plugging thermal vias
As whiplash, I'm not aware of plugging with solder mask as a usual technology. However, there are different purposes of plugging that may have different solutions:
- stop solder wicking with exposed pad vias
- increase thermal conductivity of vias
- increase electrical conductivity of vias
- place via in pad with full electrical and mechanical function, e. g. in a 0.5 mm/20 mil BGA pad
I have previously used this types of plugging
- via fill with nonconductive material, surface treatment and solderable galvanic copper cover (supplied by Ilfa, Germany and Merix, USA)
- via fill with thermal conductive material, surface treatment, non-solderable surface (cheaper than first solution, supplied by Wuerth, Germany)
I think, that filling vias with solder mask could be possible for specific solder mask processes. I doubt, if it achieves clean, solderable surface around the via, e. g. for an exposed pad. If so, it could be an interesting via fill variant. Can you, respectively the said manufacturer, give photos showing the via finish details and also tell the applicable via parameters (drill size, aspect ratio)?