Electrochemical reaction process and mechanisms of Sn and Sn-58Bi solders in MSA, SSA, DEA, TEA, and TIPA flux solutions

Due to the combined effects of high-density electric fields, water vapor, and residues, adjacent solder joints are prone to electrochemical migration. This study investigates the electrochemical reaction processes and mechanisms of Sn and Sn-58Bi in methanesulfonic acid(MSA), sulfosalicylic acid(SSA), diethanolamine(DEA), triethanolamine(TEA), and triisopropanolamine (TIPA) flux solutions. The results show that under natural corrosion conditions Sn-58Bi exhibits better electrochemical corrosion resistance than Sn. Under dynamic potential conditions, reaction rates of Sn-58Bi exceed that of Sn due to the dissolution of Bi. The dissolution threshold for Bi occurs at approximately 0.15 V in the TEA solution, 0.37 V in the TIPA solution, and 1 V in the DEA solution. Sn-58Bi in the MSA and SSA solutions primarily undergoes Sn dissolution, whereas in the DEA, TEA, and TIPA solutions, Bi dissolution is the dominant process. Under a constant voltage of 1 V vs.SCE , the dissolution current of Sn is lower than that of Sn-58Bi. Sn-58Bi in the TIPA solution shows instability in the passivation film. Under a constant voltage of 5 V vs.SCE , the stable current values for both solders are similar.