Resonant Frequency: Article Archive

Making circuit boards is an important part of your diy-synth project. Making a 'junk' board is frustrating and time consuming, so it's best to prepared for it, and do it right the first time. There are a handful of techniques below that you can try.

Pre-made Pad-Per-Hole boards

The easiest method of making a circuit board is by buying pad-per-hole boards, and simply bridge the gap between pads to make connections. You simply add solder to one pad, and pull the iron slowly to the pad beside it, and it will bridge the gap. I generally use this approach if connecting only 2 pads together that are side by side. Some solders seem to have too much flux, and it makes this difficult. The flux puddles in between the pads, and makes it more difficult to bridge.

If the bridge will span more than 2 pads, I use a piece of small, single strand wire (like the scrap from a resistor or cap lead) and solder it along the path of the trace I wish to build. I attach it first to the start and end, So it is tight to the underside of the board, running perfectly straight up a row of pads. Then you solder along the whole wire to each pad in the line, making a continuous bridge of solder.

Just as a note, a pad-per-hole board (for those who aren't familiar with the term) is the experimenter's circuit board that has a small square pad around each hole, with no two adjacent holes connected. You should also consider other designs of premade boards. There are many types that have a few busses on them for power distribution or ground, that you may find useful.

Drawing Circuits With Etch-Resist Markers

Here's where the real fun starts... etching your own custom circuits. For fairly simple circuits, I prefer this method of layout. My power supply board, for example, was etched in this fashion. Here's how it works....

Layout your circuit on paper exactly as you'd like to lay it out on the board. It my take some time to place the components in the most efficient locations. Try for the least number of places the circuit traces must cross; every crossing must be made by running a jumper across the top of the board...which is undesirable. Double check your design... if you forget a trace, it's a hassle.

Next, cut off an appropriate sized piece of copper-clad board. You can use a jeweler's saw, or even a hacksaw or coping saw. Scrub your board under running water with a mildly abrasive pad (but NOT steel wool - a "Scotchbrite" works well). You want to clean it until all of the oxidization is gone, and the board is nice and shiny. Copper board is available from Radio Shack in the US, as well as tons of mail order places.

Now, you draw the circuit onto your clean copper board with a Sharpie (by Sanford) felt tipped marker. This marker is resistant to the etchant, and prevents it from dissolving the copper from beneath it. Make sure your traces are drawn in nice and dark, to make sure you don't get any bad spots. Here's where the problem lies with this method. Drawing with a marker is not a real precise art. It's difficult to use this method with circuits using DIP style IC's, for example. It CAN be done, but there are better ways for these instances. Now, it's time to etch your board; there's more on this later in the article.

Rub-On Transfers

Just for giggles, I picked up a package of rub on circuit traces from Radio Shack, and whipped up a board with them. These look like a sheet of waxed paper with black pads on them, and some straight traces. You put these pages on a clean board and rub the back with a pencil to transfer the black etch resist onto the board. You put pads where they're necessary, then connect between them with the straight traces provided. The nicest thing about these are the small dots in the pads to line up the drill holes, and the fact that the pads are properly spaced for IC's. Also, the type I bought had larger pads for wires that leave the board. These allow you to drill a larger hole to accommodate the wire more easily, and there's enough pad remaining to not worry about jeopardizing the strength of the joint. The set also had pads configured in a triangle for transistors.

Let me tell you, though, that I don't really like this method of layout in general. These rub on transfers are difficult to use, ESPECIALLY the straight traces. I've had bad luck with several boards I tried with this method. I will sometimes layout my boards with a hybrid technique, and use the rub-on pads to correctly layout IC locations on an otherwise hand-drawn board. This seems to be the most useful purpose for these in my experience.

Iron-On Transfers

Techniks makes a product called "Press-N-Peel". It only costs about $2 per letter size sheet, which can make several smaller circuit boards. You simply put the toner sheet over a clean board and iron it on.

The smallest you can print for this method seems to be about 10 mil, although finer lines are possible. The practical trace width limit, seems to be about 12-15 mil traces.

The major drawback is the fact that the toner will bleed if you leave it under heat too long... you may want to leave extra space between traces to account for this possibility. Fortunately, if you make a mistake ironing, you can simply clean the board with a solvent, dry it, and iron on a new sheet. For a heat source, you can use either an iron, or an office laminator (which supposedly provides better results).

After the transfer is successfully ironed on, look for any shorts, and scrape them to break the connection. When you're satisfied with the look, you can then etch your board.

UV Sensitized Boards

The final method of making PCB's is to use presensitized circuit boards. These have an etch resist coating that is attacked by UV light... so if exposed to light, anywhere the board is shadowed the etch resist will remain.

To build these at home, you have to lay the boards out on a computer, and then print your design on transparency material. Note that different types of ink will work better than others, so you'll need to experiment a little (or ask someone who's made a lot of these types of board). Also remember that this must be printed to scale so IC's will fit properly.

You then place your transparency over the board, and expose it to UV light. You'll need to affix the transparency in a low-light area to avoid exposing the boards. Also, you MUST be sure the transparency won't lift or move...this will blur the design, and probably make it unusable. You may use bug lights, tanning lights, or sunlight as a UV source, and you simply let them sit out and soak up the rays. Now you just etch, and you're done.

Etching and Drilling

Now that your circuit is done, you should double check it again. There's still time to fix a mistake, before you etch. Once you're positive the circuit is ok, pour about a 1/4" of etchant into a flat plastic or glass container. Etchant is available at Radio Shack, and most mail order electronics suppliers.

Dip your board in, copper side down, and go get bored for 45 minutes. I use tongs to flip my board occasionally to look at it and check the progress. It should be fairly obvious when the etchant has finished dissolving the unwanted copper. You can then remove the board and wash it under cool water. Dispose of the used etchant...it can only be used once. Make sure you don't leave it laying around, because it's hazardous stuff.

Now, it's time to get out your little drill and drill the day away. You need to drill through all of the pads for your component leads. I use 0.8 mm bits for components and 1.0 mm for wires and larger posts (For those of you that are not metric-minded, that's a #67 drill bit or .0320" for components and #60 drill bit or .0400" for wires) IC's can be fun when you first start... it takes a little practice and skill to get the holes exactly right. I use a Dremel Tool with the mini drill-press that goes with it. It makes the tool more stable, and more precise. I've even heard of people mounting a rifle scope on the tool to zoom in at the tip of the bit for more precise drilling.... a little exotic for my blood, but should work well.

What if one of the traces is not connected? If there's 1 or 2 bad traces, it's still possible to fix the board. If the gap is small enough, you can simply bridge it with solder. If the gap is too big, you'll need to jump it with wire. I usually drill a hole in either end of the missing portion of the trace, and jump across the gap. You can also solder a wire bridge to the bottom.

Other tips...Using a heated etchant will speed the process up. You could etch in a pyrex baking dish, for example, and keep it warm on an electric warming tray. I've heard other people recommend heating VERY GENTLY on the stove, but I've never tried it. Remember never to let it get hot... only warm; you'd never want to risk boiling it. Also, agitating your etchant really helps the process. Try using an aquarium air pump and air stone to keep the etchant circulating in the tank.