The variation of glass transition as a function of the degree of cure in an epoxy-novolac system.

Integrated circuits are commonly packaged by encapsulating a metal lead frame and integrated circuit with a thermosetting plastic in a transfer molding operation. For over a decade epoxy resins have been used in this way but little data has been published on their reaction kinetics or on the change in properties which occur during curing. In our present work we have studied by DSC the kinetics of the crosslinking of several epoxy novolac resins whose functionalities range from 2.7 to 5.4. These resins have been cured with a novolac hardener using an imidazole as catalyst. The heat of reaction of the phenol group with the epoxy group has been determined previously in a model compound study. Using this value the extent of conversion of the curing reaction can be followed calorimetrically, provided that no side reactions take place.