Return loss of printed silver paste lines with different filler sizes and their surface roughness

We studied the high-frequency characteristics at 0.5-1.5 GHz of mask-printed silver paste lines with different filler sizes (nanoparticles or micro-sized flakes) and an etched copper foil on glass fiber reinforced epoxy substrate. Although the resistivity of silver-nanoparticle lines was 10 times larger than that of the etched copper foil, its return loss was almost equal to that of the etched copper foil. Moreover, the return loss of silver-nanoparticle lines was smaller than that of the silver-flake lines even though their resistivities were compatible. We confirmed that the return loss of the conductive lines decreased with their surface roughness, and not only with their resistivitiy.