PJRC.COM Offline Archive, February 07, 2004
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Printed Circuit Boards
Introduction
selected Layout Artwork
Consumables

Complex CAD Software vs Simple Paint Programs

While you can use a very expensive CAD program to produce your layout artwork, a simple paint program such as MacPaint or PC Paintbrush will also work nicely. For an occasional prototype, the time and trouble spent manually routing and drawing the wires in a conventional paint program may be less than the headaches involved in configuring CAD software, defining libraries, getting it to understand the design rule of this process and all the other hidden costs of typical CAD software. Whichever you use, the ultimate goal is simply to print your artwork onto a semi-transparent paper to be used when exposing the board. If a simple paint program is used, it should be configured to print at 100 dpi. If the program only supports 72 dpi (e.g. MacPaint), just set the print options to reduce by 72%.

Suggested Geometries and Techniques

small example Because this process does not support plate-through holes, you need to make solder pads larger than they would be otherwise. The minimum suggested size for a solder pad is 0.070 inches diameter (7x7 pixels at 100 dpi). Traces should may be as narrow at 0.01 inches (1 pixel at 100 dpi), but when space permits traces should be at least 0.02 inches (2 pixels at 100 dpi). When using a paint program, a template image makes placing the components easy by using copy-n-paste. Usually the easiest approach is to copy-n-paste all the component pads (manually draw any unusual component pads), arrange them in a way that seems to minimize routing for most of the signals, place the printed image onto a piece of foam and stick all the parts through the paper into the foam to check than you haven't got two components sharing the same space. Finally connect all the wires, typically with stick figures and once they're all routed make it like nice. The image shown here is a simple single-sided board example. The MIDI Drum Machine's board is a good two-sided example, with a solder side and component side. Note: the via pads on the MIDI Drum Machine board are smaller than the suggested 70 pixel diameter... this caused considerable trouble testing the board, since many of the vias did not solder well. Before printing your layout, it is very helpful to include some text and flip it if necessary so that it will be readable when the image is positioned correctly. It's not much fun to find out after etching that the layout image had been placed on the board with the wrong side facing up.

Printing the Layout

--look up paper type
laser printer vs photocopy
problems with toner

Making Simple Low-Volume Printed Circuit Boards, Paul Stoffregen
November 28, 2003
Last updated: November 28, 2003
Status: just starting these pc board pages
Suggestions, comments, questions??
<paul@pjrc.com>