Copper tape that has oxidized to form copper oxide is much less electrically conductive than pure metallic copper — in fact, copper(I) oxide (Cu₂O) and copper(II) oxide (CuO) are both semiconductors or insulators, depending on the thickness of the oxide layer and environmental conditions.
Key Points:
- Fresh copper tape has excellent conductivity (~1.7×10⁻⁸ Ω·m resistivity).
- Copper oxide is not a good conductor:
- Cu₂O (red oxide): P-type semiconductor with relatively low conductivity.
- CuO (black oxide): Even lower conductivity than Cu₂O.
- Thin oxide layers (e.g. a surface tarnish) may still allow current to pass through due to pressure contact or breakdown, but resistance will be higher and unreliable.
- Heavily oxidized tape may fail to conduct at all, especially for RF or low-voltage applications.
Practical Implications:
If you’re using copper tape for:
- DC connections: You might get away with mild oxidation.
- RF/EM shielding: The surface conductivity is critical, so oxide will reduce effectiveness.
- Soldering: Oxidized surfaces are poor for soldering and require cleaning.
- Antenna work: Clean, bright copper is best.
Recommendation:
If you see oxidation:
- Clean the copper with fine abrasive (e.g. Scotch-Brite pad), vinegar + salt, or isopropyl alcohol with a bit of scrubbing.
- Optionally apply a protective layer (e.g. clear lacquer or conductive grease) to slow future oxidation.