Yes, they are different.rusttree:
Is a solid via different than a regular via?
Many people specifically note to the PCB fab that they want “all vias plugged and tented”.
Often they don’t really need every via to be completely filled (plugged) and tented over with solder mask, but it is less work to treat them all the same rather than give some holes a different treatment than others.
Other times – such as when the assembled boards will endure vacuum-based bed-of-nails testing – it is convenient if every via is plugged, so there is no holes left for air to leak through.
While in theory filling thermal vias with copper would in principle give the best heat transfer, the last time I checked it was highly discouraged because of reliability problems. Instead, the PCB board manufacturer makes “plugged” vias by filling vias with polymer solder mask.
Has anyone figured out how to fill PCB vias with metal without reliability problems?
In my experience, if you don’t specifically tell the PCB fabricator how you want your vias – filled or not --, sometimes you’ll get boards with all vias filled anyway, sometimes you’ll get boards with only a few vias filled, and occasionally you’ll get a board without any vias filled. You can see a tiny hole all the way through the non-filled vias.