US Patent 9707738 Copper foil and methods of use

A copper foil having a matte side with nickel plated thereon in an amount of nickel in the range of 100,000-300,000 μs/dm2. The plated copper foils have particular utility in Positive Temperature Coefficient (PTC) devices. The plated copper foils have a surface hardness of from 50 to 200, a tensile strength greater than 45 kg/mm2 and a shiny side surface roughness (Rz) not exceeding 2.0 μm. The surface roughness of the matte side of the copper foil is in the range of 6 to 10 μm. Copper nodules are present on the matte side of the copper foil between the copper foil and the nickel plating. Methods of producing the copper foil and PTC devices incorporating the copper foil are described.