I have just made several PCBs for a large project using the photoresist method. (I ran the boards through sodium silicate developer then through ferric choride) I then rinsed off all chemicals and dried the boards.
I believe there is some chemical electronic stores sell (conformal coating? I don't know) that would protect the circuit board from any sort of corrosion (which can include introduction of open circuits).
I know the next steps are to drill holes and solder components in, but after that process is complete, how long can I leave the board like that before it is absolutely necessary to add some sort of protective coating to it?
I want my board to last forever but at the same time, I don't want it to corrode (or have traces break up) as the years go by.