Process control during copper plating

Electroplating is a process in which copper ions in copper plating solution are deposited directly on the surface of steel wire (stainless steel) by chemical displacement reaction (Cu2+ + Fe -- > Cu + Fe 2+). Attention should be paid to the following links in production:

1, bath main composition control

1) copper sulfate

Copper sulfate is the main plating agent, its concentration should not be too high or too low. When the concentration is too high, the reaction is accelerated, the growth rate of crystal nucleus is higher than the nucleation rate, which makes the coating loose and rough, and the binding force and density decrease. The reaction speed is too slow, it is difficult to obtain the copper layer with ideal thickness and luster in a short time.

Generally, the mass concentration of copper sulfate is 30-80 g/ L, and the better copper plating layer can be obtained after 2-5 s plating.

2) sulfuric acid

In the bath, sulfuric acid plays a role in activating the surface of steel wire and stabilizing the bath to prevent copper solution. When the concentration of sulfuric acid is too low, the steel wire surface can not be fully activated and affect copper plating; When the concentration is too high, the reaction speed is accelerated and hydrogen evolution is serious, resulting in porous copper layer, poor density and dark red color.

General sulfuric acid concentration in 50-120 g/ L is appropriate.

3) Additives

The additive can slow down the deposition rate of copper layer, refine the grain, passivate the effect of Fe 2+ on the copper plating layer, and inhibit the hydrogen evolution on the surface. If the additive concentration is too high, it will inhibit the deposition of copper layer and make the coating thickness thinner. If it is too low, it will not be able to refine the grain and bright coating.

The general quality fraction of additives is controlled in 0.003%-0.010%.

2. Temperature control

Copper plating generally needs to be heated, the reaction speed is accelerated after heating, can take a lower bath concentration, save production costs, and the temperature rise can better activate additives. But the temperature should not be too high, too high temperature will reduce the stability of the bath, and make the reaction too fast, may passivate additives, so that the quality of copper layer deteriorates.

Under normal circumstances, the temperature is controlled in 35-65 ℃.

3. Cleaning and maintenance of bath

With the development of production, the accumulation of impurities in the bath gradually increased, impurities mainly come from the electrolytic cleaning process and additives and Fe 2+ combined with their own decomposition products, excessive accumulation of impurities will have a bad effect on the deposition of copper layer, so should often clean the bath maintenance.

First of all, we should strengthen the maintenance of the solution before plating, remove the anode mud in the tank and the dirt floating on the liquid surface in time, reduce the impurities into the bath; Secondly, the impurities produced by the decomposition of additives and the precipitation of iron salts can be removed by the method of activated carbon adsorption and filtration to ensure the cleanliness of the bath.

In conclusion, reasonable control of bath composition concentration, temperature and good cleaning and maintenance can ensure that the copper plating layer is dense, bright and good quality of finished products.