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

H.R. Kotadia, A. Rahnama, F. Tang, J.I. Ahuir-Torres Orcid Logo, G. West, Amit Das Orcid Logo, S.H. Mannan Orcid Logo

Materials & Design, Volume: 260, Start page: 115219

Swansea University Author: Amit Das Orcid Logo

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DOI (Published version): 10.1016/j.matdes.2025.115219

Abstract

Intermetallic compound (IMC) formation significantly impacts the reliability of lead-free solder joints, with trace elements like Ni and Zn offering potential to control IMC growth. However, the mechanisms by which trace Zn influences microstructural evolution and interfacial reactions remain undere...

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Published in: Materials & Design
ISSN: 0264-1275
Published: Elsevier BV 2025
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URI: https://cronfa.swan.ac.uk/Record/cronfa71142
Abstract: Intermetallic compound (IMC) formation significantly impacts the reliability of lead-free solder joints, with trace elements like Ni and Zn offering potential to control IMC growth. However, the mechanisms by which trace Zn influences microstructural evolution and interfacial reactions remain underexplored. This study examines microstructural evolution and interfacial behaviour in five Sn–Cu–Zn solder alloys (0–1 wt% Zn). Zn destabilises the eutectic interface, producing cellular morphologies with mixed eutectic at cell centres and CuZn IMCs in interdendritic regions. Even trace Zn notably affects solidification by reducing undercooling and altering β-Sn growth. While trace Zn has limited effect on suppressing η-Cu6Sn5, ε-Cu3Sn, or Kirkendall voids on Cu, it reduces IMC thickness, indicating growth inhibition. Adding ≥ 0.8 wt% Zn reduces IMC thickness at 150 °C by 68.5 % after 1000 h, from ∼ 16.5 µm (Sn–Cu) to ∼ 5–5.5 µm, also lowering void growth. The presence of a thin γ-Cu5Zn8 layer (<100 nm) at the interface substantially alters the nucleation, growth, and morphology of the η-phase. Phase-field simulation helped explain the experimental observations indicating thin γ-Cu5Zn8 formation at the solder-substrate interface that enhanced nucleation of η-Cu6Sn5 but reduced the growth kinetics of η and ε phases by creating a diffusion barrier for Cu atoms.
Keywords: Sn-Cu solder; Pb-free solder; Intermetallic compounds (IMCs); Solidification; Phase-field simulations
College: Faculty of Science and Engineering
Funders: This research was funded by the Engineering and Physical Sciences Research Council, Grant no. EP/G054339/1. In addition to that the characterisation facility is supported from the Higher Education Funding Council for England (HEFCE) fund and the WMG Centre High Value Manufacturing Catapult is gratefully acknowledged.
Start Page: 115219

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