Encapsulant for fatigue life enhancement of controlled collapse chip connection (C4)

Controlled collapse chip connection (C4), or flip chip connection, has been used since late 1960s as a reliable interconnection technology for semiconductors. Allowing area array type of interconnection, this method provides one of the best solutions for high density packaging. However, with trends migrating to larger DNP (distance to neutral point) chips and organic substrates, the fatigue life of solder joints need to be enhanced by encapsulation. To meet the stringent requirements of flip-chip encapsulation, low viscosity resins based on epoxy chemistry have been developed by IBM. These systems having low thermal expansion, low α-particle emission, excellent flow, and wetting characteristics can provide improved mechanical and environmental protection of the solder joints. This article describes the characterization of a liquid, silica filled system for maximum processability of C4 chips. Critical thermomechanical properties have been studied to ensure that both ceramic module and card assembly conditions can be sustained. Both rheological properties and cure kinetics were optimized to provide enhanced flow and coverage of the C4s. Other key properties such as, shelf life, thermal stability, solvent and moisture resistance as well as adhesion to various surfaces are addressed