The Influence of Interfacial Thermal Conductance on the Tensile Strength of a Sn-Mg Solder Alloy

Abstract

Sn-Mg alloys are potential Pb-free solder options. However, their mechanical strength and interfacial characteristics with electronic substrates remain barely understood. This study focuses on the interfacial heat transfer aspects, microstructure, and tensile strength of a Sn-2.1wt.%Mg alloy. Samples with various thermal histories were produced using a directional solidification apparatus. In these experiments, a Sn-2.1wt.%Mg alloy was solidified on Cu and Ni substrates, which are of interest in the electronics industry. Mathematical modeling was then employed, allowing for the determination of the overall and interfacial heat transfer coefficients (hov, and hi, respectively). The results show that the Ni substrate exhibits higher interfacial thermal conductance with the Sn-2.1wt.%Mg alloy compared to the Cu substrate, as indicated by the higher hi profiles. This fact occurs mainly due to their metallurgical interaction, resulting in a stronger bond with the presence of Sn-Ni-rich intermetallics at the interface. Finally, experimental equations based on the Hall–Petch relationship are proposed to describe how the refinement of the fibrous spacing of the Mg2Sn interphase (λG) and an increase in hi enhance both yield and ultimate tensile strengths.