Dominant migration element in electrochemical migration of eutectic SnPb solder alloy

In harsher condition with elevated temperature/humidity and complex chemical species, electronic components can be electrochemically ionized and migrate by electric field. The migrated ions form conducting filament between anode and cathode across a nonmetallic medium. The filament can cause a failure of electronic system. This phenomenon is called as the electrochemical migration (ECM). A model test system for water-drop test was devised to assess the ECM characteristics of eutectic SnPb (63Sn-37Pb, wt%). The result for model test system was compared with that for real electronic component on printed circuit borads (PCBs). Although the filament formation mechanism was different, it was found that Pb atoms are more susceptible to polarization than Sn atoms for both cases. This tendency agrees well with the composition distribution of the filament on the model system and PCBs