Homebrew PCBs

G'day
I am starting to regret having mentioned collimated light. I have no
practical experience  of this except that by spacing the light source a
further 40mm from the artwork/PCB you get  less furriness of the image. 
The reference I saw (I don't recall where) used a flourescent fitting
eggcrate diffuser (which were quite common in earlier times) about 1.5 to
2cm spacing and painted these matt black to prevent reflections. This gives
an almost collimated light source (separation from the surface of intent is
still mandatory) and supposedly perfect (if longer exposure) reproduction.
Cheers
Brian
 
-------Original Message-------
 
From: Homebrew_PCBs@yahoogroups.com
Date: 01/26/05 18:29:20
To: Homebrew_PCBs@yahoogroups.com
Subject: Re: [Homebrew_PCBs] UV lamps?
 
Earl T. Hackett, Jr. wrote:
> This is getting a bit off topic.
> 
> The comments below are close and when I started working with photoresists
that was my opinion as well.  However, when we examined the results of
resolution testing, the data showed there was something other than just
columination and exposure at work.  Tests at DuPont showed that oxygen
migration within the photo resist from under the opaque areas of the
phototool had a major effect on resolution of the spaces.
snip> 

This is the first time I've heard of this effect on dryfilm resists. The
question now remains, what is the speed the oxygen diffuses near the
boundaries between the exposed and unexposed areas of resist. 
snip
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