Power cycling lifetime estimation of IGBT power modules based on chip temperature modeling

摘要

In this doctoral thesis, methods to estimate the expected power cycling life of powersemiconductor modules based on chip temperature modeling are developed. Frequencyconverters operate under dynamic loads in most electric drives. The varyingloads cause thermal expansion and contraction, which stresses the internal boundariesbetween the material layers in the power module. Eventually, the stress wearsout the semiconductor modules. The wear-out cannot be detected by traditionaltemperature or current measurements inside the frequency converter. Therefore, itis important to develop a method to predict the end of the converter lifetime.The thesis concentrates on power-cycling-related failures of insulated gate bipolartransistors. Two types of power modules are discussed: a direct bonded copper(DBC) sandwich structure with and without a baseplate. Most common failuremechanisms are reviewed, and methods to improve the power cycling lifetime of thepower modules are presented. Power cycling curves are determined for a module witha lead-free solder by accelerated power cycling tests. A lifetime model is selected andthe parameters are updated based on the power cycling test results. According tothe measurements, the factor of improvement in the power cycling lifetime of modernIGBT power modules is greater than 10 during the last decade. Also, it is noticedthat a 10 C increase in the chip temperature cycle amplitude decreases the lifetimeby 40%.A thermal model for the chip temperature estimation is developed. The model isbased on power loss estimation of the chip from the output current of the frequencyconverter. The model is verified with a purpose-built test equipment, which allows simultaneous measurement and simulation of the chip temperature with an arbitraryload waveform. The measurement system is shown to be convenient for studying thethermal behavior of the chip. It is found that the thermal model has a 5 C accuracyin the temperature estimation.The temperature cycles that the power semiconductor chip has experienced arecounted by the rainflow algorithm. The counted cycles are compared with the experimentallyverified power cycling curves to estimate the life consumption based on themission profile of the drive. The methods are validated by the lifetime estimation ofa power module in a direct-driven wind turbine. The estimated lifetime of the IGBTpower module in a direct-driven wind turbine is 15 000 years, if the turbine is locatedin south-eastern Finland.