Spread Glass Prepreg Performance in Ultra Low Skew Multilayer Stackups
Spread glass prepregs eliminate dielectric permittivity gaps across differential traces, suppressing signal skew below 1 ps/inch in 112G PAM4 stackups.
Mechanical Yarn Spreading
Fabrication Uniformity
Physical modification techniques apply tension or mechanical force to glass fiber bundles to create a flatter and more consistent weave. While traditional glass cloth has bundles with significant gaps, mechanical yarn spreading flattens these bundles to cover the empty spaces between the warp and weft yarns. This process results in a laminate with more uniform dielectric properties across the entire surface of the panel.
Consistent resin distribution is achieved when the glass fibers are distributed evenly.
Resin Saturation
Eliminating the resin rich pockets found in standard weaves reduces the variation in the local dielectric constant of the circuit board. When mechanical yarn spreading is utilized, the glass to resin ratio becomes more predictable, which is necessary for high speed digital designs where impedance control is paramount. Differential pairs that cross over alternating glass and resin areas suffer from skew, but a spread weave minimizes this timing error.
The resulting substrate provides a more stable foundation for microstrip and stripline geometries. Better resin wetting also improves the resistance of the board to conductive anodic filament growth by removing the large gaps where moisture can accumulate.
Signal Integrity
Maintaining wave shape and timing requires a homogenous medium. Because mechanical yarn spreading creates a nearly continuous glass shield, it prevents the signal from seeing the periodic structure of the weave. Laser drills also benefit from this uniformity because the laser energy interacts with a consistent material density rather than hitting thick bundles and then empty resin.
Material consistency allows for more precise via shapes and depths during the fabrication of high density interconnect boards.