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Re: gEDA-user: pcb: Track routing strategies and tips

Colin D Bennett <colin@xxxxxxxxxxx> writes:

> As a rather inexperienced PCB designer, I find that I have to throw
> away two or three layouts until I get one that is usable--and still
> not entirely satisfactory.  I always end up with such a mess of traces
> that I know I need better organization and a method to the madness.
> But I am a newb with little knowledge so I fall back on trial-and-error.
> Does anyone have any tips on how to plan a layout for easy and clean
> track routing?  In particular for 2-layer boards.

My schematics usually look almost like the layout.  The pins of the
symbols are placed like on the package.  People on this list argue that
the schematic should document the function, not the physical
implementation, but in my circuit the function is all inside the FPGA
and the processor, while the details of the layout in low noise mixed
signal or high-speed applications are very important, so I use the
schematic entry as a first opportunity to preview the place and route.

> One strategy that I have seen and recently tried is to use the top
> layer for all horizontal trace runs and the bottom layer for all
> vertical trace runs, or vice-versa.

This is a good for (slow) digital designs.  These typically benefit from
good functional schematics for review and documentation, so my physical
style of schematics is not appropriate.  OTOH, when it needs to fit on
two layers, and the logic is not too complicated, a little physical
planing on the schematic level may help later with the placement and
save a few backannotation cycles for swapped pins and slots.

> Do you ever use the pcb autorouter or do you always route by hand?

I never tried an autorouter.  But for that kind of Manhattan routing I
probably would try.

> Do you ever study other people's PCB designs to learn from them?  I
> think you could find both good and bad examples: things to emulate and
> things to avoid yourself.



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