Microelectronics Lid Seal
There are two methods of lid-seal, depending on the build-standard of the hybrid.
For metal packs, a metal lid is seam-welded to the package in a dry-nitrogen atmosphere. The picture shows the process taking place in a glove box where two copper rollers deliver high current pulses, welding the lid in place.
For ceramic packs, a ceramic cavity lid is affixed to the substrate using an epoxy mat. Again the sealing process takes place in a dry-nitrogen atmosphere.
Chip-on-board designs are protected by localised application of a silicone bond protection, usually with an overall epoxy coating.