Theme: Signal polygons, ground planes (V19+)
Via: How do I make it a thermal?
Thermal pads, or short thermals, are interruptions in the copper surface around soldering pads. These interruptions ensure that the soldering pad is thermally separated from the copper surface so that the soldering padt heats up quickly during soldering and the solder is well annealed. If the heat flows into the entire copper surface too quick during soldering, the solder agens does not bond with the copper surface well. A misconnection between copper and soldering agens might happen ("cold solder joint" or "dry joint").
Creating a via like a thermal is unusual because normally it is not meant for soldering. Therefore, you cannot automatically make vias thermals. Ticking the box "Adjust auras" in the "Create signal polygon" - dialog, vias automatically get connected all arount to the copper surface.
If necessary, you can add an aura to the via manually and manually place 4 ligaments for connection to the area made of 4 single signal tracks.
