A typical plating bath contain standard constituents plus organic adhesives used to obtain some special effect. On the table shows the optimum concentration range for each constituent of copper pyrophosphate plating bath.
For the analytical determination of copper, pyrophosphate, and orthophosphate, the simplest procedure that describe by Konishi, where all three constituents are determined by titration with EDTA. Copper can also be determined electrolytically or by titration with standard alkali, and orthophosphate gravimetrically or colorimetrically. Ammonia is analyzed by distillation and adsorption in standard acid.
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Analytical Constituent Composition, ............. g/l
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Copper, Cu2+ ......................................... 22-38
Pyrophosphate, (P2O7)4- ........................... 150-250
Nitrate, NO3- .......................................... 5-10
Ammonia, NH3 ........................................ 1-3
Orthophosphate, (HPO4)2- ...... not greater than 113
Organic additives as required
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Copper and Pyrophosphate
The copper and pyrophosphate content of the plating bath are critical in terms of the ratio of one to the other. To compare anode corrosion and to increase electrical conductivity, the solution must contain excess complexing compound. Although either may be used, potassium solution has a higher electrical conductivity because of the higher mobility of potassium ions.
Nitrate
The presence of a nitrate results in a higher maximum current density because, especially at current density above 3.2 A/dm2, the nitrate ion reduces cathode polarization by acting as a hydrogen acceptor according to the equation:
NO3- + OH- + 8 e <====> NH4+ + 3 H2O
Addition of NH4NO3 increases the permissible current density and improves quality of deposits more effectively that does the addition of KNO3.
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