PCB High-Speed Signal Design Guidelines: Agilex™ 5 FPGAs and SoCs

ID 821801
Date 11/18/2024
Public
Document Table of Contents

3.3.5. Fiber Weave

  • A composite of fiber and resin make up the PCB material. The strand bundles of fiber run perpendicular to each other. Depending on the orientation of the weave relative to the trace, there can be a resin or a fiber bundle beneath the trace. The differing dielectric constants of these two materials may introduce a phase skew among signals that comprise a differential pair, manifesting itself as an AC common mode noise at the receiver, affecting both the voltage and timing margin at the receiver. This is the fiber weave effect. To mitigate the fiber weave effect, specify a dense spread of weave (1078, 1035, 3313, 1067, etc.) rather than a sparse weave (106, 1080) for prepreg and core.