Copper flouborate is more soluble than copper sulfate. Metal ion concentration can be more than double in the flouborate bath in comparison with a copper sulfate solution containing 50 to 75 g/l of sulfate acid.
Change in sulfuric acid concentration have more influence than changes in copper sulfate concentration on solution conductivity and anode and cathode polarization. For example, specific conductivity in nearly doubled when the concentration of sulfuric acid is raised from 50 to 100 g/l. An additional increase in free acid concentration to 200 g/l, which is level widely used in electro refining, reduces the resistivity from 4.2-4.3 to 1.6-1.9 ohm-cm. Cathode polarization decrease when a small amount of sulfuric acid is added to a solution of copper sulfate, reaches a minimum at about 0.4 M (38 g/l), and increase with a further increase in sulfuric acid effect on grain size, but some grain refinement was detected as a result of increasing the sulfuric acid concentration to 1.5 N (72 g/l).
If acid concentration in the flouborate bath is too low (pH mote than 1.7), deposits are dull, dark, and brittle. Boric acid is added to stabilize the bath and prevent decomposition of copper flouborate, this increases resistivity slightly. In bath with concentration of more than 15 g/l fluoboric acid or 220 g/l copper flouboric, an increase in the concentration of either the salt or the acid lowers the resistivity.
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