Signal Dispersion
Propagation path variations in printed circuit board laminates degrade high-frequency differential signals as they travel along woven glass substrates. Glass weave scattering arises when the alternating fiber bundles and resin gaps of the board substrate cause high-speed signals to encounter variable dielectric constants. This variation creates localized phase differences and amplitude losses in the transmission line.
Propagation Skew
Phase shifts between the two halves of a differential pair result in the conversion of differential energy into common-mode noise. As one trace runs over a dense glass bundle and its partner runs over a resin-rich gap, the signals travel at different speeds. This phase skew destroys the timing margins needed for gigabit-rate data interfaces.
Laminate Selection
Manufacturing high-speed circuit boards requires specifying specialized glass styles that minimize dielectric non-uniformity across the panel. Weaves that use spread or flat glass fibers distribute the glass and resin more evenly across the board. Using these uniform materials prevents signal skew without requiring expensive and complex routing workarounds in the layout design.
Designers also route traces at a slight angle relative to the glass weave grid to average out the dielectric variations, which ensures that both conductors of a differential pair encounter identical dielectric paths.
