Printed Circuit Boards on the Othermill: Tips and Resources

Introduction

Want to start making your own printed circuit boards (PCBs) on the Othermill? Here are pointers to a number of useful guides to PCB design using EAGLE and milling those designs on the Othermill, along with some tips I’ve learned along the way. Please share any other useful resources you know of in the responses!

Resources

  • SparkFun – How to Install and Setup EAGLE
    EAGLE is a popular schematic and PCB design package for Macs and PCs, this guide from SparkFun will guide you thru getting it installed and setup.
  • SparkFun – Using EAGLE: Schematic
    Schematics are how circuits are documented, and the starting point for PCB design. Here’s SparkFun’s guide to making professional looking schematics in EAGLE.
  • SparkFun – Using EAGLE: Board Layout
    Once you’ve designed your circuit, this tutorial covers using the schematic to lay out a double-layered PCB design and what you’ll need to export to send your design to a fabrication service or the Othermill.
  • Bantam Tools – PCB Workflows
    Once you have the basics of EAGLE down, these guides from Bantam Tools will show you how to take your design and mill it. Included are articles on considerations you should account for in your design, how to deal with double-sided boards, dealing with surface-mount components, and exporting Gerber files for the Othermill.
  • Adafruit – Double-sided PCB Milling
    Another guide to PCB milling with EAGLE and the Othermill, from the team at Adafruit. This article includes some good design guidelines as well as a link to a guide on creating your own solder masks.

Tips and Tricks

  • One of the most fundamental differences between a milled PCB and one from a fabrication service is that holes are not plated thru, and so the pads on the top and bottom of the board are not electrically connected. Because of this, I try to have all my thru-hole components (DIP packaged ICs, discrete components, headers and other connectors, etc.) solder to the bottom side of the board, and I avoid using component pads as vias between layers, as it’s often tricky to solder to the top side of the board with many components. If you want to use the auto-router, the Bantam design considerations document shows how to restrict vias from parts of your board, such as device pins.
  • The Othermill can mill traces down to 6 mils, however you may encounter traces peeling up at that size. Go with the largest size trace that is reasonable for your design.
  • If using copper pours, such as for a ground plane, Bantam recommends making the clearance between the pour and traces (polygon isolation value) 1 mil larger than your largest tool. So 33 mils for a 1/32 end mill, for example.
  • The Othermill software can directly import .brd files from EAGLE. I’ve had a couple of instances, however, where parts didn’t show up in the milling software. I’ve assumed this is due to some sort of library version issue, and I didn’t see the problem if I generated Gerber files and imported those into the Othermill software, so that’s my normal workflow now. Most fabrication services will want Gerber files so it’s a useful process to learn.
  • EAGLE does have an auto-router function, but many people, myself included, like to manually route boards when possible. It often results in a more esthetic layout, and can be a fun puzzle-like exercise. As I mentioned earlier, I try and keep most of my layout on the bottom of the board if I’m working with thru-hole components, with the components on the top side.

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