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Electromigration Reliability and Morphologies of Cu Pillar Flip-Chip Solder Joints with Cu Substrate Pad Metallization

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Abstract

The Cu pillar is a thick underbump metallurgy (UBM) structure developed to alleviate current crowding in a flip-chip solder joint under operating conditions. We present in this work an examination of the electromigration reliability and morphologies of Cu pillar flip-chip solder joints formed by joining Ti/Cu/Ni UBM with largely elongated ∼62 μm Cu onto Cu substrate pad metallization using the Sn-3Ag-0.5Cu solder alloy. Three test conditions that controlled average current densities in solder joints and ambient temperatures were considered: 10 kA/cm2 at 150°C, 10 kA/cm2 at 160°C, and 15 kA/cm2 at 125°C. Electromigration reliability of this particular solder joint turns out to be greatly enhanced compared to a conventional solder joint with a thin-film-stack UBM. Cross-sectional examinations of solder joints upon failure indicate that cracks formed in (Cu,Ni)6Sn5 or Cu6Sn5 intermetallic compounds (IMCs) near the cathode side of the solder joint. Moreover, the ~52-μm-thick Sn-Ag-Cu solder after long-term current stressing has turned into a combination of ~80% Cu-Ni-Sn IMC and ~20% Sn-rich phases, which appeared in the form of large aggregates that in general were distributed on the cathode side of the solder joint.

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Acknowledgement

The authors are grateful to their colleagues, Yu-Hsiu Shao and Chiu-Wen Lee, for experimental support.

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Authors and Affiliations

  1. Central Labs, Advanced Semiconductor Engineering, Inc., 26 Chin 3rd Road, Nantze Export Processing Zone, Kaohsiung, 811, Taiwan

    Yi-Shao Lai, Ying-Ta Chiu & Jiunn Chen

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  1. Yi-Shao Lai
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  2. Ying-Ta Chiu
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  3. Jiunn Chen
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Correspondence to Yi-Shao Lai.

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Lai, YS., Chiu, YT. & Chen, J. Electromigration Reliability and Morphologies of Cu Pillar Flip-Chip Solder Joints with Cu Substrate Pad Metallization. J. Electron. Mater. 37, 1624–1630 (2008). https://doi.org/10.1007/s11664-008-0515-3

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  • DOI: https://doi.org/10.1007/s11664-008-0515-3

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