Oxidation-enhanced bonding strength of Cu sinter joints during thermal storage test

A special oxidation-enhanced property of Cu sinter joints with Cu particle paste was discovered during thermal storage test. The Cu sinter joints stored under ambient condition with oxidation showed better bonding strength (39.2 MPa) than those protected in vacuum (31.4 MPa), compared to the initial as-bonded strength of 27.6 MPa. It was found that the oxidation decreased the porosity of bonding layer by forming Cu2O shell structure on the sintered Cu microstructure, which enhanced the mechanical property of the sinter joint especially after storage time of 100 h. The corresponding electrical conductivity of solder joint at 100 h is 9.6 × 10−6 Ω, which is still acceptable compared to the as-bonded value of 1.0 × 10−6 Ω. The phenomenon implies that by introducing proper oxidation, Cu sinter joints with improved bonding strength and acceptable electrical conductivity can be achieved, which will provide another potential strengthening process of Cu sinter joining in practical applications.