> Tom, thank you very much for that information. I have a few
questions mixed in context below.
>
> > -----Original Message-----
> > From: twb8899 [mailto:twb8899@...]
> > Sent: 26 September 2006 04:17
> > To: Homebrew_PCBs@yahoogroups.com
> > Subject: [Homebrew_PCBs] Re: UV Light Sources
> >
> > It's just a standard 1000 watt mecury vapor bulb with a reflector.
There is
> > no need to worry about collimation of the beam unless you are exposing
> > very large panels. Don't break the outer glass from the lamp unless
> > you want ozone.
> Is the reflector built into the globe i.e.. is it a PAR type globe
or is it separate?
The reflectors in my exposure unit are external to the lamp. They are
made of thin polished aluminum sheet. You could probably just use
some cheap glass mirrors to do the same thing.
> >
> > Just the other day I saw a lamp assembly that would be perfect for a
> > homebrew exposure unit. It was a mercury vapor lamp with reflector in
> > a metal enclosure at the base of a flagpole. This lamp looked like a
> > 400 watt bulb but that would work great for dry film resist. Just
> > build a box around the lamp assembly and leave a slot at the bottom
> > for your contact frame to slide in and out. The bulb could be about 12
> > inches from the contact frame.
> >
> I was going to use a 250 watt self-ballasting globe. Do you think
that would be OK?
I think a 250 watt bulb would work ok. Give it a try without the
reflectors first and you may find that it works fine for smaller boards.
>
> > At 400 watts I'm guessing about 45 seconds for exposure at 12 inches.
> > My system uses the 1000 watt lamps. They idle at 1000 watts and during
> > exposure they are overdriven to 1500 watts. Exposure time for DuPont
> > 1.5 mil photoresist is 17 seconds. I do 5 mil lines and spaces daily
> > with this system. My film work is photoplotted on 7 mil thick films.
> > Dry film resist is negative acting and has a fast exposure time.
> > Positive resists are slower and will take longer to expose.
> >
> Would you use a similar distance of 12 inches for a 250 watt unit?
> Would 2 ∗ 250 watt globes be a better way to go? I will be exposing
Kinsten positive resist PCBs
I'm not familiar with Kinsten resist. You mentioned that it is
positive acting so it may take longer to expose no matter what type of
lamp you use. Try the 12 inche distance first and see how it works out.
I saw another mercury lamp this evening that was being used to light
up the side of a building. This one did have a 400 watt bulb and it
would make an excellent exposure unit. It had a polished stainless
steel reflector around the lamp. Check out one of these lamps to get
an idea of how it's set up.
BTW, my 1000 watt system also does a good job with silk screens. The
Autotype Five-Star emulsion takes 30 seconds and the diazo liquid
types take 90 seconds.
No matter what type of bulb you use it is a good idea to get a
Stouffer 21 step exposure strip to test your exposure times. If you
take just a little bit of time to calibrate your system the results
will be excellent. These Stouffer 21 step test strips are inexpensive
and a good tool to have on hand if you do any work with photoresist.
Tom
> Once again Tom thank you for your guidance.
> Regards
> John C
>