Liquid Metal Fluidic Connection and Floating Die Structure for Ultralow Thermomechanical Stress of SiC Power Electronics Packaging

Coefficients of thermal expansion (CTE) of various materials in packaging structure layers vary largely, causing significant thermomechanical stress in power electronic packages during operation. For wirebondless SiC modules, the stress is even larger due to the structure's rigidity and the high Young's modulus of SiC crystals. This letter takes a flexible printed circuit board (FPCB)/die/active metal brazed (AMB) packaging stack as an example to prove the feasibility of floating die structure enabled by liquid metal (LM) fluidic connection. The CTE mismatch among the die, printed circuit board, and AMB substrate is decoupled by the LM layer without compromise of thermal and electrical conduction. The finite-element analysis demonstrates a 56% reduction in von Mises stress of the device and more than 99% shear stress reduction at the FPCB-AMB interface, compared with a conventional rigid solder connection. Testing results show that LM-based packaging has a similar thermal and electrical conduction and higher breakdown voltage when compared with the soldered counterpart. Accelerated thermal cycling aging tests validate the stability of the insulation ring for LM-based packaging, especially under high-temperature conditions. The feasibility of using LM fluidic interconnections for a floating die structure of SiC packaging is validated.