Electrochemical Investigation on the Effect of Silver Addition on Wettability of Sn-Zn System Lead-free Solder.

The role of electrochemical reaction between solder and base metal in soldering flux has been investigated in relation to wetting. The effect of silver addition to Sn-Zn lead-free solder on the wettability of copper base metal was studied by electrochemical measurement in soldering flux.The research includes the electrode potential measurement, anodic and cathodic polarization, and contact polarization between solder and base metal in soldering fluxes. The difference of electrode potential between solder and base metal in soldering flux plays an important role to remove oxide film by contact polarization. It is concluded that the electrode potential of Sn-based lead-free solders should be lower than copper to obtain good wettability, because the anodic dissolution of tin by contacting the copper base metal enhanced the wettability by removal of tin oxide which is one of the stable oxide among base metal and solder. Sn-Zn solder has extremely low electrode potential than copper base metal, which accelerates the preferential anodic dissolution of zinc resulting in the no dissolution of tin. To suppress the preferential dissolution of zinc is important to improve the wettability of Sn-Zn solder, therefore, the reduction of potential difference between base metal and solder is effective. The addition of silver to Sn-Zn solder and the use of brass base metal was found to be effective by reducing the potential difference between base metal and solder which suppress the anodic dissolution of zinc.