JP5495429B2 - Heat dissipation composite sheet - Google Patents

Description

The present invention relates to a heat dissipation composite sheet for use as heat dissipation sheets, such as heat-generating electronic component.

  With the downsizing of electronic devices such as televisions, computers, and communication devices, the degree of integration of circuits mounted on these devices is increasing. Since the performance of electronic components mounted on the integrated circuit, particularly IC packages such as CPUs, deteriorates due to heat generation, the heat of the IC package etc. is conducted and released to the outside as a heat dissipation measure. A heat sink is used.

Furthermore, in order to increase the heat conduction efficiency, conventionally, grease, silicone rubber sheet or the like having good heat conductivity is interposed between the heat sink and the IC package.
However, conventionally, in order to increase the heat dissipation effect, it is necessary to increase the surface area of the heat sink, so the heat sink tends to have a large capacity or a large mass. Such a tendency is a serious adverse effect when considering further downsizing of electronic devices.

Therefore, a heat-dissipating sheet is disclosed that forms a film with excellent heat dissipation of far-infrared rays on the surface of aluminum or copper plates with high thermal conductivity and dissipates heat outside the system to take measures against heat. ing.
For example, a ceramic plate obtained by firing cordierite particles with a high heat dissipation rate of infrared rays is used as a heat dissipation layer, and a heat dissipation layer in which a copper thin film conductive layer is formed by electroless plating or vapor deposition on one surface of the heat dissipation layer A sheet that releases heat generated from an electronic component by bonding the conductive layer side of the plate to a substrate on which the electronic component is attached via a thermally conductive adhesive is disclosed (Patent Document 1).

However, in this technique, a ceramic plate fired with powder particles is used as a heat dissipation layer, so the sheet has high rigidity and the surface of the heat generating component to be attached is not flat but curved. There was a problem that sticking was difficult.
Moreover, since the heat dissipation layer is a ceramic plate, cutting and the like are difficult, and a mold for molding is required to obtain a shape necessary as a heat dissipation sheet. For this reason, there is a problem that not only does it have no responsiveness, but it is difficult to produce a heat-dissipating sheet, and the production requires a great deal of labor.

  In order to solve such a problem, as a flexible heat-dissipating sheet, a flexible heat-dissipating film having an infrared heat-dissipating effect is formed on the surface of a flexible heat-absorbing layer having thermal conductivity, A heat dissipating sheet is disclosed in which an adhesive layer made of a heat conductive adhesive is formed on the back surface of the heat absorbing layer (Patent Document 2).

  However, in the case of the heat radiating sheet, since the heat generating body and the heat radiating sheet are integrated through an adhesive tape having extremely low thermal conductivity, heat transfer from the heat generating body to the heat radiating sheet is not efficiently performed. In some cases, the expected heat dissipation effect could not be obtained.

Even when a heat conductive adhesive tape is used, there is a problem in reliability at high temperatures because the resin matrix is an acrylic resin.
In addition, there is a method in which the heating element and the heat-dissipating sheet are in close contact with each other using heat conductive grease or an adhesive. However, when grease is used in close contact, oil oozes from the grease or the grease itself The pumping out phenomenon that flows out of the system due to the temperature cycle cannot be avoided, and there are problems of contamination of the surrounding environment and deterioration of the heat conduction performance. Further, even when bonding, a process for curing the adhesive is required, which is disadvantageous in terms of cost.
Thus, when a conventional heat dissipation material and a heat dissipation sheet are simply used in combination, a material that satisfies both heat dissipation performance, high reliability, and low cost cannot be obtained.

JP-A-10-116944 JP 2004-200199 A

As a result of intensive studies to improve the above-described conventional drawbacks, the present inventors have found that a flexible heat-dissipating sheet having a specific spectral heat dissipation rate, a silicone resin, and a heat having a specific particle size are obtained. Heat dissipation, thermal conductivity, and reliability are improved by thermocompression- bonding a heat conductive silicone resin sheet containing a specific amount of conductive filler and having adhesiveness and heat softening properties. In addition, the present inventors have found that a heat radiating composite sheet that can be bent with a relatively small force and that is particularly useful as a heat sink for a CPU of a small electronic device can be obtained.
Accordingly, an object of the present invention is to provide a heat radiating composite sheet that is flexible and easy to mold as well as improving heat dissipation, thermal conductivity, and reliability.

That is, the present invention comprises a flexible heat-dissipating sheet layer having a spectral heat dissipation rate of 80% or more at 300 ° C. and a wavelength of 2.5 to 20 μm, and (b) a thermal conductivity of 0.5 W / m heat softening of heat conductive silicone resin sheet layer having a der Ri heat softening temperature or higher K (hereinafter, simply referred to as "heat-softenable heat conductive silicone resin sheet layer".) heat dissipation obtained by laminating A composite sheet, wherein the heat-softening thermally conductive silicone resin sheet layer (b) has a volume average particle size of 0 as measured by a laser diffraction / scattering method in an adhesive silicone resin matrix. A heat-dissipating composite sheet characterized by being a sheet layer formed by dispersing 30 to 97% by mass of a thermally conductive filler having a thickness of 1 to 100 μm.

In the present invention, the (b) heat-softening of the heat conductive silicone resin thickness of the sheet is preferably a 30 to 300 [mu] m. In addition, the flexible heat-dissipating sheet (a) is oxidized on the surface of the heat-absorbing / heat-diffusing layer made of a thin metal plate selected from aluminum or its alloy, copper or its alloy, and stainless steel. Select at least one powder selected from silicon, aluminum oxide, titanium oxide, carbon black, graphite, and carbon fiber from epoxy resin, fluorine resin, acrylic resin, and polyester resin After directly spraying the liquid obtained by blending with the binder resin thus prepared, the heat-dissipating sheet can be obtained by drying.

  According to the present invention, a heat radiating composite sheet which is excellent in thermal conductivity, heat radiating property and reliability and which can be easily molded is obtained.

Hereinafter, the present invention will be described in detail.
The heat dissipation composite sheet of the present invention is formed by laminating (a) a heat dissipation sheet layer having flexibility and (b) a heat softening thermally conductive silicone resin sheet layer. Here, the (a) heat radiating sheet layer absorbs and diffuses the heat conducted from the heating element through the (b) layer, and dissipates this from the surface as infrared rays to the outside of the system.

The thickness of the layer (a) is preferably in the range of 0.05 to 5 mm, more preferably 0.1 to 3 mm. If the thickness is less than 0.05 mm, the strength may be insufficient. If the thickness exceeds 5 mm, the flexibility of the composite sheet may be impaired, and the thickness of the entire composite sheet increases, resulting in thermal conductivity in the thickness direction. There is a risk of damage.
Wherein (a) the heat dissipation of the layer at 300 ° C., it is necessary spectral radiating at a wavelength 2.5~20μm is 80% or more, it is good preferable is 85% or more.
The spectral heat dissipation rate can be measured with a Fourier transform infrared spectrophotometer such as JIR-5500 (trade name, manufactured by JEOL Ltd.).
As the layer (a), commercially available materials such as “Super Ray” (trade name, manufactured by Furukawa Sky Co., Ltd.) can be used.

The (a) heat-dissipating sheet layer used in the present invention may be two layers, an endothermic / thermal diffusion layer and a heat-dissipating layer. In the case of two layers, a flexible heat dissipation layer having an infrared heat dissipation effect is formed on the surface of a flexible heat absorption / heat diffusion layer having thermal conductivity.
The heat absorption / thermal diffusion layer is a thin plate having thermal conductivity using a metal material such as aluminum or an alloy thereof, copper or an alloy thereof, or stainless steel, and can be bent with a relatively small force. It is necessary to have flexibility.

The heat dissipation layer is a coating film formed on the heat absorption / thermal diffusion layer, and has an infrared radiation effect of converting conducted heat into infrared rays and / or far infrared rays to dissipate heat, and bends with a relatively small force. It must be flexible so that it can be used.
The heat dissipation of the heat dissipation layer, at 300 ° C., it is necessary spectral radiating at a wavelength 2.5~20μm is 80% or more, it is good preferable is 85% or more.
The spectral heat dissipation rate can be measured with a Fourier transform infrared spectrophotometer such as JIR-5500 (trade name, manufactured by JEOL Ltd.).

  Such a heat dissipation layer is made of, for example, at least one powder selected from silicon oxide, aluminum oxide, titanium oxide, carbon black, graphite, carbon fiber, etc., epoxy resin, fluorine resin, acrylic resin, It is formed by blending with a binder resin such as a polyester resin, and spraying the obtained liquid on the surface of the endothermic / thermal diffusion layer directly by spraying and then drying.

As the liquid used to form the above-mentioned coating film, a composition containing powder of kaolin, silicon oxide, aluminum oxide or the like in an emulsion containing a silicone resin can be used. This invention is not restricted to these examples, What is necessary is just to be able to form the coating film which has an infrared radiation effect and flexibility.
An example of such a liquid is shellac α (trademark registration No. 4577163: trade name manufactured by Shellac Co., Ltd.).

In the heat-dissipating composite sheet of the present invention, the heat- softening heat-conductive silicone resin sheet layer in the heat-dissipating composite sheet is obtained by dispersing a heat-conductive filler in an adhesive silicone resin matrix. In addition to having the function of bringing the body into close contact with each other, it ensures good thermal conductivity and improves the thermal conductivity of the entire sheet.

The type of silicone resin is not particularly limited as long as it has adhesiveness and heat softening properties .
(B) layer is Ru required der thermally conductive silicone resin sheet having an adhesive property and heat-softenable. Here, the “thermosoftening property” includes not only the property of softening by heat but also the property of lowering viscosity or melting, or the property of melting and fluidizing the surface.

Heat softening of heat conductive silicone resin sheet layer (b), the heat generation due to the operation of the electronic components, a phase change from heat conductive silicone resin sheet is a solid to a liquid or fluid or semifluid, or heat since softened, can heat generator is favorably adhered with the layer (a), or, is a heating element (a) and layer adheres well to the adhesive included in the (b) layer.
Thereby, the heat conductive performance of the whole heat dissipation composite sheet improves.

As the heat conductive filler to be filled in the heat softening heat conductive silicone resin sheet layer (b), any filler can be used as long as it is a substance generally used as a heat conductive filler. Usually, metal powder, metal oxide powder, ceramic powder or the like is used. Specifically, aluminum powder, copper powder, silver powder, nickel powder, gold powder, aluminum oxide powder, zinc oxide powder, magnesium oxide powder, iron oxide powder, titanium oxide powder, zirconium oxide powder, aluminum nitride powder, boron nitride Examples thereof include powder, silicon nitride powder, diamond powder, carbon powder, fullerene powder, and carbon graphite powder.
These may be used alone or in combination of two or more.

The volume average particle diameter of the thermally conductive filler is a value measured by a laser diffraction / scattering method (microtrack method) using a microtrack particle size distribution measuring device MT3300EX (trade name, manufactured by Nikkiso Co., Ltd.), and is 0.1-100 μm. It is preferable that it is 0.5 to 50 μm.
When the thickness is less than 0.1 μm, the filling property into the silicone resin is remarkably deteriorated, so that it is difficult to improve the thermal conductivity. When the thickness exceeds 100 μm, the thickness of the heat-softening thermally conductive silicone resin sheet layer cannot be reduced to 100 μm or less, and thus it may be difficult to develop sufficient heat conduction performance.
In the present invention, two or more kinds of particles having different volume average particle diameters may be used as the thermally conductive filler.

The content rate of a heat conductive filler needs to be 30-97 mass% with respect to the total mass of a heat conductive silicone resin sheet layer (b), and it is preferable that it is 40-95 mass%. . When the content of the thermally conductive filler is less than 30% by mass , the thermal conductivity of the heat softening thermally conductive silicone resin sheet layer may be reduced. When the content is more than 97% by mass, the thermal conductivity is uniform. A heat conductive sheet layer may not be obtained.

Heat conductive silicone resin sheet layer having tackiness and heat-softenable Examples of commercially available thermally conductive silicone processed products can be used as (b), P CS series (trade name manufactured by Shin-Etsu Chemical Industry Co., Ltd.) Is mentioned.

The thickness of the heat-softening thermally conductive silicone resin sheet layer (b) is preferably 30 to 300 μm, and more preferably 60 to 200 μm.
When the heat-softening thermally conductive silicone resin sheet layer is thinner than 30 μm, the adhesion and adhesion between the (a) layer and the (b) layer, and the heating element and the (b) layer are weakened. May peel. On the other hand, if it is thicker than 300 μm, the thermal conductivity of the heat dissipation composite sheet may deteriorate.

The heat-radiating composite sheet of the present invention is manufactured by thermocompression bonding of (a) a heat-dissipating sheet layer having heat-dissipating properties and (b) a heat-conductive silicone resin sheet layer having heat- softening properties and adhesiveness. .

A specific method of laminating the thermally conductive silicone resin sheet layer of the present invention having thermal softening property is to heat the silicone resin sheet above the thermal softening temperature (for example, 80 to 120 ° C.) on a press jig, and (a ) A method of press- bonding a heat-dissipating sheet.
For the pressure bonding, roll pressure bonding or the like may be used in addition to press pressure bonding.

  Next, although an Example and a comparative example are given and this invention is demonstrated further in detail, this invention is not limited to these.

[ Reference Example 1, Example 1 and Comparative Examples 1-2]
The following materials were used as the heat-dissipating sheet layer (a) and the thermally conductive silicone resin layer (b) having adhesiveness.
(A) Heat-dissipating sheet layer a-1: High heat-dissipating aluminum functional material “Super Ray” (thickness 0.4 mm; trade name manufactured by Furukawa Sky Co., Ltd .; 300 ° C. spectral heat dissipation rate: 80% or more)
(B ) Thermally conductive silicone resin layer b-1 (Reference Example 1) Adhesive thermally conductive silicone resin layer :
TC-10SAS (silicone double-sided adhesive tape; trade name, manufactured by Shin-Etsu Chemical Co., Ltd .; thickness 100 μm, thermal conductivity 1.0 W / m-K)
b-2 (Example 1) Thermally conductive silicone resin layer having adhesiveness and thermal softening properties :
PCS-TC-10 (thermal softening silicone thermal conductive sheet; trade name manufactured by Shin-Etsu Chemical Co., Ltd .; thickness 60 μm, thermal conductivity 3.8 W / m-K)
b-3 (Comparative Example 1 ): F-9460PC (acrylic double-sided adhesive tape; trade name of Sumitomo 3M Limited; thickness 50 μm, thermal conductivity 0.2 W / m-K)
b-4 (Comparative Example 2 ): G747 (thermal conductive grease; trade name manufactured by Shin-Etsu Chemical Co., Ltd .; thermal conductivity 0.9 W / m-K)

1. Manufacture of heat dissipation composite sheet The above-described (a) and (b) were pressure-bonded with the combinations described in Table 1. The pressure bonding was room temperature pressure bonding (23 ° C.) or thermocompression bonding (100 ° C.).
When b-4 was used, b-4 was screen-coated on a heat-dissipating sheet so as to have a thickness of 100 μm.

2. Evaluation Each heat-radiating composite sheet obtained was cut into 1 cm × 1 cm, and the following characteristics were evaluated for this test piece.
(1) Sheet thickness Measured using a micrometer (manufactured by Mitutoyo Corporation, model: M820-25VA).
(2) Thermal conductivity The thermal conductivity in the thickness direction of the composite sheet was measured with a thermal conductivity meter LFA447 NanoFlash (Xenon Flash Analyzer; trade name of Netch Co., Ltd.).
(3) Reliability Each test piece is sandwiched between two standard aluminum plates, loaded with a compression load of 410 kPa, placed in an oven, and a temperature cycle of 0 ° C./30 minutes to 150 ° C./30 minutes is repeated 1000 cycles. Then, the state of the (b) layer was visually observed.

表１の結果から明らかなように、熱伝導性の低いアクリル両面粘着テープを用いた比較例１は、複合体の熱伝導率が顕著に低く、また、ヒートサイクル後に粘着層の劣化が確認され、熱伝導性、信頼性供に劣るものであることが確認された。
また、放熱グリースを用いた比較例２の場合は、熱伝導率が高いものの、圧着時にグリースが流出して周囲を汚染した上、ヒートサイクル後には、グリースの流出が確認された。
一方、実施例１は、特に熱伝導率が高く、放熱性に優れることが確認された。
The results obtained in each test are shown in Table 1.

As is clear from the results in Table 1, in Comparative Example 1 using the acrylic double-sided adhesive tape having low thermal conductivity, the thermal conductivity of the composite was remarkably low, and the deterioration of the adhesive layer was confirmed after the heat cycle. It was confirmed that the thermal conductivity and the reliability were inferior.
In Comparative Example 2 using heat dissipating grease, although the thermal conductivity was high, the grease flowed out at the time of crimping and contaminated the surroundings, and after the heat cycle, the outflow of grease was confirmed.
On the other hand, Example 1 was confirmed to have particularly high thermal conductivity and excellent heat dissipation.

Since the heat dissipation composite sheet of the present invention is excellent in flexibility, it is particularly useful as a heat sink for a CPU or the like of a small electronic device.

Claims (4)

(A) A flexible heat dissipating sheet layer having a spectral heat dissipation rate of 80% or more at 300 ° C. and a wavelength of 2.5 to 20 μm, and (b) a thermal conductivity of 0.5 W / m · K or more. der Ri a heat dissipation composite sheet formed by laminating a heat-softenable heat conductive silicone resin sheet layer having a heat softening temperature, the (b) heat-softening of the heat conductive silicone resin sheet layer, the adhesive Layer formed by dispersing 30 to 97% by mass of a thermally conductive filler having a volume average particle diameter of 0.1 to 100 μm as measured by a laser diffraction / scattering method in a silicone resin matrix A heat-dissipating composite sheet characterized by The heat-dissipating composite sheet according to claim 1, wherein the heat softening temperature of the (b) heat-softening thermally conductive silicone resin sheet layer is 80 ° C or higher . Wherein (b) the thickness of the heat-softenable heat conductive silicone resin sheet layer is 30 to 300 [mu] m, the heat dissipation composite sheet according to claim 1 or 2.   The flexible heat dissipation sheet (a) is formed on the surface of the endothermic / thermal diffusion layer made of a thin metal plate selected from aluminum or an alloy thereof, copper or an alloy thereof, and stainless steel, At least one powder selected from aluminum oxide, titanium oxide, carbon black, graphite, and carbon fiber was selected from epoxy resin, fluorine resin, acrylic resin, and polyester resin The heat-radiating composite sheet according to any one of claims 1 to 3, which is a heat-dissipating sheet obtained by directly spraying a liquid material obtained by blending with a binder resin and then drying the liquid.