Determination of Anand viscoplastic constitutive parameters for the AuGe solder alloy from experimental stress-strain curves for power systems integration FEA simulations

A determination of the Anand viscoplastic model parameters for 88Au12Ge solder alloy is presented in this work. Using experimental data from temperature and rate dependent shear stress tests, the nine characteristic parameters for the aforementioned model were obtained through non-linear fitting using a Least Squared Residual approach. The calculated estimated parameters were used to replicate the conditions of the experimental shear test using Finite Element Simulations in order to validate the final model obtained. Results show a fitting temperature dependency with understress at lower temperatures and a tendency to overstress at higher temperatures. The obtained model response shows no rate dependent behaviour (probably as a result of the small dataset used) and the non-ideal Anand distribution of saturation stresses of the experimental data. Nervetheless, the proposed approach provides a parameter dataset useful for FEA thermos-mechanical simulation of die-attach layers in power modules.