Monday, June 21, 2010

PCB isolation routing with a real PC board

I did not have the proper milling tool. I had a pointy router bit (60 degree) that is supposed to be used for engraving wood. Fiberglass and copper was too much. Nevertheless, the results were very promising. The router bit was more like a snow blower, just heaping the copper up on each side of the trench it dug.

Here is a close-up of the IC pads. It's tough to see, but it is pretty much a mess. I went at it with some 220 grit sandpaper to get rid of the bulk of the nasty high spots so I can get a peek at what was underneath.

To the right is a 20x image of some of the pads for a .100" header - after sanding. I pulled the board off the router before the pads on the right were finished. I also think I had the bit digging-in a bit too deep.

At the left is a 40x image of one of the IC Pads. In both images, even after sanding, the "piling up" of the copper around the edges of the trench is clear.

Couple of early learnings: The cool dust brushes I made obscure the PCB. This isn't a problem for routing, but it makes setting up the tooling a real nightmare. I've got to re-design the brushes such that they are either fully or partially removable.

Second, the CADsoft to gcode converter does an excellent job, technically, but the resulting gcode is very far from being optimized. I'd estimate 40 - 60% of the time to route the board is the router moving from one end of the board to the other. More than half the milling time is just plain wasted.

Next Steps: Order some real router bits. Consider using a dremel tool rather than a wood router. Try to make a gcode optimizer that I found work.


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