Silver pastes with excellent thermal conductivity

Abstract

Thermally conductive adhesives (TCAs) have been widely used in electronic packaging industry, such as for chip packages in smart phones and high-power LED lightings, as they combine the workability of polymer resins with the high thermal conductivity of fillers[1−4]. The polymer resins endow adequate adhesion strength and provide sufficient mechanical robustness. The thermally conductive fillers mainly determine the capacity of heat dissipation; and the filler can be carbon nanotube, graphene, aluminum nitride, and metal, etc. Among the metallic filler materials, silver is regarded as a competitive TCA filler because of the superior thermal conductivity (∼400 W·m−1·k−1) and resistance to oxidization. The interfacial resistance can be dramatically reduced when sintering behavior is occurred. Yet, it is still a great challenge to fabricate silver-based TCA samples at low temperature with a relatively high thermal conductivity since it is hard to sinter at a moderate temperature. In this work, a simple surface treatment of silver micro-flakes is applied. Laser flash apparatus results show that the out-of-plane thermal conductivity of 85 wt% TCAs achieve 22 W·m−1·k−1when cured at 190 °C. The out-of-plane thermal conductivity of the TCA sample is ideal for applications in high-power thermal interface materials. It is notable that the surface treatment only simply includes two steps: hydrazine hydrate treatment and iodination treatment. A careful study on the influence factors such as surface treatment, curing temperature was conducted. The excellent heat conducting behavior renders the TCA with a good deal of future applications in high-power electron packaging.