ABL Circuits PCB Manufacture Tin Plating

The next process along the plating line is to protect all the copper areas that you want to keep, which is the copper you can see, with tin. This is not the tin that is going to be on the board at the end of the process, it is there purely to protect the copper tracks from the etching process later on. So once the tin is applied, the blue film is then stripped off leaving bare copper, and all the tracks that you want to keep is protected by the tin plating.