Archive of the former Yahoo!Groups mailing list: Homebrew PCBs

----- Original Message -----
From: "Stefan Trethan" <stefan_trethan@...>
To: <Homebrew_PCBs@yahoogroups.com>
Sent: Friday, January 06, 2006 12:39 AM
Subject: Re: [Homebrew_PCBs] Re: Autorouters


> On Fri, 06 Jan 2006 00:11:07 +0100, Alan King <alan@...> wrote:
>
>>
>>
>> Eagle works brilliantly for single sided. Only open the second layer
>>
>> for the correct passes and cost it properly and it will produce
>>
>> excellent patterns with minimal jumpers to install where the 2nd side
>>
>> traces are. Easily as good as a person at smaller boards, and clearly
>>
>> better than a person at larger ones. Just watching it work on a medium
>>
>> sized complex board and the lengths it can go to to elminate or length
>>
>> minimize the out of main plane traces, it's very clear that it's well
>>
>> beyond what most people would come up with for the same board.
>>
>>
>> Only real complaint would be not the 2nd layer traces cross, which is
>>
>> easy with insulated jumpers. But thinking about it now, duh just make
>>
>> it a 4 layer board, 1 low cost, 1 highest cost, 1 highest-1, and 1
>>
>> highest-2. Nothing but a breeze to do..
>>
>>
>> Alan
>
>
> Well, i just took one of my projects and deleted all traces (yes i saved
> under different name).
> Then i tried both autorouters that come with my software, and different
> settings. The best i got was 5 signals remaining.
> Mind you this is a board that was already routed completely by hand single
> side with no bridges.
>
> I ackonweledge that i have high demands on layouts, since i believe a lot
> of it is art, but if the autorouter can't even manage to route all signals
> of a board that is easy to route what can i think of it?
>
> I'm just surprised that so many seem to get useable results out of it and
> i want to find if maybe there are better autorouters. I'm still very
> interested in pictures from various autorouter outputs without any manual
> touchup done.
>
> Leon, the top left pad, why does the trace go down between the pads and
> then left at 90 degree, why doesn't it just enter the pad from the top?
> You can spot a similar uglyness wherever you look.

That's because the bias for that layer was set at X, rather than Y. Routing
is much easier if layers alternate the bias.

> I don't agree on the placement. I agree i can't be certain without a very
> close look, but when i see "fans" of many parallel signals crisscross a
> board i can't help but think there might be a way to get the many signals
> closer, maybe accepting a tradeoff in getting the fewer signals longer.
>
> Sure, if you accept more layers and more vias and don't care how it looks
> you can autoroute any board, but it seems they are still not quite clever
> enough for me to use.

The main criterion is does the board work OK after autorouting? It generally
does if the critical stuff is routed manually. I'd rather use an autorouter
than spend days routing a complex board.

Leon