Elastic-Plastic-Creep Model with Damage for SAC Solder Alloys

We consider an elastic, visco-plastic material model with damage for SAC solders. The inelastic deformation is a combination of rate-independent plasticity and rate-dependent creep. The plasticity model is derived for nonlinear isotropic and kinematic hardening behavior and creep is introduced in the form of a hyperbolic sine function. Material damage is included in the constitutive equations as a scalar damage parameter. The latter is considered an internal state variable and can be interpreted as a density of microcracks or microscopic voids in a material volume element. Material parameters governing the constitutive equations for creep strain rate and the damage evolution are identified based on experimental results of pristine and pre-damaged samples at a constant temperature. The plasticity parameters are estimated based on displacement-controlled cycling of pristine specimens. The numerical model is implemented in the structural mechanics finite element software ANSYS. With the implemented model a numerical simulation of a solder ball temperature cycling is performed and damage evolution is analyzed.