At 03:32 PM 2/12/01 -0600, Micky Blain wrote:
>1. just go bit on a big order with power plane clearance. It seems that the
>gerbers generates the plane all the way to the edge of the keep out layers.
>Is there anyway to control the power plane and manually draw them in without
>doing them by split planes?

This question reveals a bit of misapprehension about how inner planes are 
created. The plane is not "generated." It exists before you and I were 
born. Sorry, I'm getting a little metaphysical there.... The plane is 
nothing other than the unexposed film. What is generated is anti-copper. 
Which is why inner planes are negative plots.

Protel does not really know anything about copper on inner planes. What it 
knows is only what rules there are for pads as to air gap or thermal 
relief, and it knows whether or not a pad is within any split plane areas. 
DRC does not check for actual connectivity on an inner plane. If there are 
no splits, DRC *assumes* connectivity between any pads anywhere, even if 
the pad is floating outside the workspace, I think. If you have an isolated 
pad because the blowouts from other pads surround it, the only way to find 
this is to visually inspect it. Or use Wolfgang's tool (Router Solutions,, which will check negative planes. It is not a trivial 
problem, though it is not as difficult as writing a good autorouter. But we 
all know how easy that is!

Here we see the flip side of that. The inner planes know nothing about the 
board edge.

Inner planes are plotted in the negative. Pads which are to be unconnected 
to the plane are simply plotted oversize by the radial clearance specified 
in the design rules. Pads which are to connect are either not plotted at 
all ("direct connect") or are plotted by drawing lines or arcs to form 
thermal reliefs.

It gets slightly more complicated if there are split planes; essentially 
the program must determine what split plane polygon the pad is inside, and 
then it plots it connected if it is inside a plane with the same net 
assignment as the pad, and it plots it unconnected otherwise. If it is 
inside no plane, its net assignment is compared to the default assignment 
for the layer....

The keepout lines that make up a board outline have no special 
significance, other than clearance to primitives. The plane itself is not a 

So, to keep copper from the board edge on the inner planes, which is not a 
bad idea :-), one places track around the board edge. Conveniently, as 
noted by another, this can be nothing more than a blown up version of the 
keepout or board outline. I've always placed this on the plane layers, and 
have tolerated, reluctantly, the Protel warning of inner plane primitives. 
But the CAM Manager would allow the setup of special plot instructions for 
individual layers, and we could assign one of the new mech layers to inner 
plane edge clearance, and plot it together with all the inner planes, thus 
generating no spurious warning. I've not actually done this, however....

Abdulrahman Lomax
P.O. Box 690
El Verano, CA 95433

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