Effect of Bias Voltage on the Electrochemical Migration Behaviors of Sn and Pb

Electronic devices are becoming more miniaturized, and their operating environment is becoming more severe. In a condition of high humidity, high temperature, and high voltage applied, metals in electronics can cause insulation failure by making conductive filaments, which is called electrochemical migration. To understand this phenomenon, the water-drop test (WDT) and the anodic-polarization test on Sn and Pb electrodes are conducted, and their results are compared. Under constant voltage conditions for WDT, initial current of Sn rapidly decreased, but that of Pb did not decrease due to the passivity formation of Sn. In the case of Sn, two zones are distinguishable by level of biased voltage. In the first zone, the current value of Sn is lower than that of Pb by about two orders of magnitude. In the second zone, the current value of Sn is lower than that of Pb by about one order of magnitude. This is due to the corrosion behavior of Sn: passivity formation in the first zone and the pitting corrosion occurrence in the second zone. It was shown that the higher the voltage is, the shorter the time to failure becomes. The total amount of electric charge for the insulation failure of Sn is smaller than that of Pb, which can be explained by the difference in microstructure of dendrites of each material caused by the different corrosion behavior.