Homebrew PCBs

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?
> 
> 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?

> 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
> Tom

Once again Tom thank you for your guidance.
Regards
John C