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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