Development of no-flow underfill based on non-anhydride curing system

Most no-flow underfill materials are based on epoxy/anhydride chemistry. Due to the its sensitizing nature, the use of anhydride is limited and there is a need for a no-flow underfill using a nonanhydride curing system. This paper presents the development of novel no-flow underfill materials based on epoxy/phenolic resin system. Epoxy and phenolic resins of different structures are evaluated in terms of their curing behavior, thermo-mechanical properties and reliability. Compared with anhydride cured epoxy resins, epoxy/phenolic resins show high adhesion, high fracture toughness, low crosslinking density and high viscosity. The assembly with nonanhydride underfill shows high reliability during the thermal shock test. Using an appropriate fluxing agent, no-flow underfills based on epoxy/phenolic system have been developed.