Thermodynamic Calculations and Kinetic Simulations of Soldering/Brazing Systems and Processes

For more than twenty years, thermodynamic databases developed using the CALPHAD method have been successfully applied to the modeling and simulation of steels, Ni-based superalloys, Al-/Mg-/Ti-based alloys, etc, as well as refractory and slag systems. Such databases, when combined with suitable software, can be used for accelerating alloy design as well as improving the understanding of existing alloys in terms of their processing and in-service behavior. Additionally, such databases are also essential to the modeling of microstructural evolution using methods such as phase field codes and steady state approaches when combined with kinetic databases that can also be developed using the extended CALPHAD approach.

There are similar examples applying such an approach to brazing, welding and solder systems which although tend not to be in equilibrium can help materials scientists and engineers develop a better understanding of joining technologies through modeling of various heterogeneous interaction phenomena.

This presentation describes the development of a new thermodynamic database, TCSLD1 (TCS Solder Alloy Solutions Database, v1), which has been developed using the CALPHAD methodology, based on various types of available experimental data and theoretical information. This new database contains all the important Au-/Ag-/Cu-/Sn-based solder alloy phases within a 16-element framework [Ag-Al-Au-Bi-Co-Cu-Ge-In-Ni-Pb-Pd-Pt-Sb-Si-Sn-Zn] and in total 150 phases (most of them as multicomponent alloy solutions and/or intermediate compound solutions, and the rest as intermediate stoichiometric compounds) are included.

The database can be used with the Thermo-Calc software and application programming interfaces and also DICTRA, for predicting various thermodynamic properties, stable/metastable phase equilibria and phase transformations of Au-/Ag-/Cu-/Sn-based solder systems (Pb-containing/Pb-free), and for simulating the effects of non-equilibrium solidification and micro-segregation of various soldering/brazing processes. The results from these predictions can be applied to eliminate candidate solder alloys for which the calculations reveal unsuitable freezing temperature ranges and undesired phases from further testing, and thus to accelerate design of new solder alloys as well as to improve understanding of existing solder alloys in terms of their processing and in-service behavior.