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The 16.6-2015 Allegro PCB Editor release introduces the interactive conversion of Orthogonal and 45-degree routed traces into a Zig-Zag pattern to minimize the Fiber Weave Effect in a Printed Circuit Board (PCB).
What is “Fiber Weave Effect”?
PCB Dielectric material sheets that are placed between signal and plane layers in a PCB stack-up are constructed from several woven fiberglass fabrics bonded together with epoxy resin. Traces routed directly over the fiberglass weave will see a different Dielectric Constant than the traces that are routed over the voids in the weave where only epoxy resin is present. At high data rates, this dielectric constant mismatch can cause signal integrity issues when running these high-speed signals parallel to the void areas of PCB fiberglass weave. If the condition exists on a differential pair where one member is running directly over the weave and the other running over the voids in the weave, it can result in different propagation velocities between the legs of the Differential Pair:
This feature supports both routed differential pair and single-ended nets. Users are provided the ability to specify the required zigzag angle offset and maximum segment length, as well as the option to convert full segments or define start/end points.
Route – Unsupported Prototype - Fiber Weave Effect – Add ZigZag Pattern
There are some options for Fiber Weave – Add ZigZag Pattern that need to be setup and reviewed prior to adding the ZigZag pattern. These options can be updated during the process and prior to committing the pattern to allow you to find the ZigZag pattern the works best for your design.
Options window – These settings allow the user to set the Fiber Weave options. All options are saved in the design:
You can use the Add Zigzag command to convert cline segments based on the setting defined under the Options window in several ways:
I look forward to your feedback!
Jerry “GenPart” Grzenia
Hi Jerry, I use this feature all the time when routing high speed nets. The tool works particularly well when routing PCIe nets over long distances. One of the better features that Cadence has added.