Effect of Static and Dynamic Aging on Fatigue Behavior of Sn3.0Ag0.5Cu Solder Alloy

In this paper, the effect of pretest isothermal aging and in-test aging on the fatigue behavior of Sn3.0Ag0.5Cu alloy are examined using the microstructurally adaptive creep model (MACM) and the maximum entropy fracture model (MEFM). Compared to traditional constitutive models, the MACM considers the effect of thermal history. Two microstructural parameters, the average Ag₃Sn particle size and the average primary-Sn cell size, are identified as critical to capturing the aging behavior of SnAgCu alloys and are incorporated into a modified Dorn creep form. The MEFM is next utilized to characterize the damage accumulation rate in the Sn3.0Ag0.5Cu solder alloy. The MEFM uses a single damage accumulation parameter, which connects the accumulated damage to the accumulated in-elastic dissipation. This parameter is independent of sample geometry, test temperature and strain rate. The concepts of static aging and dynamic aging are utilized to describe pretest aging and in-test aging. In 25° C tests, with longer static aging, a faster fatigue damage accumulation results. Through the relationship between the damage accumulation rate and the average primary-Sn cell size, the influence of microstructural evolution introduced by static aging on fatigue behavior is confirmed. In 100° C tests, the dynamic aging causes further rapid damage accumulation relative to the 25° C tests.