Conductor Topography
Thin sheet of copper features a treated surface with a very low peak to valley height. Using vlp copper foil is standard for high speed digital circuits where the skin effect forces signals to travel near the surface of the metal. A smoother surface reduces the distance the signal must travel, which lowers resistive loss.
The roughness of this material is typically measured at less than two microns.
High Frequency Performance
Rough copper creates a longer electrical path because the signal must follow the contours of the metal peaks. At frequencies above ten gigahertz, this extra distance significantly increases signal attenuation. The use of vlp copper foil mitigates this effect by providing a nearly flat interface with the dielectric.
This improvement is essential for meeting the strict power budgets of modern servers and network switches. Fabrication involves a careful chemical treatment to ensure the metal still bonds well to the resin.
Bond Strength
Smooth copper surfaces naturally offer less mechanical grip than rough ones. Manufacturers of vlp copper foil use specialized silane treatments to ensure that the peel strength remains high enough for reliable manufacturing. This balance allows for high speed performance without the risk of traces lifting during the soldering process.
