Deformation and Fatigue Fracture of Pb-Free Solder Alloys Under Complicated Load Conditions

Fundamental study of deformation and fatigue fracture behavior of solder alloys under complex load conditions is a key to enabling implementation of sophisticated 3-D time-dependent nonlinear FEM stress and strain analyses and life assessment for electronic packages and assemblies. In this study, the rate-dependent deformation and fatigue fracture behavior of Sn3.8Ag0.7Cu Pb-free alloy and Sn-Pb eutectic alloy was investigated with thin-walled specimens using a bi-axial servo-controlled tension-torsion material testing system, with solder alloys subjected to a variety of complex load conditions: pure shearing at strain rates between 6.7×10⁻⁷ /sec to 1.3×10⁻¹ /sec, creep at temperatures ranging from room temperature up to 125 °C, and cyclic loading with frequency of 0.001Hz to 3Hz. Bi-axial stress conditions were imposed for shearing tests to investigate effects of multi-axial stresses on deformation behavior. The effects of frequency and temperature on cyclic deformation and fatigue facture were investigated for lead-free Sn3.8Ag0.7Cu and Sn-Pb eutectic solder. Fractography of fatigue tested samples were also conducted to determine possible fatigue failure mechanisms.