PCB grounding through screw head
If you can't tolerate corrosion then don't use zinc on copper. If you look on the table below zinc on copper is ADE which means plating is consumed and corrosion increased. Another thing to consider is if the copper is plated then it will be zinc on nickel but I don't have info on that. 


Source: http://www.preservationscience.com/materials/metals/PGC.html