Hold on here. Are you asking how the copper is actually attached to the phenolic or fiberglass base??? If you indeed are, I think you might be way over your head in working the printed circuit boards at this point.
-- To the substrate? With glue.
Do you mean the glasfibers epoxy substrate?
Most epoxy resins are not resistive against high UV radiation. But I can't say anything about the epoxy used in FG4 PCB's. I expect a soldermask will give a additional UV protection.
Eventually the epoxy breaks down in sunlight, unless is has a sacrificial UV inhibitor like the grey PVC for outside use has or blue dye like Phelps Dodge fiberglass base station antennas which are more resistant to sunlight than the painted Decibel Products antennas.
I think sunlight would be the least of the problems if an exposed PCB was used outside with no cover or box whatsoever. Even if used inside a UV radiating device, you could put the PCB in a box to shield it.
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