A corona igniter assembly including an ignition coil assembly, a firing end assembly, and a dielectric compliant member is provided. The dielectric compliant member is compressed between a high voltage insulator of the ignition coil assembly and a ceramic insulator of the firing end assembly. During assembly of the corona igniter assembly, the dielectric compliant member pushes air outwards and forms a hermetic seal between the high voltage insulator and the ceramic insulation. The dielectric compliant member can have a rounded upper surface, which may improve the hermetic seal. Alternatively, or in addition to the rounded surface on the dielectric compliant member, the lower surface of the high voltage insulator can be rounded to push air outwards during assembly and provide a hermetic seal.