Thermal Design of Power Semiconductor Modules for Mobile Commnication Sysytems

We investigated the thermal performance of a power semiconductor module used in mobile communication systems. The module contained hetero-junction bipolar transistor (HBT) fingers, which were fabricated on the top of a semiconductor substrate. We calculated the thermal resistance between the HBT fingers and the bottom surface of a multi-layer printed circuit board (PCB) using a finite element method (FEM) simulation. We used steady state analysis to evaluate the effect of various design factors on the thermal resistance of the module. We found that the thickness of the semiconductor substrate, the thickness of the multi-layer PCB, the thermal conductivity of the bonding material under the semiconductor substrate, and misalignment of thermal vias between each layer of PCB were the most important factors affecting the thermal resistance of the module.