I made most of the printed circuit boards for the Pic-a-Star myself. I did get a few of them from Glenn, VK3PE, but the really hard ones to make, I did myself. The artwork for these boards were downloaded from the project group, so I didn’t design the boards myself, I only fabricated them. The process for doing this is what I’ll describe here.
The boards were made using the toner transfer process. This involves printing the artwork with a laser printer onto a medium that allows heat transferring the printer toner onto a blank copper clad PC board. There are several ways this can be done. Glossy magazine paper can be used as a transfer medium (the print on the paper won’t be a problem, though it can be difficult to see the outline of the laser printed image on top of the magazine print sometimes). Others have used various brands of glossy ink jet photo paper as a transfer medium. I have good results with the Techniks ‘press and peel’ transfer sheets, available from AllElectronics.com .
The toner transfer process is simple enough. Print the artwork onto the transfer medium with the printer set to a dark setting (but not so dark as to smear the image). Make sure that the artwork is a mirror image of what is actually required. You may have to use an editor such as Micro Soft Word, or Libre Office Draw to print the image, first using the editor to ‘flip’ the artwork from left to right. In the case of the PicaStar artwork, the image files were already reversed, and ready to be printed.
The circuit boards must be cut to size, and cleaned to perfection. There are many techniques that may be used to cut the PC board to size. Common tin snips work, but can slightly deform the edges of the board. You might need to cut them a bit over sized and then file the edges straight. Wear a dust mask when filing fiberglass PC boards, the dust is an asbestos like health hazard. I recently discovered a neat way to cut PC board easily. First score the board where it is to be cut using a Stanley knife. Use a metal straight edge to guide the knife blade, and make several light passes with the knife until you have cut all the way through the copper. Score the board on both sides. Now you can just snap the board cleanly along the score. I used a Harbor Freight bending brake to snap the board.
Use a fine grade of steel wool with a bit of kitchen scouring powder (Ajax, Comet, Bon Ami) and water to get the copper surface of the blank board clean. Dry the board, and then use some rubbing alcohol or paint thinner to remove your finger prints from the surface of the copper. Now cover the boards with paper toweling until ready to use. Cut out the desired image from the transfer sheet and place it on top of the board so it lines up. Use a hot clothes iron to press the image onto the board. Use downward pressure rather than an ‘ironing’ motion. You may need to experiment to find just how long you need to keep the iron pressed down on the transfer to get it set. Too much pressure may cause the image to ‘bleed’, closing up the traces. Not enough pressure and parts of the image won’t transfer. Allow the board to cool back down to room temperature before attempting to peel the transfer sheet off. If you are using the ‘press and peel’ sheets you can attempt a second pressing if you see an incomplete transfer when you peel up a corner. If you are using the magazine or photo paper you’ll have to run the board under warm running water to soak off the last of the paper, as it usually peels off in layers. Soaking the board in soapy water might help.
Now for the etching. If you are trying to make double sided boards (two artworks, one per side) we will do the entire process twice. Two toner transfers, and two etchant runs. Spray the other side of the board with some spray paint to protect it while you etch the current side. Ferric Chloride is the time honored chemical used to etch PC boards, but I’ve discovered a better way. I use a solution of Hydrogen peroxide and Muriatic acid (2 parts H2O2, 1 part Muriatic acid, pour the acid into the peroxide when diluting). Muriatic acid is a specific dilution of Hydrochloric (HCl) sold by swimming pool supply houses for PH adjustment. Etch the boards in a glass baking dish (some plastic containers may work too, if the plastic turns milky white from the acid it’s the wrong kind!). Slowly rock the container to agitate the etchant to speed up the process. The nice thing about using the HCL-H2O2 solution is that it is clear, you can watch the copper disappear and stop the process when done.
After the etching is done, rinse the board in cold water to remove all traces of the acid bath. Now drill out the board where required. If you are making a double sided board, you can just drill a few holes in the corners of the board. Remove the spray paint from the back of the board (double sided), and clean it like you did the first time. Repeat the toner transfer for the second side, use the holes to align the back side image with the front, perhaps using pins. Again apply the hot iron and transfer the image. Spray the front of the board with the spray paint to protect it, etch, rinse etc. Remove the spray paint from the front side, drill out all of the holes, and clean off what remains of the toner.
The final work is to clean up the board. You’ll probably find some traces that didn’t completely etch out, resulting in shorts between them. Remove these with a sharp hobby knife. You may also need to repair any traces that are open with fine wire and solder, but wait to do this until you are soldering your parts on the board.
To protect the copper from oxidizing we can ‘tin’ it. There are chemical solutions for doing this, but we can just use solder. Wipe the board with a paste flux, and then apply a very thin layer of solder to all the copper. I use a flat soldering iron tip for this. Apply a bit of solder to the iron tip and then wipe the board with it. A small amount of solder will spread over a large amount of the board surface before you need to add more to the iron tip (if you have first applied the flux to the board.) Done right, you won’t create any solder bridges, even between very close traces, the solder will tend to stick only to the fluxed copper surfaces.
Double sided boards require ‘vias’, ie plated through holes to connect traces on one side of the board with the other. For DIY boards, we just use jumpers, which can be the leads of our parts soldered to both sides of the board. The PicaStar artwork used both methods, the parts placement artwork showed which holes had to be soldered on both sides. This included some IC sockets. Augat sockets are raised off the surface of the board by individual pin sockets, they can be soldered from the top if there is enough spacing between them and other parts to get the tip of the soldering iron in.