Electrochemical corrosion of Sn-0.75Cu solder joints in NaCl solution

The corrosion behaviors of Sn-0.75Cu solder and Sn-0.75Cu/Cu joint in 3.5% NaCl (mass fraction) solution were studied by potentiodynamic polarization test and leaching measurement. The polarization curves indicated that the corrosion rate of Sn-0.75Cu solder was lower than that of Sn-0.75Cu/Cu joint. The morphology observation and phase composition analysis on the corroded product at each interesting potential suggested that Sn3O(OH)2Cl2 formed on the surface of Sn-0.75Cu solder at active dissolution stage. As the potential increased from active/passive transition stage, all the surface of Sn-0.75Cu solder was covered by the Sn3O(OH)2Cl2 and some pits appeared after the polarization test. Compared to the Sn-0.75Cu solder alloy, much more Sn3O(OH)2Cl2 formed at active dissolution stage and the pits with bigger size were observed after polarization test for the Sn-0.75Cu/Cu solder joints. The leaching test confirmed that the faster electrochemical corrosion rate resulted in the larger amount of Sn released from the Sn-0.75Cu/Cu solder joints.