Hi. In the past years I had made dozens of PCBs but now I am trying to get a professional finishing on them. The main problem is oxidation of the copper traces. Basically I use the silkscreen method to make the pattern in both layers and then etch. Later, I apply soldermask (by silkscreening too) in both layers and since I have to heat cure the soldermask in an oven, the copper oxidates too. I do not know which method will be better, if applying some kind of laquer, varnish, etc., (which also would be solderable too) and then apply the soldermask, or how I could stop the copper oxidation. Thank you very much for any help.