Homebrew PCBs

nps0 wrote:

>  
> 
>>The difficult part is finding a cheap printing press rubber 
>>roller. One of the rollers can be hard, like that from a old dot 
>>matrix, inkjet or laser printer.
>>
> 
> Possibility:  old washing machine wringer rollers (remember when?) 
> or maybe industrial mop wringer rollers.  Just a thought.  

I haven't seen these rollers around. Ink rollers are precision 
molded and very smooth. Any lumps on the rollers will cause 
"dents" in the film. I got two secondhand rollers from a rubber 
roller manufacture. There are several manufactures around my city 
Melbourne, Australia. They all seem to make custom rollers, since 
each roller is different for each application so there is no such 
thing as an off the shelf rubber roller. I was lucky they had 
some old rollers laying around the factory floor. It turned out I 
only needed one rubber roller while the other could be any 
material/diameter, such as one scavenged from a desktop printer.

Another possibility is to get some rubber sheet feed that between 
  the film and a rollers. Then two hard rollers could be used. 
The idea would be to wet the film and rubber. Place film on 
rubber sheet so it adherers with water surface tension, i.e no 
wringles and completly conforms to surface of rubber sheet. Feed 
the rubber sheet with film into the rollers with the PCB and push 
it through. It would be much easier to have a handle on the shaft 
of one of the rollers so it can be wound by hand.
Hard rollers from printers have good precision and should work 
very well.


The film has clear protective layers on both sides. One 
protective side is made from mylar, and it is made very thin so 
photo mask can sits close as possible to its surface and avoid 
light undercut. The other side is polyethylene which is no 
different from cling food wrap. The protective polyethylene film 
is removed and it is this side of the resists which goes on the 
copper. The mylar film must remain on the other side of the 
resist since it must be present during UV exposure. Apparently 
atmospheric oxygen inhibits the photo polymerization of negative 
dry film resists.



> Wouldn't like to part with a little of that old film, would you?
I can give you a meter or so x 220 mm width, email me to discuss 
postage details. I haven't tried obtaining the data sheet. Its 
standard aqueous processable resist. Developed in 25 to 35\ufffdC 8 to 
10g/L Na2CO3 in tray with gentle wipe with paint brush. Stripped 
in room temp 20 to 80g/L NaOH, tray or immersion tank, soaked for 
2 to 10 minutes or until all resists lifts off copper, depending 
on temperature and period of time has been on board.