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<p>The Sn-5&#xa0;wt.% Sb (Sn-5Sb) lead-free solder alloy is designed for high-temperature electronic applications, and Co is regarded as a promising diffusion barrier material. This study systematically investigates the interfacial reactions between Co substrates and Sn-Sb solders with varying Sb contents (0–5&#xa0;wt.%) aged at temperatures ranging from 160°C to 220°C. For Sb contents below 3&#xa0;wt.%, the dominant intermetallic compound (IMC) formed is CoSn<sub>3</sub>, exhibiting nearly linear growth kinetics characteristic of an interfacial reaction-controlled process. The addition of 1&#xa0;wt.% and 3&#xa0;wt.% Sb showed no significant effect on CoSn<sub>3</sub> growth, with IMC growth behavior comparable to that observed in pure Sn. When Sb content is 5&#xa0;wt.%, a new Sb-rich ternary IMC, designated as the <i>T</i> phase, initially forms and substantially suppresses IMC layer growth. Extended aging leads to a phase transformation from the <i>T</i> phase to CoSn<sub>3</sub>, attributed to the depletion of Sb in the solder. Moreover, phase equilibrium experiments further confirm that the <i>T</i> phase is a distinct ternary IMC in the Sn–Sb–Co system, rather than a solid solution extension of CoSn<sub>3</sub>. The transition time from the <i>T</i> phase to CoSn<sub>3</sub> significantly decreases with increasing aging temperature. The transformation kinetics follow Arrhenius behavior, with an apparent activation energy of approximately 195&#xa0;kJ/mol. This strong temperature dependence indicates that the <i>T</i> phase remains stable in the Sn-5Sb–Co system at temperatures below 120°C. The <i>T</i> phase was also observed in Sn-4&#xa0;wt.% Sb and Sn-3.5&#xa0;wt.% Sb alloys, suggesting that the IMC transition threshold lies between 3&#xa0;wt.% Sb and 3.5&#xa0;wt.% Sb. The Sb concentration critically influences interfacial phase formation and growth behavior, microstructural evolution, and thermal stability.</p>

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Influence of Sb Content on the Interfacial Reactions between Sn-Sb Solders and Co during Solid-State Aging

  • 期刊论文

  • 发表日期：

    2025年12月18日

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  • Chao-hong Wang,
  • Po-yen Huang

摘要

The Sn-5 wt.% Sb (Sn-5Sb) lead-free solder alloy is designed for high-temperature electronic applications, and Co is regarded as a promising diffusion barrier material. This study systematically investigates the interfacial reactions between Co substrates and Sn-Sb solders with varying Sb contents (0–5 wt.%) aged at temperatures ranging from 160°C to 220°C. For Sb contents below 3 wt.%, the dominant intermetallic compound (IMC) formed is CoSn3, exhibiting nearly linear growth kinetics characteristic of an interfacial reaction-controlled process. The addition of 1 wt.% and 3 wt.% Sb showed no significant effect on CoSn3 growth, with IMC growth behavior comparable to that observed in pure Sn. When Sb content is 5 wt.%, a new Sb-rich ternary IMC, designated as the T phase, initially forms and substantially suppresses IMC layer growth. Extended aging leads to a phase transformation from the T phase to CoSn3, attributed to the depletion of Sb in the solder. Moreover, phase equilibrium experiments further confirm that the T phase is a distinct ternary IMC in the Sn–Sb–Co system, rather than a solid solution extension of CoSn3. The transition time from the T phase to CoSn3 significantly decreases with increasing aging temperature. The transformation kinetics follow Arrhenius behavior, with an apparent activation energy of approximately 195 kJ/mol. This strong temperature dependence indicates that the T phase remains stable in the Sn-5Sb–Co system at temperatures below 120°C. The T phase was also observed in Sn-4 wt.% Sb and Sn-3.5 wt.% Sb alloys, suggesting that the IMC transition threshold lies between 3 wt.% Sb and 3.5 wt.% Sb. The Sb concentration critically influences interfacial phase formation and growth behavior, microstructural evolution, and thermal stability.