Effect of Aging Temperature on the Fatigue Resistance and Shear Strength of SAC305 Solder Joints

The interconnection materials that are used in electronics assembly fabrication operating in harsh environmental conditions are frequently exposed to different types of mechanical stress and fatigue. Fatigue resistance does significantly affect the reliability of electronic assemblies. SAC alloys are commonly utilized in electronic assemblies’ fabrication operating in harsh conditions due to their superior mechanical and fatigue properties. Hence, this provokes the need to model and perform a detailed statistical analysis of their reliability behavior. SAC305 is commonly used as a lead-free alloy which is being utilized as a replacement of the eutectic SnPb alloy. The main goal of this study is to investigate the effect of aging temperature on the fatigue and mechanical behavior of SAC305 solder joints using accelerated shear-fatigue and shear tests. An Instron Microtester machine with a customized fixture was used to perform the tests. A two-factor test matrix for the fatigue test was constructed; where the stress amplitude has three levels (16, 20, and 24MPa) and the aging temperature has four levels (0, 50, 100, and $150^{\circ }\text{C}$ ). Microstructural analysis was performed on samples aged at different temperatures using SEM microscopy to address the evolutions in the precipitates size and the intermetallic compound (IMC) layer. A stress-life equation and an Arrhenius model are used to develop a general reliability model as a function of aging temperature and stress amplitude. The relationship between the fatigue life and the inelastic work were analyzed using Morrow Energy equation. The results indicate a major reduction in the reliability and shear strength of the solder joints with increasing the aging temperature. Aging has been also found to have a more notable effect on the fatigue life when compared to shear strength.