CHARACTERIZATION OF THE RHEOLOGICAL PROPERTIES OF A FAST-CURING EPOXY-MOLDING COMPOUND

The viscosity of an epoxy-molding compound (EMC) has been characterize d using a parallel-plate viscometer and a specially-developed slit rhe ometer. In particular, steady-state and dynamic viscosities at low tem peratures and shear rates have been determined with a parallel-plate v iscometer. Measurements with this instrument indicate that an extended Cox-Merz relation can be used to relate the dynamic viscosity to the steady shear viscosity for the given EMC. For measurements at high she ar rates and high temperatures, a special slit rheometer has been buil t. In this viscometer, the slit is preceded by a disk-shaped reservoir where curing of the specimen takes place. The sample fills the thin r eservoir fast and has its temperature raised by heat conduction from t he hot wall. Because the reservoir is thin, the specimen quickly reach es the wall temperature with negligible cure and then cures under appr oximately isothermal conditions. The degree of cure of the sample is m easured by quenching the specimen as it is extruded out of the slit an d then performing differential-scanning-calorimeter measurements. By c ombining results from these two viscometers, the viscosity of the EMC has been obtained over the typical processing range of shear rates, te mperature and degree of cure encountered during chip encapsulation. Th e measurement results indicate that the EMC viscosity exhibits a yield -stress behavior at low shear rates and a power-law behavior at high s hear rates. The temperature dependence can be described by the WLF (Wi lliams-Landel-Ferry) equation and the degree-of-cure dependence at low cure by an equation proposed by Macosko. (C) 1997 The Society of Rheo logy.