Inelastic Deformation and Fatigue of 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 three-dimensional (3D) time-dependent nonlinear finite-element stress and strain analyses for the 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 biaxial servo-controlled tension–torsion material testing system, with solder alloys subjected to a variety of complex load conditions: pure shearing at strain rates between $6.7×10−7∕s$ and $1.3×10−1∕s$⁠, creep at temperatures ranging from room temperature up to $125°C$⁠, and cyclic loading with frequencies of $0.001Hz$ to $3Hz$⁠. Biaxial stress conditions were imposed to investigate the effects of multiaxial 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 was also conducted to determine possible fatigue failure mechanisms.