Synthesis of tertiary ester epoxy resin and application in reworkable underfill

In order to endue the underfill with reworkability, tertiary ester epoxy resin (TEER), bis[1-methyl-1-(6-methyl-7-oxa-bicyclo[4.1.0]hept-3-yl)-ethyl] isophthalate, was synthesized by the reactions of esterification and epoxidation. The structure was characterized by Fourier transform infrared With TEER as matrix, silica particles as filler, methyl hexahydro-phthalic anhydride (MeHHPA) as curing reagent and 2-Ethyl-4-methylimidazole (4E2MI) as accelerant, the underfill was successfully prepared. The ester group in the backbone would be pyrolyzed when it was heated. The sharp peak of pyrolysis curve by differential scanning calorimeter indicates the pyrolysis process has less side reaction and the pyrolysis range is around 220 °C. The pyrolysis is a carbenium intermediate process which relates to the stability of the carbenium. Tertiary carbenium is more stable which makes TEER have a lower pyrolysis temperature. Processing characteristics measurement results show that the reworkable underfill exhibits excellent processing performances and the tertiary ester epoxy resin is suitable for reworkable underfill.