Very High Performance Thermal Interface Material and Attachment Technology

This paper provides an update on work at Penn State University on advanced thermal interface material (TIM) and attachment technology. The TIM concept consists of a “Low Melting Temperature Alloy” (LMTA) bonded to a thin copper substrate. The present work includes analytical modeling to separate the interface resistance (R_int) into “material” and “contact” resistance. Modeling indicates that contact resistance accounts for 1/3 of the interface resistance (R_int). Additional alloys have been identified that have thermal conductivity approximately three-times those identified in the previous 2002 publication. Thermal degradation of the LMTA TIM was also observed in the present work after extended thermal cycling above the melting point of the alloy. Possible mechanisms for this degradation are oxidation and contamination of the alloy layer rather than the inter-metallic diffusion. Use of the high thermal conductivity alloys, and soldered contact surfaces will provide very low R_int as well as minimizing the thermal degradation. It appears that R_int as small as, or less than, 0.005 cm²-K/W may be possible. Description of the modified Penn State TIM tester is provided, which will allow measurement of R_int = 0.01 cm²-K/W with less than 30% error.