The failure of VDMOS device caused by the mismatch of coefficient of thermal expansion

VDMOS device (Vertical Double-diffused Metal Oxide Semiconductor) has the features of higher input impedance, lower drive current, higher switching speed, better frequency characteristic, bigger safety operating area and better thermal stability, which is used in many fields, such as switches in power electronic systems, so it has become the research focus of discrete power semiconductor devices. In this paper, the damage of VDMOS devices is discussed which is caused by the CTE (coefficient of thermal expansion) mismatch between the plastic encapsulated body and the chip during temperature changed environment. The surface and cross-section microstructure of the chips are observed by SEM and AFM. Thermal stress effect on plastic encapsulated body and the chip bonding and cause the interface and chip cracking, which occur on the position of chip edge specially.