No-flow underfill formulation using different epoxy resin combination

The no-flow underfill mechanism has been devised as a potential replacement for the conventional capillary flow process, where the underfill material is applied to the substrate before the chip-substrate interconnection is established. During the reflow step, the solder joints are formed prior to full curing of the underfill material. Extensive exploration has been devoted to the potential chemical systems for the no-flow underfill application in our group, and typically those no-flow underfill materials are liquid epoxy resins formulated with an appropriate curing system to fit with the solder reflow profile. Other types of epoxy resin, either liquid or solid at room temperature, have been combined with the basic liquid epoxy resin, to study the viscosity, curing profile, glass transition temperature, modulus and coefficient of thermal expansion. The liquid-liquid thermal shock tests for these formulations have also been conducted for evaluation of the preferred formulation components and loading amount. This will help to provide more material options for no-flow underfill encapsulant development.