The effects of solder voids in the device to substrate interface for electric vehicle and other power applications

The hybrid power module is a main component of the GM EV1 electric vehicle inverter system. It is a high power, high frequency, switching device that converts traction battery DC power to controlled AC power to drive the electric motor. The key to the HPM´s ability to generate and switch large amounts of power lies in the modules ability to successfully maintain a constant T_j across the IGBT and transfer heat through a reliable thermal stack. It is known that defects, such as solder voids, in the thermal stack will reduce the localized thermal conductivity of the effected area. This will lead to excessive T_j on the chip, and corresponding high delta temperatures between chip and case. High temperature conditions such as this will therefore limit device performance or lead to premature device failure. This paper investigates the integrity of these solder joints for electric vehicles and other high power applications.