Circuit Boards and Rubylith: History Lesson for Today
What is Rubylith®?
Rubylith® and Amberlith® are two layer films that
are used in the photographic industry and are common in
silkscreening. To use either, you would punch registration holes in two sides, and register the film over a copy of your
original artwork, colored layer up. The artwork is visible through the film. You cut the top layer around the border
of a colored area on the original, and remove the section of the colored layer, exposing the clear layer. If you make a
silk screen from that, the area you leave on would pass paint, and the area you peel off would have no paint. I personally
think the pinacle of that process is the back board on a pinball machine.
How do you make a PC board from it?
If the artwork you lay the Rubylith over is a 1:1 PC board artwork, and you cut on the lines, removing the areas where
you want copper, and leaving the traces red, you will have made a positive of the artwork. That positive is then used to
make a silk screen. The silk screen is used to squeegee on the resist to a million panels of boards. Even though Rubylith
is initially expensive, it turns out to be very cheap on a per-part basis, since the silk screen can make many boards
before needing to be remade.
Layout the PC board with a 1:1 drawing or stickon pads.
Lay the Rubylith over the original artwork.
Cut the top layer, exposing the clear backing.
Peel off the colored layer where you want no copper.
Use the resulting two-color image to expose a silk screen.
Resolution is based on how small you can cut the traces, and in practice, it isn't easy. There is a minimum width of
trace that can limit the resolution to 25 mils or so. In practice, that was the kind of resolution I saw on boards made
with this process, anyway. I did attempt to make a board with Rubylith many years ago, but lacked the experience to
pull it off. Some things are best left to the experts.
The most ambitious project I have ever seen up close was an integrated circuit mask made from
Rubylith. It was the size of a wall, it seemed.