Modeling the effect of trace profiles on the RF performance of additively manufactured microstrip transmission lines on polyimide substrates

The trace profile and thickness of a conductor have a significant effect on its Radio Frequency (RF) performance. Additively manufactured traces in particular, have a non-uniform thickness/profile. The thickness of the trace at the edges of a printed conductor is normally less than that at the center of the trace. At high frequencies, these edge thicknesses are less than the skin depth of the conductor thereby leading to increased losses along the line. It is therefore important to accurately model the printed transmission lines so as to have a better understanding of how these factors affect the RF performance of the printed traces. This paper models the effect of trace profiles on the RF performance of a screen printed microstrip transmission line using (ACI FE3124) a silver ink on 5 mil thick Kapton. The profile of a sample transmission line is obtained using the Keyence laser microscope. This profile is then broken down into various sections. The different profile types are then simulated using ANSYS® High Frequency Structure Simulator (HFSS) from 10 MHz to 40 GHz. RF parameters for the different trace profiles are then compared. It is observed that traces with overall thicknesses less than the skin depth result in higher insertion losses while varying transmission line widths due to printing imperfections affects the trace impedances.