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

[gene glick <carzrgr8@xxxxxxxxxxxxx>]

Colin D Bennett wrote:
> 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.

I am also new to routing my own stuff but have a bunch of experience 
telling others how to do it for me (day job ;)  On a prior job, the 
layout house did all auto-routes.  They'd start several jobs with 
different router restrictions, allow them to route for a while, then 
pick one, and optimize it - probably by hand.  Yes, starting over is common.

Kai-Martin posted that placement is more important than routing.  I'd 
say they are equally important.  The best layout guy in the world can't 
fix a lousy placement.  Bogus layout guys throw more layers at the 
problem.  So yeah, take the time to plan it out before routing.


> Does anyone have any tips on how to plan a layout for easy and clean
> track routing?  In particular for 2-layer boards.

No substitute for experience here.  But, partitioning the design by type 
 may help : analog, digital, low-speed, high-speed.  Try to think 
beyond blindly connecting the parts.  Sometimes swapping gates, adding 
parts or other strategies become clear as you route.  This is a huge 
benefit when you route your own board.  Layout guys just connect the 
pieces together.


> 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.

2-layer is tough.  You also have to account for power and ground.  The 
parts themselves also crowd routing area. 2-layer is not particularly 
suitable for high-speed anything.  Seems good for power supply design, 
and some audio work (I've seen a lot of audio ref boards on 2 layer). 
You can make good designs with 2-layer, just is more work.  Cost 
difference to 4-layer is not bad.

Yes X-Y routing is the way to go to avoid blocking.  Works great for 
digital stuff.
> Do you ever use the pcb autorouter or do you always route by hand?
I have yet to make the auto router work - but haven't really tried very 
hard.  Hand routing is my preference but it takes longer.

> Do you ever study other people's PCB designs to learn from them?  
Yeah, a lot. You will find good and bad.  There's a whole world of 
opinion out there - and you know what they say about opinions :) 
SI-LIST is a great place to exchange ideas on layout. Several industry 
experts frequently post.


gene


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