JP2000085024A - Highly heat-conductive sheet and its preparation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly heat-conductive sheet with extremely high heat conductivity as it has good adhesiveness with an electronic instrument and with excellent heat dissipation characteristics. SOLUTION: The sheet has a gel layer of a heat-conductive filler-contg. silicone resin on one face of a base body sheet consisting of the heat-conductive filler-contg. silicone resin and the max. roughness of the surface of the base body sheet on the opposite side of the gel layer is at most 30 μm and the whole heat conductivity is at least 2.0 W/m.K. As the silicone resin for the matrix of the base body sheet, heat-vulcanizable silicone resins using a peroxide, a room temp.-vulcanizable silicone resins to be vulcanized by condensation reaction, liq. silicone resins to be vulcanizable by addition reaction, etc., are used.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a computer,
ICs in information processing equipment such as word processors,
The present invention relates to a high heat conductive sheet useful for efficiently releasing heat generated from a semiconductor element such as an LSI, a CPU, an MPU, and the like, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, portable information processing apparatuses such as computers and word processors have become thinner. Along with this, semiconductor elements have been increased in density and reduced in size, and the heat generated therefrom has steadily increased, and it has become an important issue to efficiently remove it. Conventionally, this heat dissipation is performed by sandwiching a heat conductive sheet between an electronic device and a heat radiating component. In this case, if the adhesion between the heat conductive sheet and the electronic device is increased, it becomes efficient. Is also known.

There have been several proposals for improving this adhesion. For example, in Japanese Patent Application Laid-Open No. Hei 9-17923, a thermal conductivity of 1 × 10 ⁻⁴ cal / cm · sec · ° C. or more (0.04 W / m · K or more) is applied to both sides of the support. ^{-3 to} 5 × 10 ^-3 cal / cm · sec · ° C
(0.4 to 2.1 W / m · K), a heat conductive sheet provided with a silicone gel layer having a consistency of 10 to 80 and a thickness of 0.05 to 1.0 mm. However,
In order to ensure adhesion to electronic devices, it is necessary to make the gel layer itself flexible.Therefore, the method of highly filling a thermally conductive filler as in the prior art cannot sufficiently increase the adhesion, When the thickness of the gel layer, which is not so high, is increased, the heat resistance of the heat conductive sheet becomes high.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a high heat conductive sheet having high heat conductivity and excellent adhesion to electronic equipment, and a sheet thereof. It is to provide a manufacturing method.

[0005]

That is, the present invention provides the following. (Claim 1) A base sheet made of a silicone resin containing a thermally conductive filler has a gel layer of a silicone resin containing a thermally conductive filler on one surface, and the maximum roughness of the surface of the base sheet opposite to the gel layer is 30 μm. A high thermal conductive sheet, wherein the total thermal conductivity is 2.0 W / m · K or more. (2) The high thermal conductive sheet according to (1), which is reinforced with a reinforcing material. (Claim 3) A method for producing a high thermal conductive sheet, comprising the following steps (a) to (d). (A) a step of applying a slurry containing a silicone resin and a thermally conductive filler on a base film and drying to form an unvulcanized base sheet; (b) leaving the unvulcanized base sheet on the base film (C) removing the obtained base sheet from the base film and pressing again (d) applying the silicone gel containing the thermally conductive filler and the liquid addition reaction type silicone resin to the re-pressed base After applying to at least one side of the sheet, it is heated and vulcanized to form a gel layer. (Claim 4) The unvulcanized base sheet in the step (b) is:
4. The high thermal conductive sheet according to claim 3, wherein the laminate is a laminate of a plurality of unvulcanized base sheets, and a reinforcing material is disposed between at least one base sheet of the laminate. Production method.

[0006]

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

First, the base sheet constituting the high thermal conductive sheet of the present invention will be described. As the silicone resin which is the matrix of the base sheet, a heat-curable silicone resin using a peroxide, Room temperature vulcanizing type silicone resin, liquid silicone resin vulcanizing by addition reaction, and the like are used.

The thermally conductive filler constituting the base sheet includes powders of non-oxide ceramics such as boron nitride, aluminum nitride, silicon carbide and silicon nitride, oxide ceramics such as alumina, silver, copper, aluminum and the like. One or more metal powders are used. The maximum particle size of the thermally conductive filler is preferably 60 μm or less. When the maximum particle diameter exceeds 60 μm, the maximum surface roughness of the base sheet exceeds 30 μm, and the adhesiveness of the sheet surface on the side where the gel layer is not provided decreases, and it is difficult to perform more efficient heat radiation. Become.

The amount of the heat conductive filler used varies depending on the type, but the thermal conductivity of the entire sheet is 2.0 W / m · K.
In order to achieve the above, it is preferable that the base sheet contains at least 50% by volume of the thermally conductive filler.
The upper limit is about 85% by volume in consideration of the flexibility of the sheet.

In the present invention, the hardness of the base sheet itself is completely arbitrary, and an appropriate hardness is selected according to the purpose of use of the high thermal conductive sheet of the present invention. For example, those having a Shore hardness of about 80 to 100 are used. The hardness of the base sheet can be adjusted by controlling the type and amount of the silicone resin and the thermally conductive filler, the degree of curing, and the like.

The high thermal conductive sheet of the present invention is obtained by forming a gel layer described later on one surface of the base sheet, but does not form a gel layer on the other surface. Instead, the maximum surface roughness of the opposite surface is set to 30 μm or less,
Improves adhesion when incorporated into electronic equipment.

Next, the gel layer formed on the surface of the base sheet will be described. The “gel layer” in the present invention refers to a portion that has melted when the sheet is immersed in toluene and shaken for 5 minutes. The thickness of the gel layer, after performing the above-mentioned toluene treatment, dried at a temperature of 80 ° C., and then measured the weight loss,
The sheet area and the gel layer density constant are height values calculated from 1.52 g / cm ³ .

As the silicone resin and the thermally conductive filler used to form the gel layer, those exemplified in the above description of the base sheet are used. A preferred silicone resin is a liquid addition reaction type silicone resin. A preferred thermally conductive filler is boron nitride.

The ratio of the silicone resin to the heat conductive filler in the gel layer is preferably such that the heat conductive filler contains about 20 to 45% by volume.

It is desirable that the thickness of the gel layer is less than 0.05 mm, particularly about 0.01 to 0.03 mm. When the thickness of the gel layer is 0.05 mm or more, heat dissipation in the gel layer is rate-determining, and even if the base sheet itself has high thermal conductivity, more efficient heat dissipation cannot be performed. Note that the thermal conductivity of the gel layer itself is desirably 0.5 W / m · K or more. Further, the thickness of the high thermal conductive sheet itself of the present invention is preferably 0.1 to 1 mm.

The high thermal conductive sheet of the present invention may contain a reinforcing material within a range not to deviate from the conditions of a maximum surface roughness of 30 μm or less and a thermal conductivity of 2.0 W / m · K or more.

Examples of the reinforcing material used in the present invention include mesh-like insulators such as glass fiber cloth and metal foil. The amount used is within a range that does not deviate from the conditions of the maximum surface roughness and the thermal conductivity described above. Specifically, the content is about 15% or less in the sheet of the final product.

There are no particular restrictions on the location of the reinforcing material, but by setting it near the center of the base sheet, the effect on the maximum surface roughness and thermal conductivity is minimized. I can say.

Next, a method for producing the high heat conductive sheet of the present invention will be described. The production method of the present invention is compatible with the production of the above-mentioned high heat conductive sheet of the present invention.

First, in the step (a), an unvulcanized base sheet is formed. For that purpose, first, the viscosity of the slurry containing the silicone resin and the thermally conductive filler is 20,000-6.
A slurry of about 000 cp is prepared. As the organic solvent at that time, toluene, xylene or the like is used.

Next, the slurry is applied on a base film to a desired thickness and dried. The base film is preferably moved continuously in terms of productivity and producing a uniform sheet, and the slurry is preferably applied by a doctor blade method. The base film to be used is not particularly limited, but preferably has good releasability from the base sheet even after passing through the drying and vulcanization steps, and is preferably made of, for example, a fluororesin or polyethylene terephthalate. .

Drying after slurry application is performed under an air atmosphere.
It is performed at a temperature from room temperature to about 80 ° C. If the temperature is higher than 80 ° C., vulcanization is accelerated, and the volatilization of the organic solvent is also accelerated, so that pores are formed in the base sheet and the thermal conductivity is reduced.

The press vulcanization temperature in the step (b) is 4
Desirably, the temperature is 0 to 200 ° C. If the temperature is lower than 40 ° C., the base sheet is not sufficiently vulcanized. If the temperature exceeds 200 ° C., a part of the base sheet may be deteriorated.

The press vulcanization is carried out in an air atmosphere, and the press is carried out, for example, by sandwiching a base sheet between smooth metal plates and using a conventional flat plate press to obtain 50 to 150 kgf.
/ Cm ² pressure.

When the high thermal conductive sheet of the present invention further contains a reinforcing material, it is desirable to mix it in the step (b). As the method, it is preferable to interpose between a plurality of unvulcanized base sheets, and as a reinforcing material in this case, a mesh-like insulator such as a glass fiber cloth or a metal foil is suitable. The reinforcing material used in the present invention may be powder, whisker, or the like,
In such a case, it may be sprayed between unvulcanized base sheets, or may be previously mixed in the base sheet or the slurry for forming the gel layer. Furthermore, a combination of these methods is also possible.

Step (c) of the present invention is a step in which the vulcanized base sheet is removed from the base film and then pressed again. At the time of this re-pressing, a heat treatment at a temperature of about 40 to 150 ° C. may be accompanied as necessary.

The pressing in the step (c) is performed in an atmosphere at room temperature under a pressure of 100 to 500 kgf / cm ² ,
The maximum surface roughness of the base sheet is, for example, 30 μm or less. When the desired maximum surface roughness cannot be achieved only by the press treatment, auxiliary means such as a roll press may be added.

In the step (d) of the present invention, a gel layer is formed on at least one surface of the base sheet having the adjusted maximum surface roughness. The slurry used here is a mixture containing a liquid addition reaction type silicone and a thermally conductive filler, and has a slurry viscosity of about 100,000 to 200,000 cp. The adjustment is performed mainly by adjusting the viscosity of the liquid addition reaction type silicone. The slurry viscosity can also be adjusted by the amount of the thermally conductive filler. In this case, the content ratio in the gel layer is 20 to
It is preferable that the volume is 45% by volume, and the fine adjustment is performed by adding the above organic solvent. If the content of the thermally conductive filler in the gel layer is less than 20% by volume, it is difficult to increase the thermal conductivity of the entire sheet to 2.0 W / m · K or more. Hardness is increased, and adhesion to electronic devices is impaired.

The application of the slurry for forming the gel layer can be performed by screen printing, a roll coater or the like. Heat vulcanization is performed using a general hot-air dryer, far-infrared dryer, microwave dryer, etc., at a temperature of 100 to
It is desirable to carry out at 200 ° C. for 5 to 120 minutes.

[0030]

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

Example 1 A millable silicone rubber (trade name "TSE221" manufactured by Toshiba Silicone Co., Ltd.) was blended with a boron nitride powder having a maximum particle size of 32 μm and a loading amount shown in Table 1 and 2% by volume of toluene. A 2,000 cp slurry was prepared. The slurry was coated on a polyethylene terephthalate film to a thickness of 0.3 mm using a doctor blade, and then left standing for 10 minutes in a hot-air dryer maintained at a temperature of 70 ° C. to form an unvulcanized substrate sheet. . [Step (a)].

The unvulcanized base sheets thus obtained were stacked on each other and sandwiched between stainless steel flat plates at a temperature of 150 ° C. and a pressure of 100 kg.
Press vulcanization was performed for 45 minutes under the condition of f / cm ² to produce a base sheet. [Step (b)].

Next, the base sheet was peeled off from the polyethylene terephthalate film, and each of the sheets was sandwiched between stainless steel flat plates at room temperature under a pressure of 300 kgf / c.
Pressing was performed for 2 minutes under the conditions of m ² . [Step (c)].

The surface roughness of the repressed base sheet was measured using a non-contact type surface roughness meter (trade name “VF-
L50 ", a gel layer was formed on one side of the sheet according to the following to obtain a high heat conductive sheet of the present invention.
[Step (d)].

70% by volume of an addition-reaction type silicone resin (trade name "SE1886" manufactured by Dow Corning Toray Co., Ltd.) and boron nitride powder (GP grade average particle size 2 μm, "Dencaboron nitride" manufactured by Denki Kagaku Kogyo Co., Ltd.) 30 % By volume to prepare a slurry and adjust its viscosity to 120,
After adjusting to 000 cp, printing was performed to a thickness of 0.04 mm on only one side of the base sheet using a screen printer equipped with a screen having an opening of 75 μm, and vulcanized in a hot air dryer at a temperature of 100 ° C. for 30 minutes.

Examples 2 to 5 Except that the types and amounts of the heat conductive fillers to be filled in the base sheet and the gel layer were as shown in Table 1, respectively.
A high heat conductive sheet was produced according to Example 1. However, in Example 2, since the maximum surface roughness of the re-pressed base sheet after the step (c) was 40 μm, pressing was performed again with a roll press molding machine to reduce the maximum surface roughness to 20 μm.
μm. In Example 3, the slurry for forming the gel layer was applied by a roll coater.

Example 6 An unvulcanized base sheet having a thickness of 0.1 mm was formed by a calender roll using a slurry containing a thermally conductive filler shown in Table 1 [Step (a)]. A press vulcanization is performed for 45 minutes at a temperature of 150 ° C. and a pressure of 80 kgf / cm ² with an aluminum foil having a thickness of 0.04 mm interposed between the two unvulcanized base sheets to produce a base sheet. [Step (b)]. The obtained base sheet was peeled from the polyethylene terephthalate film, sandwiched between stainless steel flat plates, and pressed for 2 minutes at room temperature and a pressure of 300 kgf / cm ² [step (c)]. Next, a gel layer was formed on one surface of the base sheet according to Example 1. However, printing of the slurry was performed by a roll coater [step (d)].

Comparative Examples 1 to 5 Except that the types and amounts of the heat conductive fillers to be filled in the base sheet and the gel layer were as shown in Table 1, respectively.
A sheet was produced according to Example 1. However, Comparative Example 2
Then, the base sheet was formed by a calender roll.

With respect to the heat conductive sheet obtained above,
(1) Sheet thickness, (2) Gel layer thickness, (3) Thermal conductivity, and (4) Surface roughness of the substrate sheet on the opposite side on which the gel layer was formed were measured as follows. Table 2 shows the results.
Shown in

(1) Sheet thickness: Measured with a micrometer. (2) Gel layer thickness: After immersing the sheet in toluene and shaking for 5 minutes, drying at a temperature of 80 ° C. and measuring the weight loss, the sheet area and gel layer density constant: 1.52 g / c
The height was calculated from m ³ ), and this was defined as the gel layer thickness. (3) Thermal conductivity: After sandwiching the sheet between the TO-3 type heater case and the copper plate and compressing 10% of the sheet thickness,
A power of 5 W was applied to the copper heater case and the temperature was held for 4 minutes. The temperature difference between the copper heater case and the copper plate was measured, and the thermal conductivity (W / m · K) = {power (W) × thickness (m)} / ｛. The thermal conductivity was calculated by (temperature difference (K) × measured area (m ² )). (4) Maximum surface roughness of the base sheet: measured by a non-contact type surface roughness meter (trade name “VF-L50” manufactured by Keyence Corporation).

[0041]

[Table 1]

[0042]

[Table 2]

[0043]

As described above, the high heat conductive sheet of the present invention has a very high heat conductivity because of good adhesion to electronic equipment, and is excellent in heat radiation characteristics.

Continued on front page F term (reference) 4F213 AA24 AA33 AA45 AB11 AG01 AG03 AH81 WA04 WA14 WA53 WA58 WA83 WA87 WB01 WB13 4J002 CP031 DA076 DB006 DE146 DK006 DM006 FD206 5F036 AA01 BB21 BD21

Claims (4)

[Claims] 1. A base sheet made of a silicone resin containing a thermally conductive filler has a gel layer of a silicone resin containing a thermally conductive filler on one surface, and the maximum roughness of the surface of the base sheet opposite to the gel layer is 30 μm. A high thermal conductive sheet, wherein the total thermal conductivity is 2.0 W / m · K or more. 2. The high heat conductive sheet according to claim 1, wherein the sheet is reinforced with a reinforcing material. 3. A method for producing a high heat conductive sheet, comprising the following steps (a) to (d). (A) a step of applying a slurry containing a silicone resin and a thermally conductive filler on a base film and drying to form an unvulcanized base sheet; (b) leaving the unvulcanized base sheet on the base film (C) removing the obtained base sheet from the base film and repressing (d) applying the silicone gel containing the thermally conductive filler and the liquid addition reaction type silicone resin to the repressed base. After applying to at least one side of the sheet, heating and vulcanizing to form a gel layer 4. The unvulcanized base sheet in the step (b) is a laminate of a plurality of unvulcanized base sheets, and a reinforcing material is arranged between at least one base sheet of the laminate. The method for producing a high thermal conductive sheet according to claim 3, wherein