Electrochemical Migration of SAC305 Solders and Tin Surface Finish in NaCI Environment

The impact of chloride ion contamination on electrochemical migration (ECM) of SAC305 lead-free solder alloys, and galvanic tin surface finish was studied using water drop tests and by using an in-situ electrical and optical measuring set up as well. Tests were performed with the use of 3.5 wt NaCI solution. The “A” type SAC305 alloy had a rosin&acid/flux paste ratio of 12.5 wt%, however by the “B” type SAC305 alloy it was only 9.3 wt%. According to the mean-time-to-failure (MTTF) data it was shown that “A” and “B” type solder alloys have approximately the same ECM susceptibility, but in the case of tin surface finish failures happened typically after shorter period of time.