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<p>Thermo-mechanical cycling of microelectronic devices creates complex stress-states in Sn–Ag–Cu (SAC) solder balls, leading to Cu₆Sn₅-precipitate coarsening. Two key mechanisms — strain-induced coarsening and Ostwald ripening — are examined separately. Strain-induced coarsening, studied via plastic shear deformation, is more significant in dynamically recrystallised high-strain regions than in lower-strain shear band regions. Ostwald ripening is investigated via in-situ FESEM, and its interplay with strain-enhanced coarsening is analysed in thermo-mechanically cycled solders with varying Bi-contents. Results show that Bi, solved in the β-Sn matrix, delays dynamic recrystallisation and reduces both strain-enhanced coarsening and Ostwald ripening of Cu₆Sn₅. Nonetheless, Cu<sub>6</sub>Sn<sub>5</sub>-precipitates are 1.5–3 times larger in recrystallised high-strain regions than in single-crystalline lower-strain regions regardless of Bi-content, due to strain-enhanced coarsening during thermo-mechanical cycling. The findings indicate that mechanical strain plays a dominant role in precipitate growth, suggesting that strain-enhanced Cu<sub>6</sub>Sn<sub>5</sub> coarsening, and thusly decreased precipitate strengthening effects, correlate with increased thermo-mechanical fatigue.</p>

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Unravelling Cu6Sn5 precipitate coarsening mechanisms in SAC solders under thermomechanical cycling

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年10月28日

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  • Charlotte Cui,
  • Sebastian Krauß,
  • Hooman Hosseinkhannazer,
  • Julien Magnien,
  • Olena Vertsanova,
  • Michael Reisinger,
  • Peter Imrich,
  • Walter Hartner,
  • Roland Brunner

摘要

Thermo-mechanical cycling of microelectronic devices creates complex stress-states in Sn–Ag–Cu (SAC) solder balls, leading to Cu₆Sn₅-precipitate coarsening. Two key mechanisms — strain-induced coarsening and Ostwald ripening — are examined separately. Strain-induced coarsening, studied via plastic shear deformation, is more significant in dynamically recrystallised high-strain regions than in lower-strain shear band regions. Ostwald ripening is investigated via in-situ FESEM, and its interplay with strain-enhanced coarsening is analysed in thermo-mechanically cycled solders with varying Bi-contents. Results show that Bi, solved in the β-Sn matrix, delays dynamic recrystallisation and reduces both strain-enhanced coarsening and Ostwald ripening of Cu₆Sn₅. Nonetheless, Cu6Sn5-precipitates are 1.5–3 times larger in recrystallised high-strain regions than in single-crystalline lower-strain regions regardless of Bi-content, due to strain-enhanced coarsening during thermo-mechanical cycling. The findings indicate that mechanical strain plays a dominant role in precipitate growth, suggesting that strain-enhanced Cu6Sn5 coarsening, and thusly decreased precipitate strengthening effects, correlate with increased thermo-mechanical fatigue.