Under a BGA, vias are very close to pads, see my picture attached. So there is a risk of paste flowing through the vias. To avoid this, vias can be covered with solder resist. This should only be applied to the ring of the via and not fill the hole of the via with solder resist, as this can lead to the via not drying properly during production or the trapped air coming under pressure in soldering process and the via bursting open.
So is there a possibility in KiCad to only apply solder resist to the via ring and keep the hole open? In short, I would like to see a circle with the diameter of the hole on the mask layers.
The processor manufacturer recommends NSMD pads for use with the processor, i.e. the solder mask clearance must be positive. I have already made it slightly smaller than recommended and also made the pads slightly smaller than recommended. This results in a very thin solder stop web, which probably cannot be produced in practice.
Therefore, the best solution would be to overprint the ring of the via.
If I can’t think of anything better, I could print the vias closed on one side and leave them open on the other by exporting Gerber data twice and assembling these files by hand.
We used to use Target3001. It was a terrible program overall, but there was the option to cover only the via ring with soldermask.
Thank you for your answer. But it’s no solution for me.
I earlier made this layout with other software. Here you can see the Gerber export. Red is copper and green is the solder mask. You can see that only the hole in the vias is masked. That’s exactly what I want. How to do this with KiCad?
KiCad doesn’t really have such fine masking control for vias at the moment. Either you draw these vias as footprints (like the THT testpoints) where you can draw freely on the mask layer yourself, or you ask your manufacturer if they can apply such automatic corrections to your gerber files.
