Scholarlink

<p>Indium–tin (In–Sn) eutectic solders are crucial for low-temperature applications, but their inadequate mechanical properties limit their reliability. This study systematically investigates the effect of minor bismuth (Bi) additions (0–7 wt%) on In-(50-x)Sn-xBi alloys and the corresponding micro-joints on Organic Solderability Preservative (OSP) and Electroless Nickel Immersion Gold (ENIG) finished Cu pads. Differential scanning calorimetry (DSC) reveals that Bi addition progressively lowers the melting point from 120.3 to 106.6&#xa0;°C by altering the solidification pathway and more complex phase transformation behavior. The microstructure remains a duplex of hard <i>γ</i>-InSn<sub>4</sub> and soft <i>β</i>-In<sub>3</sub>Sn, accompanied by a small amount of BiIn phase. Tensile tests demonstrate that Bi acts as a potent solid solution strengthener, continuously increasing ultimate tensile strength (UTS), but induces a non-monotonic elongation response attributed to the changes in the size and distribution of the <i>γ</i>-InSn<sub>4</sub> phase resulting from the addition of Bi. At the joint level, surface finish dictates the interfacial structure: OSP promotes a thick, wavy Cu<sub>6</sub>(Sn, In)<sub>5</sub> intermetallic compound (IMC), whereas ENIG forms a thin, planar Ni<sub>3</sub>(Sn, In)<sub>4</sub> layer due to its Ni–P diffusion barrier. Crucially, the shear behavior is highly strain rate dependent (0.01–1000&#xa0;mm/s). OSP joints exhibit consistent ductile fracture regardless of shear speed. In stark contrast, ENIG joints undergo a fracture mode transition: from brittle interfacial failure at low speeds to ductile solder-body fracture at high speeds. This transition is governed by the competition between the strain rate-sensitive strength of the solder matrix and the relatively rate-insensitive strength of the thin IMC layer. This work elucidates the dual role of Bi as a melting point depressant and strengthening agent and reveals the critical influence of surface finish and strain rate on joint reliability, offering a design framework for high-performance, low-temperature interconnects.</p>

错误：搜索内容不能为空，请输入英文关键词
错误：关键词超出字数限制，请精简
高级检索

Effect of Bi addition on thermal, microstructural and mechanical properties of In–Sn–Bi solder alloys and their micro-joints on OSP & ENIG finishes

  • 期刊论文

  • 发表日期：

    2026年5月29日

查看全文
  • Jiajun Wang,
  • Xiaobin Luo,
  • Yuanwei Jia,
  • Xuan Zhou,
  • Qin Wang,
  • Hongbo Lu,
  • Jubo Peng,
  • Haitao Ma

摘要

Indium–tin (In–Sn) eutectic solders are crucial for low-temperature applications, but their inadequate mechanical properties limit their reliability. This study systematically investigates the effect of minor bismuth (Bi) additions (0–7 wt%) on In-(50-x)Sn-xBi alloys and the corresponding micro-joints on Organic Solderability Preservative (OSP) and Electroless Nickel Immersion Gold (ENIG) finished Cu pads. Differential scanning calorimetry (DSC) reveals that Bi addition progressively lowers the melting point from 120.3 to 106.6 °C by altering the solidification pathway and more complex phase transformation behavior. The microstructure remains a duplex of hard γ-InSn4 and soft β-In3Sn, accompanied by a small amount of BiIn phase. Tensile tests demonstrate that Bi acts as a potent solid solution strengthener, continuously increasing ultimate tensile strength (UTS), but induces a non-monotonic elongation response attributed to the changes in the size and distribution of the γ-InSn4 phase resulting from the addition of Bi. At the joint level, surface finish dictates the interfacial structure: OSP promotes a thick, wavy Cu6(Sn, In)5 intermetallic compound (IMC), whereas ENIG forms a thin, planar Ni3(Sn, In)4 layer due to its Ni–P diffusion barrier. Crucially, the shear behavior is highly strain rate dependent (0.01–1000 mm/s). OSP joints exhibit consistent ductile fracture regardless of shear speed. In stark contrast, ENIG joints undergo a fracture mode transition: from brittle interfacial failure at low speeds to ductile solder-body fracture at high speeds. This transition is governed by the competition between the strain rate-sensitive strength of the solder matrix and the relatively rate-insensitive strength of the thin IMC layer. This work elucidates the dual role of Bi as a melting point depressant and strengthening agent and reveals the critical influence of surface finish and strain rate on joint reliability, offering a design framework for high-performance, low-temperature interconnects.