The Printed Circuit Board

This is a very component-heavy project. It's looking like we'll need a printed circuit board. Hand wiring 4 12-segment displays with driver transistors both upstream and downstream would be possible, but pretty horrible. When I realized this I figured this project would be a good way to get some practice making printed circuit boards.

How I make boards

In the ancient times, the early 1980s, I made a few boards for my high school electronics class using Radio Shack's PCB kit (cat. no. 276-1576). This consists of a couple of bare copper boards, a Sharpie felt-tip pen, some etchant, and a 1/16” drill bit. You draw the PCB artwork directly onto the board, soak it in the etchant, and voila! After drilling and soldering you have yourself an honest-to-goodness electrical circuit! For the sort of stuff I made back then the kit worked pretty well. The teacher didn't require us to buy the kit, but I wanted to try it out at home.

These days much more sophisticated methods are available to the hobbyist. There is a surfeit of web pages out there about how to make your own circuit boards. They're all different, so I figured this must be one of those things that takes some experimenting. The thing that finally prodded me into making my own boards was a very beginner-friendly essay about the process on David Cook's excellent Robot Room website. The method I used for the Roman Numeral Clock board is similar.

Here's a quick run through the steps I took (click thumbnails for larger images).

	I made the pcb artwork with ExpressPCB. The linked image is a scaled-down version of the pcb artwork - the real thing is quite a bit larger, since it's at 600dpi. This version won't work to make a PCB! In the unlikely event that you want a copy of the real artwork, email me.
	Once the artwork is settled down, I print it onto “Press-N-Peel Blue” from Techniks. I've used this stuff successfully for several projects, but the ironing-on process is tiresome so I bought a laminator (a GBC HeatSeal H200). Linked is a picture of the laminator, the post-peel piece of Press-N-Peel Blue, and the etched board. The pen is for fixing gaps in the transfer. There were only 3 tiny gaps in this board, much better than I ever did with the iron-on process, and after I experiment more I bet I can achieve gaplessness. This was my first project using the laminator, and I'm quite happy with it. Even a dog hair (where could that have come from?) under the Press-N-Peel Blue was unable to mar the board, once I pulled it out and ran the board through a couple more times.
	This image is a somewhat blurry closeup of the etched board. The traces are dull because the laser printer toner is still stuck to them. You can clearly see the parts of the board I had to touch up with the pen.
	Here is the tinplated and drilled final product, ready for soldering. Tinplating isn't necessary, but it makes soldering a lot easier. I use “Tinnit” crystals from Datak. They're available from several online dealers. Beware: plating with Tinnit is a smelly process - the solution must be heated and emits a billowy sulphurous ponk like the Yellowstone geyser fields. Be sure to have good ventilation. For drilling I use a Dremel drill press and a #66 bit. It behaves beautifully, especially if you prepare your artwork with holes in the pads. The etched-out holes act like a tiny counterpunch which leads the drill bit where it's supposed to be even if your aim is a bit off.
	Soldering begins! This first step shows the Poor Man's Double-sided PCB - I designed the board as a double-sided board, trying to minimize the number of traces on the top layer and making sure they were all straight and not less than 1/20 of an inch apart. Then, I made the board with only the bottom layer, and used wires for the top-layer traces.
	And here is the board with all components mounted except for the CMOS shift registers. Considering how quickly I designed and built this board (two weeks' hobby time - one preparing artwork, one making the board, tinning, drilling, and soldering), it seems to have come together quite nicely. The displays are snapped into single-inline machine pin sockets I made by cutting up some 18-pin IC sockets. The nice thing about socketing them was it allowed enough clearance for the wires to run underneath; the downside with machined pins was that it took a lot of pressure to snap the displays in and I worried I'd break the board.

A note on the type

If you like the font I used for the board label, here it is (27K Zip, TTF, freeware but copyrighted). It's called “Rogers” and was made by Eric Grunin. I use it for everything.