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Accurately determining eutectic compositions: The Sn-Ag-Cu ternary eutectic

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  • Eutectic Solidification
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Abstract

Determining an accurate eutectic composition is more difficult than determining the corresponding eutectic temperature, a fact that was demonstrated in this study using a lead-free solder: the tin-rich Sn-Ag-Cu ternary eutectic. The solidification of this ternary eutectic involves the solid phases (Sn), Ag3Sn, and Cu6Sn5. The liquid is prone to supercooling, the intermetallics have steep liquidus surfaces (small phase fractions), and the coupled zone of eutectic microstructure formation is shifted toward silver-rich and copper-rich compositions. These issues were overcome by a combination of methods: preliminary thermodynamic calculation of the ternary phase diagram to anticipate difficulties, increased sensitivity of the thermal analysis, and a cycled heating and cooling method. The experimentally determined composition of the ternary eutectic is Sn-3.58±0.05Ag-0.96±0.04Cu at 217.2±0.2°C.

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Authors and Affiliations

  1. the Metallurgy Division, Materials Science and Engineering Laboratory, the National Institute of Science and Technology, Gaithersburg, Maryland

    K. -W. Moon & W. J. Boettinger

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  1. K. -W. Moon
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  2. W. J. Boettinger
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Author’s Note: Compositions in this paper are reported on a mass percent basis. The symbol (Sn) is used for the Sn phase to distinguish it from the element symbol Sn.

For more information, contact K.-W. Moon, National Institute of Science and Technology, Metallurgy Division, Materials Science and Engineering Laboratory, Gaithersburg, MD 20899, USA; (301) 975-6148; fax (301) 975-4553; e-mail kil-won.moon@nist.gov.

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Moon, K.W., Boettinger, W.J. Accurately determining eutectic compositions: The Sn-Ag-Cu ternary eutectic. JOM 56, 22–27 (2004). https://doi.org/10.1007/s11837-004-0068-8

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  • DOI: https://doi.org/10.1007/s11837-004-0068-8

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