Homebrew PCBs

gmc_za wrote:
> 
> I've read a million post on the net about how to create a pcb with 
> photosensative spray, and UV light and after about 30 failed attempts 
> I'm almost ready to give up.
> 
> If someone could please check my method and advise me where I'm going 
> wrong:
> 
> 1) Clean pcb - this is not a problem as its really shiny afterwards 
> with no oil on etc

Make sure there is no oil by seeing if a coating of water "beads" on it,
or stays flat.

> 2) Spray with photoresist. I've tried various thicknesses from almost 
> see through to a nice clear purple film on the board. Left it to dry 
> for 24 hrs.

Only enough to give a "sealed" smooth surface is needed.

> 3) Created a artwork on tracing paper  (90 gsm) with a deskjet 
> printer.

Do tests without the tracing paper and using a strip of cardboard
to make the shadow pattern on the pcb.

> 4) expose using uv lamps - ive  tried various exposure times. 4 mins 
> seems to give the best results.

> 5) My caustic soda solution is 3 teaspoons to 1.5L water. Again this 
> is from trial and error and sometimes seems to give the best results.

Buy the developer to eliminate a variable from your tests. Then ditch
the spoon and buy scales.

>>From the 30 attempts I've had - one board was almost usable. The 
> problem is that nothing seems consistent. One day I'll create a pcb 
> and all of the photo resist gets removed in the CS, the next day with 
> the same quantities, the outsides of the board gets removed - the 
> purple photo resist film toward the middle of the board refuses to
> get 
> removed. I've even tried rotating the board under the UV light. 
> 
> Help!! Does everyone else have hassles like this? Is there any method 
> I can use to produce good pcb's every time.

Usually it's problems with cleaning all the oil off or incorrect
developer.

I get %100 consistancy from spray-on PRP (green).