Evaluation of Delay Uncertainty in PCB Interconnects Due to Fiber Weave Effect

Delay Deviation Exceedance (DDE) and Differential Skew Exceedance (DSE) measures are proposed to quantify delay uncertainty in single-ended and differential PCB interconnects arising from Fiber Weave Effect (FWE). DDE and DSE are constructed with 3D EM analysis of traces over inhomogeneous dielectric with glass fiber bundles in resin. Measurements or 3D EM models for FWE are usually used for observations of delay or impedance dependency on position of traces over fiber bundles with the purpose to find the worst case scenario. This paper turns the results of 3D EM analysis into probabilistic measures of possible delay or skew uncertainty - probability to have delay deviation in single-ended interconnects over allowed limit (DDE measure) or to have skew over allowed limit in differential interconnects (DSE measure). The introduced measures allow formalizing the laminate selection process for parallel as well as for serial PCB interconnects.