Preventing glass-weave skew

Glass-weave skew (GWS), often referred to as the fiber-weave effect (FWE), is an often overlooked and frequently misunderstood source of differential-timing issues in a printed circuit board (PCB). Glass-weave skew occurs when the chance alignment of the glass weave within a dielectric results in anisotropic resistance over the length of differential transmission lines, resulting in slight impedance variations, causing differential skew and resulting in seemingly random board failures. Although impossible to predict, there are multiple techniques that can be employed to mitigate the effect. This white paper describes the sources of this skew and presents 11 techniques that can be used to control glass-weave skew in a PCB.

Glass-weave skew additional description

The impact of glass-weave skew on Signal Integrity (SI) is magnified by exponentially increasing bit rates, but is ultimately driven by two competing factors:

• The need for near-complete symmetry between two halves of a differential pair
• non-uniform microenvironments across dielectric materials

This white paper provides an in-depth description of the sources of this skew and presents 11 techniques that can be used to control glass-weave skew in a PCB.