Dependence of recrystallization on grain morphology of Sn-based solder interconnects under thermomechanical stress

Continuous recrystallization of Sn-based solder interconnects under thermomechanical stress is studied by electron backscattered diffraction (EBSD) characterization of the cross-sectioned samples in thermal cycling and thermal shock tests. The results indicate that the inhomogeneous deformation and recrystallization have a close relationship with the crystallographic orientations of the as-solidified solder interconnects. Recrystallization initiates and propagates along the interface of the single-grained solder interconnects, followed by the crack propagation through the interfacial region. However, in the multi-grained solder interconnects the recrystallized region is found to propagate into the interior of the bulk solder along the pre-existing grain boundaries, diverting fracture from the near-interface region to the solder bulk. When the pre-existing grain boundaries coincide with the stress concentration area, the influence of the boundaries on the crack path is significant. Besides, some multi-grained solder interconnects with grain boundaries perpendicular to the interface show less severe cracking. This is due to the fact that the unfavorable orientation associated with the applied stress results in a high resistance to creep and fatigue.

► Sn-based solder interconnects show different responses under thermomechanical stress.
► Deformation, recrystallization and cracking depend on the grain morphology.
► Recrystallization occur in the near-interface region of single-grained interconnects.
► Recrystallization often extends into solder bulk of multi-grained interconnects.
► Solder interconnects with boundaries perpendicular to interface show high reliability.