion has been promoted, and cracks have occurred or been broken in the constituent materials due to the generated thermal stress, and various troubles have occurred in which the interface of the joining portions of the constituent materials has separated and the life of the electronic component has been impaired.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a heat conductive material for effectively dissipating heat generated from components such as a semiconductor element, a power supply, and a light source used in electric appliances. An adhesive, an adhesive method, and a semiconductor device having excellent heat dissipation characteristics are provided. That is, the present invention is a heat conductive adhesive characterized by blending a carbon fiber coated with a ferromagnetic material and an adhesive polymer.

[0008] The present invention further provides a heat conductive adhesive formed by blending a carbon fiber coated with a ferromagnetic material and an adhesive polymer between adherends, and the heat conductive adhesive is applied by an external magnetic field. This is a bonding method characterized by bonding carbon fibers coated with a ferromagnetic substance in a state where they are oriented in a certain direction. Furthermore, the present invention interposes a heat conductive adhesive formed by blending a carbon fiber coated with a ferromagnetic material and an adhesive polymer between a semiconductor element and a heat transfer member, and moves the carbon fiber in a certain direction by an external magnetic field. The semiconductor device is adhered in a state where the semiconductor device is oriented in the following manner.

The carbon fiber coated with a ferromagnetic material used in the present invention may be formed by applying a ferromagnetic material to a carbon fiber by electroless plating, electrolytic plating, physical vapor deposition by vacuum vapor deposition or sputtering, chemical vapor deposition, or the like. It can be prepared by a method such as painting, dipping, or mechanochemical method of mechanically fixing fine particles to the carbon fiber surface.

[0010] Ferromagnetic materials include nickel-based and nickel-based alloys, iron-based alloys, iron nitride-based, ferrite-based, barium ferrite-based, cobalt-based alloys, manganese-based alloys, and the like.
Rare earth alloys such as neodymium / iron / boron and samarium / cobalt are used. Among them, nickel-based,
A ferromagnetic material composed of at least one metal, alloy or compound selected from iron, ferrite, chromium, cobalt, manganese and rare earths is preferred.

The thickness of the ferromagnetic material to be coated is not limited, but is preferably in the range of 0.01 μm to 5 μm. If the thickness is less than 0.01 μm, the magnetism of an external magnetic field causes the carbon fibers coated with the ferromagnetic material to be oriented so that the magnetism is insufficient and the fibers are hardly oriented. If it exceeds 5 μm, although it is easy to orient by magnetic force, it is not preferable because the thermal conductivity as an adhesive decreases. The more preferable thickness of the ferromagnetic material is in the range of 0.05 μm to 2 μm.

In addition, as a pre-process for coating the ferromagnetic material on the carbon fiber or on the surface of the carbon fiber after the ferromagnetic material is coated, silver, copper, gold, aluminum oxide, magnesium oxide, aluminum nitride, silicon carbide, It is also possible to improve thermal conductivity by coating a known metal, alloy, ceramics or the like having a large thermal conductivity such as. When the ferromagnetic material to be coated is electrically conductive such as nickel, the heat conduction of the present invention is achieved by coating the outermost surface with an electrically insulating ceramic such as aluminum oxide, magnesium oxide, aluminum nitride or silicon carbide. It is possible to make the conductive adhesive electrically insulating.

[0013] The type, size and shape of the carbon fiber are not specified. As for the raw material, the carbon fiber with a developed graphite structure, which is heat-treated at a high temperature exceeding 2000 to 3000 ° C. or 3000 ° C. after a process such as melt-spinning, infusibilization, and carbonization using a mesophase pitch system as a main material rather than a PAN system, is a fiber. It is preferable because the thermal conductivity in the length direction is large. Further, carbon fibers obtained by a vapor growth method can also be used. The thermal conductivity of this carbon fiber in the fiber length direction is preferably 200 W / mK or more, preferably 400 W / mK or more, and more preferably 1000 W / m.
K or more.

The average diameter of the carbon fiber is 5 to 20 μm.
m and the average length in the range of 20 to 800 μm are preferable because the adhesive polymer can be easily filled and the heat conductivity of the obtained heat conductive adhesive increases. When the average diameter is smaller than 5 μm or when the average length is longer than 800 μm,
It becomes difficult to mix at a high concentration in the adhesive polymer.
Further, carbon fibers having an average diameter of more than 20 μm are not preferred because their productivity is deteriorated. Average length 20μm
If it is shorter than this, the bulk specific gravity becomes smaller, and problems may arise in handling and workability during the manufacturing process. In addition, these carbon fiber surfaces may be subjected to a known oxidation treatment such as electrolytic oxidation in advance.

The adhesive polymer serving as a matrix for filling a carbon fiber coated with a ferromagnetic material includes epoxy-based polymers,
Polyimide, acrylic, vinyl such as polyvinyl acetate, urethane, silicone, olefin, polyamide, polyamideimide, phenol, amino, bismaleimide, polyimide silicone, saturated and unsaturated polyester , Diallyl phthalate,
Liquid or solid made of known resins and rubbers such as urea-based, melamine-based, alkyd-based, benzocyclobutene-based, synthetic rubber-based such as polybutadiene, chloroprene rubber, and nitrile rubber, natural rubber-based, and styrene-based thermoplastic elastomers Are preferred.

With respect to the curing form, any of known adhesive curing polymers such as thermosetting, thermoplastic, ultraviolet and visible light curable, room temperature curable, and moisture curable can be used. Among them, epoxy, polyimide, acrylic, urethane and silicone based materials having good adhesion to various metals and ceramics, various plastics and rubbers, and elastomers of materials constituting electronic parts are preferred. Molecules are preferred. Also, for the purpose of fiber surface treatment, the surface of the carbon fiber coated with ferromagnetic material is treated with a known coupling agent or sizing agent to improve the wettability with the adhesive polymer or improve the filling property. It is possible to

Further, the heat conductive adhesive of the present invention includes a thixotropic agent, a dispersant, a curing agent, a curing accelerator,
Known additives such as a retarder, a tackifier, a plasticizer, a flame retardant, an antioxidant, a stabilizer, and a colorant can be added. In addition, it is used for conventional heat conductive adhesives such as powder and fiber shaped metals and ceramics, specifically silver, copper, gold, aluminum oxide, magnesium oxide, aluminum nitride, silicon carbide, and metal-coated resins. It is also possible to use a filler that has been used or a normal carbon fiber that is not coated with a ferromagnetic material. In order to reduce the viscosity of the adhesive, it is effective to add a volatile organic solvent or a reactive plasticizer.

According to the bonding method of the present invention, a heat conductive adhesive obtained by blending a carbon fiber coated with a ferromagnetic material and an adhesive polymer is interposed between adherends, and the carbon fiber is applied by an external magnetic field. This is a bonding method characterized in that bonding is performed while being oriented in a certain direction. The heat conductivity in the length direction of the oriented fiber can be improved by orienting the carbon fiber coated with the ferromagnetic material in the adhesive along the lines of magnetic force by an external magnetic field. In order to align and orient the fibers in the gap direction of the adherend, that is, in the thickness direction of the adhesive, the N and S poles of the permanent magnet or electromagnet are opposed in the thickness direction, and the direction of the magnetic field lines is the desired fiber orientation. Install so that it corresponds to the direction.

On the other hand, in order to improve the thermal conductivity of the adhesive in the in-plane direction, the fibers are aligned in the in-plane direction by facing the N pole and the S pole of the magnet in a direction perpendicular to the thickness direction. Orientation. Alternatively, the fibers can be aligned in the in-plane direction even when the north pole and the north pole or the south pole and the south pole of the magnet are opposed to each other in the thickness direction. Further, the magnets do not necessarily have to be opposed to both sides, and even if they are arranged on only one side, the carbon fibers coated with the ferromagnetic material in the adhesive can be oriented. The magnetic field generating means used as the external magnetic field may be a permanent magnet or an electromagnet, but the magnetic flux density is practically 200 to 20,000 gauss, and a good orientation can be achieved.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION The thermally conductive adhesive of the present invention can be produced by mixing carbon fibers coated with a predetermined amount of a ferromagnetic material in an adhesive polymer and uniformly dispersing them. When mixing and dispersing, it is preferable to add a step of removing air bubbles by reducing or applying pressure. The carbon fiber coated with a ferromagnetic material increases the thermal conductivity of the adhesive as it is added to the adhesive polymer in a large amount, but when filled in a large amount, the viscosity of the adhesive becomes too high or mixed. Problems such as difficulty in removing bubbles may occur. Therefore, although it can be arbitrarily determined according to the type of the carbon fiber coated with the ferromagnetic material, the adhesive polymer, the compounding agent, and the characteristics of the intended end product, the ferromagnetic material in the thermally conductive adhesive can be determined. The mixing ratio of the carbon fiber coated with is practically in the range of 5 to 90% by volume, more preferably 10 to 60% by volume.

For applications requiring electrical insulation,
It is sufficient to use a carbon fiber in which an electrically insulating coating layer is further formed on the outermost surface of the carbon fiber coated with the ferromagnetic material. Also,
Polyimide or silicone on at least one adherend surface,
Polymeric electrically insulating layer such as polybenzocyclobutene, polybutadiene, or silicon oxide or silicon nitride,
After forming a ceramic-based electrically insulating layer such as aluminum oxide, aluminum nitride, or silicon carbide, a thermal conductive adhesive consisting of a carbon fiber coated with a ferromagnetic material and an adhesive polymer is interposed, and an external magnetic field is applied. By bonding the carbon fiber coated with the ferromagnetic material in a state where the carbon fiber is oriented in a certain direction, the present invention can also be applied to applications requiring electrical insulation.

A heat conductive adhesive comprising a carbon fiber coated with a ferromagnetic material of the present invention and an adhesive polymer is interposed between the semiconductor element and the heat transfer member, and the heat conductive adhesive is applied by an external magnetic field. The semiconductor device of the present invention as shown in FIG. 7-6 can be manufactured by bonding the carbon fibers coated with the ferromagnetic material in the agent while being oriented in a certain direction. The heat conductive adhesive can be interposed between the adherends by a known method such as screen printing, pad printing, dispenser application, potting, and spray coating. Examples of the heat transfer member include ordinary radiators and coolers, heat sinks, heat spreaders, die pads, printed boards, cooling fans, heat pipes, housings, and the like.

Hereinafter, the present invention will be described in more detail with reference to examples. As a carbon fiber coated with a ferromagnetic material, a pitch-based graphitized carbon fiber D having an average diameter of 10 μm, an average length of 100 μm, and a thermal conductivity of 400 W / mK in the fiber direction is coated with nickel by electroless plating to a film thickness of 0.1 μm. Carbon fiber A coated with 2 μm and coated with a ferromagnetic material was prepared. Similarly, the pitch-based carbon fibers shown in Table 1 (FIG. 13) were coated with nickel or cobalt as a ferromagnetic material by electroless plating to prepare carbon fibers B and C.

[0024]

EXAMPLE 1 A mixture of 15% by volume of carbon fiber A coated with nickel as a ferromagnetic material and 85% by volume of an adhesive polymer made of a bisphenol F type epoxy resin containing an amine-based curing agent was mixed by heat conduction. An agent was prepared. A 1 mm thick, 20 mm long, 20 mm wide plate-shaped mold made of aluminum is filled with the prepared heat conductive adhesive, and the magnetic flux density is 6 in the thickness direction.
It was cured by heating in a magnetic field atmosphere in which the N pole and the S pole of 000 Gauss faced each other. The thermal conductivity of the cured product was 1.4 W / mK.

[0025]

Examples 2 to 12 In the same manner as in Example 1, a heat conductive adhesive composed of a carbon fiber coated with a ferromagnetic material having the composition shown in Table 2 and an adhesive polymer was prepared. , 20 mm in length and 20 mm in width in a plate-shaped mold, and heat-cured in a magnetic field atmosphere having a magnetic flux density of Table 2 in which the north pole and the south pole of the magnet face each other in the thickness direction. Table 2 shows the thermal conductivity of the cured product. The materials used as the adhesive polymer in Table 2 were epoxy as bisphenol F epoxy resin containing an amine-based curing agent, silicone as an additional two-part silicone rubber, polyimide as a heat-curable liquid polyimide, and acrylic. Is a cyanoacrylate adhesive.

[0026]

COMPARATIVE EXAMPLE 1 A mixture of 15% by volume of carbon fiber D not coated with a ferromagnetic material shown in Table 1 and 85% by volume of an adhesive polymer made of a bisphenol F type epoxy resin containing an amine-based curing agent was mixed to conduct heat. An adhesive was prepared. Aluminum thickness 1
It was filled into a plate-shaped mold having a size of 20 mm, a length of 20 mm and a width of 20 mm, and was cured by heating. The thermal conductivity of the cured product is 0.8 W / mK
Met.

[0027]

Comparative Examples 2 to 3 In the same manner as in Comparative Example 1, a heat conductive adhesive comprising a carbon fiber D having the composition shown in Table 2 and an adhesive polymer was prepared, and was made of aluminum having a thickness of 1 mm and a length of 20 mm.
It was filled in a plate-shaped mold having a width of 20 mm and cured by heating.
Table 2 shows the thermal conductivity of the cured product.

[0028]

Embodiment 13 The silicone-based thermally conductive adhesive 3 of Embodiment 10 of the present invention was applied on a ball grid array type semiconductor package 2 mounted on the printed circuit board 1 shown in FIG. 5-1 by a dispenser (FIG. 5). -2). As shown in FIG. 5-3, the radiator 4 is disposed on the heat conductive adhesive 3 and pressurized.
Permanent magnet 1 with magnetic flux density of 6000 gauss as shown in Fig.5-4
The semiconductor device FIG. 5-5 was prepared by heating and curing the heat conductive adhesive 3 with the N-pole and S-pole of No. 1 facing each other. The area ratio between the radiator of this device and the semiconductor package serving as the heat generating portion was 2: 1. FIG. 9 shows the results of observing the temperature distribution of the radiator 4 by a thermoviewer 2 minutes and 4 minutes after the power was supplied to the apparatus. The temperature at the center of the radiator 4 after 10 minutes of energization is 38
° C. The carbon fibers coated with the magnetic material in the cured heat conductive adhesive were oriented uniformly in the thickness direction as shown in FIG. 5-6.

[0029]

Comparative Example 4 In the same manner as in Example 13, the silicone-based heat conductive adhesive of Comparative Example 3 in Table 2 was applied to a ball grid array type semiconductor package mounted on a printed circuit board.
The radiator 4 was arranged above the heat conductive adhesive and pressurized, and the heat conductive adhesive was heated and cured to manufacture a semiconductor device.
As in Example 13, the results of observing the temperature distribution of the radiator 4 with a thermoviewer 2 minutes and 4 minutes after energizing the device are shown in FIG. The temperature at the center of the radiator 4 10 minutes after energization was 61 ° C. The carbon fibers in the cured thermally conductive adhesive were randomly dispersed as shown in FIG.

[0030]

Embodiment 14 The epoxy-based heat conductive adhesive 3 of Embodiment 7 of the present invention was screen-printed on the die pad 7 of the lead frame 6 shown in FIG. 7-1 (FIG. 7-1). As shown in FIG. 7-2, the semiconductor chip 8 is arranged on the heat conductive adhesive 3 and pressurized, and the N pole and the S pole of the permanent magnet 11 having a magnetic flux density of 6000 gauss are opposed as shown in FIG. 7-3. In this state, the heat conductive adhesive 3 was cured by heating. Further, the bonding wire 9 connects the electrode portion of the semiconductor chip 8 to the lead frame 11.
Were electrically connected (FIG. 7-4) and transfer-molded with an epoxy-based sealant 10 to produce a semiconductor device shown in FIG. 7-5. FIG. 11 shows the results of observing the temperature distribution of the die pad 7 with a thermoviewer 2 minutes and 4 minutes after the power was supplied to the apparatus. The temperature at the center of the die pad 7 after 10 minutes from the energization was 43 ° C. The carbon fibers coated with the magnetic substance in the cured heat conductive adhesive were aligned in the thickness direction as shown in FIG. 7-6.

[0031]

Comparative Example 5 In the same manner as in Example 14, the epoxy-based heat conductive adhesive of Comparative Example 3 in Table 2 was screen-printed on a die pad of a lead frame. A semiconductor chip was placed on top of the heat conductive adhesive and pressurized, and the heat conductive adhesive was heated and cured to manufacture a semiconductor device. As in Example 14, the result of observing the temperature distribution of the die pad 7 with a thermoviewer 2 minutes and 4 minutes after energizing the device is shown in FIG. Energizing 1
The temperature at the center of the die pad 7 after 0 minute was 68 ° C. The carbon fibers in the cured thermally conductive adhesive were randomly dispersed as shown in FIG.

[0032]

As shown in Table 2, the heat conductive adhesive of the present invention comprising a carbon fiber coated with a ferromagnetic material and an adhesive polymer has a large heat conductivity and good heat dissipation. is there.
Furthermore, by the bonding method of the present invention, bonding between a semiconductor package having a large heat value and a radiator such as a heat sink,
Alternatively, the present invention can be applied to adhesion between a semiconductor chip and a die pad portion, and a useful semiconductor device having excellent heat radiation characteristics can be provided.

[Brief description of the drawings]

FIG. 1 shows an example of a semiconductor device using the heat conductive adhesive of the present invention (used for bonding a ball grid array type semiconductor package 2 and a radiator 4).

FIG. 2 shows an example of a semiconductor device using the heat conductive adhesive of the present invention (used for bonding a chip size semiconductor package 2 and a printed circuit board 1).

FIG. 3 shows an example of a semiconductor device using the heat conductive adhesive of the present invention (used for bonding a pin grid array type semiconductor package 2 and a heat sink 5).

FIG. 4 shows an example of a semiconductor device using the heat conductive adhesive of the present invention (used for bonding a semiconductor chip 8 and a die pad 7).

FIG. 5 is a schematic view showing a method for manufacturing the semiconductor device of the present invention shown in FIG. 1 and an orientation state of carbon fibers.

FIG. 6 shows an example of a conventional semiconductor device using a thermally conductive adhesive containing carbon fibers.

FIG. 7 is a schematic view showing a method for manufacturing the semiconductor device of the present invention shown in FIG. 4 and an orientation state of carbon fibers.

FIG. 8 shows an example of a conventional semiconductor device using a thermally conductive adhesive containing carbon fibers.

FIG. 9 is a diagram showing a temperature distribution during energization of the semiconductor device of the present invention of Example 13;

FIG. 10 is a diagram showing a temperature distribution during energization of the semiconductor device of Comparative Example 4;

FIG. 11 is a diagram showing a temperature distribution during energization of the semiconductor device of the present invention of Example 14;

FIG. 12 is a diagram showing a temperature distribution during energization of the semiconductor device of Comparative Example 5;

FIG. 13 and Table 2

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Printed circuit board 2 Semiconductor package 3 Heat conductive adhesive 4 Heat sink 5 Heat sink 6 Lead frame 7 Die pad 8 Semiconductor chip 9 Bonding wire 10 Sealant 11 Magnet 12 Ferromagnetic-coated carbon fiber 13 Conventional carbon fiber

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kikuo Fujiwara F-term (reference) 4J040 DF041 EC001 EF001 EK031 HA026 HA068 HA076 KA04 NA20 PA32 5F036 AA01 BB21 BC05 BD01 BD21

Claims (14)

[Claims] 1. A thermally conductive adhesive comprising a carbon fiber coated with a ferromagnetic material and an adhesive polymer. 2. The heat according to claim 1, wherein the ferromagnetic material comprises at least one metal, alloy or compound selected from nickel, iron, ferrite, chromium, cobalt, manganese and rare earths. Conductive adhesive 3. The carbon fiber has an average diameter of 5 to 20 μm, an average length of 20 to 800 μm, and a thermal conductivity of 2 in the fiber length direction.
3. The heat conductive adhesive according to claim 1, wherein the heat conductive adhesive is at least 00 W / mK. 4. The heat conductive adhesive according to claim 1, wherein the adhesive polymer is at least one polymer selected from epoxy, polyimide, acrylic, urethane and silicone. 5. A heat conductive adhesive comprising a mixture of a carbon fiber coated with a ferromagnetic material and an adhesive polymer is interposed between adherends, and the carbon fiber is oriented in a certain direction by an external magnetic field. Bonding method characterized in that the bonding is performed in a state of being attached 6. The ferromagnetic material according to claim 5, wherein the ferromagnetic material is at least one metal, alloy or compound selected from nickel, iron, ferrite, chromium, cobalt, manganese and rare earths. Bonding method 7. The carbon fiber has an average diameter of 5 to 20 μm, an average length of 20 to 800 μm, and a thermal conductivity of 2 in the fiber length direction.
7. The bonding method according to claim 5, wherein the bonding method is not less than 00 W / mK. 8. The bonding method according to claim 5, wherein the adhesive polymer is at least one polymer selected from epoxy, polyimide, acrylic, urethane and silicone. 9. The bonding method according to claim 5, wherein an electrical insulating layer is formed on at least one of the adherend surfaces. 10. A heat conductive adhesive comprising a semiconductor element and a heat transfer member interposed between a carbon fiber coated with a ferromagnetic material and an adhesive polymer, and the heat conductive adhesive is applied by an external magnetic field. A semiconductor device having a structure in which carbon fibers coated with a ferromagnetic substance in the inside are bonded in a state where they are oriented in a certain direction. 11. The semiconductor according to claim 10, wherein the ferromagnetic material comprises at least one metal, alloy or compound selected from nickel, iron, ferrite, chromium, cobalt, manganese and rare earths. apparatus 12. The semiconductor device according to claim 10, wherein the average diameter of the carbon fibers is 5 to 20 μm, the average length is 20 to 800 μm, and the thermal conductivity in the fiber length direction is 200 W / mK or more. 13. The adhesive polymer according to claim 10, wherein the adhesive polymer is at least one polymer selected from the group consisting of epoxy, polyimide, acrylic, urethane and silicone.
13. The semiconductor device according to 1 or 12. 14. The semiconductor device according to claim 10, wherein an electrically insulating layer is formed on at least one of the adherend surfaces.