Fundamental FEM Modeling Approach of Residual Stress Propagation in Sn-Based Electroplated Films Prone to Sn Whiskers Growth

The evolution of residual stress gradients in three different cases of electrodeposited Sn-based films on brass substrate has been evaluated using thermomechanical finite element model (FEM), with temperature as the only loading condition. The FEM model for each of the three cases consists of a brass substrate with the following films: 1) pure Sn film; 2) pure Sn film with the Ni-underlayer; and 3) composite Ni/Sn film. The simulations consider the stress behavior under temperature loading, in the electrodeposited Sn-based films with and without the Ni-underlayer(s). A simple analytical model has been developed to estimate the resulting stress gradient (considered as one of the main causes for Sn whiskers growth) in each film. The modeled stress in the films is shown to be in good agreement with the previously published experimental measurements [Dimitrovska et al., Journal of Electronic Materials 38, 2516 (2009)].