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<p>With the urgent demand for lead-free technologies in the electronics manufacturing industry, developing new solders with both excellent mechanical properties and process adaptability has become a research hotspot. This study is the first to systematically investigate the regulatory mechanism of copper addition (0–2.5 wt.%) on the microstructure and comprehensive performance of Sn-5Sb-5Bi lead-free solder. Through an innovative "grain refinement–intermetallic compound (IMC) regulation" synergistic strategy, a breakthrough optimization of solder performance has been achieved. It has been found that the introduction of copper can induce the formation of Cu<sub>6</sub>Sn<sub>5</sub> IMCs, significantly refining the solder microstructure. The matrix is mainly composed of β-Sn phase, with SnBi phase in a dispersed precipitated state, and trace copper uniformly dissolved in both phases. This unique structure brings multiple performance leaps: the melting point decreases from 237.7 to 231.2&#xa0;°C, and the melting range is shortened by more than 14% (≤&#xa0;12&#xa0;°C), perfectly meeting the strict industrial requirement of a melting range &lt; 30&#xa0;°C; the resistivity is reduced by 23.5%, and the improvement of electrical conductivity is mainly attributed to the synergistic effect of the conductive network of Cu<sub>6</sub>Sn<sub>5</sub> phase and the copper solid solution; and when the copper content reaches 2.5%, the wetting angle decreases by more than 15%, indicating that copper can effectively reduce the surface tension of the molten alloy and optimize the welding process. In terms of mechanical properties, 1 wt.% copper addition achieves the optimal balance between strength and toughness: the tensile strength reaches 63.56&#xa0;MPa (25% higher than the base alloy), and the elongation reaches 9.36% (40% higher), breaking the bottleneck that traditional lead-free solders are difficult to balance strength–plasticity. This study confirms that Sn-5Sb-5Bi-1Cu solder, with its low melting point, narrow melting range, high electrical conductivity, and excellent mechanical properties, provides a new solution for replacing traditional SnPb solder. Its regulatory law of "composition–structure–performance" also provides an important theoretical basis and experimental support for the design of high-performance lead-free solders.</p>

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Impact of Cu Addition on Sn-5Sb-5Bi Solder Properties

  • 期刊论文

  • 发表日期：

    2025年8月25日

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  • Zhe Li,
  • Guo Zheng,
  • Zhaohui Han,
  • Lei Xu,
  • Changhao Zuo,
  • Jianxun Wu

摘要

With the urgent demand for lead-free technologies in the electronics manufacturing industry, developing new solders with both excellent mechanical properties and process adaptability has become a research hotspot. This study is the first to systematically investigate the regulatory mechanism of copper addition (0–2.5 wt.%) on the microstructure and comprehensive performance of Sn-5Sb-5Bi lead-free solder. Through an innovative "grain refinement–intermetallic compound (IMC) regulation" synergistic strategy, a breakthrough optimization of solder performance has been achieved. It has been found that the introduction of copper can induce the formation of Cu6Sn5 IMCs, significantly refining the solder microstructure. The matrix is mainly composed of β-Sn phase, with SnBi phase in a dispersed precipitated state, and trace copper uniformly dissolved in both phases. This unique structure brings multiple performance leaps: the melting point decreases from 237.7 to 231.2 °C, and the melting range is shortened by more than 14% (≤ 12 °C), perfectly meeting the strict industrial requirement of a melting range < 30 °C; the resistivity is reduced by 23.5%, and the improvement of electrical conductivity is mainly attributed to the synergistic effect of the conductive network of Cu6Sn5 phase and the copper solid solution; and when the copper content reaches 2.5%, the wetting angle decreases by more than 15%, indicating that copper can effectively reduce the surface tension of the molten alloy and optimize the welding process. In terms of mechanical properties, 1 wt.% copper addition achieves the optimal balance between strength and toughness: the tensile strength reaches 63.56 MPa (25% higher than the base alloy), and the elongation reaches 9.36% (40% higher), breaking the bottleneck that traditional lead-free solders are difficult to balance strength–plasticity. This study confirms that Sn-5Sb-5Bi-1Cu solder, with its low melting point, narrow melting range, high electrical conductivity, and excellent mechanical properties, provides a new solution for replacing traditional SnPb solder. Its regulatory law of "composition–structure–performance" also provides an important theoretical basis and experimental support for the design of high-performance lead-free solders.