Metallization for direct solder interconnection of power devices

Inside the state-of-the-art power modules, interconnection of power devices is accomplished with wire bonds, which are prone to noise, parasitic oscillations, fatigue and eventual failure. The objective of this research is to design direct solder interconnection technique for power electronics modules by eliminating the use of wire bonds. To eliminate wire bonds by using solder interconnects on the power devices, such as Insulated Gate Bipolar Transistors (IGBTs) for enhanced electrical and thermal performances, we need to have solderable contact pads on the device. Currently, the IGBT manufacturers use aluminum contact pads, which are not solderable. Consequently, we have implemented a few under bump metallization (UBM) schemes on contact pads of individual IGBT dice. In this paper, a detailed description of the solderable metallization processes (thin film sputtering of Ti-Ni-Cu and Cr-Cu-Au, and electroless deposition of Zn-Ni-Au) on an IXYS IGBT (IXGD40N60A) is presented. XPS, SEM and EDX results are used to characterize the underbump metallurgy processes. Metallized IGBTs have been packaged with solder interconnects and have been electrically tested. High-power electrical tests on the solder-interconnected devices are also presented in the paper