Signal Attenuation
An electromagnetic dissipation phenomenon occurs when electrical currents flow through PCB traces and encounter finite resistance. This mechanism of conductor loss converts signal energy into heat, reducing the strength of the transmitted signal. It is determined by the cross-sectional area of the trace and the bulk resistivity of the copper.
Surface Roughness
Copper foil processing techniques usually leave a micro-textured finish to improve adhesion to the dielectric substrate. This textured surface increases the effective path length of the current, which travels along the outer perimeter of the conductor. As the skin depth decreases, the current is forced into these micro-crevices, which increases the resistance.
Chemical treatments that optimize foil adhesion without adding excessive roughness can lower the risk of signal degradation. In high speed multilayer stacks, selecting the correct foil treatment becomes a critical fabrication decision.
Trace Design
The choice of wider traces or alternative plating metals helps manage signal degradation in critical paths. Electroless nickel immersion gold finishes can increase these resistive effects due to the lower conductivity of nickel compared to pure copper. Utilizing smooth copper foil and thick dielectric layers provides a practical path to reducing the impedance shifts.
Measurement of these trace behaviors happens during time domain reflectometry testing.
