Synthesis And Heat Conduction Properties Of Thermal Interface Materials

With the miniaturization of electronic devices and higher integration ofelectronic chips, heat dissipation has emerged as a critical problem that affects deviceperformance and reliability, especially for high power devices such as high powerdiode lasers, high brightness light emitting diodes and high power transistors. Theheat generated by these high power devices during operation needs to be efficientlytransferred to the heat sink and then dissipated to ambient environment. Therefore,thermal interface material （TIM） with high thermal conductivity that is always used tofill the gap between thermal transfer surfaces is essential to meet the increasingdemands of heat dissipation for higher power device. With the requirements ofthermal and insulating properties for different thermal interface materials, in thispaper, the composites made of polymer and thermally conductive inorganic particlesand the metallic materials were studied as thermal interface materials.For polymer-based composites, aluminum nitride （AlN）/epoxy composites andalumina （Al2O3） microball/epoxy composites were successfully synthesized. Theviscosity of pre-curing inorganic particles-epoxy mixture and the thermal conductiveperformance and insulating properties of the composites were measured. Besides,surface treatment to the AlN particles was investigated and the impacts of surfacetreatment on the thermal and insulating properties were also discussed. Theexperimental results revealed that adding AlN particles or Al2O3microball into epoxyresin was an effective way to boost thermal conductivity and maintain electricalinsulation. A proper coupling agent （KH-560） was found out to reduce the viscosityof the AlN particles-epoxy mixture and further to increase the filling content of AlNparticles to60vol%. The highest thermal conductivity were about3.35W·m^-1·K^-1forAlN/epoxy composites and2.10W·m^-1·K^-1for Al₂O₃microball/epoxy composites.The dielectric strength of the AlN/epoxy composites were10¹1kV·mm^-1, whichwere large enough for the applications in high power devices. Additionally, thethermal and insulating properties of the AlN/epoxy composites did not degrade after thermal shock testing, indicating its good reliability.For metallic materials, silver nanoparticles, Sn₄₂Bi₅₈solder and indiumfoils were successfully applied in the sandwiched samples in which twocopper plates were simulated as chip and heat sink. In this paper, investigationmainly focused on their thermal conductive performance and a simple modelwas established to evaluate their thermal conductive performance. For thesilver nanoparticles, the measured thermal conductivity of the sandwichedsamples were356W·m^-1·K^-1for20³0nm,380W·m^-1·K^-1for30⁴0nm and295W·m^-1·K^-1for100¹20nm. For Sn42Bi58solder, the effective thermalresistance was lower than10mm2·K·W^-1when the thickness was about100μm.In addition, when the roughness of copper plates became smaller, the effectivethermal resistance would even be reduced to5mm2·K·W^-1. For indium foils,the effective thermal resistance would be as low as4⁷mm2K W^-1when theindium foils were as thin as15²5μm.