The Oxidation Mechanism
Copper is highly conductive but chemically reactive. In industrial environments with high humidity or sulfur presence, bare copper tape creates a non-conductive oxide layer (patina) rapidly. This surface oxidation increases the skin depth resistance, degrading the tape's ability to shunt high-frequency RF currents.
Impact on Shielding Effectiveness (SE)
While initial SE may be 60-80dB, an oxidized tape can drop by 20dB or more over a year. The oxide layer creates a barrier at overlapping joints, turning a continuous shield into a series of isolated floating conductors, which can actually resonate and amplify specific interference frequencies.
Tinned vs. Bare Copper Solutions
To prevent this degradation, engineering specifications should call for Tin-Plated Copper Foil Tape in harsh environments. The tin plating provides a stable, oxidation-resistant surface that maintains low contact resistance for the lifespan of the device, ensuring consistent EMI suppression.