I presume this is positive photoresist, in which case it looks like either
over exposure or transparencies that are not dense enough. Try adjust you
exposure a bit or double up on your transparencies if possible.
On Mon, Mar 5, 2012 at 12:45 AM, Pete <pete@...> wrote:
> ∗∗
>
>
> 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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