The effects of reducing solvent on copper, nickel, and aluminum joining using silver nanoparticles derived from a silver oxide paste was investigated by thermal analysis, transmission electron microscopy (TEM) observation, and tensile shear testing. A complete weight loss of diethylene glycol (DEG) in a paste occurred during the redox reaction, whereas a polyethylene glycol 400 (PEG) paste retained the PEG solvent until about 300°C due to its longer carbon chains. Residual PEG in the paste reduced the natural oxide film on copper and nickel substrates during bonding, facilitating a direct sinter of silver nanoparticles to these substrates. On the other hand, silver nanoparticles were sintered to the natural oxide film on an aluminum substrate by the DEG paste. The suitability of the reducing solvent for oxide film reduction of the metal substrate during bonding was explained by an Ellingham diagram.
The bondability of copper joints formed using a mixed paste of silver oxide (Ag 2 O) 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 Ag 2 O particles reduced into silver nanoparticles at 150°C, whereas the CuO reduced into copper nanoparticles about 300°C. The joints formed using the Ag 2 O/CuO mixed paste, when heated to the appropriate levels, exhibited bondability superior to that of conventional Pb5Sn 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 Cu 2 O. The ion-migration tolerance of the Ag 2 O/CuO mixed paste was approximately four times that of a layer of pure sintered silver.
The bondability of copper joints formed using a mixed paste of silver oxide (Ag 2 O) 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 Ag 2 O particles reduced into silver nanoparticles at 150°C, whereas the CuO reduced into copper nanoparticles about 300°C. The joints formed using the Ag 2 O/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 Cu 2 O. The ion migration tolerance of the Ag 2 O/CuO mixed paste was approximately four times that of a layer of pure sintered silver.
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