Fig. 2In-Pd-Sn: Composition of the samples and position of the sections for calorimetry at 900°C. *Corresponding Author: Tel.-No , FAX-No , In-Pd-Sn: Liquid Enthalpies of Mixing and Phase Relations C. Luef*, H. Flandorfer und H. Ipser Institut für Anorganische Chemie, Universität Wien, Währingerstr. 42, A-1090 Wien, AustriaIntroduction Interfacial reactions of solder materials with the substrate (contact materials as Pd, Ni, Cu or combinations of these metals) at processing as well as operating conditions are highly important for the performance and durability of solder joints. The In-Pd-Sn ternary system is one of the relevant systems within our investigations of the interaction of Ag-In-Sn alloys with Pd as substrate. We present our first results on establishing the isothermal section at 700°C based on X-ray examinations of annealed samples (Guinier-Huber technique, Si as internal standard). The investigation of a second and a third isothermal section at 200 and 500°C, respectively, and DTA measurements to determine the liquidus surface and invariant reaction temperatures are still in progress. Furthermore the enthalpies of mixing of liquid alloys at 900°C were determined using a Calvet type microcalorimeter (Fig.1). The measurements were carried out under Ar-flow (30 cm³/min), NIST sapphire was used for calibration. We were able to fit the ternary interaction parameters, which are important for phase diagram calculations, using the substitutional Redlich-Kister-Muggiano model. From these results, the isoenthalpy curves were derived. The experimental results for the integral enthalpies of mixing were compared with calculated values obtained by three simple extrapolation models to predict ternary mixing enthalpies based on binary data. Results und Discussion The enthalpies of mixing in the liquid state were determined experimentally at about 100 different concentrations. Pieces of 20 to 50 mg of the pure metals were dropped into molten mixtures of In-Sn, In-Pd and Pd- Sn, respectively (see Fig. 2). The ternary experimental data were treated by a least squares fit using the REDLICH- KISTER-MUGGIANO polynomial (Fig. 3). The binary interaction parameters listed in Tab. 1 were determined in a separate investigation accompanying this work. The fitted ternary excess parameters M can also be found in Tab. 1. Fig. 3 shows the isoenthalpy curves derived from our experimental data. Above the dashed 900°C liquidus isotherm the samples are solid and the drawn isoenthalpy lines cannot be determined experimentally. All concentrations show a negative (exothermic) enthalpy of mixing with a global minimum of -55 kJ mol -1 at about 52 at.% Pd along the binary bordering Pd-Sn system. In Fig. 5 our results are compared with the values obtained by three simple extrapolation models. The values agree quite well, especially for small Pd concentrations. In Fig. 6 we present our first results on the phase relations at 700°C. From the X-ray results it is quite likely that a ternary compound  occurs at approximately 55 at.% Pd. Further experiments will be carried out to determine its structural properties and its solubility range. The Pd 20 Sn 13 phase shows a significant solubility for In (at least 12 at.%). Future EPMA measurements will help us to determine the homogeneity ranges of all involved phases. Fig. 6In-Pd-Sn: Isothermal section at 700°C. Blue lines indicate mono-phase regions. Fig. 5Comparison of the experimental results with values extrapolated from the binaries (section B). Acknowledgements The financial support of the Austrian “Fonds zur Förderung der wissenschaftlichen Forschung” (Project No. P15620-CHE) is gratefully acknowledged. This work is a contribution to the European COST 531 Action on “Lead-free Solder Materials”. Fig. 1Calvet-type Microcalorimeter: General view and automatic sample introduction unit. Fig. 3The Redlich-Kister-Muggiano polynomial. L are the binary interaction parameters, M the ternary excess parameters, and the order of the parameters. Tab. 1In-Pd-Sn: Binary and ternary interaction parameters at 900°C. Fig. 4In-Pd-Sn: Isoenthalpy curves for the integral molar enthalpy of mixing at 900°C (kJ mol -1 ). The dashed line indicates the approximate course of the liquidus isotherm.