The board is dielectric and must be electric for plating. For this reason, some steps are necessary for deposition a thin layer on the wall of holes. These steps are here.
The alkaline cleaner is used for removing the finger print and surface degrease also for removing the residues degrease on the wall of holes from CNC step.
For making an unleveled surface and pores, the surface must be etched. This step will be done with a micro etch solution which lead to a better adhesion. The micro etch is an acidic solution.
The copper ions could be deposited on the wall of the holes. For this reason, at first palladium ions are deposited on the wall and lead to activate the wall of hole, then the copper ion will be deposited there. The palladium ions with tin ions are responsible for this action and the activation solution is provided these ions.
The accelerator solution is between the Activation and Electroless steps. This solution has two main effects. The first removes the residues tin on the board from activation step and the second one is protection Electroless bath from contamination so the Electroless solution is protected from decomposition early.
A thin copper layer is deposited on the wall hole from copper Electroless which is deposited on the surface of board simultaneously. The thickness of the deposition is low and the importance of this step is just make electric board.
Anti – Tarnish
The copper is so act and will react with O2 exist in the air since it exposes on the air and the black layer of Copper Oxide is formed. This layer is not act and for continues plating, must be removed. The Anti-Tarnish solution is responsible this step without any damage to the board.
Copper and Tin-Lead Electrolyze
In this step a thickness layer of copper about 25 microns is deposited from Copper bath on the wall holes and surface and finally Tin- Lead is deposited on the copper for protection the circuits when the board goes to stripping step.
Stripper is divided to two kinds: copper stripper and tin stripper. In copper stripping the copper from the board surface is removed and after that in Tin stripping the tin on the circuits is removed and the board is prepared for solder mask step.