Development of Polyester-Modified Epoxy Resins for Self-Organization Soldering

Novel underfill resins combining a thermoset epoxy resin with thermoplastic polyester resins have been developed for self-organization soldering. Polyester-modified epoxy resins, which are hybrid resins, exhibited minimal viscosity at the melting point of the Sn–58 mass%Bi solder, with the viscosity dependent on the content and molecular mass of the blended polyester resin. Because the epoxy resin was sufficiently compatible with the polyester resin in the hybrid, the curing reaction of the hybrid resin was similar to that of the epoxy resin. The chemical structure of the polyester resin was retained in the cured hybrid resin, imparting thermoplasticity to the hybrid resins cured with repeated heating. Successful self-organization soldering was achieved using the developed hybrid-resin-based solder paste.