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<p>This study systematically investigates the effects of surface finishes on the interfacial microstructure and shear-speed-dependent mechanical properties of Sn-Ag-Cu (SAC)-based solder joints. Two lead-free alloys, SAC305 and Innolot, were paired with four surface finishes, organic solderability preservative (OSP), immersion tin (ImSn), immersion silver (ImAg), and electroless nickel/immersion gold (ENIG), to assess their influence on intermetallic compound (IMC) formation, shear strength, and fracture behavior. Distinct IMC growth kinetics and morphologies were observed: OSP promoted rapid IMC growth with scalloped structures, while ENIG produced thinner, planar IMCs due to diffusion suppression. Innolot’s multi-element composition further refined IMC grains compared to SAC305. Shear testing across five speeds (0.01–1000&#xa0;mm/s) revealed strong dependencies on both surface finish and strain rate. SAC305 joints followed a shear strength trend of ENIG &gt; OSP &gt; ImAg &gt; ImSn, whereas Innolot exhibited more complex behavior, with OSP performing best at low speeds and ENIG at high speeds. Both alloys showed strain-rate strengthening, with SAC305 being more sensitive. Fracture modes shifted from ductile (bulk solder) to brittle (IMC interface) with increasing shear speed, with Innolot transitioning earlier. ENIG consistently outperformed other finishes by combining thin IMCs and robust adhesion, making it highly suitable for harsh environments. These findings offer valuable guidance for optimizing surface finishes in high-reliability electronic packaging.</p>

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Effect of Surface Finishes on the Microstructure and Shear-Speed-Dependent Mechanical Properties of Sn-Ag-Cu-Based Solder Joints

  • 期刊论文

  • 发表日期：

    2025年10月27日

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  • Jiajun Wang,
  • Min Shang,
  • Xiaobin Luo,
  • Qin Wang,
  • Hongbo Lu,
  • Lingyan Zhao,
  • Yunpeng Wang,
  • Haitao Ma,
  • Xiaojing Wang,
  • David P. Yan

摘要

This study systematically investigates the effects of surface finishes on the interfacial microstructure and shear-speed-dependent mechanical properties of Sn-Ag-Cu (SAC)-based solder joints. Two lead-free alloys, SAC305 and Innolot, were paired with four surface finishes, organic solderability preservative (OSP), immersion tin (ImSn), immersion silver (ImAg), and electroless nickel/immersion gold (ENIG), to assess their influence on intermetallic compound (IMC) formation, shear strength, and fracture behavior. Distinct IMC growth kinetics and morphologies were observed: OSP promoted rapid IMC growth with scalloped structures, while ENIG produced thinner, planar IMCs due to diffusion suppression. Innolot’s multi-element composition further refined IMC grains compared to SAC305. Shear testing across five speeds (0.01–1000 mm/s) revealed strong dependencies on both surface finish and strain rate. SAC305 joints followed a shear strength trend of ENIG > OSP > ImAg > ImSn, whereas Innolot exhibited more complex behavior, with OSP performing best at low speeds and ENIG at high speeds. Both alloys showed strain-rate strengthening, with SAC305 being more sensitive. Fracture modes shifted from ductile (bulk solder) to brittle (IMC interface) with increasing shear speed, with Innolot transitioning earlier. ENIG consistently outperformed other finishes by combining thin IMCs and robust adhesion, making it highly suitable for harsh environments. These findings offer valuable guidance for optimizing surface finishes in high-reliability electronic packaging.