MECHANICAL PROPERTIES OF SAC-BI SOLDER ALLOYS WITH AGING

摘要

A significant reliability problem with the baseline alloy SAC305 is the deterioration of their mechanical properties and recrystallization of the microstructure after aging. In addition to the effect of aging, multiple factors can contribute to the early failure of the solder joint at different levels. Research has shown that shear testing with high strain rate accelerates the failure mechanism of the solder joint. On the other hand, several studies have revealed that the Bi content in the solder alloy provides a better result in terms of mechanical properties and stabilization of the microstructure after aging. Therefore, this study examines the effects of aging on the microstructure and the mechanical properties for different solder alloys (SnAgCu, SnAgCu-3Bi, and SnAgCu-6Bi). Four aging periods (0, 10, 100, 1000 hrs.) at 150°C are considered in the study. The Instron 5948 Micro Tester is used to perform shear tests for individual solder joints by using customized experimental setup. The evolution in the microstructure is assessed by using both optical microscope and scanning electron microscopy. The ultimate shear stress of Bi alloys was notably higher than the ultimate shear strength of SAC 305 regardless of the aging time due to solid solution hardening and precipitate hardening. Three failure mechanisms were noticed including ductile failure, brittle failure, and a combination of ductile and brittle failures. The goal of this research paper is to investigate the effect of Bi and aging on the mechanical properties and the microstructure of the solder joints.