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°C 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.