SMTA International Conference Proceedings


Author: Y. H. Lin et al.
Company: National Central University
Date Published: 9/21/2003   Conference: SMTA International

Abstract: A new electromigration failure mechanism in flip chip solder joints is reported. The solder joints failed through a very rapid, localized dissolution of the Cu on the cathode side. The regions of the dissolved Cu include not only the Cu under bump metallurgy but also the internal Cu conducting trace on the chip. From the location and geometry of the dissolved Cu, it can be concluded that current crowding played an important role for the rapid dissolution.

The dissolved Cu atoms were then driven by electrons to the anode side, and a large amount of Cu6Sn5 was formed there. To avoid this type of failure, another metal more resistant to dissolution should be used in place of or over Cu. Moreover, the geometry of the under bump metallurgy and conducting trace might have to be carefully designed to achieve a more uniform current distribution to reduce the effect of current crowding.

Key words: electromigration, flip chip, PbSn solder, dissolution.

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