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Interface Embrittlement Between 63Sn-37Pb Solder and Au Layer. Part 2: Quantitative Compositional Analysis of Intermetallic Compound Reaction Layers

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Abstract

The interface gold (Au) embrittlement failure mode resulting when a Au protective finish is not completely removed by the soldering process. has been investigated This failure mode places high-reliability electronics, which use the eutectic 63Sn-37Pb (wt%, abbreviated Sn-Pb) solder and Au protective finishes, at risk for latent service failures. Part 1 documented the Au/Sn-Pb) interface microstructures and especially, Kirkendall void formation, as a function of solid-state aging. Part 2 determines the compositions of the Au-Sn IMC layers and particles using electron probe microanalysis (EPMA). Two interface IMC layers were identified: a high-Au, secondary Au-Sn IMC layer adjacent to the Au layer, and a low-Au, primary Au-Sn IMC layer next to the Sn-Pb solder. The secondary IMC layer had compositions between the δ (AuSn) and ε (AuSn2) phases. The primary IMC layer exhibited compositions between the ε (AuSn2) and η (AuSn4) phases. The compositions varied as a function of the solid-state aging parameters as well as solder layer thickness. The controlling mechanism was Kirkendall voids and their effect on Au diffusion along the Au/secondary Au-Sn IMC interface. Gold-Sn IMC particles in the solder exhibited compositions like those of the primary Au-Sn IMC layer, but were a function of Au scavenging from the Sn-Pb microstructure. Nickel diffusion, which occurred into the remaining Au and IMC layers, had a driving force that was sensitive to either solder layer thickness or the remaining Au layer thickness, the latter being correlated to the former. Gold diffusion was also measured, which took place in the Ni layer.

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Notes

  1. Unpublished data, Sandia National Laboratories, Albuquerque, NM. These data and the analysis are available upon request.

  2. The Ni content in the Au layer was not due to “smearing” during the cross-section preparation process because of the greater hardness to the Ni layer. Measurements confirmed this premise because the Ni concentrations proved to be consistently dissimilar between thin and thick solder layer locations.

  3. The designation, “(Au,Ni)” using the comma implies that the quantitative relationship between Au and Ni was not explicitly stated within the parentheses.

  4. The current results did not warrant further EPMA efforts to be performed on additional test samples.

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Acknowledgments

The authors wish to thank Dr. Rebecca Wheeling for her thorough review of the manuscript. Sandia National Laboratories is a multi-mission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government.

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  1. Sandia National Laboratories, Albuquerque, NM, USA

    P. T. Vianco, A. C. Kilgo, B. B. McKenzie, R. P. Grant & S. Williams

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  1. P. T. Vianco
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  2. A. C. Kilgo
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  3. B. B. McKenzie
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  4. R. P. Grant
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  5. S. Williams
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Correspondence to P. T. Vianco.

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Vianco, P.T., Kilgo, A.C., McKenzie, B.B. et al. Interface Embrittlement Between 63Sn-37Pb Solder and Au Layer. Part 2: Quantitative Compositional Analysis of Intermetallic Compound Reaction Layers. J. Electron. Mater. 52, 628–652 (2023). https://doi.org/10.1007/s11664-022-10034-w

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  • DOI: https://doi.org/10.1007/s11664-022-10034-w

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