In a message dated 10/2/2003 3:02:38 AM Eastern Daylight Time, 
[EMAIL PROTECTED] writes:


> I have a couple of questions about the autorouter and multilayer boards.  
> 
> I know everyone will say to manually route it, and I will probably end 
> up doing it manually, but is there a way to use the autorouter and 
> specify the preferred layer to route the net on?  I would like to do a 4 
> layer design and I want to use the outer layers as much as I can and the 
> autorouter just seems to pick whatever layer it feels like if I use 4 
> routing layers and no power planes.  The downfall of this is that I was 
> thinking of just placing a polygon fill for the power planes but this 
> routing strategy cuts up the polygons too much and I am not happy with 
> the gnd plane this way.
> 
> Or, is there a way to allow the autorouter to place a net class on the 
> inner ground or power plane layer?  This is why I am using 4 routing 
> layers, when really all I would like to do is to route my data and 
> address busses on the inner layers since my power nets are not 
> complicated and there is a lot of unused real estate there.
> 

I'd do this by making the inner layers planes, and "routing" the extra nets 
using split planes, as long as it's not too complicated. You can make a split 
plane arbitrarily complex (but don't nest them within one another), effectively 
making an island of whatever shape you like to route a specific net on the 
inner layers. After hand-routing the specific nets you want on the inner layers 
this way, then turn the autorouter loose on the outer layers.

Steve Hendrix


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