At 09:46 AM 2/8/01 -0800, Andrew Lowy Sybrandy wrote:
>What is the best way to put a mounting hole in a PCB?
>I had a CAM HOLD put on a job I sent to Advanced Circuits.  They said all
>the holes, which I defined as pads with zero X and Y size and the
>appropriate hole size, shorted out the two inner planes.

Not a totally strange result. If you looked at the inner planes, what was 
shown for that pad? But Protel 99SE SP6 I just tested does correctly set 
clearance for the hole. However, this immediately raises the question: what 
plane clearance design rule was set for those mounting holes?

*never* set a pad size as zero. It is common to place a pad for mounting 
holes that is large enough so that design rules will keep any track from 
being placed under the mounting hardware. Of course, you could always use 
insultating washers, but why make it complicated unless there is a good 
reason. What happens out in the field when someone takes it apart and 
accidentally puts regular metal washers there.... yeah, they aren't 
supposed to take it apart.....

In the old days, when some fabricators still bombsighted the drill 
locations, it was quite rude to have a hole without a pad.... not really 
relevant now, though.

>I want a simple hole, not connected to any net.
>Should I make the X and Y size the same as the hole size?  Which layer
>should I put the pad on?

Normally the pad would be multilayer.

If you really want to make a pad smaller than the hole, go ahead, but make 
it quite a bit smaller, smaller than any holes on the board, because a 
fabricator might use dry film and we wouldn't want a piece of hardened dry 
film resist that could float around and would be big enough to stick in a hole.

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

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