PTH（plated through hole), or call Electroless copper plating, , is a self-catalyzed redox reaction. After drilling should plated through hole plating step is performed. Firstly, it is treated with an activator to adsorb a layer of active particles on the surface of the insulating substrate, usually metal palladium particles, copper ions are first reduced on these active metal palladium particles, and these reduced metal copper crystal nuclei It itself becomes a catalytic layer of copper ions, so that the reduction reaction of copper continues on the surface of these new copper crystal nuclei. The purpose of PTH is to metalize the resin and glass beams of the non-conductor part of the hole wall for the subsequent copper plating process, to complete the metal hole wall that is sufficiently conductive and welded.