Characterisation of power modules ceramic substrates for reliability aspects

Electronic power devices used for transportation applications (automotive and avionics) experience severe temperature variations which promote their thermal fatigue and failure. For example, for power modules mounted on the engine of an aircraft, temperature variations range from 55 C (in the worst case of storage before takeoff) to +200 C (flight). In theses conditions failure (conchoïdal fracture) can occur in DBC substrates. The Weibull approach was used to model the brittle fracture of the ceramic layer from a natural defect. Besides, geometric singularities in the upper ceramic/copper interface are at the origin of cracks, which grow by fatigue and finally bifurcate and break the ceramic layer. With the framework of linear elastic fracture mechanics (LEFM) and using the finite element method, it was possible to analyse how a thermal loading history may modify the risk of failure of the DBC substrate and can increase the fatigue life of a power module. This result shows that the fatigue life and the reliability of power electronic devices could be optimized using a thermo-mechanical approach of the problem and suitable failure criteria.