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40 The PCB Design Magazine • May 2015 You can approximate the RMS heights of the drum and matte sides by Equations 6 and 7: equation 6 Where: R z_drum is the 10-point mean roughness in meters. If the data sheet reports average roughness, then R a_drum is used instead. equation 7 Where: R z_matte is the 10-point mean roughness in meters. Practical Example To test the accuracy of the model, board pa- rameters from Yuriy's Shlepnev's February 2014 article in The PCB Design Magazine [5] was used. Measured data was obtained from Simbeor soft- ware design examples courtesy of Simberian Inc. [9] . The extracted de-embedded generalized modal S-parameter (GMS) data was computed from 2-inch and 8-inch single-ended stripline traces. They were originally measured from the CMP-28 40 GHz High-Speed Channel Modeling Platform from Wild River Technology [15] . The CMP-28 Channel Modeling Platform, shown in Figure 6, is a powerful tool for devel- opment of high-speed systems up to 40 GHz, and is an excellent platform for model develop- ment and analysis. It contains a total of 27 mi- crostrip and stripline interconnect structures. All are equipped with 2.92mm connectors to facilitate accurate measurements with a vector network analyzer (VNA). The PCB was fabricated with Isola FR408HR material and reverse treated (RT) 1oz. foil. The dielectric constant (Dk) and dissipation factor (Df), at 10 GHz for FR408HR 3313 material, was obtained from Isola's isoStack web-based online design tool [10] . This tool is free, but you need to register to use it. An example is shown in Figure 7. Figure 7: example of Isola's isostack online software used to determine dielectric thicknesses, Dk, Df and characteristic impedance for the CMP-28 board. Figure 6: CMP-28 Modeling Platform from Wild river Technology. Photo credit Wild river Technology. CANNONBALL STACk FOR CONDuCTOR ROuGHNESS MODELING continues article