Prediction of activities of all components in Sn-Ag-Cu and Sn-Ag-Cu-Zn lead-free solders using modified molecular interaction volume model

Abstract In this study, the activities of binary alloys (Sn-Ag, Sn-Cu, Sn-Zn, Ag-Cu, Ag-Zn, Cu-Zn) and ternary alloys (Sn-Ag-Cu, Sn-Ag-Zn, Sn-Cu-Zn) were predicted using molecular interaction volume model (MIVM), modified MIVM (M-MIVM), Wilson equation, and nonrandom two-liquid model. The prediction deviations of the M-MIVM were the smallest among the four thermodynamic models, indicating that the M-MIVM is reliable for predicting the activity of these multicomponent lead-free solders. On this premise, the activities of all components in ternary Sn-Ag-Cu solders at 1300 K were predicted using the M-MIVM. We found that the activities of Sn, Ag and Cu exhibit negative deviations from Raoult’s law and that these deviations eventually transform into positive deviations. The activities of all components in quaternary Sn-Ag-Cu-Zn solders at 1000 K were also predicted using the M-MIVM when Zn contents were 0.1 and 0.2. This study provides a complete thermodynamic description of Sn-Ag-Cu ternary and Sn-Ag-Cu-Zn quaternary alloys.