Vias is a vertical trace in a PCB which brings in electrical communication between the different layers of PCB. The Annular Ring is the area (area of the copper pad) that surrounds the drilled and finished via.
The width of the annular ring plays an important role during PCB manufacturing. If the width of the annular ring is not adequate, the drilled holes could touch the boundaries of the pad which is termed as ‘Tangency’. In the extreme scenario, the hole could be beyond the boundary of the pad and is termed as ‘Breakout’. Both terms are a must to avoid factors.
At Lioncircuits we recommend, 0.25 mm size for Through Holes as you will get sufficient pad for soldering, and the component will be soldered properly.
Minimum Annular Ring=0.25mm