• Mikes Tips - Making PC Boards

    MyCockpit ® Presents "Mikes Tips" by Mike Powell

    Making PC Boards

    Printed circuit boards are not necessities for most of the projects we work on, but they sure are nice. PC boards ease construction, boost reliability, and add a professional appearance to projects.

    I’ve been a long time proponent of the do-it-yourself approaches to making PC boards, but the relatively low cost, zero mess, and high quality work of commercial board houses is winning me over. Here’s a high altitude overview of how easy it can be.

    I’ll use ExpressPCB as an example. There are other companies that will make prototype quantities of boards, but I’ve use ExpressPCB several times and never been disappointed.

    Commercial board manufacturers make the boards based on information in design files provided by the customer. The customer creates those files using a PCB design software suite. ExpressPCB provides an easy to use design tool for free. It’s much simpler than commercial design software, but more than adequate for our purposes. Plus, it has the advantages that we don’t need to worry about file formats, or contacting the sales department for pricing and scheduling. The ExpressPCB software takes care of all that for us.

    You can download the design software from the ExpressPCB website, www.expresspcb.com. Start it up, and this is what you’ll see:

    The yellow rectangle represents the board outline. When the program is opened it defaults to the specially priced 3.8” by 2.5” “miniboard” service. You can change the size, of course, but the cost per square inch will be a bit higher.

    At this point it helps to have a specific project in mind. We’ll use the switching light dimmer from an earlier Mike’s Tips article:

    Start by inserting pad and package outlines for the components in the schematic. The ExpressPCB software incorporates a small component library that has what we need. You’ll end up with something like this:

    Now you can do the actual layout. This involves adding connecting traces between component pads, and moving components around to minimize the lengths of those lines. Layout is not terribly difficult, though it does take a little patience when you first begin. The Help function on the ExpressPCB toolbar provides a tutorial.

    The next image shows the finished layout. I made some of the traces wider to handle the larger currents expected in portions of the circuit. I also placed some of the text on the top copper layer. I chose not to pay for the yellow silk screen layer. By placing the text on the copper layer, I got connection labels at no additional cost. The board design was compact enough that I was able to place two dimmers on a single “miniboard”, saving a little more money.

    With the design complete, I ordered the boards by clicking on the Layout option in the toolbar. ExpressPCB asks for shipping information, which options I wanted, and of course a credit card number. A few days later a package showed up at the house with three of these in it:

    The ExpressPCB software is proprietary which effectively ties you into using ExpressPCB to make your boards, but there are other companies which offer competitive rates for small quantities of boards. You’ll need to use board design software which can export non-proprietary file formats, though.
    CADsoft Eagle is a printed circuit board design suite widely used by hobbyists. It’s more powerful than ExpressPCB, and is capable of producing industry standard output files which can be used with any commercial PCB manufacturer. Not surprisingly, it’s payware, though a reduced functionality freeware version is available. The CADsoft website is an informative resource. www.cadsoftusa.com
    The Sparkfun Electronics website is another resource for tutorials (and parts). www.sparkfun.com
    While pulling references together for this article I ran across the DesignSpark PCB design suite. It claims to be the latest, greatest, FREE design suite, and it might be worth a closer look. www.designspark.com

    Mike Powell, author of

    Building Recreational Flight Simulators and

    Building Simulated Aircraft Instrumentation.