Photopolymerizable encapsulants for microelectronic devices

Photopolymerizable encapsulants for microelectronic devices may offer important advantages over traditional transfer molding resins, including improved yields and reduced wire sweep. In this contribution we discuss an encapsulation process based upon a low viscosity resin which cures rapidly upon exposure to UV light. We have characterized the cure time, coefficient of thermal expansion, thermal degradation temperature, flexural modulus, and chemical resistance of photopolymerizable encapsulant formulations based upon epoxy vinyl ester resins. The results indicate that a photocurable encapsulant loaded with 60 wt.% fused silica is very promising since the material properties are similar to current commercial encapsulants. These formulations cure in less than three minutes for an initiating light intensity of 180 mW/cm(2) and exhibit appropriate values of the thermal expansion coefficient, degradation temperature, flexural modulus, dielectric constant, and resistance to water (both acidic and basic).