Sn–Bi–Fe thermodynamic modeling and Sn–Bi/Fe interfacial reactions

Knowledge of Sn–Bi/Fe interfacial reactions and phase equilibria of Sn–Bi–Fe is of fundamental importance for Sn–Bi-based solder applications. Thermodynamic modeling of the binary Fe–Sn system and the ternary Sn–Bi–Fe system is carried out using the CALPHAD (calculation of phase diagram) method, and the calculated results show good agreement with the experimental information. The Sn–57wt%Bi/Fe interfacial reactions are examined between 250 and 500 °C. A peculiar phenomenon is observed that the reaction rates of Fe with molten Sn–57wt%Bi solder are lower at higher temperatures. This peculiar phenomenon is due to the different intermetallic compounds formed at different temperatures. The transition of the interfacial reaction products with temperatures is caused by the ternary phase equilibria tie-line shift, and can be well illustrated by the calculated Sn–Bi–Fe isothermal sections at different temperatures.