Electrochemical migration tests of solder alloys in pure water

Electrochemical migration (ECM) tests on solder alloys were conducted by applying constant voltage with a power supply or sweeping the voltage at a constant rate with a potentiostat. Distilled water was used as the test environment. Time to short and short voltage were the measure of ECM susceptibility. Similar results were obtained in both test methods. In Sn-Pb alloy system, pure lead showed the highest susceptibility. Alloys with 5-60%Sn showed similar high susceptibility. Further addition of tin lowered the susceptibility and pure tin had the lowest susceptibility. Dendrites grew from cathode and reached to the anode. The composition of dendrites of Sn-40Pb alloy was enriched in lead. Some tin base solder alloys without lead were more resistant to ECM than Sn-40Pb alloy. Pure indium, In-48Sn and In-50Pb alloys were found to be immune to ECM in pure water. Large anodic dissolution rate seems to be responsible to high ECM susceptibility. (C) 1997 Elsevier Science Ltd.