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Basic knowledge of electroplating - factors affecting the quality of electroplating

August 7, 2023

There are many factors affecting the quality of electroplating, including various components of the plating solution and various electroplating process parameters. Some of the main factors are discussed below.

1. Effect of pH
The pH value in the plating solution can affect the discharge potential of hydrogen, the precipitation of alkaline inclusions, the composition of complexes or hydrates, and the degree of adsorption of additives. However, the degree of influence on various factors is generally unpredictable. The optimum pH is often determined experimentally. In baths containing complexing agent ions, the pH may affect the balance of the various complexes present, therefore must be considered in terms of concentration. During the electroplating process, if the pH value increases, the efficiency of the cathode is higher than that of the anode, and vice versa when the pH value decreases. The pH can be stabilized within a certain range by adding buffers.

2. Effect of additives
The brightener, leveling agent, wetting agent and other additives in the plating solution can obviously improve the coating structure. These additives are divided into inorganic and organic. The reason inorganic additives work is because they are in highly dispersed hydroxide or sulfide colloids are formed in the electrolyte, which are adsorbed on the surface of the cathode to prevent metal precipitation and improve the polarization of the cathode. The reason why organic additives work is that most of these additives are surface-active substances, which will be adsorbed on the surface of the cathode to form a layer of attached film, which hinders the precipitation of metals, thus improving the polarization of the cathode. In addition, some organic additives form colloids in the electrolyte, which will complex with metal ions to form colloid-metal ion complexes, hindering the discharge of metal ions and improving the cathode polarization.

3. Effect of current density
Any electroplating must have a current density range that can produce a normal coating. When the current density is too low, the cathodic polarization effect is small, and the orange crystal of the coating is thick, or even there is no coating. As the current density increases, the cathode polarization increases, and the coating grains become finer. When the current density is too high and exceeds the limit current density, the quality of the coating begins to deteriorate, and even sponges, dendrites, burnt and blackened appear. The upper and lower limits of the current density change are determined by the nature of the plating solution, concentration, temperature and stirring. In general, when the concentration of the main salt increases, the temperature of the coating layer increases, and under the condition of stirring, a larger current density can be allowed.

4. Influence of current waveform
The impact of the current waveform is to affect the cathodic deposition process through the change of the cathode potential and current density, which in turn affects the structure and even the composition of the coating, which changes the performance and appearance of the coating. Practice has proved that the three-phase full-wave rectification is equivalent to the regulated DC, and has almost no effect on the coating structure, while other waveforms have a greater impact.

5. Effect of temperature
The increase of bath temperature can accelerate the diffusion and reduce the concentration polarization. In addition, the increase of temperature can also accelerate the dehydration process of ions. Enhanced ionic and cathodic surface activity also reduces electrochemical polarization, resulting in coarser crystals. On the other hand, an increase in temperature can increase the solubility of salts, thereby increasing conductivity and dispersion capabilities; it can also increase the upper limit of current density, thereby increasing production efficiency.

6. Effect of Stirring
Stirring can reduce cathode polarization and make grains coarser, but can increase current density, thereby increasing productivity. In addition, stirring can also enhance the effect of the leveler.