A new 3D stencil mask guides deposition of a shaped structure, typically an electromagnetic device component, onto a non-planar surface. The 3D stencil mask includes islands and bridges from prior art two-dimensional lettering stencils, but raises the islands and stencils above the side of the 3D stencil mask facing a non-planar surface, forming undercuts, so that material particles, such as from vacuum metal deposition, will form connected shapes. The 3D stencil mask is also configures so that the dimensions of the resulting electromagnetic structures are altered from a simple projected image of a structure designed for a planar surface so that the electromagnetic properties of the deposited structure are more nearly the same as those of a corresponding structure on a planar surface.