JP2000195998A - Heat conductive sheet, its manufacture, and semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve heat radiating characteristic of a semiconductor device by interposing between a semiconductor element and a heat conducting member a silicon-rubber based heat conducting sheet, wherein pitch-based carbon fibers coated with ferromagnetic films are oriented in a fixed direction. SOLUTION: As heat conductive members, there are ordinary radiators, coolers, heat sinks, heat spreaders, die pads, printed boards, cooling fans, heat pipes, and housings, etc. As pitch-based carbon fibers coated with ferromagnetic materials, the pitch-based carbon fibers made into graphites and having an average diameter of 10 μm, average length of 100 μm, and the thermal conductivity of 400 W/mK in their fibered direction are coated by an electroless plating with nickel films, having a film thickness of 0.2 μm to form the same. The 15 vol.% pitch-based carbon fibers coated with the nickel films and a 85 vol.% addition-type liquid-silicon rubber raw material are mixed distributedly with each other to obtain a vacuum degassed composition. Therefore, between a plurality of different height bearing semiconductor elements 6 mounted on a printed board 1 and a housing 10 of a heat conductive member, a heat conductive sheet 3 is interposed to be assembled in a semiconductor device.

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 requiring high heat conductivity, a method for manufacturing the same, and a semiconductor device. More specifically, the present invention relates to a heat conductive sheet that effectively dissipates heat generated from components such as a semiconductor element, a power supply, and a light source used in an electric product, a method for manufacturing the same, and a semiconductor device having excellent heat dissipation.

[0002]

2. Description of the Related Art Heretofore, a flexible heat conductive sheet such as silicone rubber has been used for the purpose of transferring heat between a semiconductor element or an electronic component that generates heat and a heat transfer member that dissipates heat. These heat conductive sheets include silver,
Metals, alloys, and compounds with high thermal conductivity such as copper, gold, aluminum, and nickel, or powdered ceramics such as aluminum oxide, magnesium oxide, silicon oxide, boron nitride, aluminum nitride, silicon nitride, and silicon carbide And a thermally conductive filler in the form of powder or granules such as carbon black and diamond.

[0003] A heat conductive sheet in which carbon fiber is mixed with silicone rubber or the like as a heat conductive filler is known. Further, according to Japanese Patent Application Laid-Open No. 9-283955, a heat radiation sheet is proposed in which graphitic carbon fibers having an average aspect ratio of less than 3 are dispersed in a matrix such as silicone rubber. In the present invention, since ordinary carbon fibers have anisotropy, the fiber direction is dispersed in a random direction by specifying the aspect ratio of the carbon fibers to be small, and the anisotropy of the thermal conductivity in the thickness direction and the plane direction is reduced. The resulting disadvantages have been eliminated. However, although the anisotropy is reduced by this method, the thermal conductivity in the thickness direction is insufficient. Also, it has not always been easy to produce inexpensively graphitic carbon fibers having an aspect ratio of less than 3 used as a raw material.

[0004] On the other hand, a production method and a sheet-like molded product in which a polymer composite material composed of magnetic particles and a polymer material is heated in a magnetic field atmosphere are known. For example, JP
Japanese Patent Application Laid-Open No. 51593/1993 discloses a basic production method of curing a mixture of a conductive magnetic powder and an insulating material while applying an external magnetic field in a fluid state. JP-A-53-53796
According to the publication, an anisotropic conductive sheet is obtained by a manufacturing method in which a magnetic linear body is magnetically oriented in the thickness direction of the sheet. Japanese Patent Publication No. 74804/1992 discloses a method in which an uncured composite mainly composed of conductive magnetic particles having a specific particle diameter and an insulating polymer elastic material is subjected to a magnetic field treatment to crosslink the specific hardness and the specific thickness. It is an isotropic conductive rubber sheet.

[0005]

However, none of the molded articles obtained by these conventional manufacturing methods using a magnetic field is intended to improve the thermal conductivity, and the molded articles obtained by using the anisotropic conductive Parts or pressure-sensitive conductive parts were the main components. In other words, since a heat conductive sheet having good heat conductive properties particularly in the thickness direction has not been developed, a large amount of heat generated from an electronic component such as a semiconductor element accelerates electrochemical migration or causes a problem in wiring or a pad portion. Corrosion, accelerated thermal stress, cracks or breaks the component material, and the interface at the joint of the component material peels off, causing various troubles that impair the reliability and life of the electronic components. I was

[0006]

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 object of the present invention is to provide a sheet, a manufacturing method thereof, and a semiconductor device having excellent heat radiation characteristics. That is,
The present invention is a heat conductive sheet characterized in that a pitch-based carbon fiber coated with a ferromagnetic material is oriented in a certain direction in silicone rubber.

Further, a magnetic field is applied to a composition comprising the pitch-based carbon fiber coated with the ferromagnetic material and the liquid silicone rubber, and the ferromagnetic-coated pitch-based carbon fiber in the composition is oriented in a certain direction and cured. A method for producing a thermally conductive sheet.

Still another aspect of the present invention is a heat-dissipating property in which a silicon rubber-based heat conductive sheet in which a pitch-based carbon fiber coated with a ferromagnetic material is oriented in a certain direction is interposed between a semiconductor element and a heat transfer member. A semiconductor device characterized by being excellent.

The pitch-based carbon fiber coated with a ferromagnetic material used in the present invention is obtained by subjecting the ferromagnetic material to the pitch-based carbon fiber by an electroless plating method, an electrolytic plating method, a physical vapor deposition method such as vacuum vapor deposition or sputtering, or a chemical vapor deposition method. It can be prepared by a method such as a mechanical vapor deposition method, painting, dipping, or a mechanochemical method of mechanically fixing fine particles to the pitch-based 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. When the thickness is less than 0.01 μm, when the pitch-based carbon fiber coated with the ferromagnetic material is oriented by the magnetic force of the external magnetic field, the magnetic property is insufficient and the fiber is hardly oriented. If it exceeds 5 μm, although it is easy to orient by magnetic force, it is not preferable because the thermal conductivity of the heat conductive sheet decreases. A more preferable thickness of the ferromagnetic material is 0.05 μm to 2 μm.
Range.

In addition, as a pre-process for coating the pitch-based carbon fiber with a ferromagnetic material, or on the fiber surface 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. If the ferromagnetic material to be coated is electrically conductive, such as nickel, the outermost surface is coated with an electrically insulating ceramic or insulating polymer such as aluminum oxide, magnesium oxide, aluminum nitride, or silicon carbide to form It is possible to make the thermally conductive sheet of the invention electrically insulating.

The type, size and shape of the pitch carbon fiber are not specified. As for the raw material, pitch-based 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 pitch system or a mesophase pitch system as a main material is preferred. It is preferable because the thermal conductivity in the fiber length direction is large. Further, pitch-based carbon fibers obtained by a vapor growth method can also be used. The thermal conductivity in the fiber length direction of this pitch-based carbon fiber is 200 W / mK.
The above is suitable, preferably 400 W / mK or more, more preferably 1000 W / mK or more.

The average diameter of the pitch-based carbon fiber is 5 to 5.
A range of 20 μm and an average length of 20 to 800 μm is preferable because silicone rubber can be easily filled and the heat conductivity of the obtained heat conductive sheet increases. Average diameter is 5μm
If it is smaller than the above, or if the average length is longer than 800 μm, it becomes difficult to mix the silicone rubber with the silicone rubber at a high concentration. Further, pitch-based carbon fibers having an average diameter of more than 20 μm are not preferred because their productivity is reduced. When the average length is shorter than 20 μm, the bulk specific gravity decreases,
It is not preferable because problems may arise in handling and workability during the manufacturing process. The surface of these pitch-based carbon fibers may be subjected to a known oxidation treatment such as electrolytic oxidation in advance. The silicone rubber serving as a matrix for filling pitch-based carbon fibers coated with a ferromagnetic material can be obtained by curing a known organopolysiloxane.

The curing method is not limited, and 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 the like. , A condensation reaction type, and a curing type using an ultraviolet ray or an electron beam. Among them, it is preferable to use a liquid addition reaction type organopolysiloxane which is easy to fill the pitch-based carbon fiber coated with the ferromagnetic material. In addition, well-known reinforcing silica, a flame retardant, a colorant, a heat resistance improver, an adhesion aid, a pressure-sensitive adhesive, an oil, a plasticizer, and the like can be appropriately compounded.

For the purpose of surface treatment of the fiber, the surface of the pitch-based carbon fiber coated with the ferromagnetic material is treated with a known coupling agent or sizing agent to improve the wettability with silicone rubber or the filling property. It is possible to improve the peel strength at the interface.

Further, the raw material composition of the heat conductive sheet of the present invention includes powdered or fibrous metals or ceramics,
Specifically, the fillers used in conventional heat conductive sheets, such as silver, copper, gold, aluminum oxide, magnesium oxide, aluminum nitride, silicon carbide, and metal-coated resins, and ferromagnetic materials are coated. It is also possible to use ordinary PAN-based or pitch-based carbon fibers which are not used. In order to reduce the viscosity of the composition, it is effective to add a volatile organic solvent or a reactive plasticizer.

The hardness of the cured heat conductive sheet may be determined according to the intended use, but the softer the lower the hardness, the better the stress relaxation property and the followability during use. As a specific hardness, a low hardness product having a Shore A hardness of 90 or less, preferably 60 or less is suitable. further

FIG. 4 shows a gel-like low-hardness product having an Asker C hardness of 30 or less when used between electronic components such as a plurality of semiconductor elements having irregularities and a heat transfer member.

The method for producing a thermally conductive sheet according to the present invention is characterized in that a magnetic field is applied to a composition comprising a pitch-based carbon fiber coated with a ferromagnetic material and a liquid silicone rubber, and a pitch-based material coated with a ferromagnetic material in the composition. The carbon fibers are oriented in a certain direction. A thermally conductive sheet formed by applying a magnetic field from the outside and orienting the pitch-based carbon fibers coated with the ferromagnetic material in the composition along the lines of magnetic force, taking advantage of the thermal conductivity in the length direction of the oriented fibers. In the same direction can be improved.

In order to align and orient the fibers in the thickness direction of the heat conductive sheet so that the N and S poles of the permanent magnet or the electromagnet face each other in the thickness direction, the direction of the line of magnetic force is oriented in the desired fiber orientation direction. Set up accordingly.

On the other hand, in order to improve the thermal conductivity in a certain direction in the longitudinal direction and the horizontal direction in the plane of the thermal conductive sheet or in the horizontal direction, the north pole of the magnet is perpendicular to the thickness direction. If the S poles are opposed to each other, the fibers can be aligned in the in-plane direction. Alternatively, the N pole of the magnet and the N
Even when the poles or the S poles and the S poles face each other in the thickness direction, the fibers can be aligned in the in-plane direction. That is, anisotropy of thermal conductivity can be imparted in any direction. Further, the magnets do not necessarily need to be opposed to both sides, and the pitch-based carbon fibers coated with the ferromagnetic material in the raw material composition can be oriented by the magnets arranged on only one side. Although a permanent magnet or an electromagnet may be used as a magnetic field generating means used as an external magnetic field,
As the magnetic flux density, a range of 200 Gauss to 20000 Gauss is practical and good orientation can be achieved.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION

The heat conductive sheet of the present invention can be manufactured by dispersing pitch-based carbon fibers coated with a predetermined amount of ferromagnetic material in silicone rubber and orienting them in a certain direction. When mixing and dispersing, it is preferable to add a step of removing air bubbles by reducing or applying pressure.

The pitch-based carbon fiber coated with the ferromagnetic material is
When a large amount of silicone rubber is filled and oriented in a certain direction, the thermal conductivity of the thermally conductive sheet in the fiber direction increases. However, in practice, when the composition is filled in a large amount, there may be caused a problem that the viscosity of the composition becomes too high or the mixed air bubbles are difficult to remove. As the viscosity of the composition increases, the fibers are less likely to be oriented.

Accordingly, although it can be arbitrarily determined according to the type of the pitch-based carbon fiber and the silicone rubber coated with the ferromagnetic material to be used, the type of the compounding agent, and the characteristics of the intended final product, the strength of the heat conductive sheet is not limited. It is practical that the filling rate of the pitch-based carbon fiber coated with the magnetic material is in the range of 5 to 90% by volume, more preferably 10 to 60% by volume.

For applications requiring electrical insulation,
As described above, a fiber in which an electrically insulating coating layer is further formed on the outermost surface of the pitch-based carbon fiber coated with the ferromagnetic material may be used. Alternatively, at least one surface of the heat conductive sheet is a polymer-based electrically insulating layer such as polyimide, silicone, polybenzocyclobutene, or polybutadiene, or a ceramic-based material such as silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, or silicon carbide. Even when a structure in which the electrically insulating layers are laminated is applicable to applications requiring electrical insulation. As the polymer-based electrical insulating layer formed at that time, a high thermal conductivity electrical insulating layer containing a filler having high thermal conductivity such as aluminum oxide, magnesium oxide, aluminum nitride, or silicon carbide is preferable.

The heat generating semiconductor elements 2 and 6 and the heat transfer member 4
With the heat conductive sheet 3 of the present invention interposed between the printed board 1, the heat sink 5, the housing 7, and the like, the semiconductor device of the present invention having excellent heat dissipation as illustrated in FIGS. 1 to 4 can be manufactured. . As a heat transfer member, a normal radiator or cooler,
Examples include a heat sink, a heat spreader, a die pad, a printed circuit board, a cooling fan, a heat pipe, and a housing.

As pitch-based carbon fiber coated with a ferromagnetic material, graphitized pitch-based carbon fiber D having an average diameter of 10 μm, an average length of 100 μm, and a thermal conductivity in the fiber direction of 400 W / mK is electrolessly plated. Nickel with a film thickness of 0.
Pitch-based carbon fiber A coated with 2 μm and coated with a ferromagnetic material
Was prepared. Similarly, carbon fibers B and C were prepared by coating the pitch-based carbon fibers shown in Table 1 (FIG. 10) with nickel or cobalt as a ferromagnetic material by an electroless plating method.

[0029]

Example 1 A composition a was prepared by mixing and dispersing 15% by volume of a pitch-based carbon fiber A coated with nickel as a ferromagnetic material and 85% by volume of an additional type liquid silicone rubber raw material and degassing in vacuo. Aluminum 0.5mm thick, 20m long
m, the prepared composition a is filled in a plate-shaped mold 8 having a width of 20 mm, and a magnet 9 having a magnetic flux density of 6000 gauss in the thickness direction as shown in FIGS. 5-1 to 5-2 and FIG. 5-3. Heat curing was performed in a magnetic field atmosphere in which the N pole and the S pole faced each other. The thermal conductivity in the thickness direction and the plane direction of the cured product is 2.8 W / mK, respectively.
0.7 W / mK.

[0030]

Example 2 The same composition a as in Example 1 was prepared, and was made of aluminum having a thickness of 0.5 mm, a length of 20 mm and a width of 20 mm.
6-1 to 6-2, and FIG. 6-3.
As shown in the figure, the N pole and S
It was cured by heating in a magnetic field atmosphere having a magnetic flux density of 6000 with the poles facing each other. The thermal conductivity of the cured product in the thickness direction and the plane direction was 0.8 W / mK and 2.9 W / mK, respectively.

[0031]

Embodiments 3 to 8 Similarly to Embodiments 1 and 2,
Each composition comprising pitch-based carbon fibers B and C coated with a ferromagnetic material having the composition shown in Table 2 (FIG. 10) and an additional liquid silicone rubber raw material was prepared, and was made of aluminum having a thickness of 0.5 mm and a length of 20 mm. A 20 mm wide plate-shaped mold was filled, and the fibers were oriented and heated and cured by a magnetic field shown in Table 2 in which the north pole and the south pole of the magnet face each other in the thickness direction or the vertical direction. Table 2 (FIG. 10) shows the thermal conductivity in the thickness direction and the plane direction of the cured product.

[0032]

Comparative Example 1 A composition was prepared by mixing 15% by volume of carbon fiber D not coated with a ferromagnetic material shown in Table 1 (FIG. 10) and 85% by volume of an additional liquid silicone rubber raw material. It was filled into 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 cured by heating. The thermal conductivity in the thickness direction and plane direction of the cured product is 0.7 W / mK, 2.4 W
/ MK.

[0033]

Comparative Examples 2 to 3 In the same manner as in Comparative Example 1, a composition composed of carbon fibers B and C having the composition shown in Table 2 (FIG. 10) and an additional liquid silicone rubber raw material was prepared. The mixture was filled in a plate-shaped mold having a size of 0.5 mm, a length of 20 mm and a width of 20 mm, and was cured by heating. Table 2 shows the thermal conductivity in the thickness direction and the plane direction of the cured product.

A heat conductive member having a thickness of 2 mm similar to that of the seventh embodiment of the present invention is provided between a plurality of semiconductor elements 6 mounted on the printed circuit board 1 shown in FIG. The semiconductor device was assembled by disposing the sheet 3. Energizing 10
After a minute, the temperature at the center of the housing 7 was 45 ° C. FIG. 7 shows a pitch-based carbon fiber coated with a magnetic material in a heat conductive sheet.
And aligned in the thickness direction. Similarly, a semiconductor device was assembled by arranging a heat conductive sheet having a thickness of 2 mm as in Comparative Example 3. The temperature at the center of the housing 7 after 72 minutes of energization was 72 ° C. The carbon fibers in the cured thermally conductive sheet were randomly dispersed as shown in FIG.

[0035]

As shown in Table 2 (FIG. 10), the thermally conductive sheet according to the present invention in which the pitch-based carbon fiber coated with the ferromagnetic material is oriented in a certain direction in the silicone rubber has a thermal conductivity. Large and good heat dissipation. Further, a heat conductive sheet having excellent heat conductivity in the thickness direction or in the plane direction can be arbitrarily obtained by the method for producing a heat conductive sheet of the present invention. Above all, a semiconductor device using a heat conductive sheet in which fibers are oriented in the thickness direction has very good heat radiation characteristics. Therefore, a useful semiconductor device having excellent heat radiation characteristics can be provided 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 shows an example of a semiconductor device using a heat conductive sheet of the present invention (disposed in a gap between 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 sheet of the present invention (disposed in a gap between a chip size semiconductor package 2 and a printed board 1).

FIG. 3 shows an example of a semiconductor device using the heat conductive sheet of the present invention (disposed in a gap between 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 sheet of the present invention (disposed in a gap between a plurality of heat-generating semiconductor elements 6 and a housing 7).

FIG. 5 is a diagram showing an example of a method for producing a heat conductive sheet of the present invention.

FIG. 6 is a view showing an example of another method for producing the heat conductive sheet of the present invention.

FIG. 7 is a schematic view showing an orientation state of a pitch carbon fiber coated with a ferromagnetic material in a heat conductive sheet of the present invention (fibers are oriented in a thickness direction).

FIG. 8 is a schematic view showing an orientation state of a pitch carbon fiber coated with a ferromagnetic material in the heat conductive sheet of the present invention (fibers are oriented in a plane direction).

FIG. 9 is a schematic view showing a dispersion state of carbon fibers in a conventional heat conductive sheet containing carbon fibers.

FIG. 10 and Table 2

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 printed circuit board 2 semiconductor element 3 heat conductive sheet 4 radiator 5 heat sink 6 semiconductor element 7 housing 8 mold 9 magnet 10 pitch-based carbon fiber coated with ferromagnetic material 11 conventional carbon fiber 12 including conventional carbon fiber Thermal conductive sheet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 7/06 C08K 9/02 9/02 C08L 83/00 C08L 83/00 D01F 9/145 H01F 1/032 B22F 3/02 H // D01F 9/145 H01F 1/02 A (72) Inventor Kikuo Fujiwara 2-4-1, Hamamatsucho, Minato-ku, Tokyo World Trade Center Building N-Echemcat Co., Ltd.

Claims (9)

[Claims] 1. A heat conductive sheet comprising a pitch-based carbon fiber coated with a ferromagnetic material and oriented in a certain direction in silicone rubber. 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 sheet 3. The pitch-based carbon fiber has an average diameter of 5 to 20 μm.
m, the average length is 20 to 800 μm, and the thermal conductivity in the fiber length direction is 200 W / mK or more. 4. A magnetic field is applied to a composition comprising a pitch-based carbon fiber coated with a ferromagnetic material and a liquid silicone rubber, and the pitch-based carbon fiber coated with a ferromagnetic material in the composition is oriented in a certain direction and cured. A method for producing a thermally conductive sheet 5. The thermal method according to claim 4, wherein the ferromagnetic material is at least one metal, alloy or compound selected from nickel, iron, ferrite, chromium, cobalt, manganese and rare earths. Method for producing conductive sheet 6. The pitch-based carbon fiber has an average diameter of 5 to 20 μm.
m, the average length is 20 to 800 μm, and the thermal conductivity in the fiber length direction is 200 W / mK or more. 7. A heat-dissipating property in which a heat conductive sheet of a silicone rubber system in which pitch-based carbon fibers coated with a ferromagnetic material are oriented in a certain direction is interposed between the semiconductor element and the heat transfer member. Semiconductor device 8. The semiconductor according to claim 7, wherein the ferromagnetic material is at least one metal, alloy or compound selected from nickel, iron, ferrite, chromium, cobalt, manganese and rare earths. apparatus 9. The pitch-based carbon fiber has an average diameter of 5 to 20 μm.
9. The semiconductor device according to claim 7, wherein m, the average length is 20 to 800 [mu] m, and the thermal conductivity in the fiber length direction is 200 W / mK or more.