This is the first tutorial here so I’m experimenting with both the subject and the format. Also I am in the process of redecorating my electronics lab/former spare bedroom, which meant that everything was where I thought it wasn’t, and nothing was where I thought it was. Still I managed to keep track of everything long enough to etch a board and take some pictures. I hope they’ll be useful.
Breadboards and stripboard are both great for prototyping. They’re quick and easy, and if you make a mistake you can just remove things and move them around. However, they quickly become frustrating if you have to deal with anything which doesn’t use a standard square 0.1″ pitch for its pins. They also tend to gradually turn into jumper spaghetti if you’re building anything really complicated. Where stripboard is unsuitable it is useful to be able to produce your own PCBs with tracks and holes wherever you want them.
For the purposes of demonstration I made a breakout board for an RS232 connector. It’s simple and easy to draw the traces for (they just link each pin to its partner on the other connector), but still likely to be useful for most people if they make one themselves.
Parts and Equipment Used:
- Single sided copper clad board
- Ferric chloride
- Permanent marker
- Hammer and centre punch (or nail, if you’re as cheap as I am)
- Isopropyl alcohol
- Sewing needle or very fine drill bits
- Strip of nine header pins
- PCB mount 9 way D-Sub connector (RS232 connector)
Draw your layout in your preferred CAD software (I use PCB from the free gEDA suite). Print the solder layer and the fab layer. Be sure to disable the option to mirror the image as the printout will be placed the same way up as the board.
Mark out the outline of your PCB on the copper clad board and cut it to size with a hacksaw. Be careful of the dust; fibreglass and lungs don’t mix.
Cut out the print out of your fab marks and align it on top of the board. Stick it down with tape so it doesn’t move while you’re marking out the holes. Next use a hammer and centrepunch to mark the copper through the paper layout at all the locations to be drilled. I don’t have a centrepunch so I just used a nail. Unfortunately, on the first board I made for this tutorial, the nail I used had an irregular point, which meant the holes weren’t accurately positioned enough to fit the components. The more accurately you mark the holes, the easier the board will be to assemble and solder.
At this point you should be left with dimples where all the holes are to be drilled, like so
Clean the board thoroughly with isopropyl alcohol (or any suitable cleaning solvent, though isopropyl alcohol is probably the safest). Now, using the solder layer printout as a guide, draw on traces and pads in permanent marker, with a straight edge to keep the lines neat. If you have a laser printer you can use the toner transfer method to transfer toner directly from the paper onto the board. However, not everyone has a laser printer, and for simple boards it is often easier to just draw the traces on (though this makes it more of a DCB than a PCB). Black Sharpie works well as an etchant resist.
If you accidentally connect two traces, just run a knife between them to re-expose a thin line of copper.
You’re now ready for the fun part. The etchant we’re going to use is Ferric Chloride. FeCl3 is widely available and reasonably safe, although the resulting Copper Chloride is toxic. It’s considerably more toxic to aquatic life, so don’t pour it down the drain. I keep my etching waste in a milk bottle bottle and take it to the dump when it gets full to be disposed of properly. Use a plastic or glass container to mix the solution and etch your board in, as being etching fluid, FeCl3 will eat through metal. It’s also stains anything it touches rust coloured, so put down newspaper over any surfaces you care about.
Ferric Chloride can be bought either as granules or as a ready made solution. If you’re using the granules, you’ll need to mix the solution up yourself. Add 1 part Ferric Chloride to 2 parts warm water water by mass. Since 1g of water is equivalent to 1ml, this is the same as 500g of FeCl3 per litre of water. Don’t worry too much about the concentration so long as it’s Strong Enough. Stir it with something plastic until all the granules has dissolved.
When you’re sure the ink’s dry on your board, drop it into the solution and wait. How long will vary with the temperature of the water, size of your board and concentration of the solution. As a guide, the first board I etched in this solution took about 45 minutes. When I came to do the second, the water had gone cold and it took about 90 minutes. Agitating the container from time to time will dislodge any loose copper and mix the solution, which should speed things up a bit.
When the board appears to be completely etched, put on some rubber gloves and fish it out. If there’s any sign of copper where you don’t want it, dunk it back in and wait a while. If not, dunk it in water and rinse off all the nasty iron and copper salts. Dry it off and use cotton wool soaked in isopropyl alcohol to remove the ink from your new copper traces traces.
For components with rows of pins, there’s not much room to spare for soldering. This leaves even less room for the holes. 0.8mm is the most common hole diameter on professional circuit boards, but bits that fine are very expensive and liable to snap when used with a hand held drill. You can get away with slightly larger holes; mine were about 1.2mm; still pretty fine. If you don’t have any drill bits that small you can use a sewing needle in place of a drill bit.
Place the board on a scrap block of wood and tape it down. Very carefully align the point with each of the dimples you made earlier. Start by running the drill slowly until the it has made a hole sufficiently deep to hold the bit in place, then spin it up until you’ve drilled all the way through. Again run it slowly in the opposite direction to remove the drill without damaging the copper pads. Clean up the holes with fine sand paper.
N.B. Needles when used for sewing as intended are unlikely to end up in your eye, unless you have some serious issues with your sewing technique. Needles spun at 2000RPM under stress are less predictable, so don’t drill too fast, and wear always wear goggles.
The final stage is to populate the board with components. If you have marked and drilled the holes with superhuman precision, the parts should just drop into place. Otherwise, you may need to use some force to push them in, or get the drill out again to enlarge some holes. Try to avoid bending the pins.
When a component’s in place just solder it up in the usual way. I find soldering homemade PCBs quite difficult because of the gap between the pins and the pads caused by my improvised drill bits.
Check for any bridges (in the solder or the copper) with the continuity tester on a multimeter and clean them up with de-soldering braid and a craft knife. If all’s well, take a picture. You just made an rs232 breakout board!
I had to trim mine off with the hacksaw because there was too much of an overhang beyond the header pins and it got in the way on the breadboard. Other than that it seems to work pretty well. It’d work better if they still put serial ports on computers, but that’s a rant for a different post.