Thermal Reaction Characterization of an Epoxy Molding Compound

Abstract

ABSTRACT:A novel epoxy molding compound for electronic industry application was used to conduct thermal analysis characterization using differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). The reaction kinetics of cure and thermal degradation have been analyzed based on a proposed iso-conversional model. The kinetic results showed that the cure and decomposition process are complex, and the values of activation energy are dependent on the degree of conversion.KEY WORDS Epoxy Molding Compound / Iso-Conversional Model / Cure Kinetics / Thermal Degradation/ Electrical and electronic devices have been encapsulated in a variety of resinous materials, including epoxy, silicone and phenolic materials. Epoxy molding compounds for the encapsulation of electronic components are considered a specialty market by the epoxy manufactures. The worldwide consumption of electronic grade molding compounds is approximately 100000000 metric tons (1997) and growing. The amount of epoxy resin used in these compounds is approximately 10% of that figure. The electronic grade epoxy resins must have a higher degree of purity than the commodity epoxy resins. The halogen content of these resins is usually less than 800 ppm and are much more difficult to manufacture than the standard resins. 1 The useful properties of epoxy resins appear only after curing. The curing step transforms the epoxy from a lowmolecular-weight material to a highly crosslinked space network. The properties of the cured resin depend on either the type of epoxide and the curing system used or the extent of cure. Recently, epoxy molding compounds have been widely used in the electronic industry and encapsulation of integrated circuits by means of transfer molding.2 Only limited information, however, may be found in the literature concerning the cure and degradation characterization of these molding compounds. Therefore, kinetic characterization of thermoset systems is necessary for a better understanding of structureproperty relationships. 3 The attractive feature of isothermal experiments is that the rate constants at each temperature are better defined and the constants obtained at different temperatures would permit the determination of the activation energy associated with the thermal degradation. 4 • 5 However, the nature of the reactions and the final products may differ at different temperatures, and the kinetic parameters thus obtained are not without ambiguity. 6 Dynamic experiments, conducted at a specified heating rate using DSC, will yield conversion-timetemperature data that are comprehensive enough to permit direct evaluations of the kinetic parameters. A single dynamic run gives as much information as do several isothermal runs. Furthermore, dynamic measurements can provide kinetic information over a larger temperature range and there is no preheating problems as is the case with isothermal experiments in which the sample must be first heated to the isothermal hold temperature during which thermal reactions may take place. It is v...