Surface and transport properties of liquid Ag–Sn alloys and a case study of Ag–Sn eutectic solder

This review represents the state of the art in the thermophysical properties of liquid Ag–Sn alloys highlighting the surface and wetting properties of Ag–Sn eutectic solder. It includes an atomistic approach developed within the framework of statistical mechanical theory in conjunction with a Quasi Lattice Theory that, through a rigorous mathematical formalism, provides exact relationships between the properties in terms of classical thermodynamics. The model predicted property values are substantiated by available experimental data. Based on the phase diagram evidence about the existence of ε-Ag₃Sn intermetallic compound, the surface (surface tension and surface composition), transport (viscosity and diffusivity) properties and microscopic functions (concentration fluctuations in the long-wavelength limit and chemical short-range order parameter) have been studied using the Compound Formation Model in a weak interaction approximation and Quasi Chemical Approximation for regular solutions. A case study of Ag–Sn eutectic alloy is presented. Taking into account its importance for design and development of lead free solder alternatives, the literature data on the wettability and the phases formed at the interface between Ag–Sn eutectic alloy and different substrates (Cu, Ni, Au, Pd) have also been analysed.