[sdiy] Eagle

[Bruce Duncan]

At 06:41 PM 9/7/2008, you wrote:
>why is this?
>i hear similar opinions a lot, but always without detail about why it's bad.
>it seems to amount to it not looking nice...
>
>i really think the majority of pcbs in the world are autorouted.
>i've had good luck with the autorouter.  i understand some signals need
>special treatment, but one can manually take care of these.
>and doing a little manual cleanup after autorouting is a ton easier than
>manually routing a complicated layout.
>
>but still, i'd like to hear any feedback about why it's so bad...
No Auto router can compete with the problem solving capabilities of 
the human router.
Also to get the best auto route it requires that routing Rules be 
VERY well defined.
This can be quite involved and takes a lot of experience.

When manually routing, components can be easily shifted to optimize 
routing. Auto routers don't do this (maybe super expensive ones do)
and there will be lots of times that tracks will end up circling the 
board looking for a completion.

Via count will be at least double with auto route and track lengths 
will usually be the same.
It can take the strength of Hercules to route some boards and 
autorouters usually give up long before a good route will materialize.

Probably on very complicated digital boards autorouting makes more 
sense but when you look at commercially made boards,
they are usually much too well laid out for that to be likely.

It is possible to do a rough route with the auto router and then 
manually clean up but depending on your luck this
can be as labor intensive as routing from scratch by hand.
It does work though sometimes and I have done a few boards this way 
if I am in a rush.
It is very important to get power and ground down well and this is 
often messed up with auto route.
Fixing this later can be almost impossible or at least difficult.
Some people do multiple auto routes with different RULE setups to get 
power and ground down first and then multiple passes to add signal
traces etc. This can work fairly well but still will never equal a 
hand routed board for neatness and efficiency.

I could be wrong..maybe PC boards are totally auto routed but I 
seriously doubt there isn't some major human intervention.

Bruce