gEDA-user: autorouting

[Vaughn Treude]

DJ Delorie wrote:
>> I'm curious. In which cases do you use the built-in autorouter?
> 
> When the layout is a jumbled tangle of traces and there's plenty of
> room.  Or for boards so simple that there's little chance of it
> screwing up.
> 

I used auto-routing on my most recent project with pretty good success. 
  It was a complicated board and I had to route the last 15 or so traces 
by hand.  One thing that helps a lot is to try erasing the rat lines, 
moving stuff around, and regenerating them, to see if a different layout 
makes lines that don't have to cross over so much.  Rotating resistors, 
capacitors around can clean things up a lot, since the program thinks 
there are specific pin numbers even when it doesn't matter.

Also, sometimes the auto-router can route a few more lines after you run 
the optimizer.

Other ideas that seemed to help me, or things I learned the hard way:
1. If you're using wider lines for power, do them first.  If the voltage 
regulators, etc, are in one place you can select those rat lines and 
route them with a bigger line width.
2. If you're putting decoupling capacitors on IC's, do them first 
manually because the autorouter will connect them to the wrong place.
3. If you've got a lot of room, increase the minimum line spacing before 
routing so it spaces them out a little more nicely, then decrease the 
minimum line spacing before doing the design rule check.  Otherwise I've 
had trouble with the DRC flagging things as errors that are actually at 
the minimum spacing.

I'm not a real experienced board designer, so you can take those 
suggestions with a grain of salt. :-)

Vaughn

> The m3a board, for example, was 100% hand routed, because it's mostly
> busses, which can be cut-n-pasted.
> 
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