Dominant effects of Sn orientation on serrated cathode dissolution and resulting failure in actual solder joints under electromigration

•Excessive serrated cathode dissolution strongly depends on the Sn grain orientation.•Sn grain orientation is a dominant factor that controls the direction of the serrated teeth.•Producing joints with fine Sn grains is one of the approaches to improve the reliability against current-induced failures in solder joints.

Excessive metal dissolution is one of the major electromigration-induced degradation mechanisms in interconnects, and it often produces a distinctive serrated cathode interface with most of the serrated teeth inclined toward a specific direction. In this study, actual flip-chip solder joints were systematically analyzed to understand this highly interesting morphology. It was unequivocally established that the Sn grain orientation is a dominant factor that controls the direction of the serrated teeth. When the c-axis of a Sn grain was nearly parallel to the electron flow direction, serrated dissolution occurred, with the serrated teeth inclined toward the c-axis. These observations were rationalized based on the diffusion anisotropy of Cu in Sn.