Hi All,
As promised I am posting the conclusion to the etch problem I request help for and for which I received many suggestions.
I can now etch the boards without problems and get repeatably good results.
Here's what I did to improve the process.
1. Increased the exposure time in the UV LED Box from 4 mins to 5 mins as well as reducing the inter LED matrix spacings from 25mm to 12.5 mm. The LEDs are 3 inches from the board and originally illuminated as spots of light, they now give a more even illumination.
2. Kept the universal developer time the same ie 1 min
3. Spray with a small pressure spray and clean water.
4. Etch in hot Ferric Choride and use a small nylon toothbrush to scrub the last few spots of copper. Most of the copper is cleared after 8 mins with the remainder clearing after 10mins when using fresh etchant.
The result is a perfectly etched board with sharp tracks even etch and no traces of copper residue.
Many thanks for all your suggestions,
Pete
--- In Homebrew_PCBs@yahoogroups.com, "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
>