Comparison of Junction Temperature Measurement Using the TSEP Method and Optical Fiber Method in IGBT Power Modules without Silicone Gel Removal

The junction temperature is a critical parameter for determining the power cycling capability of power semiconductor devices. Typically, the temperature of the chip is measured indirectly using the temperature-sensitive electrical parameter (TSEP) method or directly using classical infrared (IR) method. However, the TSEP method's suitability for measuring chip temperature in online conditions, especially for complex circuits, has not been adequately demonstrated. The direct measurement method requires removing the silicone gel, making it unsuitable for long-term operation under actual operating conditions. As an alternative approach, optical fibers have been proposed to measure the chip temperature directly through the silicone gel. This paper evaluates both the TSEP method, which measures the saturation voltage under low current, and the optical fiber method for measuring the IGBT's chip temperature under both with and without silicone gel conditions. The initial findings suggest that the presence of silicone gel affects the fiber's response and the chip's temperature distribution. However, the TSEP and optical fiber methods' results are consistent when the silicone gel is removed. The results of this study can contribute to a better understanding of the virtual junction temperature as measured by the TSEP method. Additionally, the findings highlight the advantages and disadvantages of using both the TSEP and optical fiber methods for chip temperature measurement.