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<p>The advancement of Pb-free solder systems with superior stress relaxation (SR) resistance is crucial for microelectronic reliability. In this study, trace Co additions were incorporated into low-Zn Sn–6Zn–0.05Fe (SZF) solder to optimize its microstructure and improve creep resistance. SR testing at <i>σ₀</i> = 15&#xa0;MPa and 25&#xa0;°C revealed that SZF–0.1Co exhibits strength-ductility synergy, achieving 52&#xa0;MPa tensile strength and 32.8% elongation. These enhancements arise from the growing of uniformly distributed Fe<sub>2</sub>Sn<sub>3</sub> and CoSn<sub>2</sub>@CoZn<sub>7</sub> core–shell precipitates that resist coarsening and stabilize the microstructure. Compared with unalloyed SZF, the SR resistance (<i>η</i>), Young’s modulus, and yield strength (YS) improved by 34, 30.8 and 28.3%, respectively. The SR estimated from single SR testing performed on individual specimen was found to follow the power-law creep kinetics, characterized by a stress exponent <i>n</i> = 8.1–12.8. The activation energies <i>Q</i> between 55.87 and 91.54&#xa0;kJ&#xa0;mol<sup>−1</sup> were derived from the modified single-barrier model. The obtained <i>n</i> and <i>Q</i> values indicate that SR is governed by dislocation climb assisted by pipe diffusion in all alloys, whereas lattice-diffusion-controlled creep dominates in the SZF–0.1Co composition. These results demonstrate the mechanistic role of Co microalloying in improving SR resistance and offer a reliable framework for rapid mechanical evaluation within short testing regimes.</p>

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Microstructural evolution and creep deformation of Co-modified Sn–6Zn–0.05Fe lead-free solder using single specimen and single stress relaxation test

  • 期刊论文

  • 发表日期：

    2026年4月14日

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  • Hind Alsnani,
  • A. A. Ibrahiem,
  • A. A. El-Daly

摘要

The advancement of Pb-free solder systems with superior stress relaxation (SR) resistance is crucial for microelectronic reliability. In this study, trace Co additions were incorporated into low-Zn Sn–6Zn–0.05Fe (SZF) solder to optimize its microstructure and improve creep resistance. SR testing at σ₀ = 15 MPa and 25 °C revealed that SZF–0.1Co exhibits strength-ductility synergy, achieving 52 MPa tensile strength and 32.8% elongation. These enhancements arise from the growing of uniformly distributed Fe2Sn3 and CoSn2@CoZn7 core–shell precipitates that resist coarsening and stabilize the microstructure. Compared with unalloyed SZF, the SR resistance (η), Young’s modulus, and yield strength (YS) improved by 34, 30.8 and 28.3%, respectively. The SR estimated from single SR testing performed on individual specimen was found to follow the power-law creep kinetics, characterized by a stress exponent n = 8.1–12.8. The activation energies Q between 55.87 and 91.54 kJ mol−1 were derived from the modified single-barrier model. The obtained n and Q values indicate that SR is governed by dislocation climb assisted by pipe diffusion in all alloys, whereas lattice-diffusion-controlled creep dominates in the SZF–0.1Co composition. These results demonstrate the mechanistic role of Co microalloying in improving SR resistance and offer a reliable framework for rapid mechanical evaluation within short testing regimes.