New epoxy/episulfide resin system for electronic applications. I. Curing mechanism and properties

A new epoxy/episulfide is investigated using a dicyandiamide (DICY) curing agent system. The resin exhibits better adhesion to copper, a lower thermal expansion coefficient, a lower heat of reaction, and slightly higher water absorption as compared with the standard epoxy system. The dielectric cons tant of the epoxy/episulfide system is almost the same as that of the stand ard epoxy system. The properties are due to the reaction mechanism change c aused by the addition of episulfide, which is studied using a monofunctiona l model compound system; the amino groups in DICY initially react much more easily with the episulfide than with the epoxy ring. The S- formed by this reaction reacts with the episulfide and the epoxy quickly. In the presence of copper, the episulfide and/or the S- also react with copper, forming a durable bond between the copper and matrix resin that retains strength even after water boiling. (C) 2000 John Wiley & Sons, Inc.