Foil Structure
Copper cladding on high-speed circuit boards utilizes specially processed foils to balance resin adhesion with signal transmission performance. This material, commonly called reverse treated foil, features a microscopic electrodeposited treatment applied to the smooth, drum-side of the copper sheet instead of the rough, matte side. It is laminated with this treated smooth side facing into the dielectric resin, leaving the naturally rough matte side on the outer surface for etching.
This layout results in low transmission loss at high frequencies while maintaining sufficient peel strength to prevent trace lifting.
Peel Strength
Reliable trace adhesion during PCB rework cycles depends on the mechanical anchoring of the foil to the polymer matrix. Although reverse treated foil has a lower average roughness on the bonded side than conventional electrodeposited foils, its structured nodule treatment prevents peel failures. This surface modification ensures that the copper does not lift during high-temperature reflow or manual soldering.
High Frequency
Digital signal propagation in multi-gigabit copper interconnects is restricted to the outer boundary of the conductor by the skin effect. Utilizing reverse treated foil reduces the signal path length and phase distortion compared to standard foils. This selection is a common choice for high-frequency microwave and backplane designs.
