JP2005081669A - Method for producing heat conductive sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat conductive sheet which efficiently radiates heat from an electric appliance and an electronic device and is excellent in heat resistance, conductivity, elasticity, and adhesion. <P>SOLUTION: In a method for producing the heat conductive sheet made of an organic/inorganic hybrid material obtained by a reaction between a metal alkoxide and an organic silicon compound, the hybrid material exhibits high thermal conductivity owing to a metal component contained in it and has good flexibility because of an organic silicon component contained in it and good heat resistance. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a heat conductive sheet interposed between a heat generating member such as a heat generating electric component and a heat dissipating member.

Electrical devices and electronic devices tend to increase the power consumption of semiconductor elements due to higher performance, and therefore the amount of heat dissipated from these devices also tends to increase, and heat dissipation from these devices can be performed efficiently. It has become an important issue.
The heat dissipation of these heating elements is generally performed by natural convection from the surface of the main body or forced convection that blows air to the heating element by a fan. However, a configuration in which the heat dissipation element is pressed against the surface of the heating element has been proposed to promote heat dissipation. .
In this case, there is a problem that a gap is likely to be formed on the pressure contact surface between the heating element and the heat radiating body, heat conduction from the heat generating body to the heat radiating body is hindered, and good heat dissipation cannot be obtained.
As means for eliminating the gap at the pressure contact surface between the heat generating body and the heat radiating body, a configuration in which a heat conductive resin sheet is interposed between the heat generating body and the heat radiating body has been proposed.

  Furthermore, with the recent increase in the density of electrical equipment, there is no space for mounting heat sinks such as heat radiating fins, or electronic equipment is sealed in the housing. When it is difficult to dissipate heat, a method is adopted in which heat generated from the electronic device is directly conducted to the housing. Also in this case, the space between the electronic device and the housing is filled with a thick heat conductive resin sheet.

The heat conductive sheet is required to be made of an elastic body having a sufficiently low hardness so as to be in close contact with both the heat generating body and the heat radiating body and made of a material having high heat conductivity.
Conventionally, a material mainly composed of silicone rubber is often used as the resin sheet in view of heat resistance and flexibility (see, for example, Patent Document 1 or 2).

JP-A-9-32185 JP-A-10-15479

Since silicone rubber itself has low thermal conductivity, it is necessary to add a thermally conductive filler. However, even if an attempt is made to provide high thermal conductivity by filling a large amount of a heat conductive filler, silicone rubber has a high viscosity and is difficult to be formulated with high viscosity. There is also a problem that the tensile strength, elasticity, or moldability of the heat conductive sheet is lowered.
Furthermore, recently, due to an increase in the amount of heat generated by the CPU, the required heat resistance is as high as 200 ° C. or more. With silicone rubber, it becomes difficult to cope with it, and there is a problem in long-term durability. In addition, there is a problem that the insulating property is lowered under conditions of 200 ° C. or higher.
Therefore, at present, there is a demand for elastic materials having better heat resistance and high thermal conductivity in the market.

As a means for solving the above-mentioned problems, the present invention prepares a sol solution by mixing a solution of a metal alkoxide and a solution of an organosilicon compound, and heat conductivity of the metal oxide, metal nitride, etc. in the sol solution. The present invention provides a method for producing a thermally conductive sheet in which an organic / inorganic hybrid material is produced by extruding a blended filler into a sheet using a vacuum extruder and gelling the resulting sheet by heating.
The organosilicon compound is preferably an organopolysiloxane having a functional group capable of reacting with a metal alkoxide at one or both ends.
The metal of the metal alkoxide is one or more metals selected from boron, aluminum, silicon, titanium, vanadium, manganese, iron, cobalt, germanium, yttrium, zirconium, niobium, lanthanum, cerium, tantalum, and tungsten. It is desirable.
The thermally conductive filler is desirably fine particles of metal and / or metal oxide and / or metal nitride and / or metal carbide.
The thermally conductive filler is a mixture of two or more kinds of the same or different kinds of fillers having different particle diameters, and the difference in the particle diameters is preferably three times or more.
The thermally conductive filler is preferably added in an amount of 300 to 2000 parts by mass with respect to 100 parts by mass of the organic / inorganic hybrid material produced.
The thickness of the heat conductive sheet is desirably set in the range of 0.05 mm to 50 mm.

[Action]
The organic / inorganic hybrid material obtained by the reaction of the metal alkoxide and the organosilicon compound is a material that combines heat resistance and elasticity due to the synergistic effect between the inorganic component metal and the organic silicon component. It becomes.
Furthermore, since the organic / inorganic hybrid material has a lower viscosity than silicone rubber, it can be highly filled with a thermally conductive filler. That is, with respect to 100 parts by mass of the organic / inorganic hybrid material, when the thermally conductive filler is aluminum oxide, 2000 parts by mass can be added.
Furthermore, the organic / inorganic hybrid material has an appropriate tack on the surface of the sheet due to the organosilicon portion, and has a high degree of adhesion to a heating element and a radiator.

  By this invention, the heat conductive sheet excellent in heat resistance, electroconductivity, elasticity, and adhesiveness can be provided.

The heat conductive sheet of the present invention comprises an organic / inorganic hybrid material obtained by heating and gelling a sol solution containing a metal or metalloid alkoxide, an organosilicon compound, and a heat conductive filler.
[Metal or metalloid alkoxide]
The metal or metalloid of the metal or metalloid alkoxide used in the present invention includes boron, aluminum, silicon, titanium, vanadium, manganese, iron, cobalt, zinc, germanium, yttrium, zirconium, niobium, lanthanum, cerium. , Cadmium, tantalum, tungsten, and other metals or metalloids that can form alkoxides, and particularly desirable metals are titanium, zirconium, and silicon.
Moreover, it does not specifically limit as a kind of alkoxide, For example, a methoxide, an ethoxide, a propoxide, a butoxide etc. are mentioned.
The metal or metalloid alkoxide is desirably chemically modified with a chemical modifier such as acetoacetate such as methyl acetoacetate, ethyl acetoacetate, and isopropyl acetoacetate.

[Organic silicon compound]
Examples of the organosilicon compound of the present invention include a functional group capable of reacting with a metal or semi-metal alkoxide at one or both ends, such as dialkyl dialkoxysilane, desirably one or both ends silanol polydimethylsiloxane. It is possible to use organopolysiloxane and the like.
Examples of the dialkyl dialkoxysilane include dimethyldimethoxysilane, dimethyldiethoxysilane, dimethyldipropoxysilane, dimethyldibutoxysilane, diethyldimethoxysilane, diethyldiethoxysilane, diethyldipropoxysilane, diethyldibutoxysilane, and dipropyl. Examples include dimethoxysilane, dipropyldiethoxysilane, dipropyldipropoxysilane, dipropyldibutoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, diphenyldipropoxysilane, diphenyldibutoxysilane, and the like.
As the organopolysiloxane, those having a weight average molecular weight in the range of 400 to 20,000 are generally used, but those having a weight average molecular weight in the range of 5,000 to 10,000 are preferable from the viewpoint of reactivity.
It is desirable to use an organopolysiloxane having a weight average molecular weight in the range of 400 to 15000 under low temperature conditions of 200 ° C. or lower. Moreover, it is desirable to use an organopolysiloxane having a weight average molecular weight of 15000 or more and 80000 or less under a high temperature condition of 200 ° C. or higher. When the organopolysiloxane has a weight average molecular weight of 80,000 or more, the viscosity of the sol solution becomes too high and workability is deteriorated. If the weight average molecular weight of the organopolysiloxane is 15000 or less, the resulting organic / inorganic hybrid material has poor heat resistance.
The functional group capable of reacting with the metal or semi-metal alkoxide at one or both ends of the organopolysiloxane is, for example, the following functional groups (Chemical Formula 1 to Chemical Formula 13). In the chemical formula, R and R ′ represent methylene, alkylene, and alkyl.

  Organopolysiloxane having such a functional group easily reacts smoothly with a metal or metalloid alkoxide.

(Thermal conductive filler)
Examples of the heat conductive filler used in the present invention include metal powders such as copper, aluminum, silver, and stainless steel, metal oxide powders such as iron oxide, aluminum oxide, titanium oxide, silicon oxide, and cerium oxide, and boron nitride. Metal nitrides such as aluminum nitride, chromium nitride, silicon nitride, tungsten nitride, magnesium nitride, molybdenum nitride, lithium nitride, metal carbides such as silicon carbide, zirconium carbide, tantalum carbide, titanium carbide, iron carbide, boron carbide, etc. There are fine particles, and the normal particle size is about 0.1 μm to 30 μm.
When using the heat conductive filler, it is desirable to use it as a mixture of two or more kinds of the same kind or different kinds of fillers having different particle diameters.
In addition, it is desirable that the difference in particle diameter of the thermally conductive filler is 3 times or more.

[Manufacture of organic / inorganic hybrid materials]
The organic / inorganic hybrid material of the present invention is synthesized by a condensation reaction involving hydrolysis of a functional group capable of reacting with a metal or metalloid alkoxide at one or both ends of the organosilicon compound and a metal or metalloid alkoxide. Is done. The condensation reaction is carried out in a state where the viscosity of the silicon compound is lowered by heating to 80 ° C. or higher.
In order to produce an organic / inorganic hybrid material, first, an organic / inorganic hybrid sol solution is prepared by reacting a hydrolyzate of a desired metal or metalloid alkoxide with an organic component such as the organosilicon compound. The organic component may be added to the alkoxide before hydrolysis, or may be added to the hydrolyzed alkoxide.
Specifically, the metal or metalloid alkoxide or, if desired, the metal or metalloid alkoxide modified with the chemical modifier is dropped into the solution of the organosilicon compound.
As the solution used for the organosilicon compound solution, for example, acetone, toluene, xylene, tetrahydrofuran and the like are generally used in addition to various alcohols such as methanol and ethanol.

  The organosilicon compound solution is preferably heated and distilled in order to remove excess water and low molecular weight components. If water is removed, when a metal or metalloid alkoxide is added to the organosilicon compound solution, hydrolysis of the metal or metalloid alkoxide due to residual water can be prevented, and the dropping rate of the metal or metalloid alkoxide is increased to increase the organic content. Inorganic hybrid synthesis can be performed in a short time, and problems such as stickiness of organic / inorganic hybrid due to residual low molecular weight components and deterioration of mechanical strength can be effectively eliminated.

  The organosilicon compound solution is preferably acid-treated by adding hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, acetic acid and the like. The acid is usually added to the organosilicon compound solution so that the pH of the organosilicon compound solution is in the range of 4-7.

  When the metal alkoxide added to the organosilicon compound solution is chemically modified with a chemical modifier, the chemical modifier is added in an amount of 2 mol or less, preferably 0.5 mol or more and 1 mol or less with respect to 1 mol of the metal alkoxide. used.

  The amount of the metal or metalloid alkoxide added to the organosilicon compound is usually in the range of 1: 0.1 to 1:10 in molar ratio. The organosilicon compound is preferably about 80% by volume with respect to the metal or metalloid alkoxide. When there are more metal or metalloid components than the above ratio, the metal or metalloid components form agglomerates, and swells and pores are formed in the resulting organic / inorganic hybrid material. The synergy effect due to is not shown, it approaches the characteristics of organic components.

The heat conductive filler is added to the organic / inorganic hybrid sol solution. The amount of the thermally conductive filler added is usually 300 to 2000 parts by mass with respect to 100 parts by mass of the organic / inorganic hybrid material. Since the organic / inorganic hybrid sol solution of the present invention is excellent in filler dispersibility, the thermally conductive filler can be easily dispersed uniformly.
In addition, fine particles having a particle size of about several μm among the above heat conductive fillers also act as a thickener, so that the sol solution is thickened and thixotropic viscosity characteristics are given. Therefore, a thick coating can be easily formed.
In addition to the thermally conductive filler, fillers such as antioxidants, ultraviolet absorbers, preservatives, viscosity modifiers, and the like may be added to the organic / inorganic hybrid sol solution as desired.
The organic / inorganic hybrid sol solution obtained as described above does not become cloudy and becomes a sol solution having a long pot life.

In order to produce an organic / inorganic hybrid material from the organic / inorganic hybrid sol solution, for example, the sol solution is applied onto a base material and gelled by heating.
The compound obtained from the sol solution is shaped by cast molding, extrusion molding or the like, and fired in a certain atmosphere. Moreover, it can apply | coat to the member surface used as a core type | mold and a base material, and can form organic-inorganic hybrid material of a predetermined shape on a core type | mold or base-material surface by heat-gelling. The heating conditions are usually 60 ° C. to 450 ° C. for 20 seconds to 2 hours.

[Thermal conductive sheet]
The heat conductive sheet of this invention consists of the said organic and inorganic hybrid material. The heat conductive sheet is desirably produced by kneading and extrusion molding with a vacuum forming machine using a T die or the like. In the molding, it is desirable to perform defoaming molding under vacuum conditions. This is because if the bubbles remain in the heat conductive sheet, the thermal conductivity is lowered, and the mechanical strength and the withstand voltage are also lowered.
FIG. 1 shows an apparatus (1) for producing a heat conductive sheet of the present invention. The device (1) includes a housing (3) having a hopper (2) attached to the upper side of the root end, an upper screw (4), and a lower screw (5). From the housing (3) to the lower screw (5) The cylinder (6) is extended. The end of the cylinder (6) communicates with the vacuum chamber (7), and a shredded net bag (8) is attached to the tip of the cylinder (6) that is inserted.
The compound in which the sol placed in the hopper (2) is mixed with the heat conductive filler is conveyed by the upper screw (4) and the lower screw (5), and the cylinder (6) shredded net bag (8 ) Is cut into a thin string shape to reach the vacuum chamber (7).
A kneading cam (9) is arranged at the lower part of the vacuum chamber (7). The compound cut into a fine string is deaerated while being kneaded by the kneading cam (9). Below the kneading cam (9), a final screw (10) and a T die (11) are arranged at the tip. The compound conveyed by the final screw (10) is introduced into a T die (11) and extruded from the T die (11) into a sheet.
The extruded sheet is fired in a continuous molding furnace or the like to obtain the heat conductive sheet of the present invention. The thickness of the heat conductive sheet is usually in the range of 0.05 mm to 50 mm.
Examples for more specifically explaining the present invention will be described below.

[Example 1]
0.35 mol of dimethylsiloxane (weight average molecular weight 20000, XF3905, manufactured by GE Toshiba Silicone) was heat-treated to prepare a solution A.
On the other hand, 1 mol of zirconium propoxide and 0.5 mol of ethyl acetoacetate were reacted in a nitrogen atmosphere to prepare zirconium propoxide chemically modified with ethyl acetoacetate. B liquid was dripped and mixed with A liquid, and sol liquid (3 types) was prepared.
750 g, 1000 g and 1500 g of alumina were added to and mixed with 100 g of each sol solution to obtain a blend. The alumina was prepared by mixing aluminum oxide having an average particle size of 3.0 μm (AL-30, Showa Denko KK) and 40.0 μm (AS-10, Showa Denko KK) in a mass ratio of 1: 4. Is.
Thereafter, the composition was kneaded using the apparatus shown in FIG. 1, and formed into a sheet by vacuum extrusion. The obtained sheet was baked in a heating furnace at 100 ° C. × 2 hours, 120 ° C. × 2 hours, 150 ° C. × 2 hours, 180 ° C. × 2 hours, 200 ° C. × 2 hours, 250 ° C. × 2 hours, 300 ° C. × 2 hours. Thus, a heat conductive sheet (thickness 0.3 mm) was obtained. The obtained sheet was evaluated for thermal resistance and thermal conductivity. The thermal resistance value was measured based on ASTM D5470, and the thermal conductivity was measured based on JIS R2616. The results are shown in Table 1.

  From the results, it was confirmed that any heat conductive sheet had an excellent heat dissipation effect.

  Moreover, durability was evaluated by heating said heat conductive sheet on the conditions of 200 degreeC x 500 hours. As a result of evaluation, none of the thermally conductive sheets decomposed or deteriorated on the surface under the above conditions.

[Example 2]
The heat radiating device (16) using the heat conductive sheet obtained in Example 1 is shown. It is a heat conductive sheet (12) used between a heat generating body (14) and a heat radiating body (13) (refer FIG. 2). Since the heat conductive sheet (12) has an excellent heat dissipation effect, it has excellent durability. Moreover, since it has an appropriate tackiness, it has good adhesion to the heat radiating body and the heat generating body.
The heating element (14) is a semiconductor chip, and the radiator (13) (made of Cu) is composed of a base part (13A) and a fin part (13B), and the heating element (14) is interposed via a heat conductive sheet (12). The heat generating body (14) and the heat radiating body (13) are fixed with screws (15).

  The heat conductive sheet of the present invention has good heat conductivity, heat resistance, and flexibility, and is used to efficiently dissipate heat emitted from electrical and electronic equipment.

Partial schematic diagram of thermal conductive sheet manufacturing equipment Cross-sectional view of semiconductor chip heat dissipation device

Explanation of symbols

1 Sheet manufacturing equipment
2 Hopper
3 Housing
4 Upper screw
5 Lower screw
6 cylinders
7 Vacuum chamber
8 Shredded net bag
9 Kneading cam
10 Final screw
11 T-die
12 Thermal conductive sheet
13 Heat sink
14 Heating element
15 screw
16 Heat dissipation device

Claims (7)

  A metal alkoxide solution and an organosilicon compound solution are mixed to prepare a sol solution, and a composition obtained by mixing the sol solution with a heat conductive filler is extruded into a sheet by a vacuum extruder, and the resulting sheet is heated. A method for producing a thermally conductive sheet, characterized in that an organic / inorganic hybrid material is produced by gelation.   The method for producing a thermally conductive sheet according to claim 1, wherein the organosilicon compound is an organopolysiloxane having a functional group capable of reacting with a metal alkoxide at one or both ends.   The metal of the metal alkoxide is one or more of boron, aluminum, silicon, titanium, vanadium, manganese, iron, cobalt, zinc, germanium, yttrium, zirconium, niobium, lanthanum, cerium, cadmium, tantalum, and tungsten. The method for producing a thermally conductive sheet according to claim 1 or 2, wherein   The method for producing a thermally conductive sheet according to claim 1, wherein the thermally conductive filler is fine particles of metal and / or metal oxide and / or metal nitride and / or metal carbide.   The method for producing a thermally conductive sheet according to claim 4, wherein the thermally conductive filler is a mixture of two or more kinds of the same kind or different kinds of fillers having different particle diameters, and the difference in the particle diameters is three times or more.   The method for producing a thermally conductive sheet according to claim 4 or 5, wherein 300 to 2000 parts by mass of the thermally conductive filler is added to 100 parts by mass of the organic / inorganic hybrid material to be produced.   The thickness of this heat conductive sheet is set to the range of 0.05 mm-50 mm, The manufacturing method of the heat conductive sheet of Claims 1-6.

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