Evaluation of Time-Independent and Time-Dependent Strains of Lead-Free Solder by Stepped Ramp Loading Test

This paper proposes a method which can estimate essential material constants of an elasto-plastic-creep constitutive model for lead-free solders by conducting only a tensile test. The test employs a stepped ramp wave loading which repeats instantaneous straining and strain maintaining. The time-independent strains can be evaluated by using the stress-strain relations at the instantaneous straining parts, while the time-dependent strain can be evaluated by using the stress-time relations during the strain maintaining parts. Based on the results of the evaluations, the material constants of the elasto-plastic-creep models are estimated. Simulations of the viscoplastic deformations of Sn-3.0Ag-0.5Cu solder alloy were also conducted to verify the validity of the proposed method.