Facile Preparation of Self-Reducible Cu Nanoparticle Paste for Low Temperature Cu-Cu Bonding
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Cu nanoparticle (NP) paste is considered the next-generation die-attach material because of its cost-effectiveness and high conductivity and electro-migration resistance. However, the spontaneous oxidation of Cu NPs severely restrains the incorporation of Cu NP paste into practical applications. Herein, a novel self-reducible Cu NP paste was prepared and demonstrated for low-temperature Cu-Cu bonding. The Cu NP paste was composed of 62 wt.% ultra-small Cu NPs (6.5 nm) and 38 wt.% organic components [isopropanolamine (IPA) stabilizer and ethylene glycol]. The reducing and sintering mechanisms of Cu NP paste were proposed, and the effects of sintering temperature on the mechanical properties and microstructure evolutions of Cu-Cu joints were systematically investigated. Consequently, the reducibility of the IPA stabilizer was beneficial for eliminating the surface oxides and enhancing the sinterability of Cu NPs, and the robust and high-strength Cu-Cu joints (> 20 MPa) were achieved at low temperature of 200°C in Ar atmosphere. Furthermore, the microstructure observations reveal that the robust bonding is attributed to the remarkable metallurgical interconnection between the substrates and sintered Cu NP layer.
The authors gratefully acknowledged the financial support from the National Natural Science Foundation of China (NFSC, 51275194, and 51775219), the Fundamental Research Funds for Central Universities (2016JCTD112 and 2017JYCXJJ006), and the Graduates’ Innovation Fund, Huazhong University of Science and Technology. Thanks to the Analytical and Testing Center of Huazhong University of Science and Technology for the support with TEM, FT-IR, and SEM measurement.
Conflict of interest
The authors declare there is no conflict of interest regarding the publication of this paper.