Microstructure and thermophysical properties of graphite foam/Sn-Bi alloy composites for use as a thermal sink for electronics

Two mesophase pitch-based graphite foams with densities of 0.62±0.01 (GF1) and 0.84±0.01 g/cm³ (GF2) were prepared by foaming the pitch in an autoclave at 723 K, 6.0 MPa and 763 K, 13.4 MPa, respectively, followed by carbonization at 1273 K for 2 h and graphitization at 2973 K for 0.5 h. The GFs were infiltrated by a Sn-Bi liquid to prepare GF/Sn-Bi alloy composites for use as thermal sinks for electronics. The microstructures and thermophysical properties of the composites were investigated. Results indicated that GF1 had a larger cells and thinner cell walls than GF2. The Sn-Bi liquid was well infiltrated into cells of the GFs, resulting in composites with densities of 5.60±0.01 and 3.83±0.01 g/cm³ for GF1 and GF2, respectively. The thermal diffusivity and coefficient of thermal expansion (CTE) of the GF1/Sn-Bi composite were 51.6±2 mm²/s and 16.6±0.02 ppm/K, respectively. The corresponding values for the GF2/Sn-Bi were 163.1±3 mm²/s and 8.08±0.02 ppm/K. The GF2/Sn-Bi composite had a high thermal diffusivity and a low CTE value matching that of semiconductor chips and packaging materials.