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.
Rz Roughness
Surface Profilometry
The average distance between the highest peak and lowest valley measured across multiple individual sampling lengths on a surface describes the micro-topography of copper foil. In printed circuit board fabrication, Rz roughness represents a critical quality metric for assessing the adhesion and electrical properties of copper foil. This statistical measure provides a more reliable indication of surface spikes than a simple average roughness calculation.
Physical Effect
High values of this parameter ensure a strong mechanical bond between the copper foil and the epoxy resin. However, this same roughness increases the resistive losses of high-frequency traces because currents are forced to follow the contorted surface profile. Designers must specify low-profile copper with small values of this roughness to minimize insertion losses at high data rates.
Inspection Technique
Optical interferometers or mechanical stylus tools are used to verify this parameter during incoming copper inspection. Measuring this parameter is essential for ensuring that each batch of copper foil meets both the peel strength and high-frequency loss requirements. By maintaining a tight range for this metric, fabricators can deliver consistent trace performance and prevent delamination failures during high-temperature reflow cycles.
This process is highly valuable in high-speed digital and RF boards where small variations in copper topography can cause significant changes in signal attenuation.