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

Kotadia, HR, Rahnama, A, Tang, F, Ahuir-Torres, JI ORCID: 0000-0002-3160-0223, West, G, Das, A and Mannan, SH (2025) Identification of the role of zinc in Sn–Cu solder and interfacial intermetallic growth through experimental results and phase-field simulations. Materials & Design, 260. ISSN 0264-1275

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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.

Item Type:	Article
Uncontrolled Keywords:	Sn-Cu solder; Pb-free solder; Intermetallic compounds (IMCs); Solidification; Phase-field simulations; 40 Engineering; 4016 Materials Engineering; 0910 Manufacturing Engineering; 0912 Materials Engineering; 0913 Mechanical Engineering; Materials; 4016 Materials engineering; 4017 Mechanical engineering
Subjects:	T Technology > T Technology (General) T Technology > TN Mining engineering. Metallurgy
Divisions:	Civil Engineering and Built Environment
Publisher:	Elsevier
Date of acceptance:	24 November 2025
Date of first compliant Open Access:	3 August 2026
Date Deposited:	03 Aug 2026 11:01
Last Modified:	03 Aug 2026 11:01
DOI or ID number:	10.1016/j.matdes.2025.115219
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29092

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