I tried to use a nice big ground plane floods on my 2-layer PCB design to provide a low impedance ground and to implement the reference design for the RF IC (Atmel AT86RF231) and PCB antenna designs I was using.
I know you can't have a perfect ground plane on a 2-layer board when you are routing tracks on both layers, but I figure that if there are some islands without ground plane, that's fine. Perhaps my concept is wrong. Anyway, here's the process I used: 1. Import schematic into pcb, disperse components. 2. Lay out major components (radio transceiver IC, antenna, data connector). 3. Create ground plane rectangles on both top and bottom layer. 4. Route tracks. Now after a while of routing tracks, there were so many tracks that my ground plane polygons were chopped to bits and pcb started drawing only the left half of the polygon, for instance. This obviously created problems since nets that were already successfully routed got broken. Furthermore, I couldn't edit my ground plane polygon easily since pcb doesn't draw any indication of where the vertices are, and the polygon itself was half missing. It looked like the logical thing for pcb to do would be to draw two halves of the polygon. In fact it looked like the missing half was the larger half, so it seemed a really bad choice. I tried to patch up the missing parts with more rectangles, but it was not great. It was such a mess that I had to delete my ground planes and start over. The second time, I didn't create one large rectangle, but instead inserted 3 or 4 smaller rectangles on both top and bottom layers in specific areas where I needed the ground plane. This worked better but seems cumbersome, especially in the early layout when you don't have components and tracks already figured out, so you don't know where the ground plane polygons might fit. Does anyone have any strategies or tips for general design of ground planes in 2-layer PCBs? Do you do a ground flood, or do you remove all extra copper? Regards, Colin _______________________________________________ geda-user mailing list geda-user@moria.seul.org http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
