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24 The PCB Design Magazine • February 2014 to 10% difference in the insertion loss as illus- trated in Figure 7. Note that FR-408 can be con- sidered as a medium-loss dielectric. Difference in insertion loss between model with increased LT and with proper roughness model can be as large as 30% starting from 3–5 GHz in cases of low-loss dielectrics 9 such as Megtron 6. Model with the rough conductor produces more accu- rate insertion loss estimation for broader range of strip widths. This example illustrates typical situation and importance of the dielectric and conductor roughness model identification to have analysis to measurement correspondence up to 50 GHz. Interesting results of dielectric and conduc- tor roughness models identification with GMS- parameters for multiple materials were recently reported 10 and some data are provided in Table 1 as another practical example. Note that all dielectric and conductor rough- ness models identified here are not actually re- stricted to the upper frequency 50 GHz level used in the identification process. The models are frequency-continuous and can be useful well above that frequency. This is one of the ad- vantages of the broadband model identification method over approaches with resonators where dielectric properties are identified only at some frequency points. Conclusion An overview of frequency-continuous di- electric and conductor roughness models is pro- vided in the paper. Such models must used in PCB and packaging interconnect analysis and measurement correlation up to 50 GHz and be- yond. Practical procedure for the identification of the model parameters have been described PCB AND PACkAGING DESIGN UP To 50 GHz continues feature Figure 5: Measured (red and blue curves) and computed (green curves) gMS insertion loss (left plot) and group delay (right plot) for 6-inch stripline segments—wideband Debye dielectric model with Dk=3.83 (4.6% increase), lT=0.0138 (18% increase), smooth copper surface.