Study of silicon chip soldering in high-power transistor housing

Abstract

The aim of this work is to study the possibility of reducing the labor consumption and cost of high-power silicon transistor manufacturing without compromise in transistor low thermal resistance. To this end we experimentally explored replacing Au-Si solder with lead-silver solder or other solders for silicon chip soldering in transistor housings. This will reduce gold consumption and increase the efficiency of high-power transistor silicon chip installation due to the use of batch soldering technology. We also studied the effect of different silicon wafer back side treatment and thinning methods on the thermal resistance of the transistors. To improve the soldering quality we applied preliminary Ti–Ni metallization of the reverse side of the silicon wafer.We experimentally assessed the effect of outer housing layer materials and back side chip metallization. For lead-silver soldering of silicon chips, the best housing is that with a nickel outer layer rather than with a gold-plated one, because the resultant thermal resistance is lower and the absence of gold makes the technology cheaper. We obtained a 0.6K/W thermal resistance for a 24mm2 chip area.