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PCB developing times

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Simon:
Hi guys, I made up a board last night but over etched, the previous board was fine but this one I did not leave as long in the caustic soda, maybe this was the mistake as it did not remove all the unwanted photoresist ? or coukld the etching solution be exaustng. i'm always worried about over developing the photoresist and ruining the board, but am I going the other way ? A comercial chemical recomends 30-60 seconds, i'm sure I was in at least this long

ElektroQuark:
Hi:

I use the Bungard boards. The user guide stand that the developing time is about 30-60 seconds but the photresist could be in the developer for about 5 minutes without been damaged.

Can you post some fotos of the etched PCBs?
Also, describe your procedure, including times and products used.

Iñigo.

mikeselectricstuff:
Don't  use caustic soda (NaOH). Use a silicate based developer.
Silicate has a HUGE margin between 'develop' and 'strip', making concentration and temperature much less critical than NaOH. It also has infinite shelflife, whearas NaOH tends go off after a while. 
You can make silicate up so strong that it will develop in 10 secs but not strip for a couple of minutes. Different makes of laminate do vary significiantly in their develop time.
A stronger developer also makes it easier to see when developing is complete. Wiping gently with a dry paper towel is a good way to remove the last traces of developer & gives cleaner trace edges. 
To tell if it is fully developed, a quick dip in ferric chloride will turn developed PCB pink instantly.
See my PCB page for lots of tips on making good PCBs

Simon:
Well I used a LED UV box i made myself and exsposure seems to be from 30-60 seconds, I think 45 is a good average value, i like to make sure it's well cooked but I've noticed that there are some tiny holes in the film printout and these have been etched so maybe I'm over exposing.

them I put a normal (eating) spoon of caustic soda in 1 litre(ish) of water and develop until the traces are nice and sharp and maybe a bit more (I was dubious about rubbing in case i damaged the tracks but that sounds like a good idea)

then I go into the etchant for maybe up to 5 minutes.

I think my problem might be over exposure and under development

Simon:
I think i also need to get a cheapy inkjet printer as my gel printer is not too good on printable film

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