Measurement Error Caused by the Square Root t Method Applied to IGBT Devices during Power Cycling Test

In this paper, the measurement error caused by the square root t method applied to IGBT devices during power cycling tests is analyzed in detail by the finite element simulation. The influence of power density, voltage class and chip active area on this error is discussed in depth. The simulation results show that it highly depends on the power density, and the square root t method under/over-estimating of the actual value is related to the voltage class rather than to the active area. This error looks acceptable with a power density lower than 300 W/cm ² but rises linearly with high power density and cannot be ignored, especially for transfer-molded devices. It has to be considered in the power cycling tests with high power density.