Rummaging around in a friend's box of old electronic stuff we found an old pre-sensitized positive resist PCB. Its age is around 6-10 years.

there is some visble fading near the edge where light must have gotten into the open package, but the rest of the board is still green.

Is it still viable for UV exposure? or should i wash off the resist and just use it as a plain board?

 

hi,
If stored at highish tempratures it will most likely have degraded.

If it were mine I would cut off the obvious 'bad' section of pcb and run a simple exposure/developer test on say a very simple artwork and see what I got.

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I would leave the "bad sections" on, expose, develop, then trim. It is easier that way and far less risk of getting dust and cutting debris on the surface, which can affect exposure results.

As for age, I use a different brand (Injectorall), which is orange. The photochemistry is virtually identical, though. I have found that older boards require somewhat longer exposure times. I have also found that putting the older boards in a humid box for about 10 minutes before exposing seems to help. I have no controlled experiments, though, on that to support it. By older, I mean 3 years or so. I have no experience with 6-year-old boards. The humid box is just a plastic storage box with a wet paper towel in it.

John

 

You can always use it as plain copper clad board if it turns out to be bad.

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