Ok, this is really getting me down now. I have just had another failed board. These were the changes I made.
- I redesigned my circuit so that many areas were filled with copper pour, to minimise etching.
- To try and improve the exposure part of the process, I printed my circuit twice on 90gsm tracing paper, then stuck them together so tracks lined up perfectly. When holding it up the window it seemed very dark, was much better than how it was before. Before it seemed to let some light though when holding up to a window, however the toner is always uniform, with no patches. I would say doubling it up almost lets no light through, It seems totally black even when held against a bright window.
- I poured my ferric chloride into a bottle, I then added a little more ferric chloride to make it stronger, probably about 15 grams. I than gave the solution a good shake. I then poured this into a plastic tub slightly bigger than my pcb. This tub was then put into a large tray full of boiling water. This was to ensure that my etchant would stay hot. I also had the heater on, I work in a tiny out building which gets warm quick.
This was my procedure:
Exposure time:
5min warm up
4min exposure
Development:
Was in there probably for a total of 1min, maybe slightly less. I removed it when I the tracks were brown, and the rest looked salmon in colour. I did not see photoresist floating away like others say on this forum, but the solution does get slightly darker. I believe it must be working though, as the areas that were exposed to UV light became salmon in colour, while the tracks were brown in colour.
Etching:
I placed my board into my ferric chloride (which was being warmed up with the surrounding boiled water for about 5min). I then agitated the solution for about 10secs. 10minutes later I added more boiling water to the tray, to ensure my acid still kept warm.
Results:
There has been a slight improvement, there does not appear to be any precipitate issues, mentioned with my first boards. Plus pitting on the large strip of copper is minimal. However , all tracks appear to be attacked by the etchant, they look wavy like the tracks in the previous pictures I sent. The board is still in my acid. At this point I am started to think it is the acid, but at the same time I know it should actually work really well considering how fresh it is, and the added heat. So far its been in there about 2 hours, there is no green substrate showing, so no copper has yet been fully removed. Is the board still protected with photoresist?, is this why the acid has little effect?
What do you people think I should try next, what would you do in this situation? Comments will be very much appreciated.
Jay