This process is no longer used and has been replaced by the Black hole process.
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. This thickness must be electroplated, but the walls of the holes are non-conductive glass cloth and resin. So the first step is to deposit a conductive layer over the hole walls. We use electroless copper, that is we deposit chemically a layer of copper about 1 micron thick over the walls of the hole (and incidentally across the whole panel). This is a multi-stage process as you see from the video with washing steps between the stages. We pre-treat the panel, then we seed the hole wall with micro-particles of palladium, and finally deposit the copper