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 (Tg) 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.