Experimental study of coefficient of thermal expansion of aligned graphite thermal interface materials

Carbon-based materials draw more and more attention from both academia and industry: Its allotropes, including graphene nanoplatlets, graphite nanoplatlets and carbon nanotubes, can readily enhance thermal conductivity of thermal interface products when served as fillers. Structuraloptimization in micro/nano-scale has been investigated and expected to finely tune the coefficient of thermal expansion (CTE) of thermal interface materials (TIMs). The capability of adjusting CTE of materials greatly benefits the design of interface materials as CTE mismatch between materials may result in serious fatigue at the interface region that goes through thermal cycles. Recently, a novel nano-thermal-interface material has been developed, which is composed of tin (Sn) solder and graphite nanoplatlets. CTE of such sort of TIMs can be adjusted to match well with the substrate materials. A customized, optical CTE measuring system was built to measure CTEs of these thin and flexible samples. The averaged CTEs of samples made by this new approach range from -0.267×10^-6/°C to 5×10^-6/°C between 25°C and 137°C, which matches CTEs of typical semiconductor materials (the CTE of silicon is ~3×10^-6/°C in the same temperature range). This unique CTE-matching feature of a bonding material will have great potential to impact future development of high power microelectronics devices.