Electrochemical migration of lead-free solder alloys in Na2SO4 environment

The effect of sulphate ion concentration on electrochemical migration of lead-free solder alloys was investigated with the use of water drop tests, by applying an in-situ optical and electrical inspection system. According to the Mean-Time-To-Failure (MTTF) values it was found that in the case of 0.1 and 1 mM Na2SO4 solutions X alloy (composition in wt%: Sn=90,95%, Ag=3,8%, Cu=0,7%, Bi=3%, Sb=1,4%, Ni=0,15%) has higher migration susceptibility than SAC305 alloy (composition in wt%: Sn=96,5%, Ag=3%, Cu=0,5%). However on higher concentration levels, MTTF decreased and the failures usually happened in the same time on each solder alloy type. Failures were not happened in the case of X covered boards in case of 10 mM concentration.