At 03:43 PM 2/9/01 -0800, Henrik Thurfjell wrote:
>Why does not the DRC tell the planes are shorting?

Because DRC is not, and will not be for a long time, intelligent. Rather it 
is an automaton which follows certain rules. (More accurately, it is even 
dumber than that, but hey....)

It appears that the DRC algorithms like the inner layer plot algorithms 
determine that the pad is a surface pad and don't bother to go on and 
determine if there is a hole there. Note that the display routines also 
neglect this hole; the only layer on which it appears is the layer of the 
pad (top or bottom). The inner planes show no blowout.

The drill drawing does not show a symbol for the hole.

The problem is only that the drill files include the hole.

I can see some arguments for allowing surface pads to have holes in them. 
But no drill command should be generated for a hole that does not exist on 
more than one layer. Perhaps if there is a hole, the pad should be treated 
as existing on all layers with a size appropriate for the hole. That would 
be logical; but it would require fixing display, DRC, and plot routines.

DRC should warn, perhaps, that there are surface pads with holes. As 
matters stand, these are trouble, trouble, trouble.

I suggest, in fact, that holes in surface pads not be allowed, period. If 
someone designates a surface pad with a hole, the hole data will be ignored 
for *all* purposes, including the hole editor. Perhaps it could be display 
on the pad edit display with a line through it. Or an error message should 
pop up.

Someone might accidentally edit multilayer pads to surface pads and so I'd 
rather not lose the hole information entirely.

Abd ul-Rahman Lomax
PCB design, consulting, and training
Protel EDA brokering (resale) services
Sonoma, California, USA
(707) 939-7021, efax (419) 730-4777

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