Characterization of Additively Produced RF-Structures on Low-Cost PCB Materials Based on Inkjet Technology for Industrial Applications up to 80 GHz

Usually, the printed circuit board industry has to use special subtractive manufacturing methods, if small line and space dimensions down to
$50~\mu \text{m}$
are desired. This drastically raises production effort and costs. In this article, a method is shown as to how the inkjet technology can be used to produce passive RF structures with minimum line and space dimensions of
$25~\mu \text{m}$
. For the first time, this is possible over complete panels of low-cost printed circuit board (PCB) substrates, which have a relatively high surface roughness compared to ceramic or glass carriers. To ensure process reliability, printed lines must also be plated with an additional electroless copper layer to overcome the surface roughness with conductive layers and to lower insertion loss in the two-digit GHz range. Additionally, a surface impedance model is developed, which allows broadband first time right simulations. Finally, additively produced, passive RF filters are compared to their subtractive counterparts to show their benefits regarding production costs and electrical performance up to 80 GHz.