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Reasons for the Layering and Color Change of the Gold-plated Layer of PCB Printed Circuit Board

After the gold-plated circuit board is brightly plated with copper, the surface film is not completely removed. Therefore, after cleaning, it is directly transferred into a nickel plating tank for electroplating. After electroplating, the nickel layer separates from the surface of the copper. The bright copper plating solution contains a certain amount of additives such as a brightener, a leveling agent, a wetting agent and the like. It does not significantly alter the properties of the bath in the electrolyte, but it significantly improves the properties of the coating.

Organic substances such as such additives are adsorbed on the surface of the coating. These organic substances are strongly adsorbed on the surface of the copper plating, and are difficult to remove using general flow cleaning water. They must be treated with a special treatment solution for a certain period of time to achieve a satisfactory surface effect. It is because these invisible transparent films directly affect the bonding strength between the nickel plating of the gold-plated circuit board and the copper surface.

The copper surface of the gold plated circuit board must also be micro-roughened to form a slightly rough surface on the copper surface to increase the bonding strength between the copper layer and the nickel layer. Because the nickel coating has a certain stress, this stress forms tensile stress especially on the bright copper surface, and is separated from the surface of the copper.

The purpose of micro-roughening is to increase the bonding force with the nickel plating layer. Due to the improper roughening treatment, the surface of the copper layer is uneven, and the uniformity of the distribution of the nickel plating layer is directly affected, resulting in a good local bonding force, a poor spot of the stars, and a nickel layer delaminating from the surface of the copper.

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