Three-Stage Hybridization of Ultra High Thermal Conductivity Heat Sinks and Spreaders for Advanced Radar and RF Components

By combining discontinuous graphite fiber preforms with inserts of ultra high thermal conductivity materials, we will create hybridized composites with thermal expansion matching to GaAs, SiC or GaN semiconductor amplifiers in advanced radar systems. Specifically, we will use a conventional MetGraf 4-230 skin/encapsulant (first stage, thermal conductivity = 230 W/mK) with high conductivity preforms oriented in the "Z" (through thickness) direction (second stage, TC= 672 W/mK) to rapidly remove heat from the chip. The heat will then be transported by an ultra high thermal conductivity insert (third stage TC=1401 W/mK) from the heat source to the water cooled rail of the radar system. Using the hybridization concept with matching CTE, two interface materials and bonding agents can be eliminated, resulting in further performance increase and cost savings. We estimate that the thermal conductance of LRU (Least Replacement Units) in advanced radar systems can be increased by a factor of 3 to 8 over present systems. We will show feasibility for this concept with Al matrix composites. Once feasibility has been shown for the optimized system, the experiment will be repeated with a Cu matrix so as to increase the areas of application of the three-stage hybridization concept.