Effects of thick Al wires bonding layout on reliability of power devices

The maximum avalanche energy that the power MOSFET devices can sustain is primarily determined by the device design and manufacturing process. However, the layout of the thick Al wires on the source pad of the chip also has some influences on it. In this research, two different MOSFETs (400V/5.5A; 75V/75A) were chosen and two or three Al wires were bonded with different layouts to investigate the influence of the configuration of thick Al wires bonding on the avalanche reliability of the power devices. The maximum single pulse avalanche energy (E_AS) was employed to evaluate the devices´ avalanche reliability. The avalanche test results revealed that the wires´ layout has no obvious influence on the E_AS for the low current MOSFET devices, while has significant influence on that for high current MOSFET devices. The more closely the Al wires distributed, the lower the E_AS was obtained. Results also reveal that when devices suffer the maximum E_AS, its average junction temperature (T_J) would be lower if the wires have a closer distribution. The avalanche breakdown spot tends to locate at the position around the Al wire, especially the area under the bonding. These results show that the Al wires on source electrode pad of the MOSFET should be distributed as uniformly as possible to optimize the avalanche reliability of the devices.