Saturday, June 28, 2008

Operating Condition (Acid Copper Plating)

Temperature may vary from 18 to 60 oC; however, a temperature between 32 and 43 oC is common, since it can be maintained economically with little or no heating or cooling. An increase in the temperature results in a higher conductivity and reduced anode and cathode polarization. Degreasing the temperature from 35 to 15 oC brought about a considerable grain refinement in plates deposited at 3 A/dm2. A temperature below 30oC is recommended for plating bright copper in acid baths to maintain good leveling power. These solutions are customarily agitated with air.

Current density and agitation must be balanced in order to obtain deposits having desired properties. For producing electrotypes, cathode current densities of 16 to 22 A/dm2 are generally employed when using the sulfate bath agitated with air. Fast moving endless wire can be plated at 50 A/dm2. Still higher current densities are used when sufficient agitation can be supplied. Impinging of jets of electrolyte on the surface of the cathode is said to permit a current density of 215 A/dm2. When movement of the work is impractical or when air agitation fails to provide good mixing at all significant surfaces, the density is usually kept at 3.7 to 5.4 A/dm2. It is claimed that higher current densities are practical with the fluoborate bath when agitation is the same as for the sulfate bath. Acceptable deposits 25 μm thick were obtained without agitation at 38 A/dm2.

In either the sulfate or the fluoborate bath, an increase in current density results in increased cathode polarization (but not to the extent noted for many other solutions). Cathode films become more depleted in copper(II) ion and more concentrated in sulfate ion when the current density is increased. Clear evident has been reported of grain refinement produced by increasing the current density.

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