Waveguides operating at a typical 77GHz frequency require mainly three properties on their active surface: The highest possible electrical conductivity, a minium thickness throughout the whole area and a roughness as low as possible. Silver is the best conducting metal but also rather expensive, followed by copper, which is much cheaper. Electroplating guarantees the optimal price-performance ratio with a combination of copper and silver as well as an unparalleled uniform thickness regardless of geometry or orientation of the surface. It even reduces the roughness of the underlying polymer surface in the micrometer range to further decrease signal losses which no other technology can do.

Like many other components in automotive production longterm function of waveguides will be mainly influenced by repeated changes in temperature during lifetime. They lead to cyclic expansion and contraction which consequently result in cracks in the poylmer and delamination of the coating. A higher thickness of the coating provided by electroplating supports the robustness of the whole component. Mechanical interlocking between base material and coating leads to a safe protection against delamination. This technique that has been proven already with billions of decorative parts in automotive production.

PVD is the abbreviation for Physical Vapor Deposition. It is carried out in a vacuum chamber and uses different methods of bringing metal into the gas phase which then condensates on to a substrate. For waveguide coating a special variant called "sputtering" is used, which usually leads to thin coatings of about 300nm in thickness. Extended sputter times in large linear modules can be used to extend the thickness to the required 1µm for waveguides. Since the substrates do not move in these lines and the stream of hot metal comes mainly from one direction, thickness varies very much upon the surface orientation of the waveguide structure. Electroplating on the other hand uses liquid electrolytes at near room temperature at normal pressure. Coating deposition of several microns can be done with ease in no time. Thickness hardly depends on the orientation of the surface. In contrast to PVD, electroplating needs waste water treatment, which is, however, a well established process in all existing plating lines for decorative coating.

Both PVD coating and electroplating can be done with a high degree of automation. Differences in cost will therefore be due to the initial investment, material use and energy. PVD coating needs at least 10 times the overall energy compared to electroplating. If you choose to use a five times higher copper coating with electroplating and benefit from the increased stability, it still needs just half of the energy. Copper doesn't significantly account for the overall price of the component, but silver does. PVD has much higher losses of silver in the process and needs more silver on the product due to the lack of uniformity over the structured surface. Apart from theoretical considerations costs will also be affected by the availability of prodcution facilities. PVD coating of waveguides requires very specific linear coating devices, which will usually be built just for that purpose. Also a mixed use for different products will not be feasable in most cases due to the expected contaminations. Electroplating can be done in standard lines with high availability world wide. Also a mixed use for different products is possible.

As already mentioned, PVD coating of waveguides needs very specific linear production lines to deal with the required throughput. They have to be build just for that purpose and require high investments. Metal coating with thicknesses of minimum 1µm is not standard with this technique and raises additional challenges for the required adhesion to the polymer. Even though mass production has been sucessfully demonstrated it requires a high degree of knowledge. Electroplating of waveguides on the other hand is done in existing production lines typically used for decorative chroming. Some minor adaptations are required for the etching and the silver instead of nickel and chromium. Those lines already exist all over the world. The knowledge for plating on plastics is very common and a big source of suppliers is available that already have extensive experience in automotive production.