According to the appearance of copper foil, it is divided into two types: bare copper and resin coated copper foil. The surface of the copper foil covered with a layer of tape is resin coated copper foil, otherwise it is bare copper; according to the position in the transformer, it is divided into inner copper and outer copper. Bare copper is generally used for outer copper of transformers. Copper foil generally plays a shielding role in transformers, mainly to reduce leakage inductance and excitation current. When the current passing through the winding is too high, copper foil replaces the copper wire and acts as a conductor.

1)In the copper foil winding method, except that the solder joint must be flattened, the winding edge of the copper foil should not be pressed at the corner of the bobbin. It must be wound from the center of the bobbin to prevent the formation of a short circuit between the second layer of copper foil and the first layer due to extrusion and puncture of the tape.

2)When the inner copper sheet is used as a shielding winding between layers, its width should cover the winding area of the layer as much as possible. When the thickness of the copper foil is less than 0.025mm, both ends can be exempted from rounding, but when the thickness is more than 0.05mm (inclusive), both ends need to be rounded.

3)Copper foil must be wrapped upright and flat, not to one side, and not to the retaining wall.