Packaging of high-temperature planar power modules interconnected by low-temperature sintering of nanosilver paste

In today's electric vehicles (PHEV/HEV/EV), an extra cooling loop is needed to lower the power-electronics coolant temperature below about 65°C from the radiator coolant temperature of 105°C. One way to reduce the cost of future electric vehicles is to eliminate the extra cooling loop by developing reliable high-temperature power inverter modules that can be cooled directly from the radiator coolant. This demands power packaging technologies that can enable power semiconductor devices working at junction temperature in excess of 175°C. In our research effort, we have focused on replacing solders for die-attaching power chips by an emerging low-temperature joining technology (LTJT) that relies on low-temperature sintering of silver powders. To reduce the process complexity of the conventional LTJT arising from the need of high pressure (about 40 MPa or 400 Kg-force per cm2), we developed a nanosilver die-attach material that can be processed below 260°C with less than a few MPa pressure. The nanosilver-enabled LTJT is less likely to damage the chips and allows us to implement a planar packaging scheme for interconnecting both sides of power devices. The planar power modules have low parasitic inductances thus less ringing noises from the device-switching action and can be cooled from both sides of the devices for improved thermal management. Details on design and processing of the double-side cooled power modules and test results on their electrical and thermal performance will be presented.