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JULY 2022 I DESIGN007 MAGAZINE 43 rectly enters the dielectric constant or other properties, then the field solver is hardly to blame when you get erroneous results. Using the exact materials that are stocked by your preferred fabricator can increase accu- racy by up to 5%. at is why the availabil- ity of a comprehensive dielectric materials library and dielectric material selection is so important. Years ago, when clock frequencies were low and signal rise times were slow, selecting a dielectric material for your PCB was not dif- ficult—we all just used FR-4. We didn't really care about the properties of the materials. However, with today's multi-gigabit designs, with extremely fast rise times and tight mar- gins, precise material selection is crucial to the performance of the product. Materials used for the fabrication of the multilayer PCB absorb high frequencies and reduce edge rates. at loss in the transmission lines is a major cause of signal integrity issues. But we are not all designing cutting-edge boards and sometimes we tend to over-specify requirements that can lead to inflated production costs. Over the years, a huge range of materials has been developed for multilayer PCB fabrica- tion. In fact, to give you an idea, iCD now has a choice of over 700 series of dielectric materi- als from over 60 different manufacturers, in its dielectric materials library. When each mate- rial is used for the right target application, the resultant PCB will have the lowest possible cost while still satisfying the design and perfor- mance goals of the project. Selecting the best material for an application is oen a daunting task. One needs to quickly sort through the vast array of choices to make an informed deci- sion. Figure 3 plots the loss properties of dielec- tric materials from a fabricator. One can eas- ily see which materials are best for high-speed applications and can choose a few materials from this that are in stock. Cost-to-perfor- mance evaluations must still be done to ensure the lowest cost material that will do the job is Figure 2: The iCD Stackup Planner coupled with the ZMetrix TDR and ZScan software.