Effect of trace Zn addition on electromigration of Cu/Sn–10Bi/Cu solder joints

The electromigration reliability on Sn–10Bi solder joints is investigated and the performance is tried to be improved with trace Zn addition in solder by depressing the growth of interfacial intermetallic compounds (IMCs) under electromigration. The electromigration test was realized on Cu/solder/Cu linear specimens at a current density of 1.0 × 10⁴ A/cm² with different stressing time. It was found that Bi atoms in Cu/Sn–10Bi/Cu solder joint were driven towards anode side under current driving force and then accumulated at anode interface with current stressing time increasing. The thickness and growth rate of Cu₆Sn₅ IMCs at anode interface were obviously larger than those at cathode side due to polarity effect. The addition of 0.2 wt.% Zn inhibited the migration of Bi atoms during the electromigration process, and the composition of interfacial IMCs was transformed into Cu₆(Sn, Zn)₅, which played as a diffusion barrier to effectively reduce the asymmetric growth of IMCs and the consumption of Cu substrate during electromigation.