"Transmission loss needs to be considered in the design of telecommunication systems. If telecommunication systems have high transmission loss, the signals lose too much of their strength, which results in poor reception in television networks and lost calls in cellular networks. Total transmission loss, in the MHz-GHz range, has several different loss components, some of which are poorly characterized. Conductor loss is the largest loss component and the most difficult to predict. It is known that the conductor geometry or features influences the conductor loss. However, current numerical, analytical and empirical tools do not accurately predict this loss component, and there is little experimental data available to explain and show the impact of these conductor geometries. The conductor shape is heavily influenced by the ceramic substrate surface roughness, and this is especially true for printed circuit boards fabricated with thick-film technology. The two conductor features of interest are the conductor-edge angle and conductor-ceramic interface. For thick-film circuits, the edge of the conductor does not have a square cross section but has a tapered shape or angle. The conductor-ceramic interface is also rough at the micron scale. Since the current density is concentrated at the extremities of the conductor then these features, conductor-ceramic interface and conductor edges, can potentially have a large impact on conductor loss. For this study, the surfaces of ceramic substrates were subjected to different surface finishes that resulted in distinctly different surface characteristics. This in turn resulted in a range of conductor-ceramic interfaces and conductor-edge angle geometries. The impact of the conductor-edge angle and conductor-ceramic interface features on conductor loss was measured over a range of frequencies and conductor conductivities to ascertain the level of their contribution. It was shown quantitatively that the conductor-edge angle was significantly altered by the surface roughness and heavily influenced the conductor loss result. The consensus for decades has been that greater surface roughness causes the ceramic-conductor interface geometry to have a greater impact on conductor loss, increasing the conductor loss. However, this study has shown that greater surface roughness also causes the conductor-edge angle feature to have a smaller or reduced impact on conductor loss, improving the conductor loss result - this has not been considered previously. Focusing on only one of these features can give an anomalous loss prediction; both features need to be considered for the calculation of conductor loss for thick-film applications. The low frequency loss results are as expected but the high frequency (greater than 5GHz) results depend on edge angle and therefore thick-film paste viscosity, and substrate surface roughness. "
Worcester Polytechnic Institute
Materials Science & Engineering
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Vincent, T. S. (2009). TRANSMISSION LINE FEATURES AND THEIR INFLUENCE ON GHz CONDUCTOR LOSS. Retrieved from https://digitalcommons.wpi.edu/etd-dissertations/302
GHz, interface, edge, conductor loss