Characterization of thermally reworkable thermosets: materials for environmentally friendly processing and reuse

In recent years, several research groups have created reworkable thermoset systems. A prominent use of such materials is in microelectronics packaging areas to enable the repair or reprocessing of electronic components. A wider implication of such an application is that it may facilitate the future recycling or reuse of older computer systems. Recent studies indicate millions of computers are discarded each year due to obsolescence or other factors. The research presented here involves studies of thermosets incorporating a cycloaliphatic epoxy monomer that contains a tertiary ester linkage. When part of a fully crosslinked network, the reworkable epoxy unit will disconnect the network under predetermined thermal conditions. We studied the chemical and thermo-mechanical breakdown mechanisms of the monomer and resulting polymer networks as a function of their rework conditions. Via analytical chemistry techniques, the materials were found to degrade in a controlled fashion consistent with prior polyester degradation studies. Monitoring the change in glass transition temperature of the materials under rework conditions yielded both kinetic and mechanistic data of the degradation process, as well as providing insight into the materials' mechanical strength. (C) 2001 Published by Elsevier Science Ltd.