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70 SMT007 MAGAZINE I JUNE 2026 interfaces, or narrowed geometries. This effect increases local current density, even when overall current levels appear to be within de- sign limits. In EV systems operating at 400–800 V and at high current, it becomes even more severe because small design imperfections get amplified and lead to faster degradation. In his presentation at the EV Special Session at APEX EXPO 2025, Dr. Olaf Schoenfeld noted that material interfaces are a common source of reliability issues due to improp- er surface preparation and cleanliness. 5 In short, the road to reliability starts well before final assem- bly; it starts with what the system is made of. 1,3,6 Wide-Bandgap Devices Raise Performance, and the Stakes Silicon carbide (SiC) is now a leading material for EV traction inverters, onboard chargers, and DC-DC converters because it supports higher volt- ages and higher temperatures, and offers lower switching losses than conventional silicon. The U.S. Department of Energy identifies SiC as a key technology for high-voltage vehicle power elec- tronics, offering higher efficiency and enabling faster charging and longer range. 3,7 Gallium nitride (GaN) also brings value in higher-frequency conversion, particularly where compact size and reduced passive content are attractive. 1 Yet these gains come with reliability concerns that must be managed rather than assumed away. Reviews of SiC MOSFET reliability highlight gate oxide degradation, threshold-voltage instability, body-diode stress, limitations in short-circuit rug- gedness, and defect-sensitive failure modes as recurring concerns. 1,2 A 2024 Ohio State reliability presentation also reported field failures in com- mercial SiC MOSFETs used in EV inverters, high- Figure 2: Material interfaces found in a power module die stack. (Source: Zestron) 5