Intel Agilex® 7 Device Family High-Speed Serial Interface Signal Integrity Design Guidelines

ID 683864
Date 6/15/2023
Document Table of Contents

1.3.7. 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 prepreg1 and core.
  • Use a 2-ply (1078x2, 1078+1067, 1035x2, etc.) prepreg and core to mitigate the fiber weave effect. Especially for the 112G PAM4 application, it is better to use 2-ply (1035x2, 1078x2, 1035+1078) prepreg and core.
  • For more details about the fiber weave effect, refer to AN 528: PCB Dielectric Material Selection and Fiber Weave Effect on High-Speed Channel Routing.
1 "Prepreg" is an abbreviation of "pre-impregnated material," in this case, referring to the PCB fiberglass impregnated with resin (an epoxy-based material) used in multilayer boards.