Dependence of electromigration damage on Sn grain orientation in Sn–Ag–Cu solder joints

Abstract

The relationship between the “polarity effect” of electromigration on interfacial intermetallic growth and the Sn grain orientation was investigated in Sn-Ag-Cu solder joints. The growth of the interfacial intermetallic compound was found to depend strongly on the Sn grain orientation. When the c-axes of the Sn grains were closely aligned to the current flow direction, a severe polarity effect was observed in which the anode interface was covered with a thick layer of Cu-Sn intermetallic while the intermetallic layer at the cathode interface was almost depleted. If the c-axes of the Sn grains were rotated away from the current direction, the polarity effect became less pronounced. When the c-axis was perpendicular to the current direction, the polarity effect essentially disappeared. The difference in the intermetallic layer thickness between the anode and the cathode, Δd, followed a parabolic function of the cosine of the angle, α, between the c-axis and the current direction. A kinetic model based on the highly anisotropic diffusion behavior of Cu in Sn was presented to explain the relationship between the electromigration polarity effect and Sn-grain orientation. The model showed good agreement with the experimental data.