Novel Graphite Foam for High Heat Flux MMIC Cooling

Monolithic microwave integrated circuits (MMIC) generate ever-increasing heat loads. Foam-based cooling systems have proven beneficial for high heat dissipation with low pumping and small volume requirements. In previous work, Ultramet fabricated silicon carbide (SiC) foam heat sinks for gallium nitride (GaN) power amplifiers that provided excellent corrosion resistance and a perfect thermal expansion match with SiC electronics. As a single-phase water system, SiC foam heat sinks dissipated over 1000 W/cm2 of steady-state heat flux with a resulting die surface temperature of just 53 degrees C. Cooling systems based on graphite foam are promising because graphite is lightweight and has high thermal conductivity. However, existing commercially available graphite foam has shortcomings in that the cell size is small, the windows that separate the individual cells are quite small and frequently closed, and the porosity level is relatively low (typically 5070%), all of which result in a high pressure drop and low efficiency. In this project, a novel graphite foam will be developed based on processing methods used in ongoing commercial manufacturing at Ultramet for carbon foam. The resulting open-cell graphite foam will act as a high thermal conductivity, high surface area cooling fin that will be tested under a range of heat flux and airflow conditions.