What causes tin plating to yellow?

What causes tin plating to yellow?

Tue Mar 05 08:39:06 CST 2024

Tin plating is the process of plating a layer of tin on a metal surface by electrochemical action. It plays an important role in preventing corrosion, improving electrical conductivity and welding performance. However, in the process of tin plating, sometimes there is a problem of yellowing of the coating. This situation not only affects the appearance quality of the product, but also may reduce the performance of the coating. There are many reasons for plating yellowing, and many factors in plating process need to be considered comprehensively.

The primary factor is the unbalanced chemical composition of the plating solution. Poor quality of tin-plating additives in the plating bath or the presence of too many impurity ions of other metals (e.g., copper, iron, nickel, etc.) may affect the color of the plated layer and lead to yellowing. Therefore, regular testing and adjustment of the chemical composition of the plating solution is important to obtain a good plating layer.

Control errors in plating process parameters are also a cause of yellowing of the plated layer. For example, when the current density is too high, the deposition rate of tin is accelerated, and the rapidly deposited tin layer may have a yellowish color due to grain refinement and increased stress. Similarly, improper control of plating time may affect the quality of the plated layer. Appropriate current density and plating time can ensure uniform deposition of the tin layer and help avoid abnormal plating color.

Plating bath pollution is also a common cause of plating yellowing. The organic dirt or sediment in the plating solution will be adsorbed on the surface of the cathode (that is, the workpiece to be plated), affecting the normal deposition process of tin, and then causing the color of the coating to change. Therefore, keeping the plating bath clean and the plating solution filtered is a routine practice to maintain the quality of the coating.

In addition, the surface treatment of the substrate is equally important in plating quality control. If grease, oxides or other contaminants remain on the surface of the substrate, then even if the subsequent plating process conditions are in place, the tin plating layer may still yellow due to the underlying impurities. Therefore, a thorough cleaning and activation process is an important step in ensuring the quality of the plated layer.

Post-treatment processes after plating is completed, such as cooling and cleaning, if not properly handled, residual plating solution components may form a microscopic film layer on the surface, and yellowing may occur over time. Therefore, this can be prevented by rinsing with water immediately after plating and using neutral or weakly alkaline cleaning agents if necessary.

In the first factor, we mentioned that the poor quality of tin plating additives, easy to cause yellowing of the plating layer, in order to solve this problem, electroplating plant can be added to the plating solution Bigely tin plating additives Sn-807, can be in a wide range of temperature to obtain a uniform bright pure tin plating layer, and the plating solution has good stability.

Please feel free to contact us if you are interested in tin plating additives.