Effect of Stress State on Fatigue Characterization of SAC305 Solder Joints

In this study, room temperature cyclic mechanical tests are performed at different load levels on three types of SAC305 joint-scale solder specimens: (i) M90 specimen (tensile stress state), where the solder joint is oriented perpendicular to the loading axis; (ii) M0 specimen (shear stress state), where the solder joint is oriented parallel to the loading axis; and (iii) M45 specimen (with multiaxial stress state), where the solder joint is oriented at an angle of 45° to the loading axis. Digital Image Correlation (DIC) technique is used to measure solder deformation. Cyclic equivalent strain range is estimated for each of the three loading conditions and used for comparing fatigue durability (by constructing strain-life fatigue curves) under these three different stress states. Failure analysis is conducted on the tested specimens, using SEM to understand and document the observed failure modes. Preliminary results indicate significant difference in fatigue life and failure modes of solder joints in tensile vs. shear mode. Few-grained SAC solder joints are found to exhibit poor tensile fatigue resistance compared to shear fatigue resistance. The multiaxial fatigue durability (M45 specimen) is found to be slightly worse than the shear fatigue durability. Findings of this study will provide better understanding of the contribution of axial loads and stress multiaxiality to damage and degradation mechanisms in few-grained SAC solder joints.