The answer is, of course: It depends.

The size of the mounting hole, the distance the copper is pulled back 
from the hole, and the board material used can all affect the location 
of the mask edge. And also your design intent.

You want to be sure the mask does not leave any copper exposed so the 
tolerances for your shop/processes determine that.

If the mounting hole is for a typical sized screw it will be large 
enough you can have the mask opening dia just a bit smaller than the 
hole dia as there will be little chance of the mask clogging the hole. 
Do not make the mask opening dia zero as the shop will have to make 
there own choice there as a large opening in the screen will mean too 
much mask gets squeegied thru and will need to be cleaned off the back 
of the screen too often.

If you are using a board material such as teflon, for RF for instance, 
do not run the mask to the edge of the hole or beyond (or the edges of 
the board). Since the mask does not adhere well to those materials an 
edge can be a location where the mask can catch and be easily peeled 
back, espcially by hardware going through the hole.

Greg Smith



On 2/25/2013 11:37 AM, JF wrote:
> Hi All,
>
> This should be basic, yet I can't remember the requirement nor where 
> to find the info (which spec).
>
> We have a board with some unplated holes and a copper plane on both 
> the top and the bottom. Of course, the copper planes are recessed from 
> the hole but I can't remember if the Solder Mask should be flush to 
> the holes (some are mounting holes), or just covering the planes + a 
> certain distance.
>
> Thanks in advance!
>
> JF
>
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