robertferanec , 12-17-2018, 02:27 AM
The VIAs under exposed pad will automatically not have mask as the whole area is unmasked because of the PAD. We do not add extra mask on the pad / via. However, you may want to consider size of the hole in that VIA (e.g. we often use 0.2mm), so solder will not flow on the other side of PCB (or you can use plugged/filled VIAs as suggested by Paul ... but we never do it, it adds cost to PCB manufacturing and we do not have problems not filling up the VIAs in exposed pads ... once I had problems with it, when I left the holes too big, but not since).