Low melting point thermal interface material

A high performance thermal interface material has been developed that consists of a 25 /spl mu/m coating of low-melting-temperature alloy (LMTA) tinned on each side of a 50 /spl mu/m copper substrate. The alloy has a melting point below the maximum CPU operating temperature. Steady-state tests per ASTM D-5470 show 0.058 K-cm/sup 2//W at 138 kPa contact pressure. Contact pressures as small as 34 kPa are permissible. Thermal cycling tests (1000 cycles) show negligible performance degradation, if the temperature is cycled less than 12 K above the melting point. Thermal cycling 20 K above the melting point results in degradation due to formation of a low thermal conductivity intermetallic alloy at the LMTA-copper interface. Removal and replacement of the LMTA results in negligible increase in interface resistance. Manufacturing methods are discussed, and a concept for the application of LMTA to the CPU-heatsink interface is presented. The LMTA alloy offers performance competitive with the best thermal grease, without the "messy" disadvantages of thermal grease.