Thermal Balance-Based Evaluation Method for Safe Operating Areas and Its Degradation of IGBT Power Module

Insulated gate bipolar transistors (IGBTs) power module experience significant thermal stress during short-time overload conditions, and their electro-thermal characteristics exhibit strong nonlinearities. As a result, the two-dimensional safe operating area (SOA) provided in the datasheet is unable to meet the need of device reliability assessments. In this paper, we propose a quantitative assessment method based on the thermal balance principle to define the SOA for IGBTs and assess its degradation. A three-dimensional SOA that incorporates voltage, current, and junction temperature is established to prevent IGBT from thermal failures. The proposed SOA indicates that IGBT can operate safely at more than twice the rated current, and the junction temperature can exceed 448.15K(175° C) without thermal failures. This work provides theoretical support for IGBT application design and reliability assessment. According to the physical mechanisms associated with thermal failures of IGBT power module, a criterion to characterize the thermal instability of devices is established. Further, the net heat flux analysis model that integrates semiconductor physics with heat conduction theory is established, enabling the formulation of the three-dimensional SOA of IGBT. Moreover, the effects of the degradation of electro-thermal characteristics on the SOA throughout the long-term operation of the device is considered. In addition, an electro-thermal coupling model that simulates the electro-thermal characteristics of the device is established. The results from both simulation and experiment demonstrate that the established SOA and its degradation effectively predict the reliability of the IGBT under short-time overload conditions.