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NTRODUCTION

THE Sn-Sb–based alloys are important high-temperature solders for step soldering.[1–3] Knowledge of the phase equilibria of the Sn-Sb-Ag ternary system is essential for the applications and development of the solders. Masson and Kirkpatrick[4] experimentally determined the Sn-Sb-Ag liquidus projection. Oh et al.[5] thermodynamically modeled the Sn-Sb-Ag system, based on limited results from the literature. However, the most recent experimentally determined phase equilibria of Sn-Sb and Sn-Sb-Ag systems[6,7] are not consistent with the calculated results by Oh et al. Based on the thermodynamic and phase equilibria experimental determinations, including the most updated results, this study thermodynamically models the Sn-Sb-Ag system using the calculation of phase diagrams (CALPHAD) approach,[8] and then calculates its liquid projection and isothermal section. Except for the Sn-Sb binary system, which has been modeled recently,[6] the Sb-Ag and Sn-Ag binary systems are also thermodynamically modeled. II.

THERMODYNAMIC MODELING PROCEDURES

The CALPHAD[8] approach was used in this study. Experimental determinations of phase equilibria and thermodynamic properties of all the related phases were assessed, and proper thermodynamic models of these phases were developed. The thermodynamic parameters were determined by optimization, using ThermoCalc WOJCIEH GIERLOTKA, Postdoctoral Researcher, Department of Chemical Engineering, National Tsing Hua University, is Assistant Professor, Non-Ferrous Metals Department, AGH University of Science and Technology, Krakow 30-059, Poland. YU-CHIH HUANG, Graduate Student, and SINN-WEN CHEN, Professor, are with the Department of Chemical Engineering, National Tsing Hua University, Hsin-Chu 300, R.O.C. Taiwan. Contact e-mail: [email protected] Manuscript submitted March 24, 2008. Article published online October 28, 2008 METALLURGICAL AND MATERIALS TRANSACTIONS A

(Thermo-Calc Software, Stockholm, Sweden) and Pandat software packages (CompuTherm LLC, Madison, WI),[9,10] following the guidelines prepared by Schmid-Fetzer et al.[11] Each piece of the selected information was given a certain weight based on personal judgment; this was critical for good modeling. The modeling procedures started with the three constituent binary systems. The optimization was performed first on the liquid and terminal phases. The second step was about the intermetallic compounds, which were treated as line compounds; the line compound models were changed to compound energy models, where necessary. All parameters were finally evaluated together, to provide the best description of the systems. The ternary parameters were determined with the thermodynamic descriptions of the binary systems and experimental information of the ternary system.

III. EXPERIMENTAL MEASUREMENTS ON THERMODYNAMIC PROPERTIES AND PHASE EQUILIBRIA A. Ag-Sb System As shown in Figure 1(a), there are five phases in the Ag-Sb binary system in the temperature range of interest. They are the liquid phase, two terminal solid solutions, t