Predictive Hydrodynamic Modeling of High-Viscosity Epoxy Flow in Ultra-Heavy Copper Cavities
Predictive non-Newtonian flow modeling prevents micro-voiding in ultra-heavy copper cavities by matching prepreg viscosity minimums to press force ramps.
Glass Weave Exclusion
Routing Zone
Design constraint rules implemented inside electronic computer-aided design software establish restricted routing zones that prevent high speed signal traces from aligning parallel to glass fiber bundles. Known as glass weave exclusion, this layout strategy avoids differential signal skew caused by inhomogeneous dielectric constants between glass filaments and resin pockets. Printed circuit board substrates consist of woven glass yarn embedded in epoxy, creating localized dielectric constant variations across small spatial dimensions.
Signal conductors routed directly over glass bundles experience higher effective permittivity than traces running over adjacent resin-rich cavities. The restriction rule stops applying when substrates utilize spread glass fabrics or uniform hydrocarbon dielectrics that eliminate spatial permittivity periodicities.
Skew Control
Differential pair skew degrades signal integrity when pair legs travel over unequal dielectric environments at high data rates. Angle routing, zigzag trace patterns and off-grid layout techniques enforce glass weave exclusion across critical differential lines. Physical testing using time domain reflectometry measures propagation velocity mismatches caused by localized dielectric variations across long signal paths.
Failure to enforce exclusion boundaries during board layout leads to eye diagram closure and timing jitter in high speed serial interfaces. Fabricators verify layout compliance by inspecting CAM artwork prior to photo-imaging inner layers.
Layout Constraint
High frequency circuit designs operating beyond ten gigahertz require strict clearance rules around fiber bundle pitch dimensions. CAD clearance rules prevent differential pair traces from running parallel to warp or weft glass threads over long routing runs.