Watts bath

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. 

Temperature should be kept constant to maintain H BO level. Low (45°C) temperature Watts baths can be mn if Ni is reduced to about 45 g/L total and H BO is increased to about 50 g/L. 

Both Watts and sulfamate baths are used for engineering appHcation. The principal difference in the deposits is in the much lower internal stress obtained, without additives, from the sulfamate solution. Tensile stress can be reduced through zero to a high compressive stress with the addition of proprietary sulfur-bearing organic chemicals which may also contain saccharin or the sodium salt of naphthalene-1,3,6-trisulfonic acid. These materials can be very effective in small amounts, and difficult to remove if overadded, eg, about 100 mg/L of saccharin reduced stress of a Watts bath from 240 MPa (34,800 psi) tensile to about 10 MPa (1450 psi) compressive. Internal stress value vary with many factors (22,71) and numbers should only be compared when derived under the same conditions. 

Plating solutions used in nickel electroforming are primarily the Watts bath and the nickel sulfamate bath. Watts baths exhibit higher stress and require additives for stress control, which may affect other properties. Sulfamate baths produce much lower stress and are preferred where purer nickel or nickel—cobalt deposits ate needed. ASTM specifications are available that describe the mandrels and plating solutions (116,162). 

The composition of the codeposition bath is defined not only by the concentration and type of electrolyte used for depositing the matrix metal, but also by the particle loading in suspension, the pH, the temperature, and the additives used. A variety of electrolytes have been used for the electrocodeposition process including simple metal sulfate or acidic metal sulfate baths to form a metal matrix of copper, iron, nickel, cobalt, or chromium, or their alloys. Deposition of a nickel matrix has also been conducted using a Watts bath which consists of nickel sulfate, nickel chloride and boric acid, and electrolyte baths based on nickel fluoborate or nickel sulfamate. Although many of the bath chemistries used provide high current efficiency, the effect of hydrogen evolution on electrocodeposition is not discussed in the literature. 

Watson, James, 77 10 Wattersite, 6 471t Watts baths, 9 817, 819, 832 Waveform... 

Composition of Watts bath NiS04 (240 g dm ) NiCl2 (45 g dm boric acid (30 g dm... 

The polystyrene latex (PSL) spheres were obtained from Seragen Diagnostics. The nominal sizes of these standards were from electron microscopy measurements. The samples were prepared by diluting the 10% solids in filtered, doubly distilled water, adding a small amount of SDS to help disperse the samples and sonicating with Branson 60 watt bath sonicator for 30 seconds to disperse any aggregates. The relative volumes (weights) of the two sizes of PSL in the mixed sample were estimated to be accurate to about 5-10%. 

Watts bath — The Watts bath is the classical electrolyte for the -> electrodeposition of functional nickel coatings. It contains nickel sulfate (240-450 gL-1 of the hexahy-drate), nickel chloride (45-90 gL-1 of the hexahydrate), and boric acid (30-50 g L-1) and is usually operated between pH 2 and 4.5 and at 40-70 °C. The chloride content of the bath is crucial to ensure the dissolution of the nickel anode. In combination with - leveling agents and brighteners the Watts bath is also used for decorative nickel coatings. Its applicability for -> electroforming is limited due to tensile stresses in the deposits. 

Figure 6.3 Stability of various fiber textures of nickel electrodeposits vs. pH of a Watts bath and partial current density of nickel deposition [6.61].

Nickel deposition from a Watts bath in the absence and presence of inhibitors was thoroughly studied by Wiart et al. [6.79-6.81]. The appearance of an inductive loop at low frequencies has been ascribed to an adsorbed intermediate (NiOH)ads. 

Two electroplating solutions were used in our experiments the first one had 100 g/L of nickel sulfate, 10 g/L of nickel chloride, and no boric acid the pH value was 4. The second (Watts bath) had 330 g/L of nickel sulfate, 45 g/L of nickel chloride, and 38 g/L of boric acid the pH value was again 4. In each case, the solution was deaerated with bubbling nitrogen before the experiments and electrodeposition was performed, as in the previous cases, at ambient temperature without stirring. 

Figures 20.18 through 20.20 visually illustrate these findings. Figure 20.18 shows that in the absence of boric acid bubbles are present and the deposit is of rather poor quality. This is in sharp contrast with Figures 20.19 and 20.20 that correspond to electrodeposition in the Watts bath at two different applied voltages, —1 and —4 V. The quality improvement with respect to Figure 20.18 is quite striking. Although the boric acid does not altogether suppress the evolution of bubbles, it does strongly decrease it with the reduction of the cracks in the deposit.

Alkaline CuCN solutions were used for the first time to electrodeposit homogeneous and adherent Cu films onto silicon. Tire obtained Cu/n-Si(lll) junctions show a nearly perfect rectifying behavior. The Schottky parameters (barrier height 3>b = 630 mV ideality factor n = 1.2) do not change importantly with time. It is also demonstrated that highly adherent Ni films can be plated onto n-Si(lll) from an acidic Watts bath, if copper clusters were elecrodeposited onto the silicon surface first. 

The excellent adherence of Cu layers gives the opportunity of preparing electroplated adherent films of various metals onto n-Si(lll), using a two step process in which Cu clusters are first grown as precursors and then, the metal of interest is plated. Figure 5 shows an in plane TEM view of Cu clusters electrodeposited on n-Si(lll) (Vd = -1.75 V, td = 40 s). They represent the minimum quantity of copper necessary to obtain nickel films from a modified Watts bath (pH 3). Nickel was electrocristallized at Vd = - 1.30 V and we emphasize that it was not possible to achieve Ni deposition on n-Si(lll) at this potential without the presence of Cu clusters. Ni films are also very adherent and they successfully passed the... 

In summary, this study shows the great possibility of generating Cu/n-Si junctions with a nearly perfect rectifying behavior from CuCN solutions. Diode characteristics are comparable to those reported for contacts prepared by physical methods and are not appreciably subject to modification with time. The second promising point is the high adherence of Cu films, which was exploited to electrodeposit adherent Ni films from a modified Watts bath. This two step procedure seems to solve the major difficulty encountered upon growing thick metal layers onto H-Si surfaces from acidic solutions and enables to prepare stable electrical junctions with defined electrical properties. 

S.4.2.3 Nickel-phosphorus Excellent corrosion protection is observed if the nickel layer contains phosphorus. This was first observed with electroless NiP layers (see Sect. 5.5.4.2.4). During the last years, electrochemical plating processes for nickel phosphorus have been developed. In these processes, a phosphorus source has to be added to the electrolyte either sodium phosphite or sodium hypophosphite are used. The other components of the electrolyte are similar to a Watts bath (see Sect. 5.S.4.2). Table 6 lists a typical composition. 

K. S. Willson and J. A. Rogers, Orientation, Crystal Structure and Appearance of Nickel Deposits from a Watts Bath Containing Coumarin, Tech. Proc. American Electroplaters Society. Vol. 51,1964, 92-95. 

For nickel deposition from a Watts bath (a weakly acidic bath containing sulphate and chloride), two types of brightener are recognized. The first are aromatic sulphones or sulphonates and they lead to bright deposits without lustre and also reduce stress. The second are molecules containing —C=N, N—C=S or C=0 entities, e.g. thiourea and coumarin, which produce deposits with a high lustre but also raise the stress and brittleness in the metal. In practice both types are used in combination. The aromatic sulphonates are also brighteners for tin or copper. 

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