Investigation of a Sic Module with a High Operating Temperature for Power Applications

A silicon carbide (SiC) module with a high operating temperature has been designed, fabricated and tested at a device temperature of 200degC. The module has a multi- layered structure consisting of a SiC chip, a direct bond copper (DBC) SiN ceramic substrate, a copper-based plate, and water-cooled heatsink. The module was designed to have a temperature distribution of 200degC at the chip joint, 150degC at the DBC substrate joint and 65degC at the heatsink. A lead-free high temperature solder made of Au-Sn alloy was chosen to connect the SiC chip/DBC substrate joint in order to withstand the device temperature of 200degC. The joint of the DBC substrate/copper based plate was completed with Sn-Ag-Cu lead-free solder. The module was assembled by using a two- step reflow process for the above joints. The reflow conditions were optimized to reduce the void-area ratio to less than 5% for both solder junctions. High temperature aging tests were carried out for 1000 h at 150degC and 200degC, and for 600 h at 250degC. No significant cracks were observed in the Au-Sn solder joint after the 250degC test. A crack appeared in the Sn-Ag-Cu solder joint after 600 h in the 200degC test. The module was operated by feeding a 100 A DC current into the SiC device to maintain the device temperature at 200degC. A high operating temperature test was performed on the module for 12 h to confirm its reliability, and no significant degradation was observed. The temperature distribution was also measured in this test and compared with simulation results. The two temperature distributions were in good agreement. The results confirmed the possibility of applying this mounting technology to a SiC module for use at a high operating temperature of 200degC.