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44 DESIGN007 MAGAZINE I JULY 2022 selected. Keep in mind that material costs vary with quantity. Matching material performance numbers of the dielectric constant (Dk) is also important. A small difference in this value between mate- rials can impact impedance, line widths/clear- ances, and thus losses significantly. Also, the dielectric constant of a material determines the propagation speed of the signal in the medium. So, if Dk values vary on different layers of the substrate, then bus timing may also be an issue. One should consider construction options that allow a drop-in material that matches the impedance for each mirrored layer of the stackup. As signal speeds get up into the gigahertz range, the 2D field solver is an essential tool that every PCB designer must employ to main- tain design integrity and performance. Imped- ance is the foundation of the system perfor- mance and reliability, so using a 2D field solver to get it right is not an option. Key Points • Field solvers employ Maxwell's equations to calculate the parasitic elements of a solution space. • EM fields are not restricted to the mul- tilayer substrate and if proper care is not taken may emit radiation causing electro- magnetic interference. • In a uniform cross-section transmission line, a propagating signal sees the same instantaneous impedance all the way down the line. • Since the 2D BEM solver results in a smaller solution space it is considered faster than other 2D solvers. • Filed solvers are limited to the numerical accuracy of solving Maxwell's equations, Figure 3: Example of a fabricator's dielectric materials loss profile. (Source: iCD Materials Planner)