At 09:52 PM 3/28/01 -0800, Jim Mcgrath wrote:

>In most cases I don't have the luxury of modifying the schematic. If possible
>can you build a footprint with a multylayer pad with a drill zero? If so
>build one and overlap the pads on the common point to the 2 resistors.

I would not normally attempt to share a pad between two parts. The only 
advantage to sharing is a very small space savings, and, as another writer 
noted, the resistor footprints could overlap as here:

Instead of
A    AB    B (where AB represents a pad shared between two parts)
A    A-B    B
do this:
A    B-A   B
A B--A B
which takes even less room, so not only is there no space savings, sharing 
the pad takes up *more* room than not sharing.

Simply taking two parts and putting a pad from each down in the same 
location, if nothing else is done, will create two drill hits at the same 
place. This can break drills, I understand, though I would think good drill 
software would filter these things out. Even so, the drill drawing hole 
count would then be one hole off.

But normally I would simply place the parts next to each other without 
overlap. Why? Because the silkscreen (overlay) legend is then very clear 
and easy to understand.

However, if, for some reason, you must place two component pads on top of 
each other, edit one of them to a surface pad with no hole. (Don't use a 
surface pad with a hole: these little critters give Protel indigestion. A 
multilayer pad with 0 hole might also work, but it creates more entities 
for the router to consider; bad enough that it has two pads.) I would not 
expect this to cause autorouter problems, but I haven't tested it.

It's a good idea to think twice before doing something outside the normal. 
I've written about this before. When one does something "creative" with the 
program, one may be entering an area where the program is untested, and 
untested software is almost always buggy. I'm not saying one should not be 
creative, but check later to make sure that *everything* connected with the 
new situation is working properly, just as you would with any untested 

I would not have anticipated a problem routing to a double pad. But it 
doesn't surprise me.

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

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