Matthew Smith wrote:
> Quoth Adam Seychell at 2008-06-05 18:23...
>> 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 - I'll fire the same question back at you - with which brand did
> you have this specific problem - Kinsten? If so, I'd be interested to
> hear as I've got a load of "mature" Kinsten stock that I'm about to use,
> having been out of the game for a couple of years.
>
>
I think the resist was Macdermid brand, negative active. I got a roll of
it several years ago and apply it myself. Because I develop the PCB
almost immediately after applying, I never have the residue problem.
Apparently the professionals never leave resist on any more than 24
hours or it becomes too difficult to develop.
The only way around the problem is to develop about 2 or3 times longer.
If its really bad then the resist will get damaged due to excessive
developing before all the residue has had a change to be removed.
I develop in 1% NaCO3 30~40 deg.C as you do for all negative resists. I
I use a paint brush for the scrubbing.
The problem I found is the residue is invisible so it looks like the
developing is complete. But when you go to etch , the photoresist
residues are quickly revealed by un-etched copper areas.