Homebrew PCBs

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