A method includes creating an opening in a first outer layer of a multilayer sheet of material, the sheet of material having three or more layers of material, including the first outer layer and a second outer layer. A selective etchant is introduced through the opening, where the etchant selectively etches an interior metal layer of the multilayer sheet of material compared with the first and second outer layers. The selective etchant is permitted to etch material of the interior metal layer under the first outer layer.