High temperature reliability of pressureless sintered Cu joints for power SiC die attachment

This paper presents a reliability study on pressureless sintered Cu joints for attaching SiC power devices (5 mm x 5 mm). The samples were prepared using an optimized sintering process which has been identified by evaluating the shear strength of die attachment joints attaching dummy Si dies. The reliability and thermal performance of sintered Cu die attachment joints was investigated and compared with high temperature lead free solder joints under active power cycling test of 30 to 150 degrees C. It was also evaluated by using a thermal shock test with a temperature swing of -50 to 175 degrees C and a dwelling time of 30 min at peak temperatures. Microstructure of the sintered/soldered die attachment joints were characterized by a range of methodologies before and after test. Results show that the pressureless sintered Cu die attachment joints have a power cycling reliability lifetime of at least 3 times longer than the high temperature Sn5Sb soldered die attachment joints, assuming a 20 % increase in thermal resistance as failure criterion. The pressureless sintered Cu joints also present a nearly unchanged thermal resistance in the original 40 k cycles. This is because continued densification takes place in the pressureless sintered joints during reliability test, trading off the effect of defects induced by thermo-mechanical stress in the assembly.