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Factors affecting plating quality

Apr 27, 2018

There are many factors that affect the plating quality, including various components of the plating solution and various plating process parameters. The following describes some of the major factors.

1) Effect of pH

The pH value in the bath can affect the hydrogen discharge potential, the precipitation of alkaline inclusions, and can also affect 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 value may affect the balance of the various complexes present and must therefore be considered in terms of concentration. In the electroplating process, if the pH value increases, the cathode efficiency is higher than the anode efficiency, and the pH value decreases. By adding a buffer, the pH can be stabilized within a certain range.

2) Effect of additives

Brighteners, levelers, wetting agents and other additives in the plating bath can significantly improve the plating structure. There are inorganic and organic additives for this additive. The reason why inorganic additives work is that they form highly disperse hydroxide or sulfide colloids in the electrolyte, adsorb on the cathode surface to prevent metal precipitation, and increase cathode polarization. The reason why organic additives work is that these additives are mostly surface active substances, they will adsorb on the surface of the cathode to form a layer of attached film, hindering metal precipitation, thus increasing the cathode polarization. In addition, some organic additives form colloids in the electrolyte, complex with metal ions to form colloidal-metal ion complexes, hinder metal ion discharge and increase cathode polarization.

3) Effect of current density

Any plating must have a current density range that produces normal plating. When the current density is too low, the cathodic polarization is small and the plated orange is coarse, even without plating. With the increase of current density, the polarization of the cathode increases, and the grains of the coating become finer. When the current density is too high and exceeds the limiting current density, the quality of the coating begins to deteriorate, with the appearance of spongy, dendritic, charred and blackened. The upper and lower limits of the change in current density are determined by the nature of the plating solution, the concentration, the temperature, and the stirring. Under normal circumstances, the main salt concentration increases, the coating temperature increases, and under stirring conditions, it is allowable to use a larger current density.

4) Influence of current waveform

The influence of the current waveform is that the cathodic deposition process is affected by changes in the cathode potential and current density, which in turn affects the microstructure and even the composition of the coating, which changes the properties and appearance of the coating. Practice has proved that three-phase full-wave rectification and regulated direct current are comparable, with little effect on the plating microstructure, 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 temperature increase can also accelerate the dehydration process of ions. Enhanced ion and cathode surface activity also reduces electrochemical polarization, leading to coarsening of the crystals. On the other hand, the temperature increase can increase the solubility of salts, thereby increasing the conductivity and dispersion ability; it can also increase the current density upper limit, thereby increasing the production efficiency.

6) Effect of stirring

Stirring reduces cathodic polarization, making the crystal grains coarser, but increases current density, which increases productivity. In addition, stirring can also enhance the effect of the leveling agent.

The surface of the product clean, flat substrate surface coating effect is better, the product shape also affects the current distribution, position positioning.

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