Board soldered airtight capsule
If you have a can, preferably made with a continuous external flange,  it could be soldered to a mating copper loop on the board. However vias would represent holes through the board under the can. Blind and buried vias are possible, but add to cost and NRE.   

You would communicate this with drawings following a meeting to discuss options.

Such a seal would not be considered hermetic, you’d want ceramic and feedthroughs etc. for that.