Electroplated copper thicknesses are more variable with electroplated surfaces vs. non-plated copper. It is not
uncommon to see a 10% variation in a circuit’s copper plating thickness as current densities cause features to plate
at higher or lower rates. This variation can translate to a similar variation in the impedance. Pads only Plating of
circuitry requiring impedance control will result in less variability within an individual part and between multiple
Another critical aspect of impedance control is the Relative Dielectric (ER) constant of the dielectric stack up. The dielectric stack up can consist of one or more layers of dielectric film bonded together with adhesives. The adhesive has a different dielectric coefficient than the dielectric film. Using adhesiveless laminates reduces the variation caused by adhesive and will normally result in a more consistent impedance.
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