Many years ago I made a bunch of boards using Datak Negative resist,
sprayed it on with a pump sprayer. Do you mean you paint it on with
those very soft fine foam makeup sponges?
Get a red bulb rather than the yellow bug light. You don't need a very
bright bulb ;') if you let your eyes become dark adjusted. I think I
used a 15 or 25W when I was doing this.
Dry them in a bigger box. A small box will get full of fumes of the
solvents and may never let the coating truly dry out. You might even
put it in the shoebox but then set that in a warm oven. Run the oven
up to about 150F, then set the box inside and shut the oven off and
leave it overnight with the oven door shut. Careful if you are using a
gas oven! I don't know if the fumes are flammable, although there
shouldn't be much.
I used a plant grow floodlamp. They specifically have some UV in them,
where a normal floodlamp is optimized for visible light. Especially if
it is not even a quartz halogen flood, normal floodlamps put out
barely any UV. And quartz halogen lights have filters to block the UV.
I've had this goofy idea I've never tested, using a xenon strobe tube
to expose boards. The idea: a camera flash (xenon strobe) has a filter
over it, not just to balance the light but also to block the UV it
gives off. So if you had a largeish unfiltered strobe, perhaps a
specific number of flashes would properly expose a board. Test it,
find the range over which it works, and hit the middle. As the bulb
ages you may find you need to fire off a few more flashes.
Anyway, that was my goofy idea. I have no idea of that would take an
inordinate number of flashes, as that would be the real test of
whether or not it was worth it.
Steve Greenfield
--- In Homebrew_PCBs@yahoogroups.com, "ednspace" <ed@c...> wrote:
> Hello,
>
> This is a plea for help!
> I am on my 5th trial with this and while each trial improves somewhat
> in end quality, and certainly in the process, (no longer spilling
> solvent all over the basement), I still have yet to produce a board
> that I thought could be etched.
>
> The traces are very weak to washed out to non existant. At first I
> thought I was under exposing now I suspect I am over exposing or just
> not getting a good build up of the resist on the board to start with.
>
> I am looking for someone familiar with this method to bounce a few
> emails with so that I can get it right.
>
> At this point I am:
> In a 60watt bug light environment (Problem?)
> Coating the boards with makeup swab rather then spraying, much nicer
> coat and no smears, nice and shiny, dust free mostly.
>
> Drying over night in a sealed shoebox, inside another box
>
> Using tracing paper as negative nice black laser print (Reported to
> work in many places)
>
> Exposing with a 250watt photoflood for various times and developing
> following supplier instructions with the recommended developer.
>
> Exposure times have been, 22, 10, 5 with a couple of retrials in
> between, no, luck. Any help would be greatly appreciated.
>
> Thanks,
> Eric