Issue link: https://iconnect007.uberflip.com/i/1498723
22 DESIGN007 MAGAZINE I MAY 2023 planner has five default profiles ranging from basic FR-4 to ultra-low loss materials, as in Table 1. is enables the designer to compare dielectric materials based on manufacturer, fabricator, frequency, dissipation factor (loss), and dielectric constant. Another issue is that materials available locally (vs. offshore) can vary from fabricator to fabricator. Typically, prototype boards are fabricated locally, whereas those made in Asia are a more economical option for mass produc- tion. Profiles of PCB fabricators can be set up to display the complete range of materials each fab shop stocks, enabling comparison among shops. Figure 3 plots the loss properties of dielec- tric materials from an Asian fabricator. One can easily see which materials are best for high- speed applications and can choose among a few materials that are in stock. Cost-to-perfor- mance evaluations must still be done to ensure that the lowest-cost material is selected to do the job. Also, keep in mind that material costs vary with quantity. Matching material performance numbers of the dielectric constant is also important. A small difference in the value between materi- als can significantly impact impedance, line widths/clearances, and thus losses. Also, the dielectric constant of a material determines the propagation velocity of the signal in the medium. So, if Dk values vary on different layers of the substrate, then bus signal timing may also become an issue. One should con- sider construction options that allow a drop-in material that matches the impedance, and Dk, for each layer of the stackup. PCB designers need to quickly choose the best, most cost-effective material for their application from among the vast array of choices available. Sorting through numerous slash sheets and datasheets is very time-con- Figure 3: Example of a fabricator's dielectric materials loss profile. (Source: iCD Materials Planner)