Evolution of the Cyclic Stress-Strain and Constitutive Behaviors of Doped Lead Free Solder During Fatigue Testing

One of the most common method of failure in electronic packaging is the fatigue failure of solder joints. The constituent materials forming the electronic assembly have different coefficients of thermal expansion (CTE). When the assembly is subjected to a temperature changing environment, the solder joints experience a cyclic loading due to this difference in CTE, thus resulting in the fatigue failure. Although the knowledge of the Bauschinger effect is known, which states that the stress-strain behavior of materials is affected by the reversal of inelastic strain, there hasn't been much research on how the mechanical properties of the doped lead free solders degrade during fatigue testing. The main purpose of this study was to investigate the accumulation of damage by studying the cyclic constitutive and stress-strain behavior in doped lead free solders during fatigue testing. Initially, the samples were mechanically cycled for various durations. Stress-strain and creep tests were then conducted on the prior cycled samples. The fitted experimental data were plotted and various mechanical properties such as yield and ultimate strength, modulus of elasticity and creep strain rate were determined while also examining the plastic strain range, peak stress, and hysteresis loop area.