Part 12 - Electroless copper deposition
Channel: Eurocircuits
Date: 2014-05-08

The first step in the plating process is the chemical deposition of a very thin layer of copper on the hole walls.  The operator clamps the production panels into the jigs.  The line is fully computer controlled and the panels are carried through a series of chemical and rinsing baths by the overhead crane.  Almost all PCBs with 2 or more copper layers use plated through holes to connect the conductors between the layers.  A good connection needs about 25 microns of copper on the walls of the holes.

http://www.eurocircuits.com/index.php/making-a-pcb-eductional-movies/42-electroless-copper-deposition