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<p>This study investigates the effect of reflow time on the soldering behavior and joint performance of Sn-40.0Bi-1.0Ag-0.5Cu low-temperature lead-free solder paste during the reflow soldering process. The wettability, interfacial microstructure evolution, intermetallic compound (IMC) layer growth, and shear strength of solder joints formed under different reflow times were systematically characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and shear mechanical testing. The results indicate that reflow time plays a critical role in determining solder joint quality, with wettability, interfacial reactions, and mechanical properties exhibiting a typical trend of initial improvement followed by degradation as the reflow time increases. An optimal reflow time of 60&#xa0;s results in the most favorable wetting behavior, yielding a maximum spreading ratio of 86.33%. Insufficient reflow time leads to incomplete melting and limited spreading of the solder, whereas excessive reflow time promotes reoxidation and wetting shrinkage, thereby deteriorating joint quality. At the optimal reflow time, adequate flux activity enables effective oxide removal from both the solder and the Cu substrate, facilitating enhanced atomic diffusion toward the interface and the formation of a dense and uniform IMC layer with moderate thickness. Under these conditions, the solder joints achieve the highest shear strength of 35.52&#xa0;MPa. Fracture predominantly occurs within the solder matrix and is characterized by brittle fracture features without obvious defects. These findings demonstrate that reflow time critically governs the coupled evolution of wettability, interfacial microstructure, and mechanical performance in Sn-Bi–based solder joints, providing valuable guidance for optimizing reflow parameters in low-temperature soldering applications.</p>

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Effect of reflow time on wettability, intermetallic compound evolution, and mechanical properties of Sn-40Bi-1Ag-0.5Cu lead-free solder joints

  • 期刊论文

  • 发表日期：

    2026年7月17日

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  • Dongxia Xu,
  • Wenbo Wang,
  • Shenshen Xu,
  • Yue Zheng,
  • Dongbin Wang,
  • Jun Li

摘要

This study investigates the effect of reflow time on the soldering behavior and joint performance of Sn-40.0Bi-1.0Ag-0.5Cu low-temperature lead-free solder paste during the reflow soldering process. The wettability, interfacial microstructure evolution, intermetallic compound (IMC) layer growth, and shear strength of solder joints formed under different reflow times were systematically characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and shear mechanical testing. The results indicate that reflow time plays a critical role in determining solder joint quality, with wettability, interfacial reactions, and mechanical properties exhibiting a typical trend of initial improvement followed by degradation as the reflow time increases. An optimal reflow time of 60 s results in the most favorable wetting behavior, yielding a maximum spreading ratio of 86.33%. Insufficient reflow time leads to incomplete melting and limited spreading of the solder, whereas excessive reflow time promotes reoxidation and wetting shrinkage, thereby deteriorating joint quality. At the optimal reflow time, adequate flux activity enables effective oxide removal from both the solder and the Cu substrate, facilitating enhanced atomic diffusion toward the interface and the formation of a dense and uniform IMC layer with moderate thickness. Under these conditions, the solder joints achieve the highest shear strength of 35.52 MPa. Fracture predominantly occurs within the solder matrix and is characterized by brittle fracture features without obvious defects. These findings demonstrate that reflow time critically governs the coupled evolution of wettability, interfacial microstructure, and mechanical performance in Sn-Bi–based solder joints, providing valuable guidance for optimizing reflow parameters in low-temperature soldering applications.