Treating the copper?

[davent]

I ran into the same problem with Liquid Tin in that it eventually oxidized on me and i was back at square one. With lacquer no matter how long after i've waited to get to soldering never an issue.

dave

[danfrank]

I wrap my bare copper PCBs in seran wrap making sure all the air is out of the wrap. When I'm ready to solder the board, I do it all in one session. After that is done I use flux remover to clean the board and let it dry. After it's dry, I spray the board with Krylon (or any brand) crystal clear spray laquer. It's basically the same stuff as electronics "conformal coating" but cheaper

[Zerro]

I always use rosin while soldering anything - it helps me to safe and reliable contacts. And, you can use it before population the desk too, and after it, as a protection layer.
Before: put some strong technical alcohol to smal glass (a few ml) and add rosin, to solve it there, to get laque density. Then use it as laquer at the desk. Let to dry several hours.
After: clear populated pcb desk with soft metall brush, then wash with technical alcohol and again add lacqueer layers with that solved rosin. Very usefull for future soldering too. Cheap and great!