Electromigration of Sn-8Â wt.% Zn-3Â wt.% Bi and Sn-9Â wt.% Zn-1Â wt.% Cu solders

Stripe-type Cu/solder/Cu reaction couples were utilized to investigate electromigration behaviors of Sn-8Zn-3Bi and Sn-9Zn-1Cu (in wt.%) solders under current stressing with a density of 105 A/cm2 at 80-125 °C. Two cooling conditions, fan and furnace cooling, were performed after the solders was reflowed on the Cu stripe. No noticeable microstructural change was found in the fan-cooled Sn-8Zn-3Bi solder at 80 °C except that Bi migrated along with the electron flow toward the anode. While significant microstructural change was found at 125 °C, indicating that electromigration effect is enhanced at higher temperatures. Sn was extruded in front of the Cu electrode at the anode side and voids were formed in the solder near the cathode side. For the furnace-cooled solder, microstructural change was found even at 80 °C. For the Sn-9Zn-1Cu solder, regardless of fan or furnace cooling, Sn extrusion and voids were formed at the anode and cathode sides, respectively, after current stressing at 80 °C. Voids were formed in the solder and mainly surrounded the Cu-Zn compounds.