In-situ observation on electrochemical migration of lead-free solder joints under water drop test

Abstract

Electrochemical migration (ECM) of lead-free solder joints were investigated by water drop test method. Nine types solder pastes were employed to compare the ECM susceptible. The effects of applied voltage, electrodes spacing and flux residue on the ECM were in-situ observed. The microstructure and composition of the growing dendrites during ECM were detected. The results revealed that higher voltage and narrower spacing weakened the ECM reliability of solder joints. The flux residua inhibited the occurrence of ECM. The main migration element was Pb in Pb-bearing solder joints. For Sn-Ag-Cu solder joints, it was Sn and Cu to migrate during the ECM process. Zn was the only migration element in the SnZnBi solder joint. Sn-Zn-Bi solder exhibited the best ECM reliability.