The Geotechnology Page: Misc: Word Processor Layout

Word Processor PC Board Layout

Carl Moreland

Fabricating a PC board has become much easier thanks to the transfer film, but how do we get the PCB pattern? Most of the projects that are posted on this web page include PCB patterns that are ready to print, with the possibility that they need to be inverted before printing. But you can also make your own PCB pattern. Do you need expensive layout software for this? Not necessarily, as almost any single-sided board can be laid out using a common word processor, and even double-sided boards if you are careful and patient.

The image below shows a PC board layout using a word processor, in this example Adobe FrameMaker. To use a word processor for layout it must support two things: basic graphical drawing tools, and a 1/10 inch snap grid setting. Note that the rulers in the picture below are set to 0.1 inch; the actual snap grid was 0.025 inches (25 mils). This allows you to route between 100 mil IC pins.

To begin the layout I created simple donuts first, then the oblong donut was arrayed into DIP footprints. I then routed the traces with the line drawing tool and created large filled areas with filled rectangles. One thing you want to use (if your word processor supports it) is lines with rounded ends instead of squared ends. The picture to the right illustrates how rounded ends make cleaner looking junctions. If you only have squared ends available then you can either restrict yourself to manhattan routing (90 degree junctions only) or you can simply not worry about it as it is only cosmetic.

One thing you do not get with a word processor that most CAD packages offer is schematic verification. Therefore, you must carefully check and re-check your layout to ensure correctness. In my first attempt above, I missed connecting two leads of one of the 8-pin DIPs. Another potential pitfall of using a word processor is miscalculating the footprint of a component. The footprint includes not only the solder pads but also the perimeter outline of the device. The perimeter is often larger than the pad placement; a good example is an electrolytic capacitor where the leads might have a 200 mil spacing but the body has a 500 mil diameter. You must leave enough board space for the entire component, and consider that some brands of components are physically larger than others.

So for fairly simple mostly single-sided PC boards a good graphical word processor can do the job with proper planning and care. If you plan on doing several layouts, or ones that are multi-layer or complex, then it is best to invest in a good schematic and layout package. For this, I can offer no advice.