For 15mil tracks, you might be better getting the artwork plotted at 2x
'life' size & then getting it professionally photo reduced onto film. Be
sure that the artwork as printed on the final film you will use to expose
the PCB is printed on the side of the film which faces the pcb. If not you
will get some measure of scattered light getting at areas you don't want. It
may not make much difference, but it's easy to avoid a potential problem
altogether. When I was making these using photo resist this is how I did
them for hi-density thin tracks. For normal stuff, I printed the artwork
using a laser printer & sprayed the page using a transparantizing spray
(used to be available in art stores, don't have any left & can't remember
the brand name). ~The resulting page was good enough to use directly on the
UV box. Exposures were longer than for an acetate sheet as the page was
translucent rather than transparent. 

I never did get good results printing directly to acetate sheet. (small
holes in the print etc.)

Joe

> -----Original Message-----
> From: piclist-bounces@mit.edu 
> [mailto:piclist-bounces@mit.edu] On Behalf Of Tamas Rudnai
> Sent: 26 September 2006 12:21
> To: Microcontroller discussion list - Public.
> Subject: Re: [EE]Homemade PCB
> 
> 
> I do not know if this is a good procedure or not, but you can 
> read it on Maplin's site:
> 
> Single and double-sided copper clad SRBP and glass fibre 
> boards coated with a positive photo-resist suitable for use 
> with our UV exposure box. The boards are covered with light 
> proof protective film, which should not be removed until the 
> board is used. The PCB should be exposed using our UV 
> exposure box and a circuit overlay transparency. Exposure 
> time will be from 8 to 15 minutes. Mix together 0.5l approx 
> with one teaspoonful of sodium hydroxide (available from most 
> chemists) and pour into a tray (CH38R). Gently rock the 
> exposed PCB in the tray until the unwanted photo resist is 
> dissolved away. Etch the board in a bath of ferric chloride 
> and after rinsing, expose the PCB in the UV box for a further 
> 10 minutes. Wash of all the remaining etch resist in a tray 
> of sodium hydroxide solution.
> 
> 
> 
> On 26/09/06, Mike Harrison <mike@whitewing.co.uk> wrote:
> >
> > On Tue, 26 Sep 2006 14:40:57 +0800, you wrote:
> >
> > >how do you cut presensitised boards without exposing them...
> >
> > Guillotine or jigsaw/hacksaw. Boards come with stick-on lightproof 
> > film.
> >
> > >> Ive got line width as thin as 15mil in ultiboard.. will 
> this method 
> > >> be
> > >>> able
> > >>> to etch that thicness in the PCB... Or is there a better lowcost
> > method..
> > >>
> > >> Painful... difficult enough to make toner stick to a 
> glossy surface 
> > >> in the first place. Expect a lot of touch-up.
> >
> > With the UV photo method & decent board material, 
> linewidths & spacing 
> > of 10mil are easily achievable.
> >
> > >>> can ordinary inkjet be used instead of a toner from a 
> > >>> photocopier.. I printed an image using HP inkjet(reffiled 
> > >>> cartridge not the real hp
> > ink)
> > >>> on
> > >>> a transparency film and put it on a ferric chloride 
> solution for 
> > >>> over
> > a
> > >>> day
> > >>> now and it does not seem to dissolve.. although I have 
> not tried 
> > >>> to
> > etch
> > >>> anything from it, I was wondering if it could be used and if 
> > >>> anybody
> > here
> > >>> tried it...
> >
> > The copper should turn pink instantly on contact with 
> ferric chloride. 
> > If it doesn't there is still resist there.
> >
> >
> > >> Inkjet printer, inkjet overhead projector slide, small UV tube
> >
> > Tracing papaer works better than OHP slides, especially on a laser 
> > printer. Better opacity & adhesion, & cheaper. Results are 
> variable on 
> > inkjets from what I've heard.
> >
> >
> > For tons of info on making good homemade PCBs, see my page : 
> > www.electricstuff.co.uk/pcbs.html
> >
> >
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> 
> 
> 
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