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/109391378120539635298On 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