Density and dynamic viscosity of Sn, Sn–Ag, and Sn–Ag–Cu liquid lead-free solder alloys 

Abstract

Traditionally, the soldering process was carried out, applying mainly lead-based solder materials. However, the prohibition against using lead (Pb) in electronic equipment under the Restriction of Hazardous Substances Directive (RoHS) shifted the focus of research towards developing lead-free alloys. At the same time, tin (Sn) and tin-based alloys became viable alternatives. The development of solder alloys for long-term industrial applications necessitates a methodical characterization of material properties. Thermophysical properties are essential for modeling, designing, and employing lead-free solders to obtain strong joints. Such thermophysical properties as viscosity and density become more and more important as the research in advanced hybrid materials moves forward. This study presents an examination of density and dynamic viscosity in common lead-free solder materials, namely, pure Sn, Sn–3.5Ag, and Sn–3Ag–0.5Cu. The focus of research essentially moved onto the tin-based materials as it has a relatively low melting point and, thus, can serve as an alternative to lead in solder alloy research area and applications. Hence, Sn, Sn–3.5Ag and Sn–3Ag–0.5Cu were selected as research objects. A detailed literature review on the available models for theoretical evaluation of the above materials’ density and dynamic viscosity is provided. The available scientific efforts on dynamic viscosity assessment are extensive, but no specific model was described in the literature as more beneficial than the other. This study allows evaluating the density and dynamic viscosity using different models with the subsequent comparison of the results. Comparative analysis ensures a better model assessment for calculating thermophysical properties and contributes to high-quality modeling and designing of lead-free solder alloys.