Home-made Circuit Boards




Once you're set up to make PCBs, at home or in the workplace, it's very easy. All of the tools you need to do it are quite cheap and readily available.




Here's a circuit that I needed to test LCD screens salvaged from scrap equipment. The software in the PIC communicates with the screen to see if it will accept data and commands.




Circuit board layout is some mix of instinct and style. For this simple board there aren't too many ways to go wrong. As there's just one major component, put that in the middle and draw outwards. The grid I use is run off on a dot matrix printer from a GWBASIC program. It's roughly a 0.2" grid or twice actual size. You could use a more precise one, but I've seen no reason to change this way of doing it for 20 years


Draw on the grid as you see the circuit. When you're happy with it, darken the lines and mark drill holes with a marker pen. Those spots will soak through to the other side and help you to not miss any drill holes. Flip the paper over and hold it up to the window. Trace from the back. This is a reverse image of what you'd drawn on the grid side, and is the pattern that goes down on the board as tracks. Add about 0.1" to the dimensions to allow for cutting and sanding. This one is 1.6" (41mm) x 1.9" (49mm) on paper and I cut it to 43mm x 51mm




Measure the board up and cut it. I prefer to use a bandsaw with a piece of mdf board to support the cutting area. A hacksaw is OK too, but it can wander. Belt-sand or file the edges straight and take the burr off with a file and sandpaper. I use 240-grit garnet paper as it's fine, lasts a long time and doesn't clog.




The board is sanded lightly to take the dullness off it. I've found that polishing it too much makes the tracks made by some "runny" etch-resist pens ball up. Drawing is easier with some patina and it doesn't seem to affect the etching process. Wash the board with hot soapy water and a nail brush and let it dry thoroughly. Put down the pads first as they're easy to remove with a modelling knife if you have any second thoughts. Next draw the tracks. If you get a track wrong, the cleanest way to remove it is to wait for the etch resist to dry completely and go brittle before you scrape it off. This can be done by putting it on a warm surface for a while. Pads can be drawn, just use a pin to make the small hole for the drill bit. On this board I had to make some tracks pass between PIC pins and used the smaller pads. Build up the small pad with etch-resist. If you don't there's the possibility that the drill bit will lift the whole pad off.



Tip - from time to time the felt nib of the etch resist pen dries out and drawing becomes difficult. Soaking it overnight or even for a few days in acetone gets all the old crud out and it's like new




This has always been my method of etching. It's a 1 litre container with about 10mm deep etchant inside a 2 litre container with very hot water. Some people use bubbletanks, and it seems everyone who doesn't (and uses a water bath like this) puts the board at the bottom of the etchant. I prefer to float my boards upside-down on top of the etchant. If you do it this way make sure the surface of the etchant is clean. One advantage of my way is that the etched copper falls off the board and there's no need for constant agitation. The surface tension is high enough for the board to float easily, and as the board becomes lighter as copper falls off, the board floats even better. It can sink though, so you have to be fairly careful putting the board in. Another advantage is that you can see through the board to see how far the etching has got. Plastic tongs or tweezers are needed - anything metal is corroded quite badly





After about 10 minutes the board is done. If it takes longer than that it's probably time to get new etchant. Wash it off in the heating water, and then remove the etch resist and pads with wire wool and soapy water. Check for any unetched holes in pads. If you find any, or want to make extra holes, a bradawl can be used as a fine centre punch to guide the drill. I've tried high-speed steel drill bits but don't think they're economic. They're a lot cheaper than carbide or cobalt bits, but they don't last long. My current 1mm tungsten bit has been in use for over 5 years now and has drilled many thousands of holes. Carbide and cobalt bits are brittle though, and you have to be very careful about the pressure you use. Any sideways bending will break them. As they're sharp, the weight of the drill is enough to get them started. If you're careful you can also use them at an angle to clean up any rough spots or unetched dots. You should use very little pressure to do this though as the bit is on an angle. 1mm is OK for all holes on most boards. The only others I use commonly are 1.2mm for the legs on preset pots, 1.5mm for some connectors and 3mm or larger (in a hand drill or press) for bolt holes










An alternative to "proper" etch-resist pens are the Sharpie felt-tip marker pens. This board shows test traces (top and right) drawn using a Super Sharpie 33101, which is not the finest tip in the range. Light-smudging has made the traces appear wider than they actually are. These would be around 10mil