--- In
Homebrew_PCBs@yahoogroups.com, Paul <paul@...> wrote:
> It does of course depend on the UV source and the photo board but 15s sounds
> far too short.
I also agree. Back in the 70s, I used an old arc-light unit--complete with
carbon rods--that put out blinding light . . . I mean, really, really
bright, and because it was from an arc, it was super rich in UV--of all
kinds. Still, with that powerhouse exposure unit, it took at lest 90
seconds for an acceptable PCB exposure with pretty-much the same type of
emulsions used today. If there weren't any fine lines on the board, I'd
give it another 30 seconds.
I'm not even sure 15 seconds of direct exposure to the sun would be enough.
In fact, I think per square centimeter that old arc light was brighter than
the sun.
Best
,
Todd
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QRP (CW & SSB) / EmComm / SOTA / Homebrew / Design
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