Study of non-anhydride curing system for no-flow underfill applications

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 non-anhydride 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 term of their curing behavior, thermo-mechanical properties and the 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 non-anhydride underfill shows high reliability during the thermal shock test. Using proper fluxing agent, no-flow underfills based on epoxy/phenolic system have been developed.