1) Drill Panels
Holes of various sizes are drilled through the panel or a stack of panels.
The locations of holes are determined by the pcb designer to fit specific components and to create interconnections between inner layers.
After drilling panels will be deburred (removed the raised edges of the metal or burrs surrounding the holes that occur during the drilling)
and desmeared (removed thin coating of resin that appears inside the hole due to heat produced by motion of the drill bit).
1) Copper Deposition
Once the smear is removed, a thin coating of copper is chemically deposited on the hole walls.