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Old 5th Jul 2017, 10:22 pm   #7
David G4EBT
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Join Date: Feb 2003
Location: Cottingham, East Yorkshire, UK.
Posts: 3,269
Default Re: UV Dry Film PCB technique - experiences to date.

Well done on the progress to date. I don't think anything is critical. Provided you've got a totally opaque PCB mask which allows no light through when held up to a light, you can't really 'over expose' a board, but of course you can under expose it. In days gone by, when I used to rely on acetate photocopier copies and tape two or three together to try to maximise opacity of the tracks, exposure time was certainly critical and hit and miss. I either ended up with lacquer still on the board with no sign of any tracks, or lacquer totally dissolved from the board, (with no sign of any track), or if I was lucky, a usable board.

One definition of insanity is doing the same thing over and over again and expecting a different outcome.

Now that I use micro-porous film, providing a totally opaque mask, I find that 60 seconds exposure is fine for dry film negative resist, and four minutes for positive lacquer. I always warm up the tubes for five minutes before I use the box. No idea whether the need to do that is just an 'urban myth' or whether it does make a difference - people say the same thing about warming a teapot with hot water before making a pot of tea!

Have fun.
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