JP2006143978A - Thermally conductive silicone composition - Google Patents

Abstract

The present invention provides a thermally conductive silicone composition capable of reducing the thickness of a heat dissipation layer, realizing low heat resistance, and realizing excellent heat dissipation efficiency.
The thermally conductive silicone composition of the present invention contains polyorganosiloxane and a thermally conductive filler as essential components, respectively, and the thermally conductive filler substantially contains particles having a particle size of 30 μm or more. It is what is not contained in. Such a thermally conductive silicone composition comprises (A) a polyorganosiloxane having at least two alkenyl groups bonded to silicon atoms, and (B) a polyorganohydrogen having at least two hydrogen atoms bonded to silicon atoms. It can be an addition reaction curable silicone composition containing siloxane, (C) a platinum-based catalyst, and (D) a thermally conductive filler substantially free of particles having a particle size of 30 μm or more.
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Description

  The present invention relates to a heat conductive silicone composition, and more particularly to a heat conductive silicone composition useful as a heat dissipating potting agent, heat dissipating adhesive, and the like for electric and electronic parts.

  Conventionally, in order to prevent heat storage of electronic components (semiconductor elements) such as power transistors, ICs, and CPUs, heat radiation grease (thermal conductivity) having good thermal conductivity between the heat radiation member such as heat radiation fins and the semiconductor element. Conductive grease) and heat dissipation sheets (heat conductive sheets) are used.

  Thermally conductive grease has the advantage that it can be easily applied without being affected by the shape of the electronic component, but it can contaminate other components or cause oil to leak out after long-term use. There was a problem.

  On the other hand, the heat conductive sheet does not cause problems such as contamination of other parts or oil outflow, but its adhesion is inferior to that of the heat conductive grease. Therefore, a proposal has been made to increase the adhesion by reducing the hardness. ing. (For example, see Patent Document 1 and Patent Document 2)

  By the way, silicone rubber is often used as a base polymer of a heat conductive sheet because of its excellent properties. In order to improve the heat conductivity of this silicone rubber, a filler having higher heat conductivity than silicone rubber. (Hereinafter, referred to as a heat conductive filler) is known to be added. And as a heat conductive filler used as a binder, use of silica powder, alumina (aluminum oxide), boron nitride, aluminum nitride, magnesium oxide, etc. is proposed.

However, recent electronic components generate more heat as the output increases, and a heat dissipation member or heat dissipation layer with higher heat dissipation capability is required. -Although it is requested | required to make it mix | blend and to improve the heat conductivity of a heat radiating member, in the conventional heat conductive silicone rubber, the improvement of the compounding rate of a heat conductive filler was not enough. It is also considered to reduce the thermal resistivity (thickness / thermal conductivity) and improve the heat dissipation efficiency by reducing the coating thickness etc., but it is not fully realized at present. there were.
Japanese Unexamined Patent Publication No. 1-449959 Japanese Patent No. 2623380

  The present invention was made in order to solve these problems, and the heat conductive silicone composition capable of reducing the thickness of the heat dissipation layer, realizing low heat resistance and excellent heat dissipation efficiency. The purpose is to provide goods.

  As a result of intensive studies to achieve the above object, the inventors of the present invention can reduce the thickness of the heat dissipation layer by limiting the particle size of the thermally conductive filler, thereby reducing the thermal resistance. The present inventors have found that the rate can be effectively reduced and have completed the present invention.

  That is, the thermally conductive silicone composition of the present invention is a composition containing polyorganosiloxane and a thermally conductive filler as essential components, respectively, and the thermally conductive filler contains particles having a particle size of 30 μm or more. It is characterized by not being substantially contained.

  According to the thermally conductive silicone composition of the present invention, the thickness of the layer formed by coating or the like can be extremely reduced, so that the thermal resistivity can be effectively reduced and excellent thermal conductivity is achieved. A heat dissipation layer can be obtained. Therefore, the heat generated from the electronic component such as a semiconductor element can be efficiently transmitted to the heat radiating member such as the heat radiating fin, and high heat radiating efficiency can be realized.

  Embodiments of the present invention will be described below.

  The heat conductive silicone composition in the present invention is a composition containing a polyorganosiloxane and a heat conductive filler as essential components, and more specifically, a silicone rubber composition, a silicone gel composition, or a silicone. It is a grease composition. And a heat conductive filler is what does not contain substantially the particle | grains which have a particle size of 30 micrometers or more, It is characterized by the above-mentioned.

  In the case of a silicone rubber composition or a silicone gel composition, an addition reaction curable polyorganosiloxane composition containing the following components is preferable from the viewpoint of productivity and workability.

  That is, the thermally conductive silicone composition of the embodiment includes (A) a polyorganosiloxane having at least two fatty alkenyl groups bonded to silicon atoms, and (B) a polyorganosiloxane having at least two hydrogen atoms bonded to silicon atoms. It contains an organohydrogensiloxane, (C) a platinum-based catalyst, and (D) a thermally conductive filler that does not substantially contain particles having a particle size of 30 μm or more in the particle size distribution.

  In this embodiment, the component (A) is a base polymer and is a polyorganosiloxane having at least two alkenyl groups bonded to silicon atoms in one molecule. The molecular skeleton may be linear or branched, or a mixture thereof.

  Examples of the alkenyl group bonded to the silicon atom include a vinyl group, an allyl group, a 1-butenyl group, and a 1-hexenyl group, but a vinyl group is most preferable from the viewpoint of ease of synthesis. These alkenyl groups may be present at either the end or the middle of the polyorganosiloxane molecular chain, or both, but they give excellent mechanical properties to the cured composition. For this, it is preferably present at least at the end.

  Other organic groups bonded to the silicon atom include alkyl groups such as methyl, ethyl, propyl, butyl, hexyl and dodecyl; aryl groups such as phenyl; 2-phenylethyl and 2-phenylpropylene. And an aralkyl group such as a hydrogen group; a substituted hydrocarbon group such as a chloromethyl group and a 3,3,3-trifluoropropyl group. From the viewpoint of ease of synthesis, a methyl group or a phenyl group is preferable.

  Moreover, you may use the polyorganosiloxane containing vinyl group described in Unexamined-Japanese-Patent No. 2002-188010. This polyorganosiloxane is particularly suitable for blending and filling a heat conductive filler at a high ratio.

Such (A) alkenyl group-containing polyorganosiloxane is composed of cyclic siloxanes such as hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, tetravinyltetramethylcyclotetrasiloxane, and R ₃ SiO _0.5 (R is monovalent). The organosiloxane having a (hydrocarbon group) unit can be obtained by equilibration polymerization with an appropriate catalyst such as an alkali or an acid, followed by a neutralization step and a step of removing excess low-molecular siloxane.

  The viscosity of the alkenyl group-containing polyorganosiloxane as component (A) is not particularly limited, but the viscosity at 23 ° C. is preferably in the range of 0.01 to 50 Pa · s. If the viscosity is too low, the thermally conductive filler will be separated immediately. On the other hand, if the viscosity is too high, the amount of the thermally conductive filler is limited, so that the desired thermal conductivity cannot be obtained.

  In the embodiment of the present invention, the polyorganohydrogensiloxane having at least two hydrogen atoms bonded to silicon atoms as the component (B) is a component that serves as a crosslinking agent. Examples of the other organic group bonded to the silicon atom include the same groups as those other than the alkenyl group in the aforementioned component (A), but a methyl group is most preferable from the viewpoint of ease of synthesis. Also, it may be any of linear, branched and cyclic,

  The blending amount of such (B) polyorganohydrogensiloxane is such that the hydrogen atom bonded to the silicon atom in the component (B) is 0.1 per alkenyl group (for example, vinyl group) in the component (A). The amount is 2 to 5.0, more preferably 0.3 to 4.0. If it is less than 0.2, curing does not proceed sufficiently. On the other hand, if it exceeds 5.0, the cured product becomes too hard or adversely affects the physical properties and heat resistance of the cured composition. It is not preferable.

  The platinum-based catalyst as the component (C) is a catalyst that promotes the addition reaction (hydrosilylation) between the alkenyl group of the component (A) and the Si—H group of the component (B). Examples of the platinum catalyst (C) include platinum alone, chloroplatinic acid, platinum-olefin complexes, platinum-vinylsiloxane complexes, platinum-phosphorus complexes, platinum-alcohol complexes, and platinum black. The compounding amount of the platinum-based catalyst is an amount of 0.1 to 1000 ppm in terms of platinum atoms with respect to the alkenyl group-containing polyorganosiloxane of the component (A). If it is less than 0.1 ppm, curing does not proceed sufficiently, and even if it exceeds 1000 ppm, no improvement in the curing rate can be expected.

  In the embodiment of the present invention, the component (D) is a heat conductive filler for imparting heat conductivity to the composition, and particles having a particle size distribution of 30 μm or more as a particle size distribution are substantially equal to or more than the amount of impurities. Is prepared so as not to be included. More preferably, it is preferable not to include particles having a particle diameter of 20 μm or more.

  As the thermally conductive filler, known inorganic fillers can be used. However, when the composition requires high thermal conductivity and heat dissipation, alumina, magnesium oxide, boron nitride, aluminum nitride, Examples include silica powder, metal powder, diamond, aluminum hydroxide, carbon, and those obtained by surface treatment of these powders.

  In order to prevent the thermally conductive filler from substantially including particles having a particle size of 30 μm or more, for example, coarse particles having a particle size of the above value or more may be removed. The method for removing coarse particles is not particularly limited, and a known method such as air classification or wet classification can be employed.

  In the embodiment of the present invention, the range of coarse particles to be removed is extremely important. That is, if the lower limit value of the particle size to be removed is too high, there is almost no effect in thinning the heat dissipation layer. Conversely, if the lower limit value is too low, only the fine particles remain and high filling of the heat conductive filler. Becomes difficult. As a result of diligent examination of this lower limit, it was found that by removing coarse particles having a particle size of 30 μm or more, it is possible to satisfy both the requirements of thinning of the heat dissipation layer and high filling of the heat conductive filler. It was.

  In addition, in the blending of the heat conductive filler (D), it is easy to mix the one having a small particle size and the one having a relatively coarse particle size, the ease of filling, the high heat conductivity, and the viscosity of the composition. It is preferable because it is easy to maintain an appropriate value. Further, as one of these particle groups, by selecting one having an average particle diameter of 1 to 15 μm, more preferably 3 to 17 μm, the effect is further exhibited in terms of heat dissipation characteristics.

  Furthermore, a combination of particles having a particle size distribution of monodisperse and an average particle size of 1 to 15 μm (large particle) and particles having a particle size distribution of monodispersion and an average particle size of less than 1 μm (small particle) It is preferable to do. And when it mix | blends combining a large diameter particle and a small diameter particle, it is preferable that those compounding ratios (weight ratio) shall be the range of large diameter particle: small diameter particle = 7: 3-9: 1.

  In the embodiment of the present invention, the blending ratio of the thermally conductive filler as the component (D) is preferably 50 to 95% by weight of the entire composition. A more preferable blending ratio is 70 to 94% by weight. When the blending ratio of the heat conductive filler is less than 50% by weight, the heat conductivity and heat dissipation of the composition are poor. On the other hand, when it exceeds 95% by weight, the fluidity and extrudability of the composition are deteriorated, and the composition becomes substantially unusable.

  The heat conductive silicone composition of embodiment of this invention can be prepared by mixing each component of (A)-(D) using a well-known kneader. If necessary, heating, decompression, or other known treatments may be performed. At that time, in order to blend and fill the heat conductive filler at a higher ratio, the heat conductive filler may be subjected to surface treatment in advance, or may be subjected to surface treatment during kneading. Moreover, you may use together the adjuvant component for making it highly filled illustrated by Japanese Patent Application No. 2003-337806.

  An adhesiveness imparting agent, a reaction inhibitor, a pigment, a flame retardant, a heat resistance imparting agent, an organic solvent, and the like can be blended in the composition of the embodiment as necessary.

  Since the heat conductive silicone composition of the embodiment obtained in this way is blended with a heat conductive filler prepared so as not to substantially contain coarse particles having a particle size of 30 μm or more, the coating layer Thus, it is possible to reduce the thickness to 45 μm or less, and it is possible to form a thin layer that is greatly reduced in thermal resistivity and excellent in heat dissipation. Therefore, it is suitable as a heat conductive layer or a heat dissipation / adhesion layer provided between a heat-generating electronic component (for example, a semiconductor element such as a power transistor) and a heat dissipation member that dissipates heat generated from such an electronic component. .

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to an Example.

Examples 1-3, Comparative Examples 1-3
First, the following components were prepared.

(A) Component (A-1) Component: Polydimethylsiloxane (A-2) component having a viscosity at 23 ° C. of 0.4 Pa · s with both ends blocked with dimethylvinylsilyl groups: represented by the following chemical formula Polydimethylsiloxane containing alkoxy groups and cyclic siloxy groups

Component (B): Polymethylhydrogensiloxane (C) component in which both ends are blocked with trimethylsilyl groups and the hydrocarbon group bonded to the side chain is composed of 53 mol% of methylhydrogen groups and 47 mol% of dimethyl groups: Component: platinum chloride Acid vinyl siloxane compound (containing 1.8% platinum atom)

(D) Component (D-1) Component: Monodispersed alumina (D-2) component having an average particle size of 8 μm and a particle content of 0% by weight or more, and an average particle size of 0.5 μm, Monodispersed alumina (D-3) component having a particle diameter of 30 μm or more and a content of particles of 0 wt%: monodispersed alumina having an average particle diameter of 8 μm and a content of particles having a particle diameter of 30 μm or more (2 wt% Component D-4): monodispersed alumina (D-5) having an average particle size of 0.5 μm and a content of particles having a particle size of 30 μm or more of 0.1% by weight: an average particle size of 14 μm and a particle size of Monodispersed alumina (E) reaction inhibitor having a particle content of 30 μm or more: 10% by weight: Triallyl isocyanurate / 3,5-dimethyl-1-hexyn-3-ol 10/1 mixture (weight ratio)

  The above components (A) to (E) were blended so as to have the composition shown in Table 1. That is, first, the component (D) was added to the component (A) placed in the mixing container, and the mixture was gradually heated and kneaded at 150 ° C. for 1 hour, and then the mixture was cooled to room temperature to obtain a base compound. (B) component, (C) component, and (E) component were added to this so that it might become the composition shown in Table 1, respectively, and it mixed uniformly.

  Subsequently, the following evaluation was performed about the composition obtained in this way. That is, a rubber sheet was prepared by heating at 150 ° C. for 1 hour to cure, and the hardness was measured according to JIS K 6249. Further, the thickness of the coating layer of the composition was measured after being sandwiched between a silicon wafer and a heat sink and heated at 150 ° C. for 1 hour so as to be as thin as possible. Furthermore, the thermal resistivity of the coating layer was obtained after first measuring the thermal conductivity by the method defined by ASTM E1461. These results are shown in Table 1.

  According to the thermally conductive silicone composition of the present invention, the thickness of the layer formed by coating or the like can be extremely reduced, so that the thermal resistivity can be effectively reduced and excellent thermal conductivity is achieved. A heat dissipation layer can be obtained. Therefore, heat generated from electronic components such as semiconductor elements can be efficiently transferred to heat radiating members such as heat radiating fins, and high heat dissipation efficiency can be realized. It is possible to sufficiently cope with the increase in

Claims (6)

  A composition comprising a polyorganosiloxane and a heat conductive filler as essential components, respectively, wherein the heat conductive filler is substantially free of particles having a particle size of 30 μm or more. Thermally conductive silicone composition.   2. The thermally conductive silicone composition according to claim 1, wherein a content ratio of the thermally conductive filler is 50 to 95% by weight of the entire composition.   The thermally conductive silicone composition according to claim 1 or 2, wherein the thermally conductive filler contains particles having an average particle diameter of 1 to 15 µm.   The thermally conductive filler includes two or more kinds of particle groups having a monodispersed particle size distribution and different average particle diameters, and the average particle diameter of at least one kind of particle group is 1 to 15 μm. The heat conductive silicone composition of any one of Claims 1 thru | or 3. (A) a polyorganosiloxane having at least two alkenyl groups bonded to silicon atoms;
(B) a polyorganohydrogensiloxane having at least two hydrogen atoms bonded to silicon atoms;
(C) a platinum-based catalyst;
(D) a composition containing a thermally conductive filler,
The thermally conductive silicone composition according to any one of claims 1 to 4, wherein the thermally conductive filler is substantially free of particles having a particle size of 30 µm or more.   A composition for forming a heat conductive layer interposed between a heat-generating electronic component and a heat radiating member that releases heat generated from the electronic component, and the thickness of the heat conductive layer is 45 μm or less. The heat conductive silicone composition of any one of Claims 1 thru | or 5 characterized by these.