Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

Phil,

You sound like me. Decades ago I also tested mercury lamps with the outer glass envelope broken off.

Surprisingly it worked worse than with the envelope intact. I eventually figured out that the bare bulb was running too cold and never reached the operating temperature.



Later I found an industrial 400W UV bulb with a matching power supply so I can blast anything with more than needed UV.



The commercial units use a mechanical light shutter so the bulb runs continuously and are up to speed so the exposure times are very fast and consistent.



I also built a 10kW focused carbon-arc lamp with a filtered DC supply. Interestingly, it does not sound like an arc welder, it very quietly slightly hisses.

Bertho



From: Phil@Yahoo Sent: Sunday, July 07, 2013 18:27



Wow.

Interesting story, though it doesn't seem very relevant.

I guess that's the sort of thing we can look forward to
as a result of emphasizing self-esteem over achievement
in our public schools. If we manage to dumb down
everyone to the lowest common denominator then no one
will ever do anything dangerous because they won't know
how. And we wouldn't need groups like this one.

Here's something that will make your hair stand on end:
My exposure box design is the eventual result of a YouTube
video I saw where a guy used Hg vapor lamps with the
glass envelop broken off because apparently ∗any∗ such
bulb will produce the necessary radiation if the borosilicate
envelope is removed. I was trying to make the thing as cheap
as possible, so I tried it. Turned out the exposure time was
longer than I wanted and then I found an Hg bulb made for
"safe" UV and so used that. $10 for the bulb and $40 for
the ballast, some MDF and cheap drawer slides and voila!
A spiffy exposure box with reasonably fast exposure times.
Does it leak? Sure, some, but not much. I squint when I
slide the drawer out. The problem with Hg lamps is that
they require a minute to "warm up" and you can't turn them
on again right away if you turn them off, so interlock switches
are not practical. I thought about some elaborate mechanical
interlocks, but decided not to make "perfect" the enemy of
"good enough." The advantage of the Hg lamp is it is nearly
a point UV source. I haven't been able to do 8/8 yet but I
have done 12mil traces with spaces probably less than 8.
My biggest problem now is making high-enough quality masks.
--
Phil M.





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