Part 3 – Creating the circuit board
[ Note: There is an update on this process on Coprolite here that includes pictures and instructions for using a new press that is available. ]
The first step to creating the circuit board is laying it out electronically. We use PCB, a program that runs on *NIX operating systems. If I was doing this for Windows, I’d probably use ExpressPCB. If you want to etch your boards yourself rather than order the boards from ExpressPCB, here is an article on just that. There are some good general tips as well that may help you with PCB-generated circuit boards. Here is a screenshot of PCB with the Cat5 cable tester circuit, here is a pcb file of the single board, and here is a pcb file of four boards at once. If you would rather not fiddle with the design, here is a postscript file of the single board, and here is a postscript file of the four boards at once. To print these out, just run on a *NIX box:
lpr cabletester.four.pcb.ps lpr cabletester.pcb.ps
I’m sure there must be an easy way to print this on Windows. Cygwin has Ghostscript, maybe it can print these files.
The next step in creating the circuit board is to apply resist to the copper board before etching. This resists ething when you put it in a both of etchant that eats copper. There is a cool product called PnP-Blue, available from Techniks that lets you print off your circuit board on a laser printer with a special film. You can then iron the film onto the circuit board with a regular clothes iron, peel off the film, and etch the board. Recently, our laser printer started jamming. We solved this by taping the film to another piece of paper, leaving just a narrow strip of paper at the top. We use dry Ferric Chloride for etchant and mix it ourselves. You can get the stuff pre-mixed from Radio Shack. We also use Tinnit to tin the boards. Tinnit is a brand name of Datak part No. ER18. All Electronics has both items. Now, for some pictures:
Loading the PnP film
Ironing. Notice that the lines aren’t dark
Wiss M-300 scissors are the best for cutting circuit boards You can purchase them here. I got mine at Home Depot.
There are five parts to this article:
Build Your Own Cat5 Cable Tester – Introduction