Enhancement of Power Cycle Life Time of Power Modules Using Water Cooled Multilayer Ceramic Substrates

Abstract

We investigated a high-performance power module mounting technology with high connection reliability for the purpose of making small power supplies for industrial maintenance-free equipment. In particular, we have developed both water-cooled multilayer ceramic substrates and high-reliability mounting technologies for power devices to realize high-performance and high-power modules for practical use. By forming a Cu circuit pattern on the surface layer of the developed board, the mounted bare chip can be effectively cooled. Furthermore, since the heat dissipation effect of the water cooled multilayer ceramic substrate is high, the temperature rise of the bare chip can be dramatically reduced as compared with the air-cooled method. However, since the temperature fluctuations of the bare chip surface due to power ON/OFF are very fast and large, cracks may develop in the Pb-5Sn solder joint, and the power cycle life may be shortened. Therefore, we investigated the effects of the coefficient of thermal expansion of the clip and solder thickness on the power cycle lifetime in the water cooled multilayer ceramic substrate. By changing the linear expansion coefficient of the clip from 16 ppm/K Cu to 8 ppm/K Cu-Mo, the power cycle life of the module can be extended by more than 4 times relative to that of a module using a Cu clip and 100 μm thick solder even if the thickness is as little as 10 μm. We expect that a reliability of 20 years or more can be achieved with the developed module.