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I have a 0.167mm diameter via under a BGA component to provide ground connections to two adjacent pads (ENIG-finish PCB). Our PCB fab house recommended that we plug the via to prevent solder from flowing into the via which might leave the pads with insufficient solder.

I am using Altium Designer 20. I'm familiar with tenting vias with soldermask (I generally tent the top and leave the bottom open to avoid trapping heated gas). How do I specify that the via should be plugged? I haven't been able to find any appropriate property to set in Altium. Is this commonly done by callout on the drill guide layer or some other method?

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    \$\begingroup\$ This isn't an answer, but I'm genuinely curious: Why isn't tenting the via adequate for this? \$\endgroup\$ – Hearth Dec 16 '19 at 18:54
  • \$\begingroup\$ what @Hearth said. with such a small diameter the via will be essentially "plugged" by solder mask anyway. \$\endgroup\$ – Maple Dec 16 '19 at 19:18
  • \$\begingroup\$ @Hearth I'm not entirely sure that tenting isn't adequate. Since it's under a BGA component, I was unsure if tenting a single pad would be technically possible. \$\endgroup\$ – JYelton Dec 16 '19 at 21:38
  • \$\begingroup\$ @JYelton Why not tent all vias? \$\endgroup\$ – Hearth Dec 16 '19 at 21:40
  • \$\begingroup\$ @Hearth All others on the board are tented. This one in particular was not because I added it late in the design and for whatever reason thought it might not be able to be tented. \$\endgroup\$ – JYelton Dec 16 '19 at 22:07
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With my usual Chinese proto house it's specified on the order form, and adds about $150 US to the cost for 5 100x100mm boards, also adds a few days to the lead time.

If your board house does not have that, you can put it in the readme file or fab drawing along with material, stackup etc.

If you want some of the vias plugged and not others, you'll have to talk to them and find a way to differentiate them if they agree to in fact do it. I suggest making the plugged ones unique in some way (eg. slightly different size to the rest).

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    \$\begingroup\$ For OP, it's common to designate some holes as 10.01 mil or 0.251 mm (for example), not expecting that they have a 10.01 mil drill, but simply to distinguish them from the "10.00" mil holes that you don't need to be plugged. \$\endgroup\$ – The Photon Dec 16 '19 at 21:40
  • \$\begingroup\$ @ThePhoton Great suggestion, thank you. \$\endgroup\$ – JYelton Dec 16 '19 at 23:10

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