Through hole plating process is a key to multilayer pcb's

To make printed circuit boards that have more that one layer, there must be a way to connect the lines from one side to other. In home proto pcb manuracturing there are not that many good options. In small proto pcb labs like the one at university of Oulu and in industry the main method to make through hole's conductive is electrolytic process.

Electrolytic process is an electro chemical way to add copper to the hole wall's and so make lines connect from any to all layers of pcb. This process can be done for two layer boards as well as two+ layers. As mainly uni. of Oulu pcb lab makes two to four layer boards and the process is the same for these layer sets, only this process will be explained. In industry there are some specific cases of through hole making that will not be discussed here.

To simplify the process, holes are drilled to the board. Holes are threated with suitable chemicals and graphite based solution in added to the hole wall's. Graphite will make the pcb laminate (usually glass fiber) conductive. After this copper is added to the hole walls by electrolytic process by using copper as anode and pcb as catode and running current through a path suitable for the process. This will grow desired copper to the holes and connect layers as wanted.

For the through hole plating machine, see the main page.