JPS6364285B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an insulating heat dissipating sheet, and particularly to a method for manufacturing an insulating heat dissipating sheet in which a glass fiber cloth layer is provided in the middle of a silicone rubber sheet filled with a large amount of inorganic filler. Generally, heat generating electronic components (hereinafter referred to as electronic components) such as power transistors, thyristors, etc. are used under conditions where the temperature does not exceed 100°C. However, electronic components are sensitive to heat and are often destroyed by heat, so in order to quickly remove the generated heat, a heat dissipation system with good insulation and thermal conductivity is installed between the electronic components and heat dissipation fins (hereinafter referred to as heat dissipation body). A sheet is interposed. Heat dissipation sheets used for such purposes include (1) mica or polyester film coated with grease, (2) synthetic rubber filled with inorganic fillers such as mica, alumina, silica, etc., (3) ) Silicone rubber is filled with an inorganic filler and a glass fiber cloth is provided in the middle. However, although (1) is inexpensive, it has insufficient thermal conductivity, requires the application of grease, and deteriorates in a short period of time. (2) has excellent long-term stability and has the advantage of not using grease, but has poor thermal conductivity. (3) has the disadvantage that the heat dissipation sheet adheres to the electronic component or the heat dissipation body when replacing the electronic component, resulting in damage to the heat dissipation sheet. To explain how to arrange electronic components on a heat sink using an exploded cross-sectional view, as shown in FIG. It is attached via an insulating bush 5 with a nut 6. When transistor 1 breaks down, it is usually preferable to replace only transistor 1 without replacing heat dissipation sheet 2 with a new one, but since the heat dissipation sheet will be damaged when removing transistor 1, it should be reused. It is not possible. Normally, damage to the heat dissipation sheet occurs as shown in Figure 2.
Adhesion force with heat dissipation fin 3 or transistor 1
This occurs when F ₁ and F ₂ are greater than the strength of the heat dissipation sheet 2, that is, the strength of the silicone rubber containing inorganic filler F ₃ and the adhesive force between the glass fiber cloth and the heat dissipation sheet F ₄ , and the heat dissipation occurs. This occurs inside the sheet and at the interface between the heat dissipation sheet and the glass fiber cloth. In addition, the inventor's experiments have shown that when a heat dissipation sheet with a glass fiber cloth layer in the middle is used at a temperature of 150°C, which is close to its operating limit, there is a 20% chance of adhesive failure in 72 hours. The result was clear. The present invention aims to solve these drawbacks, and uses silicone rubber, an inorganic filler with excellent electrical insulation and thermal conductivity, and glass fiber cloth treated with silane coupling in the presence of an organic solvent. This prevents damage to the heat dissipation sheet,
The present invention aims to provide an insulating heat dissipation sheet that can be reused even when replacing a transistor. That is, the present invention uses 70 to 90% by weight of an inorganic filler with excellent electrical insulation and thermal conductivity and 30 to 10% by weight of silicone rubber, which has a glass fiber cloth layer in the middle.
In a method for producing a silicone rubber sheet consisting of a ratio of 0.1 to 5% by weight for inorganic filler, silicone rubber, organic solvent and inorganic filler,
% by weight of a silane coupling agent to form a slurry, this is applied onto a base material using a doctor blade method to form a sheet, and the organic solvent contained in the sheet is then removed to form a sheet.
Stack the sheets and place 1 to 5 silane coupling agents in between.
It is characterized by placing a glass fiber cloth containing % by weight and press vulcanizing. The present invention will be further explained in detail below. First, the present invention relates to a method for producing an insulating heat dissipating sheet in which a glass fiber cloth layer is provided in the middle of a silicone rubber sheet containing a large amount of inorganic filler. Compared to conventional products, even if electronic parts are used at a temperature of 150°C, there is no breakage due to adhesion of the sheet even after 72 hours, and the product of the present invention has excellent mold release properties. F ₃ and F ₄ , which have a large effect and are mentioned above, are F ₁ ,
Since it is larger than F ₂ , it has the effect that the heat dissipation sheet does not adhere to electronic components or heat dissipation bodies. In the present invention, a slurry containing an inorganic filler, silicone rubber, an organic solvent, and a silane coupling agent is applied onto a base material using a doctor blade method to form a sheet, and then the organic solvent contained in the sheet is removed. This method is characterized by stacking two sheets, placing a glass fiber cloth layer treated with a silane coupling agent between them, and press-curing. As the inorganic filler used in the present invention, known materials having good electrical insulation and thermal conductivity such as mica, alumina, silica, and boron nitride can be used, but boron nitride is preferable. Commercially available silicone rubber is used, but
The silicone rubber used is a heat-vulcanized type. The ratio of silicone rubber to inorganic filler is 30 to 10% by weight of silicone rubber and 70 to 90% by weight of inorganic filler powder, but if it is less than 70% by weight, thermal conductivity will decrease. Moreover, if it exceeds 90% by weight, the amount of filling increases and there is a problem in terms of strength. Preferred types of silane coupling agents include vinyl silane and epoxy silane. Note that aminosilane-based materials are not suitable because they cause discoloration and the like. A surface treatment agent such as titanate also has the same effect as the silane coupling agent, but is not suitable because it inhibits vulcanization of the silicone rubber or causes discoloration. The blending ratio of silane coupling agent to inorganic filler is
About 0.1 to 5% by weight is sufficient. Any organic solvent may be used as long as it dissolves the silicone rubber and can be easily removed. A specific example is chlorocene, but is not limited thereto. If the amount of organic solvent blended is too large, it will take time to remove it, while if it is too small, it will not be possible to form a slurry and it will not be possible to form a sheet by the doctor blade method. As shown in Figure 3 of Example 3, if the amount of organic solvent blended is about twice the total amount of silicone rubber and inorganic filler, the silane coupling agent will quickly reduce the viscosity and form a sheet. be able to. Normally, if the viscosity of the slurry is less than 10,000 cps, it can be applied to the substrate using the doctor blade method.
A sheet can be obtained by applying such a slurry and removing the organic solvent. Furthermore, as shown in FIG. 4 of Example 3, the silane coupling agent has the effect of suppressing changes in the viscosity of the slurry over time. Therefore, if a silicone coupling agent is added to form a slurry, the amount of organic solvent used will be reduced.
The porosity of the sheet after vulcanization is reduced and the dielectric strength is improved. Further, when forming into a sheet, changes in coating thickness are suppressed, and a sheet with a uniform thickness can be obtained. Next, the sheets thus obtained are stacked, a glass fiber cloth treated with a silane coupling agent is placed in the middle, and press vulcanization is performed to obtain an insulating heat dissipating sheet having the glass fiber cloth in the intermediate layer. The glass fiber cloth used in the present invention has a thickness of 0.03 to 0.15 mm and a lattice spacing of 50 to 5000μ.
It is preferable from the viewpoint of thermal conductivity and strength. Additionally, glass fiber cloth treated with a commercially available silane coupling agent can be used, but
Its content is preferably 1 to 5% by weight. As explained above, the present invention uses silicone rubber, an inorganic filler, a silane coupling agent, and a solvent as a slurry when producing a silicone rubber sheet filled with a large amount of inorganic filler and having a glass fiber cloth in the middle. This is a method for producing an insulating heat dissipating sheet, in which the sheets are made into a sheet using a doctor blade method, the organic solvent contained in the sheet is then removed, the resulting sheets are stacked, a glass fiber cloth is placed in between, and press vulcanization is performed. According to the invention, since the amount of organic solvent used is small, a sheet with low porosity can be obtained, which improves dielectric strength, and can be formed into a sheet by the doctor blade method, resulting in a sheet with a uniform thickness. It has the effect of being Furthermore, when used as an insulating heat dissipation sheet, the sheet will not be destroyed even if removed and can be reused. The present invention will be explained below using examples. Example 1 After adding Denka Boron Nitride Powder GP (hereinafter referred to as GP) manufactured by Denki Kagaku Kogyo Co., Ltd. and dimethyl type silicone rubber in the amounts shown in Table 1 to 200 g of chlorocene, silane manufactured by Nippon Unica Co., Ltd. A coupling agent (trade name: A-172) was added in an amount of 1% based on the weight of GP, and finally a predetermined amount of catalyst was added to form a slurry. Thereafter, the slurry was applied to a uniform thickness using a doctor knife onto a polyethylene terephthalate film set on a glass substrate, and further dried at room temperature for 3 hours to prepare a green sheet. Two green sheets made in this way were placed facing each other with the polyethylene terephthalate film outside, and a glass fiber cloth (Kanebo After sandwiching the Stevens Co., Ltd. product name "KS1090"), the temperature
Press vulcanization was carried out at 170°C for 30 minutes at 100 kg/cm ² . For comparison, a sheet without using a silane coupling agent was prepared using the same process. each sheet
It was cut to a size of 30 x 30 mm, and a hole with a diameter of 3 mmφ was punched in the center to prepare a sample sheet. This sheet was placed on a polished aluminum plate with a hole of 3 mm in thickness and 5 mm in diameter, and the TO-
8kg with a 220 type transistor and M-3 screws
The set is tightened with fcm, and the temperature is 150℃.
It was then placed in a blow dryer for aging. After aging for 72 hours, the set screw was removed and the sheet was taken out. It was checked to see if the sheet would break when taken out. The results are shown in Table 1. Example 2 Nippon Unica Co., Ltd. silane coupling agent trade name “A”
-172'', changing the treatment concentration and treatment amount,
In other respects, a sheet was prepared in the same manner as in Example 1, and the sheet was aged and the state of destruction of the sheet was examined. The results are shown in Table 2. Nos. 5 and 8 in Table 2 are comparative examples, and the others are examples of the present invention. Example 3 25g of silicone rubber and boron nitride powder
When 1.0g of silane coupling agent "A-172" manufactured by Nippon Unica Co., Ltd. is added to 75g of GP and when it is not added, organic solvent (chlorocene) is added at 1.5 to 2.5% based on the total weight of silicone rubber and boron nitride powder. Double amounts were mixed to make a slurry, and the viscosity after stirring for 2 hours was measured using a B-type viscometer. The results are shown in FIG. The left curve in FIG. 3 is the case when the silane coupling agent is added, and the right curve is the case when it is not added, but as in the present invention,
By adding a silane coupling agent,
We were able to prepare a slurry of less than 10,000 cps that can be made into sheets using the doctor blade method using about twice the amount of organic solvent used. Furthermore, FIG. 4 shows the results of measuring changes in viscosity over time for a slurry containing twice the amount of organic solvent. The lower curve in FIG. 4 is for the case where the silane coupling agent is added, and the upper curve is for the case without it. However, by adding the silane coupling agent as in the present invention, We were able to prepare a slurry with almost no change in viscosity over time. Furthermore, adjust the slurry marked △ in Figure 3 so that it has the same viscosity, use the slurry to create a green sheet with a doctor blade, and then vulcanize the sheet without glass fiber cloth at a temperature of 170°C for 30 minutes. I got it. The thickness of the sheet was 0.4 mm.
The porosity of the sheet obtained at that time was 0.5% with the silane coupling agent and 2.5% without.
When I checked the dielectric breakdown voltage, the former was 35KV/mm and the latter was 35KV/mm.
It was 29KV/mm.

【table】

[Table] Example 4 In the same manner as in Example 1, sheets were prepared by changing the amount of silane coupling agent added to boron nitride powder or glass fiber under the conditions of 25 g of silicone rubber and 75 g of boron nitride, and the thermal conductivity,
The state of destruction of the sheet was investigated. Furthermore, after setting the TO-3 type transistor with a tightening torque of 5 kgfcm, the thermal resistance (unit: °C/W) was measured with a load of 15 watts applied to the transistor. This measurement is related to the hardness of the sheet, and the harder the sheet, the larger the value and the less practical it becomes. The results are shown in Table 3. Nos. 1, 5, 6, and 9 in Table 3 are comparative examples, and the others are inventive examples.

【table】 [Brief explanation of drawings]

The drawings illustrate embodiments of the invention,
Figure 1 is a schematic diagram of installing an insulating heat dissipation sheet, Figure 2 is a sectional view of transistor installation, Figure 3 is a diagram of the relationship between the amount of organic solvent and slurry viscosity, and Figure 4 is a diagram of the relationship between time and slurry viscosity. It is. Code, 1... Transistor, 2... Insulating heat dissipation sheet, 3... Heat dissipation fin, 4... Bolt, 5...
...Insulation bushing, 6...Nut, 7...Transistor collector section, 8...Glass fiber cloth,
F ₁ ... Adhesive strength between the insulating heat dissipation sheet and the heat dissipation fin,
F ₂ ... Adhesive strength between the insulating heat dissipation sheet and the collector part,
F ₃ ...Strength of the heat dissipation sheet, _F4 ...Adhesion strength between the heat dissipation sheet and the glass fiber cloth.

Claims (1)

[Claims] 1. A method for producing a silicone rubber sheet comprising a glass fiber cloth layer in the middle and a proportion of 70 to 90% by weight of an inorganic filler with excellent electrical insulation and thermal conductivity and 30 to 10% by weight of silicone rubber,
The inorganic filler, silicone rubber, organic solvent, and inorganic filler are mixed with 0.1 to 5% by weight of a silane coupling agent to form a slurry, which is then applied onto a base material using a doctor blade method to form a sheet. Next, two sheets obtained by removing the organic solvent contained in the sheet are stacked, a glass fiber cloth containing 1 to 5% by weight of a silane coupling agent is placed between them, and press vulcanization is performed. A method for manufacturing an insulating heat dissipating sheet.