Determining the gel point of an epoxy-hexaanhydro-4-methylphthalic anhydride (MHHPA) system

The DEBGA-MHHPA epoxy system has found increasing applications in microelec tronics packaging for which the ability to understand and model the cure ki netics mechanism accurately is crucial. The present article reports on the work done to elucidate accurate knowledge of the gel point by rheological m ethods. To determine the gel point using the G'-G" crossover method was fou nd not to be accurate, and the gel point obtained by this method was found to be frequency-dependent. Using the point where tg delta was found indepen dent of the frequency can accurately define the gel point at different temp eratures. At the gel point determined by this method, G' and G" were found to follow the same power law, demonstrating the accuracy of the method in d etermining the gel point. The scaling exponent obtained was 0.75-0.79. The activation energy for the cure reaction of the system was determined to be 75.1 kJ/mol by the obtained gel times at different temperatures. The steady -shear rheology test was also used to observe the viscosity change at the g el point. (C) 2000 John Wiley & Sons, Inc.