Gerber mask tolerances?


Is there a way to control tolerances on the mask layer during Gerber file generation. I have a fine pitch component. I assigned 2mil mask clearances for each pad of the component. It looks fine in PCBNew. Each pad is separated by a 0.0025" thickness of the mask. When I generate gerbers, however all the pads get merged into one big aperture. Is there a way to control how gerbers are generated? I tried to change default line width, but that didn’t’ seem to change anything


Never mind, found it. For some reason the PCBNew setting for solder mask minimum width affects Gerber generation. I had min width set to 0.003" and had one footprint local mask clearance settings set to 0.002". When I generated Gerbers it changed all the mask clearances to 0.003". So you can’t really plot correctly the footprints with local mask clearances set to something less than the global settings.


This is “solder mask min width”. If you have it set to 0.003 and the mask (the physical substance in the real board, the black area in the design) between two pads would be under that, the mask is taken away. If you want to keep 0.0025 strip between two pads, you must set 0.0025 as the minimum.


Watch out that you don’t make it too thin. Check with your vendor for minimum mask web width. If the web (i.e. the lines of solder mask between SMT pads) is too thin then there may be some manufacturing issues.

This link helps explain:


You miss my point. If I set up global mask clearances to 0.003" and local clearance for one footprint to 0.001" they will not show properly in the Gerbers. Gerbers will all be 0.003" which would not match my design in PCBNew.


@ArtG What is not discussed much is the difference in pad creation between SMD and NSMD defined pads.

BGA Pad Creation – SMD vs NSMD?

In my opinion, the default Pads to Mask clearance should be set to zero in PcbNew; as this should be the “normal” “global” expectation (the board house may make their own changes to this setting).

Your design recommends zero clearance, but you might want your boards to come with a different solder mask color on your next order. I expect the fab house to make the changes they need in house for the change from red to black.