Effect of Sn grain orientation on Cu diffusion in SnAgCu solder interconnect undergoing electromigration

Effect of electromigration (EM) on microstructural evolution of the Cu/Sn3.0Ag0.5Cu/Cu line-type interconnect was in situ investigated. It is interesting to note that Sn grain orientation was becoming the most crucial factor to dominate the EM behavior of downsizing bumps. When the c-axis of β-Sn grain was parallel to the electron flow direction, a larger EM flux was induced from the cathode toward the anode, resulting in the excessive dissolution of Cu occurred at the cathode and a thick Cu-Sn intermetallic compounds (IMCs) layer formed at the anode. Instead, when the c-axis of β-Sn grain was perpendicular to the electron flow direction, EM would be retarded due to the lower Cu diffusion flux. No evident dissolution or symmetrical growth IMCs was found at either interface. The mechanism of the effect of β-Sn grain orientation on the microstructural evolution undergoing EM was discussed from the diffusion flux point of view.