Saturday, June 14, 2008

Acid Copper Plating Principle

The Principle of Electroplating:

The copper (II) (Cu2+) salts in either the sulfate on the flouborate bath are highly ionized except for small amounts of less ionized complex salts formed with certain addition agents. The addition of sulfuric acid to the sulfate solution, or flouboric acid to be flouborate bath, is necessary for obtaining acceptable deposits. Because of the highly conductivity of commercial solutions, and because anode and cathode polarizations are small, voltages required for depositing copper are less for acid than for alkaline baths. Electrorefining plants employ the copper sulfate bath largely for this reason. Tank voltages for refining copper are frequently as low as 0.2 V for a cathode and anode current density of 1.6 to 2.2 A/dm2.

Anode and cathode polarizations are nearly negligible in purified solutions used at low current densities. Even at the high cathode current density of 21.5 A/dm2, 6 V current source is ample when the solution is efficiently agitated. Excessive polarization of the solution is efficiently agitated. Excessive polarization of the anodes in the sulfate bath may occur when the anode current density exceeds about 5 A/dm2 without encountering excessive anode polarization.

Because of the low cathode polarization, the acid baths do not have as good throwing power as alkaline solution. The plate distribution closely approximate; the primary current distributions, the deviation was found to be 10.8 % or less for the sulfate bath. This disadvantage is largely overcome in electroforming practice by appropriate current shields.

Anode and cathode efficiencies are nearly 100% at all practical current densities. The rate of deposition obtainable depends chiefly on the efficiency of agitation in preventing excessive polarization. Acceptable deposits were reported at a current density as high at 260 A/dm2, equivalent to 3.63 mm/hr, with violent agitation.

The character of copper deposits is influenced by the concentrations of copper salts and of free said, the temperature, the cathode current density, and the nature and degree of agitation. Dense deposits with good surface smoothness up to a thickness of 500 μm or more can be produced without addition agents.

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