JPH09199880A - Heat dissipating sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a required heat dissipating sheet of high thermal conductivity to be formed of boron nitride powder of irreducible minimum amount by a method wherein silicone rubber is made to contain boron nitride powder and spherical silica powder and reinforced by glass cloth. SOLUTION: 250 pts.wt. of boron nitride powder of average grain size of 15μm and average grain thickness of 1μm, 50 pts.wt. of spherical silica powder is of average grain size of 6μm and has such a ratio that an average ratio of major axis to minor axis is 1.1:1 are mixed into 100 pts.wt. of millable-type silicone rubber, furthermore 1.5 pts.wt. of vulcanizing agent and a small amount of flame retarder and dispersant are added to them, and the above mixture is dissolved in toluene and a green sheet is formed with a doctor blade. A glass cloth is sandwiched between the green sheets and thermocompressed into a heat dissipating sheet. Thus, a required heat dissipating sheet of thermal resistance 0.15 deg.C/W, thermal conductivity 3.14W/mK, and tensile strength 260kg/cm<2> can be formed of boron nitride powder of irreducible minimum amount.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-dissipating sheet made by dispersing and containing boron nitride powder and spherical silica powder in silicone rubber and reinforced with glass cloth.

[0002]

2. Description of the Related Art In electronic parts, how to remove heat generated during use has been an important issue, and it has been a conventional problem to electrically insulate heat when attaching electronic parts such as transistors and thyristors to heat radiation fins. Heat dissipation sheet is used. This heat dissipation sheet is made of silicone rubber in which a heat conductive filler is dispersed and contained, and boron nitride powder is used as the heat conductive filler.

In recent years, the thermal conductivity of the heat dissipation sheet has been improved by increasing the filling amount of the filler, but since the boron nitride powder is an aggregate of scale-like particles, the filling property is not so good. There is a limit to high filling. Therefore, it has been proposed to use boron nitride powder in combination with a filler having a good filling property to increase the filling rate of the entire filler. At that time, since boron nitride is expensive, the filling amount thereof is set to the minimum amount capable of exhibiting desired thermal conductivity, and the rest is made of filler such as alumina powder and silica powder.

On the other hand, in order to improve the strength of the heat dissipation sheet,
Reinforcement with glass cloth is also performed, but a step of applying a certain pressure is necessary to obtain a sufficient reinforcement effect. In this case, since the boron nitride powder is fragile, there is no adverse effect on the glass cloth even if pressure is applied, but when the other filler used in combination with the boron nitride powder is, for example, a hard and sharp crushed silica powder, the glass cloth is There is a problem that it may be damaged and a sufficient reinforcing effect cannot be obtained.

In order to solve this, it is conceivable to increase the diameter of the glass cloth, increase the number of glass cloths, etc. In this case, however, the openings of the glass cloth are reduced, and the heat dissipation of the glass cloth having poor heat conductivity is caused. The content ratio with respect to the sheet also increases, and the thermal conductivity of the heat dissipation sheet decreases.

[0006]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and the diameter, the number, and the aperture of glass cloth are set to the minimum necessary range for obtaining the desired strength, Keep the filling amount of boron nitride powder to the minimum necessary,
An object of the present invention is to provide a heat dissipation sheet having improved thermal conductivity and reinforcing effect.

[0007]

That is, the present invention is a heat dissipation sheet comprising a silicone rubber containing boron nitride powder and spherical silica powder and reinforced with glass cloth. .

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

The silicone rubber used in the present invention is a liquid silicone rubber which is vulcanized by an addition reaction, a heat vulcanizable millable type silicone rubber which uses a peroxide as a vulcanizing agent, and the like.

The boron nitride powder used in the present invention is not particularly limited, but it is preferable that the BN particles have a major axis (a-axis direction) of 2 μm or more. However, if the major axis exceeds 150 μm, the BN on the surface of the sheet is BN particles. The particles are exposed and the surface is roughened, the flexibility of the heat dissipation sheet is impaired, and the contact with the heat generation surface of the transistor, thyristor or the like or the heat dissipation fin surface is deteriorated, and the heat dissipation effect is impaired.

As the spherical silica powder used in the present invention, those having an average major / minor diameter ratio of about 1 to 1.3 and an average particle size of about 1 to 150 μm, especially about 2 to 50 μm are suitable. Such spherical silica powder can be produced by passing crushed silica crushed to a predetermined particle size through a flame and melting it.

The glass cloth used in the present invention may be a commercially available glass cloth, but in consideration of thermal conductivity, the thickness thereof is preferably 150 μm or less, particularly 50 to 100 μm. .

The ratio of boron nitride powder to spherical silica powder is
10 parts by weight of boron nitride powder to 100 parts by weight of silicone rubber
It is preferably 0 to 300 parts by weight and 10 to 200 parts by weight of spherical silica powder. If the boron nitride powder is less than 100 parts by weight, a sufficiently high thermal conductivity cannot be obtained, and if it exceeds 300 parts by weight, the mechanical strength of the heat dissipation sheet decreases when it is used together with the spherical silica powder. On the other hand, spherical silica powder is 20
If it exceeds 0 part by weight, a sufficiently high thermal conductivity cannot be obtained, and if it is less than 10 parts by weight, there is no effect of improving the filling rate of the entire filler by using the spherical silica powder.

The heat radiating sheet of the present invention comprises a method in which boron nitride powder, spherical silica powder and, if necessary, conventional additives are added to silicone rubber, and a mixer such as a roll kneader or a Banbury mixer is used, or a solvent. It can be manufactured by adding and adding to a slurry to mix, then molding a green sheet, sandwiching a glass cloth between the green sheets, pressurizing it, and heat vulcanizing it. The thickness of the heat dissipation sheet is about 0.1 to 1 mm.

[0015]

The present invention will be described below more specifically with reference to examples and comparative examples.

Examples 1 to 2 Comparative Examples 1 to 3 Millable silicone rubber (trade name "TSE2913U" manufactured by Toshiba Silicone Co., Ltd.) was used to form boron nitride powder having an average particle size of 15 μm and an average particle thickness of 1 μm (a product of Denki Kagaku Kogyo Co., Ltd.). Name "Dencaboron Nitride") and average particle size 6 μm,
Spherical silica powder with an average major / minor axis ratio of 1.1 (trade name "FB-6S" manufactured by Denki Kagaku Kogyo KK) or crushed silica powder with an average particle size of 10 µm (trade name "FS-44" manufactured by Denki Kagaku Kogyo KK)
Was mixed at the ratio shown in Table 1, and 1.5 parts by weight of the total amount of the vulcanizing agent (2,4-dichloroperoxide), a small amount of the flame retardant imparting agent (platinum-containing isopropyl alcohol) and the dispersant were added. After dissolving it in toluene, a green sheet was molded with a doctor blade.

Next, the glass cloth shown in Table 1 (trade name "KS-1090" or "KS-1600" manufactured by Kanebo Co., Ltd.) was sandwiched between the green sheets and heated and pressed to produce a heat dissipation sheet.

The obtained heat dissipation sheet was sandwiched between a TO-3 type copper heater case and a copper plate, and tightening torque was 5 kgf.
After setting at -cm, power of 15 W is applied to the heater case and held for 4 minutes, the temperature difference between the heater case and the copper plate is measured, and thermal resistance (° C / W) = temperature difference (° C) ÷ power (W) , The thermal resistance was calculated.

The heat transfer area of the heater case and the copper plate is 6 cm ² , and the thermal conductivity (W / mK) = [power (W) ×
The thermal conductivity was calculated by the formula: sheet thickness (mm)] / [heat transfer area (m ² ) × temperature difference (° C.)].

Further, the tensile strength of the heat dissipation sheet was measured according to JIS K-6301.

The above results are shown in Table 1. From Table 1, it can be seen that the heat dissipation sheet of the present invention is superior to the comparative example in thermal conductivity and tensile strength.

[0022]

[Table 1]

[0023]

According to the present invention, a heat dissipation sheet having a desired high thermal conductivity can be obtained with a required minimum amount of boron nitride powder, and the reinforcing effect is high.

Claims (1)

[Claims] 1. A heat dissipation sheet comprising a silicone rubber containing boron nitride powder and spherical silica powder and reinforced with glass cloth.