In this paper, a method to fabricate radio frequency (RF) circuit structures is described. This method involves inkjet printing of a silver nanoparticle-based ink on a functional substrate material to create the seed track (i.e., the seed layer), onto which copper is subsequently deposited by an electroless plating method, to obtain the desired thickness and conductivity of the RF structures. This process combination was validated by fabricating an S-band filter on a high-frequency substrate and comparing the RF performance of this filter with that of a filter fabricated using the conventional lithography-based method. The adhesion of the circuit structures to the substrate was qualitatively ascertained by the scotch tape test method. The performance of the inkjet-printed-electroless-plated filter was comparable to that of the conventional filter, thus proving the suitability of this novel method for practical RF applications.
This paper describes the optimisation of the surface characteristics of a high-frequency substrate material widely used in the PCB (printed circuit board) industry by means of CF 4 /O 2 plasma etching, in order to make it suitable for the fabrication of RF (radio frequency) circuit structures by a combination of inkjet printing and electroless plating. A statistical DoE (design of experiments) based on a CCRD (central composite rotatable design) was used to systematically vary the plasma etching parameters and explore the characteristics of the etching process. This experimental design yielded 31 substrates, all of which were assessed in terms of surface energy, surface roughness and adhesion. Out of these substrates, 5 were identified as having the most favourable surface characteristics. Finally, RF circuit structures in the form of S-band filters were fabricated on these substrates using an inkjet printing-electroless plating combination, and the RF performance of these structures was characterised and compared.
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