A thermodynamic assessment of the Bi-Sn-Zn ternary system was carried out using the CALPHAD approach along with thermodynamic descriptions from new assessments of the Bi-Sn and Bi-Zn systems. Selected experimental data from the literature and our own work were also used. New sets of optimized thermodynamic parameters were obtained that lead to a very good fit between the calculated and experimental data. The Bi-Sn-Zn system is one of the candidates for lead-free solder materials.

The binary Bi-Sn was studied by means of SEM (Scanning Electron Microscopy)/EDS (Energy-Dispersive solid state Spectrometry), DTA (Differential Thermal Analysis)/DSC (Differential Scanning Calorimetry) and RT-XRD (Room Temperature X-Ray Diffraction) in order to clarify discrepancies concerning the Bi reported solubility in (Sn). It was found that (Sn) dissolves approximately 10 wt% of Bi at the eutectic temperature.The experimental effort for the Bi-Zn system was limited to the investigation of the discrepancies concerning the solubility limit of Zn in (Bi) and the solubility of Bi in (Zn). Results indicate that the solubility of both elements in the respective solid solution is approximately 0.3 wt% at 200 • C.Three different features were studied within the Bi-Sn-Zn system. Although there are enough data to establish the liquid miscibility gap occurring in the phase diagram of binary Bi-Zn, no data could be found for the ternary. Samples belonging to the isopleths with w(Bi) ∼ 10% and w(Sn) ∼ 5%, 13% and 19% were measured by DTA/DSC. The aim was to characterize the miscibility gap in the liquid phase. Samples belonging to the isopleths with w(Sn) ∼ 40%, 58%, 77/81% and w(Zn) ∼ 12% were also measured by DTA/DSC to complement the study of Bi-Sn-Zn. Solubilities in the solid terminal solutions were determined by SEM/EDS. Samples were also analyzed by RT-XRD and HT-XRD (High Temperature X-Ray Diffraction) confirming the DTA/DSC results for solid state phase equilibria.

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Bi-Sn-Zn is one of the systems being used as substitute of the traditional lead solders. Therefore a deeper knowledge of its phase diagram is a priority. Due to the lack of data about the thermodynamic properties of terminal solid solutions as well as on their phase boundaries, only binary contributions were utilized and the ternary terms were ignored on the published assessments [1, 2]. Samples corresponding to several vertical sections were prepared and DTA, SEM/EDS and XRD at room and high temperatures were performed. It was concluded that ternary terms should be held in consideration in a future assessment of the system.