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.
Inner Layer Copper Topography
Surface Profile
Surface roughness of copper foils on internal circuit layers affects both signal attenuation and mechanical adhesion within a multilayer board. To ensure robust lamination, inner layer copper topography must be carefully prepared using chemical or mechanical treatment to increase bonding surface area. This micro-roughness helps the prepreg resin lock into the copper during the hot press cycle, preventing delamination.
High-frequency electrical performance is also affected by rough surfaces because they increase skin-effect losses in high-speed digital traces.
Bonding Chemistry
Chemical adhesion promoters are applied to the processed copper layers prior to final pressing to modify the metallic surface. By creating a uniform micro-structure, these treatments optimize the physical bond between the metal and the composite resin. During the multi-layer lamination process, inner layer copper topography determines how well the flowing resin fills the gaps between dense trace patterns.
Low-profile copper foils are increasingly specified for high-frequency boards to limit electrical losses, though they require more advanced bonding chemistries to maintain mechanical pull strength.
Defect Prevention
Imperfect lamination interfaces can harbor moisture and lead to conductive anodic filament growth. If the inner layer copper topography is uneven or poorly cleaned, trapped air or incomplete resin fill can cause catastrophic delamination during subsequent lead-free solder reflow.