Cooper protection

For amateur use silver plating is expencive, so how to protect cooper in some
stripline circuit or patched antennas in home made "production" ?
For microwave especialy.
How cooper oxside perform to microwave (1-6Ghz) ?
Is ist better to leave it clean or protect it with thin film of some paint ?

lead-tin solder coat is pretty inert stuff. Just keep it thin at 6 Ghz