A time dependent damage indicator model for Sn3.5Ag solder layer in power electronic module

• This paper proposes an approximate time dependent damage model for Sn3.5Ag solder layer in power electronic module.
• The proposed time dependent damage model is influenced by inelastic strain from microstructural evolution viscoplastic model.
• Experimental data of Sn3.5Ag and a numerical approach were utilised to extract the parameters of the damage model.
• The damage model was compared with other damage models for cyclic and random load profile.

This paper reviewed the existing damage evolution models in the literature for solder layer in microelectronics and then proposed a two dimensional approximate time dependent damage indicator model for Sn3.5Ag type lead free solder layer in power electronic module application. The proposed time dependent damage indicator model is influenced by inelastic strain from microstructural evolution Anand viscoplastic model. The experimental evaluation of parameter values of the proposed damage indicator model was not feasible. Hence, we adopted a numerical approximation methodology to extract the parameter values of the damage model. A MatLab code was generated to simulate the stress versus strain curve of the solder layer during the thermal variance loading. A data from public domain for crack initiation and crack propagation of SnAg solder layer was also utilised to estimate the parameter values of damage indicator model. The developed approximate time dependent damage model was numerically compared with a damage model in the literature based on Coffin Manson and Paris law fatigue model for prediction accuracy.