In situ study the electrochemical migration of tin under unipolar squarewave electric field

Electrochemical migration (ECM) behaviors of tin under unsteady state electric field were investigated via thin electrolyte layer (TEL) method using optical and electrochemical techniques. Unipolar square waves with various time periods and duty cycles were first used as the unsteady state electric field for ECM investigation, where a 3-V-bias and a 0-V-bias were applied across the two electrodes during the ON time and OFF time, respectively. The results show that there is a reverse polarization applied across the two electrodes during the OFF time to ensure the 0-V-bias. The presence of reverse polarization will result in ions migration reverse to their original migration direction and the tin ions that migrated back may even be reduced back to metal tin. Therefore, the reverse polarization is adverse to the ECM process of tin. At the same time period, the rate of dendrites growth increases with the increase of duty cycle. While, for the same duty cycle, the prolongation of time period is favorable for the precipitates formation and/or dendrites growth. The influence mechanisms of time period and duty cycle on ECM behaviors have also been proposed, respectively.