Work

Identification of the role of zinc in Sn–Cu solder and interfacial intermetallic growth through experimental results and phase-field simulations

Year: 2025

Type: article

Abstract: This study investigates the microstructural evolution and interfacial phenomena in five Sn–Cu–Zn solder alloys, focusing on the impact of Zn addition (0–1 wt.%). The findings reveal that Zn destabilises the eutectic interface, inducing cellular morphologies with fine and coarse eutectic at cell centres, while CuZn intermetallic compounds (IMCs) form in the interdendritic regions. Remarkably, even trace Zn additions significantly influence the solidification dynamics by reducing undercooling and altering the growth mode of primary β-Sn. However, these trace amounts have limited impact on suppressing η-Cu₆Sn₅ and ε-Cu₃Sn interfacial IMCs or Kirkendall void formation on Cu substrates.A Zn content exceeding 0.8 wt.% is required to effectively suppress IMCs over long-term high- temperature exposure. Nevertheless, the presence of a thin γ-Cu₅Zn₈ layer (<100 nm) at the interface substantially alters the nucleation, growth kinetics, and morphology of the η-phase. Phase-field simulations support these findings, demonstrating qualitative agreement with experimental data. The simulations further explain how the γ-phase modifies diffusion gradients, affecting the growth and distribution of η and ε phases. This work highlights the critical role of Zn in controlling solder microstructure and interfacial IMC development, offering valuable insights for optimising high- temperature lead-free solder joints.

Source: Materials & Design

DOI: 10.1016/j.matdes.2025.115219