Homebrew PCBs

Autorouters aren't an instant solution. Don't expect to hit a button and 
instantly get a perfect layout. They only obey the rules they are given. 
To get a good layout you need to keep experimenting with the settings. 
When using the autorouter I usually follow this cycle:

1) load ratsnest and place the parts that must be in specific places 
(connectors etc)
2) place the rest of the parts, trying to keep the ratsnest looking as 
simple as possible.
3) run autorouter.
4) identify the problem areas, unroute board or just an area and 
rearrange parts. Go back to 3
5) If the layout looks messy, experiment with different router settings 
until it looks as clean as possible. Often you need to use different 
settings for different areas of the board.
6) Route any tracks that the autorouter fails to route
6) Unroute any areas that still look nasty and tidy them up by hand.

On a more complex board I may end up running the autorouter 20 or more 
times until I am happy. Even the best autorouters still tend to produce 
layouts that look messy. The human brain is very good at recognising 
patterns. Computers aren't. They simply follow rules that they are 
given. If the layout complies with all the rules then the board will 
work. Although it is very satisfying to produce a pretty board, how many 
people will actually be looking at the track layout?

On very tight boards you still have to go back to manual routing. Look 
at PC motherboards. Some of them are truly works of art.

Les


Stefan Trethan wrote:

>Well, give me four layers and i route you that mess too ;-)
>I mean that's not really good routing, is it? it's just running traces  
>until you hit another one and setting a via.
>
>Also, the parts placement is not good either. It looks like the parts are  
>just put there more random than anything. Some busses seem to run right  
>across the board, much longer than they'd need to.
>
>Now if we ignore these large scale issues (i'm not gonna make 4 layer  
>boards with 1287 pins tomorrow), and look at the detail work, it's still  
>crap. i mean, look at the very top very left pad, what is that?  
>practically whereever i look i see something i don't like.
>
>This tells me i'm not just too stupid to get my autorouter working  
>properly, yours is just as crappy.
>
>Could you try a smaller, single sided board?
>
>thanks
>
>ST
>
>  
>