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<p>To address the demand for lead-free solders in electronic packaging and overcome Sn-Cu alloys’ high melting point and insufficient mechanical properties, this study prepared Sn-0.7Cu-0.1Te-xBi solders (<i>x</i> = 0,2,3,4 wt%) via Te-Bi composite microalloying combined with resistance melting and directional solidification, investigating their microstructure, post-welding interfacial features, mechanical properties, and conductivity. Results showed Bi refined the β-Sn phase and modified Cu<sub>6</sub>Sn<sub>5</sub> morphology. Directional solidification suppressed Bi segregation to realize a uniform component solid solution, while resistance melting easily caused Bi precipitation at grain boundaries. For directional solidification, 3 wt% Bi was optimal—the solder had 65&#xa0;MPa tensile strength and good ductility, with a continuous, defect-free scallop-like intermetallic compound layer after welding. For resistance melting, 4 wt% Bi obtained the best hardness of 33.3 HV and tensile strength of 82.03&#xa0;MPa, but ductility degraded sharply with only 8.86% elongation. Regarding conductivity, directional solidification solder resistivity rose steadily with Bi content, while resistance melting solder resistivity first increased then decreased. This study clarifies the solder’s optimal composition and process, supporting high-performance Sn-Cu-based lead-free solder development.</p>

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Investigation of Bi Content Effects on Sn-0.7Cu Microstructure and Properties Under Different Processing Conditions

  • 期刊论文

  • 发表日期：

    2026年4月2日

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  • Zhuhuan Yu,
  • Ziyan Wang,
  • Xiong Yang,
  • Haiyan Lv,
  • Junfeng Qiang,
  • Zi Yang,
  • Xirui Shangguan,
  • Tianxiao Ma

摘要

To address the demand for lead-free solders in electronic packaging and overcome Sn-Cu alloys’ high melting point and insufficient mechanical properties, this study prepared Sn-0.7Cu-0.1Te-xBi solders (x = 0,2,3,4 wt%) via Te-Bi composite microalloying combined with resistance melting and directional solidification, investigating their microstructure, post-welding interfacial features, mechanical properties, and conductivity. Results showed Bi refined the β-Sn phase and modified Cu6Sn5 morphology. Directional solidification suppressed Bi segregation to realize a uniform component solid solution, while resistance melting easily caused Bi precipitation at grain boundaries. For directional solidification, 3 wt% Bi was optimal—the solder had 65 MPa tensile strength and good ductility, with a continuous, defect-free scallop-like intermetallic compound layer after welding. For resistance melting, 4 wt% Bi obtained the best hardness of 33.3 HV and tensile strength of 82.03 MPa, but ductility degraded sharply with only 8.86% elongation. Regarding conductivity, directional solidification solder resistivity rose steadily with Bi content, while resistance melting solder resistivity first increased then decreased. This study clarifies the solder’s optimal composition and process, supporting high-performance Sn-Cu-based lead-free solder development.