Homebrew PCBs

I had a very unpleasant surprise with a commercial uv box ($600) that 
was unable to create SMD images on PCB. It turned out the collimation 
was teh issue. When I tried the same film ina collimated UV exposure 
box, the result was stunning. Later I tried to make SMD PCBs with a 
regular GE sunlight and it was almsot insanity. Times were allover 
the map due to heatup, images were fuzzy. Then I switched to Nuarc 
26, a comemrcial exposure unit. Voila, quality is beautiful. 
Few things matter:
1. Like you said, collimation
2. Source of light fluorescent or Hg
3. Timing
4. Repeatability (if Hg)

thinker tinker shows some detailed isntructions how to build it.

Mike


--- In Homebrew_PCBs@yahoogroups.com, "Leon Heller" 
<leon.heller@d...> wrote:
> ----- Original Message ----- 
> From: "Brian Clancy" <bclancy1@b...>
> To: <Homebrew_PCBs@yahoogroups.com>
> Sent: Monday, January 24, 2005 5:26 AM
> Subject: Re: [Homebrew_PCBs] UV lamps?
> 
> 
> >
> >
> > G'day Jason,
> > My understanding of it is that you need to have collimated light, 
i.e. all
> > light rays are coming vertical to the artwork so that it does not 
go under
> > the edges of the artwork.
> > This is the reason that a negative should be placed with the 
emulsion on 
> > the
> > PCB to reduce any chances of the light going under the edges.
> >
> > I saw somewhere where they used an egg-crate diffuser (from a 
flourescent
> > light fitting) painted matt black, to collimate the light. This 
meant a
> > reduction in effective light output but a cleaner image.
> 
> For home use, collimated light isn't really necessary, as most of 
us can't 
> create high-resolution artwork that can make use of it. In fact, 
none of the 
> low-cost UV exposure boxes that one can buy use it, they just have 
two or 
> four tubes quite close to the PCB/artwork. I get quite good results 
with a 
> couple of tubes about 15 cm from the PCB. Exposure is quite long at 
13 
> minutes, I keep meaning to add another two tubes.
> 
> Leon
> --
> Leon Heller, G1HSM
> http://www.geocities.com/leon_heller 
> 
> 
> 
> -- 
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