Shielding is usually done to reduce unwanted electrical interference from RF signals. Shielding needs to fully cover the unit affected and properly grounded. Often I see shielding around the perimeter of a single coil pickup and often not grounded. Even though the shielding is around the coil, unwanted electrical interference can penetrate the top and bottom of the bobbin that is often unprotected from shielding.

Many think that the shielding will help reduce 60 cycle hum that is associated with single coil pickups. Copper foils and paints will not significantly reduce the unwanted magnetic fields that can penetrate the coils of single coil pickups.