Screaming Circuits: Custom CAD parts libraries


Custom CAD parts libraries

Back to Mark Rules and the mini control board again. He's using Eagle CAD which comes with good and not so good. The good is that Eagle is pretty powerful, yet inexpensive and easy to learn and use. The no so good is that the parts libraries tend to not have the newest parts or packages. The means before getting started with the schematic, Mark had to create the libraries.

He found a PIC18 with a QFN28 package variant, but the package didn't quite match the manufacture recommendations or Screaming Circuits' guidelines. It was a decent start but needed adjustments on the solder paste layer and the solder mask layer.

He started with a similar DFN8 packaged regulator, but in the end found it easier to start from a blank slate. The DFN10 motor driver used the regulator part as a base but required a lot of work to4qfns_paste_llayer_1  get the copper aligned, the mask in the right place and the solder paste set up. The center pad now has a segmented solder paste patter with room for two rows of three thermal vias. He needs to find a board shop that can drill and fill 8 mil vias. The FlipChip package was fairly easy, but again, will require a board house that can really register the solder mask.

The image shows copper, slik outline and solder paster layers.

Duane Benson


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