I have a problem where a surface mount connector footprint requires a couple of mechanical NPTH locating holes that are very close to pads. The DRC flags these as violations of the minimum clearance rule for the relevant net.
I presume that the main importance of minimum clearance is to limit copper-to-copper proximity for electrical and manufacturing reasons. But in this case, there is no ‘copper’ as such and the peg that locates in the hole will be plastic.
Is there a way I can get rid of the errors without having to reduce the minimum clearance for relevant net classes, thereby losing the DRC clearance functionality?
If not, could there be a way to specify that the DRC should ignore minimum clearance for this situation? It might make sense to be able to set this in the footprint design per hole, so that if the user knows that there will only be ‘plastic’ in the hole, no clearance is needed - it would be different if, say, a metal locating peg were to go in the hole.
+1, NPTH holes are drilled after etching and plating, so you can have a fragile track very close to the drill. Drills always have a positioning tolerance. What clearance are you looking for.
In the end DRC is a warning that can be ignored if you understand why the error
You’ll see that there are two mechanical locating holes and if the footprint is created exactly as per the drawing, the hole comes quite close to the pads. Depending on the net’s minimum clearance, those holes can violate the DRC. It would be nice if the DRC could be made to ignore those holes. I absolutely appreciate what other posters are saying: that you need non-zero clearance for manufacturing tolerances, but I think that could be a bit smaller than the necessary electrical clearance in this case.
Yes, I agree that you need some mechanical clearance, but I think you might want it to be smaller than the electrical clearance. I’ve pasted the data sheet in answer to another reply to my question so you can see what I mean.
Speak to your board house. I used some wurth mounting pillars recently which have a npth and the kicad footprint had copper right up to the hole. The boardhouse cut the copper back by 8thou
FWIW, you can special-case a particular footprint’s hole clearance in 6.0 (and for that matter, hole clearances are treated different to copper clearances in 6.0).