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<p>Micro-alloying has been established as an effective strategy for enhancing the performance of low-Ag Sn–Ag–Cu (SAC) lead-free solder alloys. In this study, the low-Ag Sn–Ag–Cu-Bi-Ni-In (SACBNI) solder alloys were fabricated and their thermal properties, wettability, micro-hardness, microstructure and mechanical properties were systematically investigated. The results indicated that the addition of Bi, Ni, and In effectively refined the matrix microstructure and promoted more uniform distribution of intermetallic compounds (IMCs) within the matrix. Compared to low‑Ag SAC solder alloys, the developed low-Ag SACBNI solder alloys exhibited lower melting point, superior wettability and micro-hardness. Furthermore, the low-Ag SACBNI solder joints exhibited significantly enhanced shear strength, achieving an average value of 68.31&#xa0;MPa. Notably, among all joints studied, the Sn‑2.0Ag‑0.5Cu‑3.0Bi‑0.05Ni‑4.0In solder joints retained excellent thermo‑mechanical stability after aging at 150&#xa0;°C for 600&#xa0;h, showing only a minimal reduction in shear strength of 6.35%. Theoretical analysis confirmed that the improved reliability arises from the solid‑solution strengthening effect of Bi within the matrix, combined with the suppression of Cu<sub>3</sub>Sn formation by Ni and In. This work offers valuable material selection in advanced packaging for portable electronic devices.</p>

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Study on microstructure evolution and thermo‑mechanical reliability of low-Ag SACBNI solders

  • 期刊论文

  • 发表日期：

    2026年5月12日

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  • Liangchen Wang,
  • Shuang Zhao,
  • Yuanyuan Qiao,
  • Ning Zhao

摘要

Micro-alloying has been established as an effective strategy for enhancing the performance of low-Ag Sn–Ag–Cu (SAC) lead-free solder alloys. In this study, the low-Ag Sn–Ag–Cu-Bi-Ni-In (SACBNI) solder alloys were fabricated and their thermal properties, wettability, micro-hardness, microstructure and mechanical properties were systematically investigated. The results indicated that the addition of Bi, Ni, and In effectively refined the matrix microstructure and promoted more uniform distribution of intermetallic compounds (IMCs) within the matrix. Compared to low‑Ag SAC solder alloys, the developed low-Ag SACBNI solder alloys exhibited lower melting point, superior wettability and micro-hardness. Furthermore, the low-Ag SACBNI solder joints exhibited significantly enhanced shear strength, achieving an average value of 68.31 MPa. Notably, among all joints studied, the Sn‑2.0Ag‑0.5Cu‑3.0Bi‑0.05Ni‑4.0In solder joints retained excellent thermo‑mechanical stability after aging at 150 °C for 600 h, showing only a minimal reduction in shear strength of 6.35%. Theoretical analysis confirmed that the improved reliability arises from the solid‑solution strengthening effect of Bi within the matrix, combined with the suppression of Cu3Sn formation by Ni and In. This work offers valuable material selection in advanced packaging for portable electronic devices.