Composite plating, bath

Electrokinetic behavior of gold alloy and composite plating baths, B. Bozzini, P. L. Cavallotti, and G. Giovannelli, Met. Einish., 2002, 100(4) 50. 

Black and colored plates can also be obtained from chromic acid baths. The plates are mostly oxides (177). Black chromium plating bath compositions are proprietary, but most do not contain sulfate. The deposit has been considered for use in solar panels because of its high absorptivity and low emissivity (175). 

Copper-plating bath compositions of various types have been used. A typical bath formulation consists of 200 g copper sulfate crystals, 30 mL cone, sulfuric acid, 2 mL phenylsulfonic acid, and 1000 mL distUled water. A pure copper anode may be used a copper anode containing a trace of phosphoms reduces sludge accumulation in the plating bath. 

Silver-plating bath compositions are somewhat variable a typical composition contains 36 g silver cyanide, 60 g potassium cyanide, 45 g potassium carbonate, and 1000 mL distilled water. A pure silver anode is required (179). 

Chromium. AppHcations of chromium plating can be separated into two areas hard chromium, also called functional, industrial, or engineering chromium, and decorative chromium. The plating bath compositions may be the same for both. In most cases, the differentiating factor is plate thickness. Decorative chromium is usually less than about 1 p.m hard chromium can be from about 1 p.m to 500 p.m or more. 

Acid Copper. Bath compositions are shown in Table 8. The acid sulfate bath is by far the most widely used copper plating bath, both for plating and for electroforming and electrowinning. The fiuoborate baths have been Htde used in spite of the high current densities possible. Additional information can be found in the Hterature (98,99). 

Nickel. Nickel plating continues to be very important. Many plating baths have been formulated, but most of the nickel plating is done in either Watts baths or sulfamate baths. Watts baths contain sulfate and chloride nickel salts along with boric acid, and were first proposed in 1916 (111). Nickel was first plated from sulfamate in 1938 (112) and patented in 1943 (108). The process was brought to market in 1950 (113). Typical bath compositions and conditions are shown in Table 14. 

Plating baths contain a number of salts and compounds in addition to those of the ion to be reduced to metal. Much commercial electroplating is from proprietary solutions whose use is covered by patents, and which are supplied completely or partly compounded. The precise composition is generally a trade secret, and the patents may sometimes be very widely drawn to include a larger range of compositions and ingredients than is successful. A broad classihcation of additional ingredients includes ... 

The principal use of gold is as a very thin coating about 0-05 /xm thick for electrical and electronic applications. Because of the thinness of gold electrodeposits, porosity must be very carefully controlled since seepage of corrosion products from substrate or undercoat exposed at these pores can have serious adverse effects on both appearance and electrical properties of the composite. The porosity can vary with the thickness of the deposit (Fig. 13.1), and with the type of plating bath and with its method of operation (Fig. 13.2), and the phenomenon has been extensively studied by Clarke and many other workers. 

Electrodeposition of metal onto structured objects, such as circuits, is controlled in part by a template. At the same time, the deposit must fill all the recesses uniformly and seamlessly, the texture and crystal structure must fall within tolerances, and the quality of the features must be sustained over a large workpiece. The distribution of material within recesses or onto widely separated portions of the workpiece is subject to a limited number of macroscopic control-parameters such as applied potential and plating bath composition. Success therefore depends on exploitation of the natural pathways of the process. The spontaneous and unconstrained development of structure must be taken into consideration in the production of highly organized and functional patterns. 

In ZnCl2-EMIC (1 1) melt containing Cu(I), the electrodeposition of Cu-Zn alloys on tungsten and nickel electrodes was carried out [180]. The composition of the Cu-Zn deposit was changed by deposition potential, temperature, and Cu(I) concentration in a plating bath. 

It is known that trichromates [Cr3OI0]2- and tetrachromates [Cr4Oi3]2- may crystallize from strongly acid solutions as their alkali metal salts. Tetrachromates are believed to be major constituents of a plating bath for which the following composition is typical ... 

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