Hello All:

I have used many of these types of holes for mounting screws.  We call them
"manhole covers". We use non-plated thru hole for mounting screws to
minimize the possibility of metal fragments coming loose when the screws are
installed and removed.  There is also the chance that the connection to the
ground plane can be compromised by damage caused by the screw.  We want a
good reliable connection between the chassis and the ground plane at our
mounting hole.

I make a component with 7 pads numbered 1-7.  Pad 1 is the center hole and
is not plated thru with a larger diameter pad on top and bottom.  Then I add
pads 2-7 around the perimeter.  I also make a schematic symbol for the
mounting holes.  This way, all of the perimeter holes can be connected to
the planes correctly.  The center hole is not connected to the plane
directly but gets it's connection thru the surface pads/perimeter pads.

I suspect that this may be what Mr. Salehi is attempting.  He may need to
use a larger pad size than .225" to leave enough room for the perimeter pads

I hope this was of some help.



Cliff Gerhard, P.E.
Director - EE Group
E-M Designs, Inc.

-----Original Message-----
From: Abd ul-Rahman Lomax [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, September 18, 2001 3:04 PM
To: Protel EDA Forum
Subject: Re: [PEDA] Pad with multiple holes surrounding it.

At 10:36 AM 9/18/01 -0700, Afshin Salehi wrote:
>     I have been having a problem trying to create a pad with a .125 hole
> and .225 pad size.  I am trying to place six smaller holes on the pad
> area of the large hole to create a screw hole with very hood through
> board connection.

I'm puzzled as to what Mr. Salehi wants to do here. A screw hole is a round
hole and would be made with a single drill, i.e., a single pad. If one
wants a slot, we could discuss that; with such a large drill size multiple
drill hits side-by-side may be practical. (With smaller holes, overlapping
holes can break drill bits).

If you want through-board connection, presumably the pads will be assigned
a net. If they are not, that is why a DRC error is coming up. Or another
rule is being violated.

Every component pad assigned a net should have a corresponding pin on the
schematic; to be completely explicit, these pins should all have unique
names (like MH1, MH2, etc.), but if all the pads have the same name and
there is only one occurrence of that name in the net list, all the pads
will be assigned that name. So if you must have multiple pads, it may be
sufficient to give them all the same name.

Note that if one is using the old Load Netlist method of bringing the
netlist into the board, there is a bug still remaining with SP6 that can
cause problems. As I recall, this does not happen when using the Update PCB
command from schematic.

So I recommend a little more discussion of this issue, or else we might be
advising Mr. Salehi how to do something which might not be such a great
idea. Perhaps I have failed to understand, wouldn't be the first time ....

Abdulrahman Lomax
Easthampton, Massachusetts USA

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