Modification of epoxy resin with siloxane containing phenol aralkyl epoxy resin for electronic encapsulation application

A process was developed to incorporate stable dispersed polysiloxane particles into a phenol aralkyl novolac epoxy resin. which was used as an ingredient in the encapsulant formulation to withstand the thermal stress. The mechanical and dynamic viscoelastic properties and morphologies of rubber-modified epoxy networks were studied. A "sea-island" structure ("islands" of silicone rubber dispersed in the "sea" of an epoxy resin) was observed in cured rubber-modified epoxy networks via SEM. The dispersed silicone rubber-modified aralkyl novolac epoxy resin effectively reduces the stress of cured epoxy molding compounds by reducing flexural modulus and the coefficient of thermal expansion (CTE), while the glass-transition temperature (T-g) was hardly depressed. Electronic devices encapsulated with the dispersed silicone rubber-modified epoxy molding compounds have exhibited excellent resistance to the thermal shock cycling test and have resulted in an extended use life for the devices. (C) 2000 Elsevier Science Ltd. All rights reserved.