Effects of the crystallographic orientation of Sn on the electromigration of Cu/Sn-Ag-Cu/Cu ball joints

Electromigration behavior and fast circuit failure with respect to crystallographic orientation of Sn grains were examined. The test vehicle was Cu/Sn-3.0 wt% Ag-0.5 wt% Cu/Cu ball joints, and the applied current density was 15 kA/cm2 at 160 °C. The experimental results indicate that most of the solder bumps show different microstructural changes with respect to the crystallographic orientation of Sn grains. Fast failure of the bump occurred due to the dissolution of the Cu circuit on the cathode side caused by the fast interstitial diffusion of Cu atoms along the c-axis of the Sn grains when the c-axis was parallel to the electron flow. Slight microstructural changes were observed when the oaxis was perpendicular to the electron flow. In addition, Cu6Sn5 intermetallic compound (IMC) was formed along the direction of the oaxis of the Sn grains instead of the direction of electron flow in all solder ball joints.