Epoxy composite films of superior dielectric properties promoted by active ester hardeners for applications in electronic packaging

Epoxy composites with ultralow dielectric dissipation factors (Df) are highly desired in advanced electronic packaging architectures to cater for high-frequency signal transmission. However, Df of epoxy systems traditionally cured by amine, anhydride or phenolic resin is too high due to the generated high-polarization groups like hydroxyl moieties. Using active esters as curing agents is an effective strategy to reduce polarization of cured epoxy by replacing hydroxyl moieties with ester groups. Herein, diallyl-based active ester hardeners (DAAE) are synthesized via one-step esterification reaction with a high yield of > 90 %. When DAAE is used to cure epoxy films containing SiO2 fillers, the cured epoxy composite films (DAAE-ECFs) demonstrate low dielectric constant (Dk, ∼3.0) and low Df (∼0.005) above 5 GHz at 25 ℃. Importantly, whether immersed in room-temperature water for 24 h or in boiling water for 1 h, DAAE-ECFs absorb < 0.6 wt% water with stable Dk and slightly increased Df (<0.0085). Moreover, DAAE-ECFs show excellent thermal stability (Td5% >365 ℃), dimensional stability (CTE of ∼ 30 ppm ℃-1 below 80 ℃), high storage modulus (∼10 GPa at 30 ℃). The appealing dielectric, thermal and mechanical properties imply that DAAE-ECFs could serve as promising candidates for electronic packaging materials in high-frequency signal transmission.