Do you know what are the methods to prevent discoloration after tin plating
Author: Marisa
Do you know what are the methods to prevent discoloration after tin plating？
① There are many surface active agents in sulfate tin plating solution, which aim to increase the polarization of the cathode, refine the crystallization, and obtain a bright coating as a carrier. However, this carrier will form an organic thin film on the surface of the coating. This layer of film will gradually change color. To prevent discoloration, the organic film should be removed in a 10% concentration phosphoric acid solution before drying after plating. Then, it should be washed repeatedly with cold and hot water, and finally rinsed with hot deionized water
② It is best not to rinse the tin plating in reverse flow, otherwise the coating is prone to fogging. After pouring the workpiece from the drum into the basin, immediately add clean water, stir evenly, pour water again, repeat three times, then soak in a dilute solution of trisodium phosphate at around 50 ℃, and wash with water multiple times.
③ First coat a layer of copper on the copper substrate to improve the adhesion and uniformity of the coating, which is conducive to preventing zinc ions in brass from penetrating into the tin metal layer.
④ After tin plating, it is necessary to neutralize passivation, neutralize residual acid, and form a protective film on the surface of the tin layer. Neutralizers generally use phosphate salts with weaker alkalinity. After neutralization, it is washed with water and transferred to the passivation process. The passivation solution uses dichromate at a temperature of 60-80 ℃ for one or two minutes to form an oxide film on the tin surface.
⑤ To prevent yellowing of the tin plating layer, three points should be noted during operation: first, to avoid poor cleaning after plating, which may cause water marks; second, to avoid excessive current density; Thirdly, avoid plating solution
The temperature is too high.
⑥ The plated parts have undergone passivation treatment (K2Cr207, 10g/L, Na2C03, 20g/L), which is effective in preventing discoloration, but must be cleaned thoroughly Immersing in stearic acid solution to form a protective film on the surface of the plated part is an economical and effective method for preventing discoloration.