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34 DESIGN007 MAGAZINE I MAY 2024 Materials used for the fabrication of multi- layer PCBs absorb high frequencies and reduce edge rates. at loss in the transmission line is a major cause of signal degradation. How- ever, not all of us are designing cutting-edge boards and sometimes we tend to over-specify requirements that can lead to inflated produc- tion costs. In this month's column, I will look at the types of materials commonly used for PCB design and how to select an adequate material to minimize costs. Signals carried by electromagnetic energy propagate through the PCB medium, guided by the signal traces. It is the dielectric material between the copper signal and plane layers in the PCB that affects signal velocity. Dielectric Dielectric Material Selection Guide constant (Er or Dk) and dielectric loss (dis- sipation factor/loss tangent, Df ) play crucial roles in signal propagation: • Dk describes how the material increases capacitance and decreases speed. Higher Dk increases capacitance and decreases signal velocity. It also reduces the imped- ance of the transmission line. • Df quantifies the inherent dissipation of electromagnetic energy within the mate- rial. It is best to select materials with a low dissipation factor. High Df leads to energy dissipation and signal attenuation. While lossy materials may impact impedance, they are oen more cost-effective. Beyond Design Feature Column by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA

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