Homebrew PCBs

Leon wrote:
> I've just noticed something that might be useful to other people using 
> pre-coated boards.
> 
> I was using up some rather old off-cuts while I waited for some new material 
> to arrive, without much success. The new material arrived this morning and I 
> noticed that the faint yellow pattern on the resist after UV exposure was 
> much more noticeable than it had been on the old stock.
> 

They could be a different brand/formula photoresist. could you explain 
what problems you had ? Is it negative or positive resist ?
Was it a exposure, developing issue, or copper residue problem. The only 
problem I've experienced with aged resists (>2 years) is a stubborn 
residual invisible film left behind on the copper surface after 
developing. It requires rigorous developing to remove it, and etching to 
remove the rest.

Adam