Abstract
For the epoxy encapsulant cured by diethanolamine, optimal epoxy/hardener stoichiometry could hardly be predicted due to the complex curing mechanisms. In this paper, the influences of stoichiometry were investigated by FTIR, DMA and tensile testing. The results showed that stoichiometry has a dominating effect on both Tg and tensile properties of the cured epoxy. The largest Tg, highest crosslink density as well as excellent ductility appeared in epoxy encapsulant cured with 14 wt% diethanolmine. When the content of diethanolamine was lower than 14 wt%, epoxy encapsulants showed smaller glycidyl conversion even with long-duration post-cure. Larger tensile strength and modulus were also observed in the glycidyl-rich epoxies, which could be explained by anti-plasticization effect. The amine-rich epoxy, however, had extremely high glycidyl conversion and presented brittle tensile behavior. A diethanolamine content of 12-14 wt% for the epoxy encapsulant is suggested to obtain optimal thermal and tensile properties.
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