Finite elements analyses of early-stage crack propagation in aluminum wire bonds due to power cycling

This paper focuses on the thermomechanical behaviour and the consecutive damage of the bond-wire contacts in power semiconductors. Electro-thermal-mechanical finite element analysis of power cycle loads was used to model realistic transient temperature loadings as well as mechanical stresses. Mechanical damage modelling using the cohesive zone approach was used in conjunction with coupled finite element analysis. Parallel to the theoretical research, a pulse width modulation power cycling test bench was realized, and thermal cycles tests were carried out on power modules with temperature swing Delta T-j = 30 degrees C and minimal temperature T-j,T-min = 55 degrees C. Electron Back Scatter Diffraction was used to investigate crack early-stage crack propagation and crack propagation of the samples. Fatigue cracks were found to be always initiated from the interface wire -metallization and propagate exactly at the contact.