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<p>This study introduces a novel microstructural design for Sn-3.5Ag-0.5Cu (SAC355) solder via the synergistic co-addition of 0.1 wt.% Ni and 3.0 wt.% Bi. The Ni-Bi combination fundamentally alters solidification kinetics, as experimental results confirm a 64% reduction in undercooling (from 17.1 to 6.1&#xa0;°C) and a constricted pasty range of 6.7&#xa0;°C. This is linked to (Cu,Ni)₆Sn₅ intermetallic compounds and Bi-rich boundaries acting as potent nucleation sites. Microstructurally, the synergy yields a refined matrix that suppresses coarse β-Sn dendrites and Ag₃Sn platelets. Crucially, ultrasonic analysis reveals a unique elastic property profile: Bi enhances damage tolerance (Poisson’s ratio, <i>υ</i> = 0.329), while Ni induces solid-solution softening, reducing Young’s modulus (<i>E</i> = 121.6 GPa) and shear modulus (<i>G</i> = 37.4 GPa). This combination of microstructural refinement and optimized elastic constants collectively impedes crack propagation under stress, providing a transformative framework for high-reliability lead-free solders in demanding applications.</p>

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Structural and Thermal Optimization via Ni-Bi Synergy in SAC355 Solder Alloy: Undercooling Suppression and Solidification Kinetics

  • 期刊论文

  • 发表日期：

    2025年12月16日

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  • A. M. El-Taher,
  • Rageh K. Hussein,
  • M. Ragab,
  • Sally A. Eladly,
  • Ashraf S. Abd Elrahman,
  • Sharif Abu Alrub,
  • M. M. Fadel

摘要

This study introduces a novel microstructural design for Sn-3.5Ag-0.5Cu (SAC355) solder via the synergistic co-addition of 0.1 wt.% Ni and 3.0 wt.% Bi. The Ni-Bi combination fundamentally alters solidification kinetics, as experimental results confirm a 64% reduction in undercooling (from 17.1 to 6.1 °C) and a constricted pasty range of 6.7 °C. This is linked to (Cu,Ni)₆Sn₅ intermetallic compounds and Bi-rich boundaries acting as potent nucleation sites. Microstructurally, the synergy yields a refined matrix that suppresses coarse β-Sn dendrites and Ag₃Sn platelets. Crucially, ultrasonic analysis reveals a unique elastic property profile: Bi enhances damage tolerance (Poisson’s ratio, υ = 0.329), while Ni induces solid-solution softening, reducing Young’s modulus (E = 121.6 GPa) and shear modulus (G = 37.4 GPa). This combination of microstructural refinement and optimized elastic constants collectively impedes crack propagation under stress, providing a transformative framework for high-reliability lead-free solders in demanding applications.