Surface Roughness
A specialized copper sheet featuring a highly uniform, smooth surface on its treatment side reduces conductor losses in high-frequency printed circuit boards. Using low profile foil minimizes the signal degradation caused by the high surface roughness found on conventional copper foils. This smoothness is measured by profiling the surface peaks and valleys, which are kept below two microns.
By maintaining a flat boundary between the metal and the dielectric, the foil preserves signal integrity at millimeter-wave frequencies.
Signal Loss
Alternating current at high frequencies tends to concentrate on the outer skin of a conductor rather than flowing evenly through its center. When this skin depth becomes smaller than the metal’s surface roughness, the electrical signals must travel a longer, tortuous path along the peaks and valleys, which increases conductor loss. This phenomenon is particularly severe in high-frequency boards where the skin depth is measured in nanometers.
Specifying low profile foil provides a straight, low-resistance path that minimizes signal attenuation and heating. Consequently, transmitters can operate with lower output power while maintaining reliable communication links.
Adhesion Tradeoff
Smooth copper foils exhibit lower mechanical adhesion to the dielectric resin than rougher foils. Fabricators must use advanced resin systems or surface treatments to prevent the smooth copper lines from delaminating during thermal cycles or assembly soldering. This requirement increases both material cost and fabrication complexity.
