Air Gap Corrections in Clamped Stripline in Plane Permittivity Extraction
Air gap corrections eliminate systematic two to six percent dielectric underestimation in clamped stripline tests, preventing finished board impedance failures.
Peak-to-Valley Height
Surface Topography
The maximum vertical distance between the highest peak and the lowest valley within a specified assessment length defines the surface roughness of copper foils used in printed circuit boards. This peak-to-valley height represents a primary metric for evaluating the surface profile of copper before it is laminated onto the dielectric. If the profile is too rough, the metal acts as a physical anchor for the epoxy resin but degrades high-frequency signal propagation.
This trade-off between electrical loss and mechanical adhesion is a central constraint in high-speed digital design, demanding specialized surface treatments that maintain board integrity without introducing signal loss.
Physical Impact
High profile height increases the physical path length that high-frequency currents must travel due to the skin effect. This increased path length leads to higher conductor loss and signal attenuation at microwave frequencies. Consequently, ultra-low-profile foils are specified for high-speed boards to minimize loss while maintaining sufficient mechanical adhesion.
Metrology Method
Stylus profilometry or non-contact optical techniques are used to measure this topographic parameter on fabricated copper surfaces. This measurement is critical for ensuring that the copper foil is compatible with both the lamination process and the high-frequency design limits. By controlling this parameter, board manufacturers can balance the mechanical peel strength against the required electrical loss performance.