Comparison of an Inkjet Fabrication Method on Low-Cost PCB Substrates With Semi Additive And Subtractive Technologies Regarding RF-Performance

Abstract

In this paper, an additive manufacturing method based on inkjet printing is presented which allows the production of passive RF-structures on low-cost PCB substrates for industrial applications up to 100 GHz. Due to the relative high surface roughness of the underlying PCB substrates, compared to glass or ceramics, overprinting of several layers often leads to poor results because of concomitant unwanted bulging effects. As a result, suitable plasma processes must be applied, to guarantee small line and space dimensions down to $25\ \mu \mathrm{m}$. To increase the conductivity, to close possible micro cracks and to lower insertion loss in the two-digit GHz range the printed line segments are additionally plated with an electroless copper layer. By using these fabrication method, excellent design rules can be achieved over complete PCB panels. This allows the cost-effective realization of compact, passive RF-filters which have comparable manufacturing- and RF-performances to filters produced with competitive subtractive or semi additive processes (SAP).