Overview Lead-Free SolderThe methods for modeling the thermodynamic properties of multicomponent systems are described in this article. The rules for creating a consistent database for muticomponent systems are described in general terms and documented in relation to the thermodynamic database for lead-free solders, developed within the scope

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.

a b s t r a c tThe binary system Ni-P is one of the constituents of the ternary system Ni-P-Sn which provides the basic knowledge for understanding the interactions between Sn-based solders and common Ni(P) metallization. In this study a new version of the Ni-P phase diagram was established based on XRD, EPMA and DTA measurements. The present diagram differs in some important details from the literature version. For the phases Ni 5 P 2 high temperature (HT) and Ni 12 P 5 HT the existence of a considerable homogeneity range is proposed. In Ni 5 P 2 the transformation between HT and low temperature (LT) modification comprises a peritectic and a eutectoid reaction, whereas for the transition in Ni 12 P 5 two eutectoids are proposed. Unfortunately, the high temperature phases cannot be stabilized by quenching, so that all data have to rely on the results of thermal analyses. Furthermore, Ni 5 P 4 was found to be formed by a peritectic reaction, and a eutectic was observed between Ni 5 P 4 and NiP. The phase NiP 1.22 that had been reported in the literature could not be found at all. Although the experimental work was complicated by the high vapor pressure of phosphorus at P concentrations higher than 40 at.% (which caused the explosion of quartz tubes and prevented the preparation of equilibrium samples at higher temperatures), it could still be shown that the phase NiP 3 is probably stable down to room temperature in contrast to the literature reports.

Due to the use of phosphorus-containing nickel substrates in microelectronics, understanding of their reaction with Sn-based solders and knowledge of the corresponding reaction products is highly important. Therefore the ternary Ni-P-Sn system was investigated experimentally using x-ray diffraction (XRD), scanning electron microscopy (SEM) + energy dispersive x-ray spectroscopy (EDX)/wavelength-dispersive x-ray spectroscopy (WDS), and differential thermal analysis (DTA). Sample preparation was done by alloying powders of the starting components contained in alumina crucibles in evacuated quartz tubes. In this study the phase equilibria in the Ni-rich part of the ternary Ni-P-Sn system are described in the form of three partial isothermal sections at 550°C, 700°C, and 850°C. A total of five ternary compounds exist in the Ni-rich part, and the binary Ni 3 Sn 2 HT phase was found to dissolve 17.6 at.% P at 850°C. This well agrees with literature reports, while a different extent and shape of the large homogeneity range of this phase were found. Between 850°C and 700°C phase equilibria change significantly due to the formation of the ternary phases Ni 10 P 3 Sn 5 (T3), Ni 13 P 3 Sn 8 (T4), and Ni 2 PSn (T5).

The methods for the modeling of thermodynamic properties of multicomponent systems are described here. The rules for the creation of a consistent database for multicomponent systems are described generally and documented on the Thermodynamic Database for Lead-free Solders developed in the scope of COST 531 Action. The reassessment of the Sb-Sn system is shown as an example, illustrating the application of consistency rules.

The binary Pd‐Zn system was assessed in the scope of this paper. The experimental data from the literature were used for the assessment, together with our own data obtained by SEM‐EDS analysis and by the DTA. The paper is focused particularly on the Pd‐Zn system, but the Pd‐Sn and Sn‐Zn systems are also analysed in this paper. Finally, first prediction of the isothermal sections of the ternary Pd‐Sn‐Zn system was made.

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