On 13 Apr 2016 12:58:28 -0700, you wrote:
>Way back in my hand taping days before CAD layout tools, we would lay a board out using Mylar film, ruby tape and Bishop dip and doughnut pads. This was done at 2:1 then sent to an industrial photo house to be reduced 2:1 on lito-film. IIRC it was about $20 to $50 for a set of negatives and more if you wanted a set of contact positives.
There were two ways of doing this. One was to use black donuts and
black crepe paper tape. This would work well with one sided boards.
The other method was to use the black crepe for the pads, and then red
transparent and blue transparent tape for the other layers. Red tape
could be shot with Kodalith, because it was sensitive to blue only and
red was no light (hence opaque). Blue tape was shot with panchromatic
film with a red filter (making the blue drop out). Panchromatic film
was sensitive to all colors.
>I saved some cost at home by doing my own contact positives. Making the contact prints was fairly easy -- just a couple pieces of glass to clamp the films together, a darkroom safe light, some slow litho-film, developer and fixer. Took around 20 minutes to do the entire process. The positives were used with boards spin coated with Shipley AZ111 positive resist, exposed then etched. Turn around for the photo house was 24 hours but you could pay for 1 hour service if you were in a rush. Eventually all the photo houses switched over to laser plotters once PCB CAD systems became available. Even the photo plotting houses went by the way side
>once the PCB fabricators started to accept digital Gerber input files.
And it took a bit to get there. Good computers and all sorts of
stuff.
>
>You can still buy litho-film, the developer and fixer from places like Freestyle Photographic Supplies. Though the web site seems to be down. The ideal thing would be to build your own photo plotter
Or do toner transfer, or send out to China for the boards, etc....
Main problem is the sensitized board, which can be a bit dear.
Harvey
>
>Criag