Effects of crystallographic orientation of Sn on electromigration behavior

Abstract

Electromigration behavior of SAC flip-chip joints with respect to the crystallographic orientation of Sn grains was investigated. The test sample had direct contact of Sn-3.0wt% Ag-0.5wt% Cu on Cu-OSP (organic surface preservative) and the applied current density was 15 kA/cm2 at 160 °C. Without current stressing, no microstructural change depending on the crystallographic orientation of Sn was observed. With current stressing, however, the bumps showed the substantial microstructural changes with respect to the crystallographic orientation of Sn. When the orientation of the current flow was parallel to the c-axis, fast failure of the bumps occurred due to the massive dissolution of the Cu electrode on the cathode side caused by the fast diffusion of Cu atoms along the c-axis of Sn grains while only a slight microstructural change was observed when the c-axis of Sn grains was perpendicular to the electron flow.