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I detected a shortcircuit between two vias in one of our PCBs. The shortcircuit was caused because an offset on the solder mask leaves part of the via's ring "half opened". When the PCB was assembled, a little amount of tin produced an electrical contact between the vias. The PCB has PTH and SMT components.

Solder mask offset

I think there should not be any offset on the solder mask at all. I will contact the PCB manufacturer. But I have some questions regarding this issue.

Is this offset error on the solder mask a remarkable manufacturing mistake?

In other PCBs without offset on the solder mask, it is still possible to have electrical contact on the vias, because the via's hole is open. But I have seen some PCBs with the vias completely hidden, filled with solder mask.

No offset but hole not filled

In case filling the vias were desired is there a special manufacturing process for it, or that depends only on the diameter of the via's hole?

Thanks!

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    \$\begingroup\$ If you want the vias to be covered with soldermask, you need to 'tent' them. Different CAD tools use different terms, but if you right click on a via, there should be a tenting option or 'cover with soldermask' option. \$\endgroup\$ – IgorEE Mar 31 '16 at 9:29
  • \$\begingroup\$ That is definitely a shortcoming of the manufacturer. Le me guess, you bought them cheap from a Chinese manufacturer? There should not be soldermask offset at all, and any decent company will be able to get that right. That being said, if your via holes are less than 12 mils I suggest tenting, as IgorEE suggested. I try to tent wherever possible as it really helps with insulation. It doesn't always fully cover the vias, but it helps! \$\endgroup\$ – DerStrom8 Mar 31 '16 at 11:51
  • \$\begingroup\$ This company is based in Europe, but I am pretty sure they order in China, as @derstrom8 meant, we get always very good prices in comparation to other manufacturers in Europe, but if the quality is not good, we will change it. Thanks for the advices! \$\endgroup\$ – jcambra Mar 31 '16 at 17:00
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    \$\begingroup\$ The assembly process should also be looked into. Because even if the vias are not covered at all, if there are proper spacings in between with soldermask, then bridging should not occur between adjacent vias. \$\endgroup\$ – rioraxe Apr 1 '16 at 8:08

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