As mentioned by Donald, heating your etchant helps a lot. I've lost the
link, but there was a white paper published by some company that suggested
that heating improves your speed without significantly increasing your
undercutting. Whereas agitating more causes more undercutting.
You could also choose to agitate certain areas more. I'm working on a
bubbler that has four different sections, each controlled by a different
valve. That way you can target the areas with more copper.
Sent from my iPad
On 2012-03-04, at 8:20 PM, Andrew Leech <coronasensei@...> wrote:
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.
> --
> ∗Plain Text∗ email -- it's an accessibility issue
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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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