Extraction of Stripline Surface Roughness Using Cross-section Information and S-parameter Measurements

To characterize additional conductor loss introduced by conductor surface roughness, various models have been proposed to describe the relationship between foil roughness levels and surface roughness correction factor. However, all these empirical or physical models require a PCB sample to be manufactured and analyzed in advance. The procedure requires dissecting the PCB and is time- and labor-consuming. To avoid such a process, a new surface roughness extraction process is proposed here. Only the measured S-parameter and nominal cross-sectional information of the board are needed to extract the roughness level of conductor foils. Besides, this method can also deal with boards having non-equal roughness on different conductor surfaces, which is common in the manufactured printed circuit boards (PCB). The roughness level on each surface can be extracted separately to accurately model their contribution to the total conductor loss. The presented method is validated by both simulation and measurement. A good correlation is achieved between extracted roughness level and the measured value from the microscope.