Dominant effect of Sn grain orientation on electromigration-induced failure mechanism of Sn-3.0Ag-0.5Cu flip chip solder interconnects

Abstract

The effect of anisotropy in β-Sn grain on electromigration (EM)-induced failure mechanism of the Ni/Sn-3.0Ag-0.5Cu/Ni-P solder interconnects was in situ investigated. Sn grain orientation was a crucial factor in dominating the EM behavior. When the c-axis of Sn grain was parallel to the electron flow direction, a larger EM flux was induced, resulting in an excessive dissolution of Ni at the cathode. Sn hillocks were squeezed out at intermetallic compounds (IMCs)/solder interface on the anode side to relieve surficial compressive stress in the current crowding regions. When the c-axis of β-Sn grain was perpendicular to the electron flow direction, EM-induced void formation and propagation at the cathode resulted from the lower Ni diffusion flux. Furthermore, (Ni,Cu) 3 Sn 4 -type IMCs precipitated along the c-axis in single β-Sn grain in the bumps.