A hermetic seal includes a spring seal compressed with a limited sealing force between sealing surfaces. The sealing surfaces surround a gas-filled cavity that houses heat sensitive components. The hermetic seal includes a film that joins the spring seal to the sealing surfaces. The film includes a material that is softenable by heat to hermetically seal the spring seal to the sealing surfaces. The hermetic seal includes an externally accessible surface for selectively application of the heat to the film, without overheating the heat sensitive components.