The bondability of copper joints formed using a mixed paste of silver oxide (Ag2O) and copper oxide (CuO) that contained reducing solvents was evaluated in order to achieve bonds that exhibited high migration tolerance and could serve as Pb-free alternatives to the conventional bonds formed using high-melting point solders in electronics packaging. The Ag2O particles reduced into silver nanoparticles at 150℃, whereas the CuO reduced into copper nanoparticles about 300℃. The joints formed using the Ag2O/CuO mixed paste, when heated to the appropriate levels, exhibited bondability superior to that of conventional Pb-5Sn joints. The oxide film formed on the copper substrate was reduced by the combustion of polyethylene glycol 400, and bonding was achieved between the sintered layer and the copper substrate. A longer period resulted in the oxidisation of a few layers of sintered copper layers into Cu2O. The ion-migration tolerance of the Ag2O/CuO mixed paste was approximately four times that of a layer of pure sintered silver.
