Electroless copper deposition

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

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