Investigation of Conductive Die-top Thermal Capacitors during Short Circuit Operation of Silicon Carbide Devices

Silicon carbide (SiC) power devices have garnered significant attention in recent years due to their superior thermal and electrical properties compared to traditional silicon devices. However, SiC power devices suffer from severe reliability issues arising from their mechanical properties. This is because the Young's modulus of SiC is about three times larger than that of silicon, which correspondingly raises the mechanical stresses acting on the bonding structure, often leading to device failure under power shock events. Traditional packaging materials and designs tend to constrain SiC performance, as hot-spot temperature resulting from a power shock is one of the key factors to device degradation or damage. Studies have shown that SiC devices in conventional packages can have only one-third of the lifespan compared to similar silicon devices. To address these challenges, most recent work has focused on advanced packaging techniques that offer lower thermal resistance, higher thermal capacitance, and better efficiency of cooling, including dual-sided cooling and 3D packaging, which promises to extend device lifetime considerably. The objective of the research is to enhance the short-circuit ruggedness of SiC devices at the packaging level by increasing die-top thermal capacitance to absorb heat flux that could lead to thermal runaway. The research compares different die-top materials to achieve reduced hot-spot temperature rise. Additionally, applying our technique to press-pack packaging structures was investigated to evaluate whether integrating a monolithic spring as the die-top block could serve as a viable solution and a first-line defense against short circuits or if enabling short-circuit failure mode would be a necessity for ensuring device reliability and continuity of operation after short-circuit faults.