Early dissolution behavior of copper in a molten Sn–Zn–Ag solder

The early dissolution behavior of Cu in a molten Sn–Zn–Ag solder was studied at 250 °C by fast quenching the dissolving specimen in liquid nitrogen. The atomic level dissolution behavior of Cu in the molten solder was revealed by high-resolution transmission electron microscopy. The dissolution of Cu occurs through channel dissolution and thermal vibrational dissolution. The dissolution channel has a dimension of less than 0.5 nm. The formation of channels, and thus the channel zone, is initiated by preferential removal of Cu atoms from the surface vacant site of Cu lattice. Relict strips of lattice between channels subsequently dissolve into the molten solder with the aid of thermal vibration and the interaction with liquid Zn atoms. The dissolved atoms form an atomic cluster zone. These clusters are the intermediate state of the dissolution of Cu from the channel zone into the molten Sn–Zn–Ag solder. The clusters convert into an amorphous structure prior to further formation of compound.