Abstract
An organic ligand-free aqueous-phase synthesis of copper (Cu) nanoparticles (NPs) under an air atmosphere was successfully achieved by reducing copper(II) oxide particles with a leaf-like shape in the presence of Ni salts at room temperature. The resulting Cu NPs with a mean particle diameter of ca. 150 nm exhibited low-temperature sintering properties due to their polycrystalline internal structure and ligand-free surface. These Cu NPs were applied to obtain Cu NP-based nanopastes with low-temperature sintering properties, and the resistivities of the obtained Cu electrodes after annealing at 150 °C and 200 °C for 30 min were 64 μΩ∙cm and 27 μΩ∙cm, respectively. The bonding strength between oxygen-free Cu plates prepared using the Cu NP-based nanopastes reached 32 MPa after pressure-less sintering at 260 °C for 30 min under a nitrogen atmosphere. The developed manufacturing processes using the developed Cu nanopastes could provide sustainable and low-CO2-emission approaches to obtain Cu electrodes on flexible films and high-strength bonding between metal plates as die-attach materials for power devices under energy- and resource-saving conditions.
Highlights
An organic ligand-free aqueous-phase synthesis of copper (Cu) nanoparticles (NPs) under an air atmosphere was successfully achieved by reducing copper(II) oxide particles with a leaf-like shape in the presence of Ni salts at room temperature
In liquid-phase synthetic systems of inorganic NPs based on nucleation followed by particle growth, the particle size can be controlled by complexation of the precursors with organic ligands because the initial nucleation number determining the final mean particle size obeys the solubility product of the resulting complexes in the system[40]
We have established an organic ligand-free aqueous-phase synthesis of Cu NPs that are applicable for use in Cu NP-based nanopastes with low-temperature sintering properties
Summary
An organic ligand-free aqueous-phase synthesis of copper (Cu) nanoparticles (NPs) under an air atmosphere was successfully achieved by reducing copper(II) oxide particles with a leaf-like shape in the presence of Ni salts at room temperature. Silver particle-based inks and pastes are the most representative and useful due to their advantageous characteristics, such as low resistivity, low-temperature sinterability, and high antioxidation ability[9] These advantages have been applied in the combination of PE and integrated circuit (IC) production technologies, namely, flexible hybrid electronics (FHE) technology[10,11,12]. The resulting Cu NPs were used to prepare a Cu NP-based nanopastes applicable for the fabrication of Cu electric circuits on flexible films and as a die-attach material for the fabrication of next-generation power devices under mild sintering conditions, such as pressureless and N2 atmosphere conditions
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