Effect of Sn grain orientation on polarity effect in Sn-Ag-Cu solder joints during electromigration

In this research, a sandwich construction Cu/SAC/Cu joints was introduced for EM tests. A 1.5 kA/cm² density current is applied in the tests at 110°C. The solder joint is composed of only a few big tin grains with a similar crystal orientation. The microstructural evolutions in correlation with the crystal orientations of the Sn grains after the EM tests were observed. The “polarity effect” is negatively related to the angle ω between the c-axis of tin grains and the electron flow direction. The relation between the IMC thickness differences vs the diffusion rate of Cu in Sn corresponding to angle ω is nearly fit to a linear function.