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44 DESIGN007 MAGAZINE I MAY 2024 electrical, thermal, and other critical proper- ties. Choosing the appropriate dielectric mate- rial hinges on the required frequency range and operational environment. As demands shi from conventional dielectric constants and thermal attributes (such as Tg and Td), there may be an associated increase in material costs as we move from standard materials to the more exot ic materials. Materials boasting the lowest Dk and Df values tend to be pricier and may suffer from limited inventory availability, significantly impacting lead times. e Dk value is known as dielectric constant or relative per- mittivity, and the Df value is the dissipation fac- tor or loss tangent, it and tells the designer how lossy (electrical energy loss) a material may be. In simpler terms, it defines the ability of an insu- lator to store energy. It measures a material's ability to store electrical energy in an electric field. Additionally, when signal integrity and signal loss are critical, the micro-topography of copper foil cladding requires considerable atten- tion. Numerous low-profile foils are available to mitigate and address signal loss. In general, and I cannot stress this enough, the optimal approach to material selection involves early collaboration with an experi- enced PCB manufacturer. eir expertise can streamline the material shortlisting process and identify the most suitable solution for your design requirements, balancing perfor- mance, cost, and availability. Many manufac- turers are willing to pre-order materials with extended lead times once the designer finalizes the material and copper cladding selection, thereby expediting the build process when the design is ready for implementation. ere are industry tools available to assist you in the selection process such as Z-planner Enterprise and Polar Instruments PCB Stackup, just to mention a couple, but, again, the industry best practice is early collaboration with your PCB manufacturer. is ensures the highest poten- tial for meeting your design requirements and downstream success. Some designers are now designing high- speed and even RF boards with traditional FR-4 materials instead of automatically specifying Rogers, etc. (Resin systems have improved a lot in the last decade or so.) What are some potential hurdles that designers should be aware of when underconstraining materials in this way? Typically, most designs function up to approx- imately the 10 to 20 GHz range using conven- tional FR-4 materials, although not without encountering performance challenges and obstacles. As frequencies increase, dissipation factors (Df ) become a more pressing concern. Standard FR-4 materials typically demonstrate a Df ranging from 0.015 to 0.021. In contrast, high-performance materials, coupled with lower Dk, boast Df levels in the vicinity of 0.002 to 0.0013, roughly 10X lower. Additionally, standard FR-4 materials are susceptible to changes in Dk and Df due to moisture absorption, heightened operational frequencies, and thermal factors. High-per- formance materials offer the added advantage of lower moisture absorption and, given their inherently low Df, tend to exhibit superior per- formance at higher frequencies. Stephen Chavez