Electrochemical migration behavior of Sn–3.0Ag–0.5Cu solder alloy under SO2 polluted thin electrolyte layers
The effect of HSO3− on the electrochemical migration (ECM) of Sn–3.0Ag–0.5Cu lead-free solder alloy under thin electrolyte layers was investigated using the thin electrolyte layer method. The results showed that the migration element of Sn–3.0Ag–0.5Cu alloy was Sn and the faster-growing branch of the dendrite resulted in a sharper tip during the dendrite growth process. Increasing the amount of HSO3− decreased the probability of ECM. Due to the hydrolysis of HSO3, the pH value of electrolyte in thin electrolyte layer shifted toward a strongly acidic environment and a lower pH condition was favorable for dendrite formation. However, HSO3− reacted with tin ions to form some insoluble compounds during the ECM process, resulting in a decrease of tin ion concentration under thin electrolyte layers. A protective film formed on the anode surface, thus blocking the anodic dissolution process. Possible reactions were proposed to explain the inhibitory effect of HSO3− on the ECM of Sn–3.0Ag–0.5Cu alloy.
The authors thank the National Natural Science Foundation of China (No. 51571098) and the National Natural Science Foundation of Wuhan (Grant No. WX18Q21 to YC) for their financial support.
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