Homebrew PCBs

Russell,

Since you have mentioned teh word 'columination' so many times, I did 
some checking and yes, there is a word 'columination' but the the 
effect that matters to nice UV exposures is called 'collimation'. 
Just to set the record straight and yes it is a full moon.  Mike



--- In Homebrew_PCBs@yahoogroups.com, Russell Shaw <rjshaw@n...> 
wrote:
> 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.  Oxygen inhibits free radical 
polymerization.  High intensity light generates so many free radicals 
in the clear area of the phototool that dissolved oxygen is consumed 
almost instantly and polymerization proceeds quickly.  As oxygen 
migrates from under the opaque areas of the photo tool those areas 
loose the only thing that prevents polymerization.  Stray light from 
poor columination or reflection from the copper surface would 
initiate polymerization in what should have been shadowed areas.  If 
you get the clear areas polymerized quickly the dissolved oxygen 
doesn't
> 
> h
> >  ave time to migrate and it prevents polymerization in areas of 
lower light intensity.  In other words, high intensity will overcome 
the effects of poor columinization.  The reverse is not necessairly 
ture because of scattered reflection from the copper surface.  This 
effect was demonstrated in dozens of production shops.  
> > 
> > However, this is really getting down into the weeds as most home 
brew folks don't have (or shouldn't have) the high intensity mercury 
arc lamps that are needed for fast exposure times.  Even though I 
have one in my shop I'm yet to turn it on because I have not yet 
installed sufficient protection from the radiation it will produce.  
I'd rather develop a solid documented toner transfer process which 
will do everything I need than fuss around with high resolution 
photoresists.
> 
> The black-light blue mercury HID lamps (125W, 250W, and 400W) are 
sold for stage
> lighting effects and don't put out the shorter wave UV. With 
columation in a decent
> lightbox, fine traces and spacing are easy. I'm using a 125 watt 
HID mercury blacklight
> in a cylindrical reflector, 60cm globe-pcb spacing, and 90sec 
exposure time.
> 
> The commonest HID blacklight seems to be HPW125 (i got a GE one).
> 
> http://www.lamptech.co.uk/Spec%20Sheets/Philips%20HPW125.htm
> http://www.lamptech.co.uk/Spec%20Sheets/Philips%20HPR125.htm
> 
> They need a ballast choke and PFC capacitor.