Effects of shrinkage on conductivity of isotropic conductive adhesives

The authors´ previous study proved that intimate contact between conductive fillers caused by resin cure shrinkage, rather than lubricant removal, was the main mechanism for conductivity establishment of isotropic conductive adhesives (ICAs) during cure. The purpose of this study is to investigate the property changes, especially dimension change (cure shrinkage), of an ICA during cure and correlation between them and conductivity establishment. An ICA was dynamically cured by raising temperature from 30°C to 250°C and its cure profile, storage modulus change, cure shrinkage, and electrical conductivity establishment were studied using a differential scanning calorimeter (DSC), rheometer, thermomechanical analyzer (TMA), and multimeter, respectively. It was found that all of these properties changed dramatically at the same temperature range. Changes of these four parameters of this ICA with time in the course of an isothermal cure were also investigated. It was found that all of the parameters showed significant changes within the same period of time. In addition, the conductivity of three ICA formulations which were filled with a blank Ag powder and whose resins had different cure shrinkages was measured and compared. From this study, it was concluded that (a) conductive adhesives achieved high conductivity only when their resins were cured and enough shrinkage was achieved, and (b) ICAs with higher cure shrinkage showed higher conductivity