A thermodynamic framework for damage mechanics is proposed. The damage evolution function uses entropy as a damage metric. A damage-coupled viscoplastic model with kinematic and isotropic hardening is implemented in a commercial finite element code to simulate the thermo-mechanical behavior of eutectic solder interconnects in microelectronics packaging. The damage, as an internal state variable, is coupled with a unified viscoplastic constitutive model to characterize the cyclic deterioration of the material under thermo-mechanic fatigue loads. Several computational simulations of uniaxial monotonic tensile and cyclic shear tests are conducted to validate the model with experimental results. The behavior of a Ball Grid Array (BGA) package under thermo-mechanic fatigue loading is also simulated and compared with experimental results.
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