Thermal Behavior in Vertically Stacked Cascode GaN HEMT Power Modules Including Mutual Heating, Dissipation Disturbance, and Solder Voids

Vertically stacked cascode gallium nitride (GaN) power devices provide strong electrical advantages, including reduced parasitic inductance, compact design, and high power density, compared to conventional lateral configurations. However, stacking a silicon MOSFET directly above a GaN HEMT introduces significant thermal challenges. This study identifies three major thermal issues: mutual heating between dies, restricted heat dissipation paths, and thermal degradation caused by solder voids. Finite element analysis (FEA) simulations show that the stacked design experiences approximately 30 percent higher peak temperatures than lateral counterparts due to these effects. Simulations also reveal that solder voids, especially those beneath the silicon MOSFET, disrupt vertical heat flow and intensify hot spot formation. Experimental validation using custom-fabricated modules under repeated swi…