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Flip Chip Metallurgies for Lead-Free Solders

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Abstract

The most commonly used lead-free solders contain large amounts of tin, which makes them incompatible with the conventional Cu-based underbump metallization (UBM) schemes. The tin in the solder reacts with the copper layer of the UBM, depleting the UBM of copper and causing loss of adhesion and a weak interface. Use of new under bump metallization schemes with Ni or CuNi alloys as the solderable layer were investigated in this study. Instead of Cr, a Tibased adhesion layer was used to decrease the amount of stress in the CuNi layer. Flip chip solder joints were made in which three Sn-Bi-Ag based lead-free solders were reflowed to several UBM pads of different compositions. The resulting interfacial microstructures were examined by SEM/EDX analysis of cross-sectioned samples. The joints were also mechanically tested in fatigue and shear to assess the quality and reliability of the interface.

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Author notes

  1. T. M. Korhonen

    Present address: Department of Materials Science and Engineering, Cornell University, Ithaca, NY, 14853, USA

Authors and Affiliations

  1. Department of Materials Science and Engineering, Cornell University, Ithaca, NY, 14853, USA

    S. J. Hong, M. A. Korhonen & C.-Y. Li

Authors
  1. T. M. Korhonen
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  2. S. J. Hong
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  3. M. A. Korhonen
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  4. C.-Y. Li
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Korhonen, T.M., Hong, S.J., Korhonen, M.A. et al. Flip Chip Metallurgies for Lead-Free Solders. MRS Online Proceedings Library 515, 79–83 (1998). https://doi.org/10.1557/PROC-515-79

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  • DOI: https://doi.org/10.1557/PROC-515-79

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