Current-induced phase partitioning in eutectic indium-tin Pb-free solder interconnect

Structural changes from high-density electric currents were examined in a eutectic In-Sn/Cu interconnect. Under electrical loading, Sn and In migrated in opposite directions, creating a partition of the Sn- and In-rich phases between the anode and the cathode. At the anode, a net gain of Sn atoms resulted in the formation of massive, columnar hillocks on the surface, but a net loss of In led to dissolution and disappearance of the In-rich intermetallic layer. At the cathode, the exodus of Sn left valleys adjacent to the In-rich regions on the surface, while the amount of the In-rich phase grew, due to the net influx of In at the expense of the In-rich intermetallic layer.