Jan 18, 2012
Hitachi Chemical Co., Ltd.

Development of Electrically Insulating Adhesive Sheets with High and Isotropic Thermal Conductivity

- Realization of the World-Class Thermal Conductivity of 40 W/mk -

Hitachi Chemical Co., Ltd. (Head Office: Tokyo; President and CEO: Kazuyuki Tanaka; Capital: 15.5 billion yen; hereinafter referred to as "Hitachi Chemical") has developed isotropic insulating adhesive sheets that have simultaneously attained thermal conductivity, electrical insulating capability and adhesiveness, which are usually traded off against each other. The adhesive sheets show the world class(*) thermal conductivity (40 W/mK) in all in-plane directions as well as through their thickness. By the end of FY2012, Hitachi Chemical will have started to provide a small amount of samples, and intends to establish the technology needed for mass production in FY2015.

As power electronic devices are further downsized and highly integrated, a great deal of heat is generated inside them, making efficient heat removal a significant challenge and a factor in the performance and lifetime of such devices. This makes the design of heat dissipation mechanisms and efficient cooling devices hot topics. Currently, due to the poor thermal conductivity of the epoxy resin that is essential as electrical insulation, the conventional method is to add a large amount of an inorganic ceramic filler such as boron nitride (BN) to the resin so as to improve its thermal conductivity. However, BN cannot provide both insulation and adhesiveness at the same time because BN, which is flaky, has highly anisotropic thermal conductivity, and because it lacks wettability. If BN is aligned across the thickness of the sheets, their insulating ability will be impaired, although their coefficient of thermal conductivity will be greatly increased. However, if BN is aligned in the in-plane direction, the sheet's thermal conductivity will be lowered even as its electrical insulating ability is enhanced. This is the trade-off between the two functionalities.

Despite this, Hitachi Chemical has succeeded in producing high thermal conductivity in all directions, together with excellent insulation quality and adhesiveness. This has been realized by (1)improving our unique highly thermoconductive epoxy resin composites, including curing agents, that control the higher-order structure by self-alignment that we have developed, (2)developing resin composites with low melt viscosity that can be loaded with large amounts of BN filler, despite its poor wettability, and then (3)establishing the process of randomly dispersing and highly filling the BN filler. The thermal conductivity of this product is 40 W/mK in the thickness direction and 50 W/mK in the in-plane direction, being almost isotropically high. As for electrical insulation, its breakdown voltage (BDV) uniformly exceeds 60 kV/mm, which means that void-free and remarkably high insulation have been achieved.

Hitachi Chemical will start to provide this product as a small amount of samples by the end of FY2012, while working to establish the technology to begin mass production in FY2015. Part of this work was supported by the project "Super-hybrid material technology development" of METI/NEDO(The Ministry of Economy, Trade and Industry/the New Energy and Industrial Technology Development Organization).

This product will be displayed as a prototype at the 4th LED/OLED Lighting Technology Expo - LIGHTING JAPAN - (Dates: Jan. 18 through 20, 2012, Location: Tokyo Big Sight West Hall 1, Booth: West L1-64).

* According to the research conducted by Hitachi Chemical on January 18, 2012.

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