Enhancement of pressure-free bonding with Cu particles by the addition of Cu–Ni alloy nanoparticles

Cu-Ni alloy nanoparticles ( similar to 20 nm) were synthesized with precise control over the resulting Cu and Ni proportions. Nanoparticles composed of 29 wt% Cu and 71 wt% Ni exhibited significant resistance to surface oxidation and were readily sintered, suggesting that they could serve as bonding materials. The adhesive strength of Cu plates bonded by Cu particles of 150-200 nm in size was enhanced by adding these Cu-Ni alloy nanoparticles to the larger Cu particles. This is the first example of the use of base metal nanoparticles at a low-temperature (250 degree C) under pressure-free conditions to achieve bonding strengths equivalent to those obtained when applying the standard Pb-free solder (Sn-Ag-Cu). Furthermore, a sintered Cu film with good electric conductivity was obtained using the mixture of Cu-Ni nanoparticles and Cu particles. The enhanced properties of these bonded layers were due to the formation of a densely sintered layer resulting from the addition of the Cu-Ni alloy nanoparticles to the Cu paste. This method could potentially have applications in the electrical packaging industry, since it represents a simple, economical process that results in highly conductive bonds.