Effects of Composition and Processing on the Properties of Sn-3Zn-4Bi and Sn-Ag-Cu Solder Alloys for Electronic Packaging
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Abstract
The mechanical properties of lead-free solder alloys are critical for ensuring the reliability of electronic packaging, with shear strength and hardness being particularly important as electronic devices become smaller and interconnection densities increase. Thermal fluctuations and external mechanical impacts further intensify shear stresses on solder joints, raising concerns about long-term performance. In this study, the shear stress behavior of Sn-Ag-Cu and Sn-3Zn-4Bi solder joints was examined under different reflow temperatures. Sn-Ag-Cu, a widely researched lead-free solder, demonstrated strong resistance to high stress levels, reinforcing its suitability for high-reliability applications; however, its relatively high melting temperature (~221 °C) limits its use in low-temperature reflow processes. By comparison, Sn-3Zn-4Bi solder, with a melting temperature only ~12 °C higher than eutectic SnPb solder, showed potential for low-temperature soldering, while also exhibiting higher microhardness values than Sn-Ag-Cu, suggesting improved structural robustness. Despite these advantages, concerns remain regarding its compatibility with copper substrates, where interfacial reactions may affect joint integrity. Overall, the results suggest that Sn-Ag-Cu is preferable for applications requiring high strength and thermal resistance, whereas Sn-3Zn-4Bi offers notable benefits for low-temperature processing, provided substrate interactions are properly managed.
Manuscript received: 15 Aug 2025 | Revised: 30 Sep 2025 | Accepted: 4 Oct 2025 | Published: 30 Nov 2025
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