Metal Foil
Specialized electrochemical treatments produce copper sheets with a surface topography that is exceptionally smooth on the interface side. High frequency signals benefit from the use of vlp copper because it minimizes the skin effect losses associated with rough metallic boundaries. This material avoids the deep tooth structure found on standard foils, which normally aids adhesion but interferes with electronic signal speed.
It allows for the fabrication of complex microwave and millimeter-wave circuits with low signal attenuation.
Interface Structure
Standard manufacturing techniques for very low profile surfaces reduce the average roughness to below two microns. Because vlp copper has less surface area for mechanical bonding, specialized chemical adhesion promoters are applied to the prepreg to prevent delamination during soldering. This change in morphology helps reduce signal phase jitter by providing a uniform path for the current traveling along the exterior of the conductor.
Circuit designers select these foils when frequencies exceed ten gigahertz to maximize overall link budgets. They are more difficult to process than standard types as they require exact control over the lamination temperature and duration to keep the interface secure.
Reliability Factor
Reducing the depth of the metal hills into the resin also decreases the chances of signal noise resulting from conductive anodic filament growth. The flat interface eliminates the sharp points where high electric fields could otherwise initiate failures through the insulating layers.
