Structural Reliability Methods Applied to Power Switch Devices: Example of an Aeronautical IGBT Module

In this paper, an Insulated Gate Bipolar Transistor (IGBT) module designed for aeronautic applications is investigated using structural reliability methods coupled with Finite Elements (FE) modeling. The lifetime of the module with respect to its solder joints failure, is evaluated using its thermomechanical response, in association with a low cycle fatigue model. The simulation of an aeronautic typical Accelerated Thermal Cycling (ATC) test configuration allows checking in a first step, the relevancy of the numerical procedure by assessing the experimental lifetime of the connections, and comparing them to experimental results. Then, the structural reliability of the module is evaluated over the target aircraft predicted useful lifetime, comparing the First Order Reliability Method (FORM) and Monte-Carlo Simulation (M-CS). The appropriate temperature mission profile and flight time are therefore considered with their scatters, in addition to those of the parameters of the fatigue model. Regarding these latter parameters, a simulation based approach is proposed and applied for the determination of their probability density function (pdf). For reasonable reliability analysis time, the thermomechanical response of the module was surrogated using Kriging metamodels. The paper ends with the exploitation of the reliability importance factors for identifying and proposing improvements, with the demonstration of considerable reliability increase.