Cyclic Stress-Strain and Constitutive Behaviors of SAC-Bi-Ni-Sb Solder Alloys During Fatigue Testing

Fatigue of solder joints is considered to be one of the major methods of failure in electronic packages. Every electronic assembly is made up of different parts with varying thermal expansion coefficients (CTE). Many applications subject such assemblies to fluctuating temperature conditions. Mismatches in the CTE values of the components of the electronic assembly bring about a cyclic loading on the solder joints. Prolonged cyclic loading subsequently leads to the fatigue failure of these solder joints, thus resulting in the failure of the whole electronic package.The main focus of this investigation was to study the damage accumulated in bulk lead free solder alloys by analyzing the stress-strain behavior and the corresponding constitutive properties in SAC-Bi-Ni-Sb lead free solder (Innolot) subjected to fatigue testing. Circular cross- sectioned solder specimens were reflowed, and these samples were then mechanically cycled. The cyclic stress-strain curves obtained were studied to observe the degradation of hysteresis loop properties (peak stress, hysteresis loop area and plastic strain range) with cycling. In addition, samples with various durations of prior cycling were subjected to tensile and creep testing to determine the effect that mechanical cycling has on the modulus of elasticity, ultimate tensile strength, and creep strain rate of the material. The measured data were compared to the results from previous studies conducted on SAC305 and SAC+Bi (SAC_Q) lead free alloys.