Pad centers are punched with sharp core. Use prod, nail or sharp screw for this. Punched holes are drilled with 0.8 mm drill
and then 1 mm (if required). Drill holes on copper side. If PCB is two-sided, drill on side with greater number of copper
pads. Examine drills to control whether they are sharp, blunt drills pass more force to PCB and can tear copper pad from
sheet surface. Drilled holes should be perpendicular to sheet surface for better matching of sides.
Holes diameter should be minimal, and IC's terminals does not require 1 mm holes. Too big holes causing difficult soldering.
Piston holes are drilled to 2.5 mm, mounting holes for screws - to 3.3 mm.
It's better to avoid drilling big diameter right after small, and use medium drill, i. e. 0.8 mm first, then 1.5 mm, then 3.3 mm.
If copper of pad is raising at hole edges, this means the drill is blunt. Sharpen it with diamond needle file or grindstone.