Evaluating Spread Prepreg Styles for Timing Jitter Reduction in PAM4 Signal Lines
Spread prepreg styles flatten glass yarns to eliminate dielectric window voids, reducing differential phase skew below 1.5 ps per inch in PAM4 signal lines.
Style 3313
Glass Specification
Spreadable woven glass fabric provides a balanced thin reinforcement layer for high-speed printed circuit board laminates requiring low fiber-weave skew. Standardized by glass textile classifications, style 3313 utilizes flattened yarn bundles to achieve nominal pressed prepreg thicknesses around three mils. Mechanical spreading flattens individual filament strands, reducing the size of resin-rich openings between warp and fill yarns.
Higher glass coverage yields more consistent dielectric permittivity across the substrate surface compared to traditional open-weave styles. Circuit designers select this reinforcement for dense high-speed inner layers where dielectric uniformity is required.
Processing Advantage
Flattened yarn geometry improves mechanical drilling quality by minimizing drill bit deflection when transitioning between resin and glass regions. The dense bundle layout resists resin wash during high-pressure lamination, maintaining predictable dielectric layer thickness across large panel surfaces. Uniform fiber distribution enhances mechanical stability during thermal reflow, reducing panel warpage in complex HDI board constructions.
Laser ablation forms clean microvia target pads with minimal glass bundle fraying, ensuring reliable copper plating coverage during via filling operations. Laminate vendors produce prepregs with this glass style to meet stringent thickness tolerance demands.
Skew Mitigation
Reduced dielectric variation across flattened bundles suppresses phase delay differences between differential signal pairs. Microstrip and stripline channels maintain matched phase propagation velocity without requiring off-axis routing techniques on high-speed circuit boards.