Homebrew PCBs

I've also seen this exact problem from under exposure.
If possible agitate / rotate board (or leds) during exposure, to ensure 
even coverage. You may need to experiment with exposure times more, I 
had to do this quite a bit with my home made uv ccfl box.

As a last resort, when you get to a stage of only having a little bit of 
copper left on an open area you can spot-etch it:
Pull the board out of the etchant and give it a rinse.
Put on rubber gloves and dip a bit of sponge into the etchant, then just 
wipe that gently and repeatedly over just the under etched area to 
finish it off. Alternately you gan buy a sponge-on-a-stick from a craft 
or paint supply store, hardware stores often have them under painting, etc.

Andrew

On 5/03/2012 1:53 PM, Donald H Locker wrote:
>
> I'd say a process problem. Agitate more often and more vigourously. 
> The stripes are from the glass beneath the copper - the copper I 
> believe is slightly thinner over the glass strands so etches faster 
> than the slightly thicker copper surrounding it.
>
> Try continuous agitation (rocking the tray) and warm FeCl (it will 
> etch faster than 16 min) and see what happens.
>
> HTH,
> Donald.
> --
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>
> ----- Original Message -----
> > From: "Pete" <pete@... 
> <mailto:pete%40ridcom.fsnet.co.uk>>
> > To: "Homebrew PCBs" <Homebrew_PCBs@yahoogroups.com 
> <mailto:Homebrew_PCBs%40yahoogroups.com>>
> > Sent: Sunday, March 4, 2012 5:45:40 PM
> > Subject: [Homebrew_PCBs] Etching problem - Help please
> > Hi,
> >
> > I am trying to etch a small PCB and finding it etches unevenly leaving
> > a small area of copper which is stubborn to remove. Just leaving in
> > the etchant for longer starts to undermine the tracks that etched ok.
> >
> > Here's what I do:
> >
> > 1. Print the track layout on inkjet printer using transparency film.
> >
> > 2. Lay the film ink side down onto a 3" x 2" single sided photo resist
> > coated copper clad board (cut from a Maplin Size 4 ref KU14)
> >
> > 3. Expose in a home made LED Light box for 4 minutes
> >
> > 4. Develop in Universal Developer (PBD2) Sodium Metasilicate for 1
> > minute.
> >
> > 5. Etch in Ferric Chloride track side down for 16 mins, agitating
> > every minute or so.
> >
> > The result is most of the copper dissolves after 10 mins then it
> > leaves a small area which refuses to disappear after waiting a further
> > 5 minutes.
> >
> > A photo of the etched board is here
> >
> > https://picasaweb.google.com/109391378120539635298
> >
> > On close inspection of the board the unetched copper is left as
> > stripes. So I am wondering if this is a board problem or the process.
> >
> > Any help is appreciated.
> >
> > Thanks
> > Pete
> >
> >
> >
>



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