Abstract
Copper nanoparticles (NPs) with an average particle diameter of 50–60 nm were successfully obtained by reducing an aqueous solution of a copper(II)-nitrilotriacetic acid complex with an aqueous hydrazine solution at room temperature under an air atmosphere. Copper NP-based nanopastes were printed onto a glass substrate using a metal screen mask and pressureless sintered under a nitrogen atmosphere at 200 °C for 30 min. The electrical resistivity of the resulting copper electrode was 16 μΩ · cm. For a metal-to-metal bonding test, copper nanopaste was printed on an oxygen-free copper plate, another oxygen-free copper plate was placed on top, and the bonding strength between the copper plates when pressureless sintered under a nitrogen atmosphere at 200 °C for 30 min was 39 MPa. TEM observations confirmed that highly crystalline metal bonding occurred between the copper NPs and the copper plate to introduce the ultrahigh strength. The developed copper NPs could provide promising advances as nanopastes for sustainable fabrication of copper electrodes and die attachment materials for the production of next-generation power semiconductors.
Highlights
A focus on applications as nanoinks for circuit-forming materials[23,24,25,26] and die attach materials[27,28,29]
To obtain copper NPs with a mean particle diameter of several tens of nanometers, we focused on a reduction of an in situ-prepared organocopper reagent in an aqueous-phase system
The results suggest that NTA plays an important role in controlling the size and shape of copper NPs, and Cu1, which was obtained without using NTA, was not applicable for copper nanopastes due to its large diameter
Summary
A focus on applications as nanoinks for circuit-forming materials[23,24,25,26] and die attach materials[27,28,29]. The lower oxidation resistance, lower storage stability, and higher sintering temperature of copper NPs than those of the corresponding silver NPs are fundamental problems for practical applications of copper-NP-based paste technology. Burke[44] and Kusama[45] theoretically and experimentally demonstrated, respectively, that polycrystalline particles show lower sintering behavior than the corresponding metal particles Based on this information, we consider that copper NPs with a mean particle diameter of several tens of nanometers with a small crystallite size (Cs) in the NP core could be expected to have an excellent low-temperature sintering ability, high oxidation resistance, and high storage stability. The copper NP-based pastes obtained exhibit a low resistivity and ultrahigh bonding ability as a die attach material applicable for practical usage
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