Directional Solidification of Sn-Cu₆Sn₅ In Situ Composites

Abstract

The Sn-Cu system presents an important interest from academic and technological point of view because it is part of the family of alloys proposed as lead-free solder alloys for electronic components and also due to the mechanisms involved during the growth of the different phases. Sn-Cu system has two intermetallic phases, i.e., ε-Cu3Sn and η-Cu6Sn5, and η can be used as the negative (anode) electrode in Li-ion batteries, alone or as part of (Co,Ni)xCu6−xSn5-type composites. Obtaining this η phase from liquid with the appropriate chemical composition is a very difficult task because it has a formation temperature lower than liquidus for such a composition. In this way, the η phase appears as a consequence of a solid-solid transformation from the ε phase However, it is possible to find the η phase as the primary or secondary phase after a eutectic reaction for lower concentrations of Cu. On the other side, the Cu6Sn5 phase shows a hexagonal to monoclinic solid-solid transformation around 187°C, which could affect the mechanical system stability when it is used as solder. In this work, directional solidification at different growth velocities of hypereutectic Sn-Cu samples was performed. The resultant microstructure varies with the growth velocity, but it is formed for a fibber-like primary phase Cu6Sn5 which is projected towards the liquid phase. Behind this region, these fibbers are rounded by a two-phase Sn-Cu6Sn5 structure. In this way, three zones could to be defined in the sample during the directional growth: (i) an entirely solid two-phase region, formed by η rounded by β(Sn) + η eutectic-like structure, (ii) a two-phase solid (η) + liquid, and (iii) the remnant liquid in front of the interface.

Effect of Y Addition on the Microstructures and Tensile properties of Sn-Bi-Al Alloys

“…After the European RoHS (Reduction of Hazardous Substances) announced a ban on the use of lead solders, to develop lead-free solders is necessary. Subsequently, the operational to develop innovative lead-free solder alloy continues to grasp the attention of researchers [1,2]. The researchers were mainly focuses on Tin-based alloys, various compositions were studied, and the most common were Sn-Ag, Sn-Cu, Sn-Zn and Sn-Bi.…”

Microstructure, Mechanical, and Electrical Properties and Corrosion Analysis of Lead‐Free Solder CSI Joints on Cu Substrate Using Novel Concentrated Solar Energy Soldering (CSES) Method

“…SnPb solders were used for the past few decades due to their good mechanical and corrosion resistance properties. Advantages of being economical and good wettability added to their extensive use [1][2][3][4][5][6][7]. In July 2006, the European Reduction of Hazardous Substances (RoHS) banned lead [8,9].…”