Evaluation of In Situ Thermomechanical Stress-Strain in Power Modules using Laser Displacement Sensors

Digital design has been successfully employed in development of new compact wide bandgap power modules, achieving unprecedented switching speeds while maintaining low thermal resistance. Owing to the achieved performance, the next step in the field is ensuring that proposed designs are mechanically robust and reliable. The new power module structures lack the long history of experimental experience as is the case with conventional silicon power modules. To limit the number of physical prototypes that needs to be built and to speed up development time, having a verified simulation model of the thermomechanical behavior is of great value to designers. In this article, a finite element simulation of the thermomechanical induced stress and strain is presented of an integrated GaN full-bridge switching cell. The simulated strain of the power module is verified by an experimental test. During the test, one of the semiconductor devices of the module is subjected to a power loss. A laser displacement sensor is used to measure the in situ deflection of the ceramic substrate caused by the temperature increase. The experimental results confirm the ability of the simulation model to accurately predict the deflection within an error of only 7.3%.