An electromagnetic, EM, device, includes: a substrate having a dielectric layer and a first conductive layer at a first side of the substrate, the substrate having a via that extends at least partially through the substrate from the first side toward an opposing second side of the substrate; at least one dielectric structure having at least one non-gaseous dielectric material that forms a first dielectric portion that extends outward from the first side of the substrate, the first dielectric portion having a first average dielectric constant, the at least one dielectric structure further having a second dielectric portion that is contiguous with the first dielectric portion; wherein the second dielectric portion extends into the via of the substrate, the via having a mechanical interlock surface; and wherein the at least one dielectric structure includes a mechanical interlock between the second dielectric portion and the mechanical interlock surface of the via of the substrate.