Direct Sensing of IGBT Junction Temperature using Silicone Gel Bonded FBG Sensors

In order to safeguard the chips and bond wires, conventional wire-bond IGBT power modules commonly employ a flexible silicone gel filling. This study evaluates the utilisation of the same silicone gel to secure an optical sensor that is installed on the surface of the IGBT chip for the purpose of direct junction temperature measurement. The silicone gel’s impact on the in-situ FBG sensor’s wavelength-to-temperature (λ-T) characteristics was evaluated throughout its curing process and found to be negligible. Additionally, the thermal sensing performance of the gel bonded FBG sensor was analysed in the nominal operating current range of the test commercial IGBT module and verified against measurements taken with a thermal camera. The findings suggest that the silicon gel provides a suitable bond viscosity for securing the sensing fibre in a desired location while not disturbing its free λ-T characteristic.