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JUNE 2019 I DESIGN007 MAGAZINE 69 ancy (EMC) are due to excessive noise on the PDN coupling into external cables and radiat- ing emissions. Figure 5 projects the radiation of the power planes relative to the FCC Class B limits. One also needs to ensure that the har- monics do not exceed the imposed limits. The PDN is linked to the stackup; there- fore, any adjustments to the stackup config- uration—whether it be materials, vias, trace, clearance, or thickness parameters—should be reflected in the PDN. The PDN can be fine- tuned by adding more planar capacitance without affecting transmission line imped - ance. The optimization of the PDN is a tri- al-and-error process that needs to be done in conjunction with the stackup materials to ful- ly exploit all avenues. It is surprising how many designers do not get the basic key pillars of stability right. For very little extra effort, your design can have improved performance and reliability over a wide range of operating environments, giving you greater confidence in your product's per- formance for the projected lifetime. Key Points • Premature failures are of particular concern and are typically the result of poor design practice or substandard manufacture • The cost of development is dramatically reduced if the simulation is employed early in the design cycle • Simulation identifies issues early in the design process and rectifies them before they become a major problem • The key to ensuring product reliability all begins in the design phase • Selecting the most suitable dielectric material for the substrate is one of the most important factors in establishing a reliable product • The electrical properties of dielectric material can be described by two terms: dielectric constant and dissipation factor • The designer needs to compare dielectric materials based on the manufacturer, fabricator, frequency, dissipation factor (loss), and dielectric constant Figure 6: PDN noise between planes. (Source: iCD PDN Planner)

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