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Interfacial transformation of preoxidized Cu microparticles in a formic-acid atmosphere for pressureless Cu–Cu bonding

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Abstract

Wide bandgap (WBG) power devices have been attracting increasing attention for next-generation electronic applications. Cu–Cu bonding has been developed to accommodate the high temperature and current characteristics encountered in WBG semiconductors service conditions. In this study, we demonstrate and optimize a pressureless Cu–Cu bonding method by reductively sintering preoxidized Cu microparticles in a formic-acid atmosphere, and provide information on the bonding mechanism and relationship between behaviors of Cu microparticles and bonding quality. The transformation of Cu microparticles was examined at different preoxidation intervals, which were followed by a reduction reaction. The Cu oxide produced by preoxidation is critical for reliable Cu–Cu bonding because it forms linkages between Cu microparticles during the process; additionally, it fills the gaps between the individual particles to increase bonding density. In both thermal aging and cycling test, it was found that the Cu–Cu bonding exhibited similar microstructures and oxidation behavior, but followed different degradation and failure modes.

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Acknowledgements

Runhua Gao thanks the China Scholarship Council for doctoral research assistantships (Support Number: 201706050096).

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Authors and Affiliations

  1. Joining and Welding Research Institute, Osaka University, Osaka, 567-0047, Japan

    Runhua Gao, Siliang He, Jiahui Li, Yu-An Shen & Hiroshi Nishikawa

  2. Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan

    Runhua Gao & Jiahui Li

  3. School of Mechanical and Electrical Engineering, Guilin University of Electronic Technology, Guilin, 541004, Guangxi, China

    Siliang He

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  1. Runhua Gao
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Correspondence to Runhua Gao.

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Gao, R., He, S., Li, J. et al. Interfacial transformation of preoxidized Cu microparticles in a formic-acid atmosphere for pressureless Cu–Cu bonding. J Mater Sci: Mater Electron 31, 14635–14644 (2020). https://doi.org/10.1007/s10854-020-04026-x

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