Utilization of Zn alloy for the manufacture of automotive power device modules

The wide-band-gap power devices such as SiC and GaN semiconductors have excellent physic properties, such as high breakdown voltage, high power density, high switching frequency and very low power loss under high temperature, and are believed to be the key components of power switching for electric vehicle and renewable energy applications. For this purpose, ITRI is developing various high-temperature-resistance assembly technologies such as Ag sintering and solid-liquid interdiffusion bonding (SLID) for the package of wide-band-gap power devices. Zn-based allloys have high thermal resistance and good mechanical strength under high temperatures, and are attractive to adopt as soldering materials for power electronics package. However, Zn-based alloys have not been widely used for mass production because of the high melting temperatures and they oxidize easily even under room temperature. A strong flux shall use to remove the oxides on the surface in soldering process but the high process temperatures may damage the other parts during the manufacture. A new assembly technology by using Zn alloy to bond direct bonding copper (DBC) on a Ni-plated Cu heatsink was proposed in this investigation, the peak temperature of process was reduced to 280°C and the dimension of voids within the solder joint was less than 3%. A very stable intermetallic compound, AuZn₈ replaced the others to form at the interface between Zn alloy and Ni layer, its thickness varied slightly even aged at 150°C for 1000 h and the reliability performance was supposed being acceptable for the package of power electronics.