Quantification of Delay and Skew Uncertainty due to Fiber Weave Effect in PCB Interconnects

To quantify delay uncertainty caused by Fiber Weave Effect (FWE) in single-ended and differential PCB interconnects, two new metrics are introduced: Delay Deviation Exceedance (DDE) and Differential Skew Exceedance (DSE). DDE and DSE are probabilities to have delay or skew exceeding some limit. They are derived with 3D EM analysis of traces over inhomogeneous dielectric with glass fiber bundles in resin. An approximate formula for the exceedance is proposed. The formula has just one parameter that can be obtained with measurements or numerical model. The proposed metrics can help formalize the laminate selection process for parallel as well as for serial PCB interconnects.