Critical appraisal of thermo-mechanical reliability of medium-power heterojunction bipolar transistors for base station and military applications mounted in SOIC-8 leadframe based plastic overmold packages with conductive silver epoxy

Medium power GaInP/GaAs heterojunction bipolar transistors (HBTs) operating up to 2.5 Watts of dc dissipation have been evaluated vis-a-vis thermo-mechanical reliability when packaged into SOIC-8 leadframe packages with conductive silver-based epoxy. Thermo-mechanical analyses (TMA) was used to characterize the glass transition temperature (T_G) of the molding compound, and detailed finite difference analysis (FDA) based thermal models were generated to characterize the thermal profiles across the package. The thermal model results show that the molding compound layer has a much lower temperature distribution than the high device junction temperatures, and also lower than the measured glass transition temperature, hence minimizing the risk of delamination due to thermo-mechanical residual stresses.