How close the soldering joint for pcb?
The minimum breakdown voltage for a gap of any size in air at 1 bar is about 360V. That minimum occurs with a gap of about 8um. Image from 2006 paper &quot;Electrical breakdown across micron scale gaps in MEMS structures&quot;

0.008mm is a very small gap so basically you don't need to worry about it. Of course if conductive debris or liquid falls on the board it will be more likely to cause problems with a narrow gap.

Mains voltage is another matter, and it's good to maintain gaps in the &gt;8mm range, perhaps more, depending on various factors.