Electroless (ELS) copper plating process has been commonly used in the metallization process of printed circuit boards (PCBs), because the sidewalls of the through holes (THs) of PCBs are composited of resin and glass fiber, which are not conductive materials. Hence, before plating these THs, their sidewalls have to be metallized by ELS copper plating. The process causes harmful influence to environment because it contains precious metal (i.e., Pd as a catalyst), formaldehyde and chelating agents. However, reduced graphene oxide (rGO) grafting process, proposed in this work, is environment-friendly and can replace the ELS copper plating process to make the sidewall of the TH of a PCB be conductive for copper electroplating. The rGO grafting process has less steps and an environment-friendly formulation. In this work, the rGO is grafted on the sidewalls of THs of a PCB with a high aspect ratio (AR). We observed that the copper nucleation mechanism of electrochemical deposition on a PCB is progressive. In addition, we studied the suppression of various levelers on copper electrodeposition in order to control the copper to be less deposited at the hole opening but much more deposited at the hole center. Finally, the throwing power (TP) of the copper electrodeposition in the TH can be significantly enhanced.
In our research, the effects of electroplating baths, operating parameters and electroplating additives, especially levelers, were investigated for obtaining a high TP of THs. On the other hand, the suppression of various levelers was evaluated by electrochemical analysis, such as linear sweep voltammetry (LSV) and galvanostatic measurements. The results indicate that the electroplating bath containing the leveler with stronger suppression can control the copper to be specifically deposited at the hole opening. Hence, a high TP of plating TH was achieved by using the rGO process. Moreover, the plated TH can pass thermal shock test. That means, a brand-new and promising rGO process can replace the ELS copper plating in the future for producing advanced electronic products.