Tenting via's does have disadvantages:
- They can 'exploded' during the reflow process
- Chemicals trapped inside the via can corrode it.
Via protection is either through:
- Surface finish
- Filling and covering it.
Fabricators often open the holes even if you selected tenting just to prevent the disadvantaged mentioned above.
See another blog: https://www.eurocircuits.com/blog/covering-vias/
I set the solder mask expansion for via's to be 50um from the hole edge.
This gets the best of both worlds:
- Reduces chemicals trapped in the via
- Prevents shorts between them
- Reduced (or eliminates) the ability for solder paste to go into the via
- Allows you to probe them (measure voltage etc.)