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<p>This study systematically investigates the effects of different Bi contents (2.5 wt.%, 3.0 wt.%, 3.5 wt.%, and 4.0 wt.%) on the microstructural evolution and creep behavior of low-silver lead-free Sn-0.3Ag-0.7Cu (SAC0307) solder alloys. Microstructural characteristics were examined using optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDS). Constant-stress tensile creep tests were conducted under temperatures ranging from 25 to 125&#xa0;°C and applied stresses of 9-15&#xa0;MPa to evaluate the high-temperature creep response. The results indicate that with increasing Bi content, Bi tends to segregate and agglomerate within the alloy, particularly at grain boundaries and triple junctions, forming coarse Bi-rich regions that reduce microstructural stability and ductility, thereby accelerating creep failure. Fractographic analysis reveals that, under constant temperature conditions, the average void size increases with decreasing applied stress, while under constant stress conditions, the void size increases as the testing temperature decreases, indicating more pronounced void growth at lower stress or temperature due to prolonged creep exposure. When the Bi content increases from 3.0 to 4.0 wt.%, the creep activation energy (Q) decreases from 64.20 to 54.62&#xa0;kJ/mol, and the stress exponent (n) decreases from 3.37 to 3.12, suggesting that the creep deformation is predominantly governed by a dislocation-climb-controlled mechanism. These findings provide experimental insights for composition optimization and reliability design of low-silver lead-free solders under high-temperature service conditions.</p>

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Influence of Bi Addition on Microstructure and Creep Properties of Sn-0.3Ag-0.7Cu Low-Silver Lead-Free Solder Alloy

  • 期刊论文

  • 发表日期：

    2026年4月28日

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  • Junchen Liu,
  • Abdullah Aziz Saad,
  • Yuezong Zheng,
  • Hongchao Ji,
  • Zuraihana Bachok

摘要

This study systematically investigates the effects of different Bi contents (2.5 wt.%, 3.0 wt.%, 3.5 wt.%, and 4.0 wt.%) on the microstructural evolution and creep behavior of low-silver lead-free Sn-0.3Ag-0.7Cu (SAC0307) solder alloys. Microstructural characteristics were examined using optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDS). Constant-stress tensile creep tests were conducted under temperatures ranging from 25 to 125 °C and applied stresses of 9-15 MPa to evaluate the high-temperature creep response. The results indicate that with increasing Bi content, Bi tends to segregate and agglomerate within the alloy, particularly at grain boundaries and triple junctions, forming coarse Bi-rich regions that reduce microstructural stability and ductility, thereby accelerating creep failure. Fractographic analysis reveals that, under constant temperature conditions, the average void size increases with decreasing applied stress, while under constant stress conditions, the void size increases as the testing temperature decreases, indicating more pronounced void growth at lower stress or temperature due to prolonged creep exposure. When the Bi content increases from 3.0 to 4.0 wt.%, the creep activation energy (Q) decreases from 64.20 to 54.62 kJ/mol, and the stress exponent (n) decreases from 3.37 to 3.12, suggesting that the creep deformation is predominantly governed by a dislocation-climb-controlled mechanism. These findings provide experimental insights for composition optimization and reliability design of low-silver lead-free solders under high-temperature service conditions.