Thermomechanical Fatigue Life Prediction of 63Sn/37Pb Solder

Abstract

Isothermal and thermomechanical fatigue of 63Sn/37Pb solder is studied under total strain-controlled tests. A standard definition of failure is proposed to allow inter-laboratory comparison. Based on the suggested failure criterion, load drop per cycle, the Young’s modulus and the ratio of the maximum tensile to maximum compressive stresses remain constant, and the fatigue response of the solder is stable before failure, although cyclic softening was observed from the beginning. Experimental results of isothermal fatigue tests for a total strain range from 0.3 to 3 percent show that the log-log plot of the number of cycles to failure versus the plastic strain range has a kink at the point where the elastic strain is approximately equal to the plastic strain. In this paper, it is shown how the isothermal fatigue life of near-eutectic solder at lower strain ranges can be predicted by using the experimental data of fatigue tests at high strain ranges and early stage information of a fatigue test at the strain range in question. A thermomechanical fatigue life prediction is also given based on a dislocation pile-up model. Comparison with experimental results shows a good agreement.