A systematic evaluation of thermal performance of interface materials in high power amplifiers

A comprehensive study has been undertaken to better understand the thermal conditions within high power, radio frequency (r.f.) signal amplifiers. Here, the results of investigation of the interface thermal resistance between the primary heat dissipating transistors and the heat sink are presented. With individual devices dissipating up to 130W each, junction temperatures have been shown to approach 200/spl deg/C when ambient temperatures reach 60/spl deg/C. Under these conditions the interface thermal resistance currently accounts for 20% of the total drop from junction to ambient temperature. Experiments were conducted to determine the interface thermal resistance of a number of candidate materials allowing comparison of application specific data obtained here with the manufacturer published data. The data was also used to compare the performance of the current thermal grease compound with several commercially available alternatives. At maximum power dissipation, transistor temperatures were reduced by up to 20/spl deg/C through the use of a high conductivity thermal grease in conjunction with careful preparation of the contact surfaces to ensure consistent flatness.