[sdiy] Photosensitive PCB's

[The Old Crow]

On Fri, 24 May 2002, Michael Schulze wrote:

> I'ma having a hard time getting the photo sensitive pcb process to work.
> I've sprayed my own boards and exposed them with negative art.  When I
> etch there seems to be not enough contrast between light and dark, so
> the traces are not clearly defined.  By the time I can see the
> fiberglass in between the traces the traces are half gone too.

  It sounds like the exposure time is not long enough.  For years I've
used pre-coated board stock from Kepro and an 11x17 lightbox that houses
four UV "plant growing" lamps for my exposure system.  Even though Kepro's
black film is not nearly as easy to work with as their orange film used to
be, I can still get good results from a negative-on-paper by using a
5-minute exposure.  For acetate film to PCB exposure, 40 to 50 seconds
always appears to work well.

  One note of caution: the UV lamps as used above are not safe to look at 
directly.  Anyone that uses them should make sure their lightbox blocks 
the UV from the operator.

Crow
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