A unified thermo-viscoplastic phase-field framework for fatigue fracture of solder joints under thermal cycling

Solder joint reliability in advanced electronic packages is governed by strongly coupled thermo-mechanical fields, rate-dependent inelasticity, and complex interfacial fracture processes under long-term thermal cycling. To address the lack of physically consistent fracture models for SAC305 solder joints, this work develops a thermo-viscoplastic phase-field framework that couples a temperature-dependent Anand model with a history-driven fracture formulation. The framework is validated against published uniaxial tensile and cyclic experimental data over five temperatures (298.15–398.15 K) and three strain rates (10⁻³–10⁻⁵ s⁻¹), and reproduces the temperature- and rate-dependent tensile response, hysteresis evolution, and peak-stress degradation of SAC305 solder. The model is further applied to a representative BGA structure under power cycling, where the predicted interfacial damage localization and crack propagation path are consistent with experimentally observed cross-sectional fracture morphology. The results show that outer solder joints are the most critical locations for damage accumulation and crack growth under thermally induced loading. The proposed framework provides a mechanism-based tool for solder joint reliability assessment beyond conventional empirical life prediction approaches.