A Lifetime Prediction Method for SiC MOSFET Under Low Air Pressure Environment Considering Variation of Convective Heat Transfer Coefficient

In low air pressure environments (LAPE), the reduced cooling capacity of air shortens the SiC MOSFET's lifetime. Quantifying the shortened lifetime of SiC MOSFET under LAPE effectively is challenging due to the lack of targeted lifetime prediction methods. This paper proposes a novel lifetime prediction method that considers thermal transfer characteristics of the SiC MOSFET relying on natural convection for cooling under LAPE. The junction temperature of devices under LAPE can be calculated by deriving the functional relationship between air pressure (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P_a</i>) and convection heat transfer coefficient of heat sink and air. Then, a relationship between solder layer fatigue degradation and failure criteria is established to enable lifetime prediction of the SiC MOSFETs. The power cycling experiment demonstrates that the lifetime of SiC MOSFETs at 700 hPa is 4,700 cycles shorter compared to that at 1,013.25 hPa. Under both Pa conditions, the prediction errors of the proposed approach remain within 360 cycles. Lifetime performance of devices under real operating conditions is further analyzed to shed light on the assessment of device lifetime under LAPE. The proposed method provides a convenient and effective analytical tool for lifetime design and assessment of SiC MOSFET under LAPE.