Recent advances in the synthesis of copper-based nanoparticles for metal-metal bonding processes

This review introduces our study on the development of Cu-based nanoparticles suitable as fillers in the metal-metal bonding process. Colloid solutions of various nanoparticles such as cuprous iodide, cupric oxide (CuO), CuO mixed with silver oxide (Ag2O/CuO), cuprous-oxide (Cu2O), metallic Cu, plolypyrrole-coated metallic Cu, and metallic Cu containing metallic Ag (Ag/Cu) were prepared by liquid phase processes such as reduction and a salt-base reaction. Metal-metal bonding properties of their powders were evaluated by sandwiching the particle powder between metallic discs, annealing them at a pressure of 1.2 MPa, and measuring the shear strength required for separating the bonded discs. Various particles (above-mentioned), various metallic discs (Cu, Ag, and Ni), various bonding temperatures (250-400 °C), and different atmospheres in bonding (H2 and N2) were examined to find nanoparticle filler suitable for metal-metal bonding. As a result, it was confirmed that the metallic Cu, the CuO, the Ag2O/CuO, and the Ag/Cu particles were suitable for CuCu bonding in H2, low-temperature CuCu bonding in H2, AgAg bonding in H2, and CuCu bonding in N2, respectively. The metallic Cu particles also had functions of AgAg and NiNi bondings in H2. These results were explained with the particle size, the amount of impurity, and the d-value.