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Prevention of spalling by the self-formed reaction barrier layer on controlled collapse chip connections under bump metallization

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Abstract

The spalling phenomenon on under bump metallization (UBM) is one of the current urgent reliability issues for the Pb-free solder implementation in flip chip technology. In this paper, we report that spalling of Ni thin UBM can be prevented during the soldering reaction, if a Cu reservoir is introduced into the structure of controlled collapse chip connections (C4) solder joints. Once molten Sn-3.5Ag solder was saturated with Cu atoms, Cu precipitated out as a layer of Cu-Sn compound on Ni thin UBM. The Cu-Sn compound layer served as a reaction barrier to retard the consumption of Ni thin UBM. So, spalling was retarded. After prolonged reflowing, Ni thin UBM was converted to ternary Cu-Sn-Ni compounds. Unlike interfaces of the Ni-Sn compound/Cr, the interface of the Cu-Sn-Ni compound/Cr was very stable and no spalling was found.

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Authors and Affiliations

  1. Department of Chemical Engineering and Materials Engineering, National Central University, Chung-Li, Taiwan, Republic of China

    C. Y. Liu & S. J. Wang

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  1. C. Y. Liu
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  2. S. J. Wang
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Liu, C.Y., Wang, S.J. Prevention of spalling by the self-formed reaction barrier layer on controlled collapse chip connections under bump metallization. J. Electron. Mater. 32, L1–L3 (2003). https://doi.org/10.1007/s11664-003-0251-7

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  • DOI: https://doi.org/10.1007/s11664-003-0251-7

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