Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

OK, I made PC boards in my garage back in the 70s. I used a variety of techniques.

First, you wonder how the copper got on the boards. Well, even back in those dark ages, you just bought them that way. The factory put the copper on them: I never even considered the possibility of doing it myself. Oh, they did sell pens that drew conductive lines, but I never trusted them so I did not even try them. It was a conductive paint, not solid copper.

You could buy either plain copper clad boards or sensitized copper clad boards. The sensitized ones had the photo resist already sprayed on them in a nice even coat. You needed a high density negative or positive, depending on the type of resist on the board. It was before the days of inexpensive computer CAD so I made 2 times actual size layouts using graph paper with a 1/10th grid of "drop out" lines. That means the lines did not get picked up on the negative or positive transparency which was the next step. I used drafting aids like black adhesive tape in various line widths and self adhesive doughnut pads and IC patterns. All of these were available from drafting supply stores. I carefully placed them on the grid with due care for trace separation. My primary tool was an Xacto knife.

Then that artwork was taken to a drafting or blueprint company who had a copy camera. That was a camera that had the lens, film holder, and art holders all mounted on floor tracks. It could make negatives or positives in exact geometric ratios. Since my original was 2X, I had 1/2 size negatives made. Of course, you could make your own negatives but then you had to work with 1X artwork on transparent plastic and a contact print frame.

Then the boards were exposed to either direct sunlight or a bulb that had heavy IR content in it's light. They were developed using a solvent solution and allowed to dry. Then placed in an etchant until the excess copper was removed. Then the resist was scrubbed off with steel wool or dissolved with a different solvent.

I also liked to use a tin plating solution to improve the solderability. Dip, wait two minutes, remove and rinse.

Finally, they were drilled with the various sized drills needed for the individual pads.

Or you could buy the plain boards and spray the resist on from spray cans. A company called Kepro had all these supplies, but they no longer exist.

Or you could use those self adhesive pads directly on the bare copper board to form the pattern on. This was OK for a one-off board, but tedious if you needed several. And the etchant could get under the traces where they overlapped a doughnut hole due to the height of that doughnut pad.

Another way was to start with the bare copper board (one side or two) and use a perf board to mark the pad locations. Then drill them. Then use a resist pen or a Sharpie marker to draw the foil pattern. Etch, clean, tin plate and use.

Others used other techniques. You could make a Zerox copy of the artwork and use an iron to transfer the toner to the bare copper board. I believe some people still do this today. Some retouching with a resist pen or Sharpie was generally needed.

Like I said, many ways, even back in that ancient era of the 70s.

I assume you are trying to do this in an authentic manner, but back in the 70s I usually saved the PCB process for boards where I needed four or more identical boards. If I only needed one, two, or three I usually used the Vector slit and wrap, wire wrap pens. I built many professional projects that way. I made wire lists and was very careful in making the connections properly. I never had a bad WW board.

Paul A.