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<p>This work presents a comparative study of microstructure, mechanical strength, thermal and electrical properties of eutectic Sn–3.5Ag and Sn–3.5Ag–<i>x</i>Er (<i>x</i> = 0.1, 0.2, 0.3, 0.4 and 0.5 wt%). Six solder samples were processed using melt-spun apparatus and characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and Vickers microhardness technique. The XRD results indicated that presence of an Ag<sub>3</sub>Sn intermetallic phase as a needle-like shape distributed within a tetragonal <i>β</i>-Sn solid-solution matrix. The morphology showed a highly refined Ag<sub>3</sub>Sn intermetallic in the solder containing a 0.5 wt% Er compared with the plain solder. However, via microindentation method, the hardness of the solder was improved by about 72.34% after adding 0.5 Er particles due to the microstructural refinement. The addition of small amounts of Er particles enhances creep resistance as the micro-creep results indicated that grain boundary sliding is a plausible deformation mechanism in solders with low Er content, whereas diffusion creep becomes the dominant mechanism in solders with high Er content. It was also concluded that the wettability of the Sn–3.5Ag solder improved with increasing Er content, owing to the surface activity of the added Er particles. On the other hand, doping the eutectic Sn–3.5Ag alloy with Er reduced the melting point (<i>T</i><sub>m</sub>) of the Sn–3.5Ag by a few degrees, from 225 to 218.5&#xa0;°C. It was found that the electrical resistivity increases linearly with increasing Er content. The electrical resistivity of solder of a given compositions at a specific temperature is affected by the microstructure and the crystal structure of the present phases. The increase in the electrical resistivity of the solders with increasing Er content can be attributed to the mechanism of electrical charge transport in the solder matrix. Electrical resistivity also increases due to increase in lattice distortion, which hinders charge carrier motion and intensifies the scattering of both electrons and phonons. Furthermore, lattice vibrations become more pronounced at higher Er content, increasing the probability of collisions as well as electron–phonon and phonon–phonon interactions. These effects strongly impede the free movement of electrons and phonons, leading to higher electrical resistivity. The aim of the study is to identify scientific challenges and recent trends in the current formulation of rare-earth-reinforced solder alloys.</p>

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The role of intermetallic phase on the mechanical and thermal properties of erbium rare-earth reinforced Sn–Ag lead-free joints for environmental applications

  • 期刊论文

  • 发表日期：

    2026年7月7日

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  • Raad Ishkhayyir Al-Zaidi,
  • Abdulhammed Alzarka,
  • Rizk Mostafa Shalaby

摘要

This work presents a comparative study of microstructure, mechanical strength, thermal and electrical properties of eutectic Sn–3.5Ag and Sn–3.5Ag–xEr (x = 0.1, 0.2, 0.3, 0.4 and 0.5 wt%). Six solder samples were processed using melt-spun apparatus and characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), and Vickers microhardness technique. The XRD results indicated that presence of an Ag3Sn intermetallic phase as a needle-like shape distributed within a tetragonal β-Sn solid-solution matrix. The morphology showed a highly refined Ag3Sn intermetallic in the solder containing a 0.5 wt% Er compared with the plain solder. However, via microindentation method, the hardness of the solder was improved by about 72.34% after adding 0.5 Er particles due to the microstructural refinement. The addition of small amounts of Er particles enhances creep resistance as the micro-creep results indicated that grain boundary sliding is a plausible deformation mechanism in solders with low Er content, whereas diffusion creep becomes the dominant mechanism in solders with high Er content. It was also concluded that the wettability of the Sn–3.5Ag solder improved with increasing Er content, owing to the surface activity of the added Er particles. On the other hand, doping the eutectic Sn–3.5Ag alloy with Er reduced the melting point (Tm) of the Sn–3.5Ag by a few degrees, from 225 to 218.5 °C. It was found that the electrical resistivity increases linearly with increasing Er content. The electrical resistivity of solder of a given compositions at a specific temperature is affected by the microstructure and the crystal structure of the present phases. The increase in the electrical resistivity of the solders with increasing Er content can be attributed to the mechanism of electrical charge transport in the solder matrix. Electrical resistivity also increases due to increase in lattice distortion, which hinders charge carrier motion and intensifies the scattering of both electrons and phonons. Furthermore, lattice vibrations become more pronounced at higher Er content, increasing the probability of collisions as well as electron–phonon and phonon–phonon interactions. These effects strongly impede the free movement of electrons and phonons, leading to higher electrical resistivity. The aim of the study is to identify scientific challenges and recent trends in the current formulation of rare-earth-reinforced solder alloys.