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Flip Chip Metallurgies for Lead-Free Solders

Published online by Cambridge University Press:  10 February 2011

T. M. Korhonen ,
S. J. Hong ,
M. A. Korhonen  and
C.-Y. LI
T. M. Korhonen
Affiliation:
Department of Materials Science and Engineering, Cornell University, Ithaca NY 14853
S. J. Hong
Affiliation:
Department of Materials Science and Engineering, Cornell University, Ithaca NY 14853
M. A. Korhonen
Affiliation:
Department of Materials Science and Engineering, Cornell University, Ithaca NY 14853
C.-Y. LI
Affiliation:
Department of Materials Science and Engineering, Cornell University, Ithaca NY 14853
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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.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 515: Symposium J – Electronic Packaging Materials Science X , 1998 , 79
Copyright
Copyright © Materials Research Society 1998

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References

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