Microstrip Phase Velocity Fundamentals across Multi Layer Glass Stackups
Microstrip phase velocity depends on outer layer inhomogeneous dielectric fields, glass reinforcement architecture, copper roughness, and lamination compression.
3313 Glass Fabric
Fabric Specification
Textile reinforcement provides the structural skeleton for thin prepreg layers in printed circuit boards. Using 3313 glass fabric allows for a nominal thickness of approximately 0.08 millimetres while maintaining better resin retention than coarser weaves. This specific style employs a balanced yarn count in both warp and fill directions to ensure uniform mechanical stability during the lamination process.
Weave Pattern
Flat yarns distinguish this material from standard round-fiber alternatives. Because 3313 glass fabric utilizes spread fibers, the finished laminate surface is smoother and the dielectric thickness is more consistent across the entire panel area. This flatness minimizes the knuckle effect where yarn intersections normally create high points.
Laser drilling accuracy increases when the beam encounters a uniform glass-to-resin ratio instead of alternating between thick glass bundles and pure epoxy pools. Signal integrity also improves as the more uniform glass distribution provides a stable dielectric constant for high-speed traces. The reduced topography on the glass surface facilitates finer line widths and spacing in high-density interconnect designs.
Resin Integration
Adhesion properties depend on the silane finish applied to the individual glass filaments. During the impregnation stage, the open weave of 3313 glass fabric permits thorough resin wet-out which prevents internal delamination under thermal stress. It is compatible with lead-free assembly temperatures and high-reliability resin systems including polyimide or high-Tg epoxy.
This fabric choice is restricted to applications requiring thin core or prepreg sections where 2116 or 7628 styles would be too bulky for the design envelope.