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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H. K. Kim, H. K. Liou and K. N. Tu, Appl. Phys. Lett. 66, p. 2337, 1995
H.K. Kim and K. N. Tu, Appl. Phys. Lett. 67, p. 2002, 1995
T. Liu, D. Kim, D. Leung, M. A. Korhonen and C.-Y. Li, Scripta Materialia 35, 1996
S. Bader, W. Gust and H. Hieber, Acta Metall. Mater. 43, p. 329, 1995
R. S. Rai. S. K. Kang and S. Purushothaman, Proc. 45th Electronic omponents & Technology Conference (IEEE), p. 1197, 1995
M. Harada, R. Satoh, O. Yamada, Proc. 47th Electronic Components & Technology Conference (IEEE), p. 866, 1997
T. M. Korhonen, S. J. Hong, P. Su, C. Zhou, M. A. Korhonen, and C.-Y. Li, “Under Bump Metallization Development for High Sn Solders”, MRS Fall Meeting, Boston, Dec. 1-5, 1997 (to be published in MRS Symp. Proc. 505)
S. J. Hong, T. M. Korhonen, M. A. Korhonen, and C.-Y. Li, “Under Bump Metallization Development for Eutectic Pb-Sn Solders”, MRS Spring Meeting, San Francisco, Apr.13-17, 1998 (to be published in MRS Symp. Proc. 515)
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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