Thermal analysis of GaAs power monolithic microwave IC's mounted with epoxy attachment

The effect of chip-mounting attachment on the thermal resistance of GaAs power field effect transistor (FET) modules has been experimentally investigated. The thermal resistance was evaluated for different GaAs chip thickness of 150 and 250 /spl mu/m through an electrical method utilizing temperature dependence of Schottky-barrier in the GaAs metal semiconductor FETs (MESFETs). The thermal resistance of low-cost epoxy-mounted GaAs chips, suitable for uniplanar monolithic microwave ICs (MMICs), was found not to increase even up to a chip thickness of 250 /spl mu/m, while that of AuSn-mounted GaAs chips increased as was conventionally expected. Numerical simulation has also been presented for the similar case of GaAs power MMICs. The result of simulation suggests that lower thermal conductivity of attachment material, such as epoxy attachment, leads to larger optimum chip thickness that minimizes the total thermal resistance.