Fatigue Life Degradation Modeling of SnAgCu Solder Joints After Aging

The reliability of electronic assemblies is exceedingly reliant on the life of solder joints. Many factors may influence the fatigue life and mechanical properties of solder joints. Aging is one of the main factors that adversely affect the reliability of solder joints. In this article, the mechanical reliability of individual SnAgCu solder joints is studied at different aging conditions. The experiments include aging then cycling solder joints in stress-controlled shear fatigue at different stress amplitudes (16, 20, and 24 MPa) until complete failure. The aging conditions include three levels of aging temperatures (50 degrees C, 100 degrees C, and 150 degrees C) and four levels of aging time (2, 10, 100, and 1000 h). The effect of stress amplitude, aging time, and aging temperature on the fatigue life is investigated. The evolutions in the hysteresis loop, including the inelastic work dissipation, are explored by studying the stress-strain diagrams. The results showed that the fatigue life was affected by the stress amplitude, where increasing the stress by a factor of 2 leads to life reduction by a factor of 22. It was also found that increasing the aging time leads to nonlinear life reduction, where the first few hours of aging had the largest effect. Increasing the aging temperatures aggregates the aging time effect and leads to less fatigue resistance. Overall, increasing the aging time, temperature, and/or stress amplitudes leads to an increase in the work dissipation per cycle, which creates more damage and leads to less number of cycles to failure. The effect of these factors was fit into mathematical equations. Then, a general reliability model as a function of those parameters was developed.