Bath copper pyrophosphate

Copper Pyrophosphate. Baths using copper pyrophosphate [10102-90-6] shown in Table 9, are not in wide use in the United... 

An important constituent in copper pyrophosphate baths is nitrate, which enhances the maximum permissible current density [31]. Fig. 8-30 shows the respective chromatogram with the separation of nitrate and orthophosphate. The latter is the hydrolysis product of pyrophosphate that is formed during the plating process. The main component pyrophosphate may also be separated on a latexed anion exchanger. It is detected after complexation with ferric nitrate in a post-column reaction by measuring the light absorption (see Section 3.3.5.2). 

Fig. 8-30. Analysis of mineral acids in a copper pyrophosphate bath. -Separator column IonPac AS3 eluent 0.003 mol/L NaHC03 + 0.0028 mol/L Na2C03 flow rate 2.3 mL/min detection suppressed conductivity injection 10 pL sample (1 1000 diluted).

While alkali and alkaline-earth metals can also be rapidly and very sensitively detected by other instrumental analysis methods, the advantage of ion chromatography lies in the simultaneous detection of the ammonium ion. In copper pyrophosphate baths, for example, the addition of ammonia improves the plating evenness. However, as the ammonia concentration continuously decreases at higher bath temperatures, it must be added to maintain optimal bath conditions. As seen in Fig. 8-40, after separation on an anion exchanger the ammonium ion can be detected quickly and reliably separated from sodium and potassium. 

Although in most cases of not major importance in industrial electroplating formulations, phosphate-containing bath compositions have been patented for the plating of Cu, Ag, Au, Zn, Cd, Ni, Sn, Pt, Pd and Rh and some of their alloys. Copper pyrophosphate is, however, currently widely used for copper plating and is particularly applicable in printed circuit technology [33]. 

Phosphates have the great advantage of low toxicity compared to the much-used cyanides. Copper pyrophosphate is non-corrosive, has good throwing power and leads to hard and uniform metal deposits. A typical bath composition is as follows ... 

The copper pyrophosphate bath contains complex anions such as Cu(P207)2" and CuP207", and the operating pH and CU/P2O7 ratio are fairly critical. Below pH 7, precipitation of CU2P2O7 or CUH2P2O7 occurs, and above pH 11, Cu(OH)2. 

Copper is electrodeposited commercially mainly from cyanide, sulphate and pyrophosphate baths. For rapid deposition in electro-forming, a fluoborate bath may also be used. 

Internal stress of copper deposits may vary between —3.4MN/m (compressive) and -1- l(X)MN/m (tensile). In general, tensile stress is considerably lower in deposits from the sulphate bath than in those from cyanide solutions " , while pyrophosphate copper deposits give intermediate values. In cyanide solutions, tensile stress increases with metal concentration and temperature decreases if the free cyanide concentration is raised. P.r. current significantly lowers tensile stress. With some exceptions, inorganic impurities tend to increase tensile stress . Thiocyanate may produce compressive stress in cyanide baths . 

Copper-tin deposits can be plated from cyanide or pyrophosphate -baths and deposits are of good corrosion resistance (approximately equivalent to the same thickness of nickel). Hardness values of up to 314 Hy are obtainable for the copper-rich alloys , and up to 530 Hy for the tin-rich alloys can be obtained. (See also Section 13.5.)... 

The use of mixed complex baths is interesting since the concentration of one free metal ion may be altered by varying the amount of one ligand. Thus, in a copper—tin bath, cyanide content may be varied to alter the activity of copper ions, with little or no effect on tin which is present as stannate or as a pyrophosphate complex. It is evident that some knowledge of the coordination chemistry will reduce the degree of empiricism in developing alloy plating baths. 

The specific resistivity of the solution, p, is important. It could be decreased by adding a supporting electrolyte, but this approach is limited in scope. A value p 5 Q cm measured in acid copper baths containing CUSO4 and H2SO4 is about as low as one can go. Another approach is to add a complexing agent, as discussed for Cu deposition from a pyrophosphate salt (cf. Section 19,2.4). It should be... 

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