Variation in electrical conductivity of air-curable copper pates composed of a phenolic-based binder during soaking in several environments

Phenolic resin based electrically conductive pastes containing copper micro-fillers were prepared using several carboxylic acids (formic, acetic and oleic acids) as the surfactant. These pastes successfully exhibited relatively low electrical resistivities (10
^-3
-10
^-4
Ωcm) after curing in air. Electrical integrity of the samples during exposure to a humid environment was quite different depending on the surfactant. Although the electrical resistivity significantly increased during exposure to 85 °C/85 %RH when oleic acid was used as surfactant, introduction of formic and acetic acids was found to be effective to suppress the increase in electrical resistivity. To improve reliability of copper-filled conductive pastes, interfacial chemistry between the binder and fillers is required to be controlled by using appropriate surfactants.