Specification of Electroplating Process - Copper Plating Process (I)

Copper must cover up the defects of the steel roller, but also show the best work surface for the next process, electric carving. Copper plating is an extremely complicated process, and its control should be extremely strict. Slightly sloppy, it takes a lot of time, manpower, and material resources to correct the problems that arise.

(I) Copper Plating Process

Jingong Roller → Inspection → Production Drum Roller → Drum Pretreatment → Pre-plating Nickel → Polishing Cleaning → Copper Plating → Unloading Drum → Turning Mill

(b) The principle of drum plating

The copper plating layer is pink, soft and has good ductility.

The main components of the electrolytic solution in the copper plating bath are sulfuric acid (H2SO4) and copper sulfate (CuSO4·5H2O). Copper is present as copper ions (Cu2+) in this solution. Electrolytic copper is used as an anode, distributed semi-circularly in the electrolytic solution, and connected to the anode of the power supply. The drum is placed horizontally in the electrolyzer. Some of the surface of the drum is immersed in the electrolytic solution, and some are semi-immersed or 1/3 immersed in the electrolytic solution. It is connected to the cathode and rotates at a certain rotational speed. After the electricity is applied, the yin and yang electrodes react chemically. The copper ions have a positive charge and are attracted by the cathode. The electrons are obtained at the cathode to form copper atoms, which adhere to the roller and complete the plating. In fact, due to certain reasons, the positive and negative ions will not be balanced due to the interference of this reaction process, so it is not easy to produce a satisfactory plating roller in actual production. In view of this situation, we can only do our best to reduce the interference factors. According to our company's conditions, we can match various equipment and processes to obtain a satisfactory plating roller.

(III) Strengthening Conductivity Management

To improve the quality of the copper layer, it is important to control the current difference to ensure that the conductive parts are clean and in good contact, so that the current value is distributed evenly, so that the hardness of the copper layers at both ends of the drum and the middle is the same.

(IV) Main components of copper plating solution

Gravure plating uses sulphate copper plating. The basic components of the bath are copper sulphate and sulphuric acid. Copper sulphate is used to supply copper ions in the bath. Sulfuric acid plays a role in preventing copper salt solution, increasing the conductivity of the bath and cathode polarization. Due to the high current efficiency of the bath (nearly 100%), a thicker plating can be applied. Of course, we must ensure the purity and stability of various chemicals. The main components of the copper plating solution are as follows:

1. Copper sulfate (CuSO4·5H2O) is a blue crystal. The size of the pellets, such as corn kernels, should be as yellow as possible. Industrial grades are available. According to the production conditions and different requirements, the copper sulfate content of some company specifications are 200 ~ 250g / L, some 210 ~ 230g / L, and some are 180 ~ 220g / L. The low content of copper sulfate allows a low operating current density and low cathode current efficiency. The increase in the content of copper sulfate is limited by its solubility, and the solubility of copper sulfate decreases with the increase in the content of sulfuric acid in the plating. Therefore, the content of copper sulfate must be lower than its solubility in order to prevent its precipitation.

2. Sulfuric acid (H2SO4) can significantly reduce the bath resistance in the bath and prevent the copper sulfate from hydrolyzing and precipitation. Its chemical reaction formula is as follows:

CuSO4+2H2O Cu(OH)2 +H2SO4
If you smell like ammonia, there is a problem. If the bath concentration is not suitable, Cu2+ will be produced, causing pitting and pinholes on the copper plating surface.

When the sulfuric acid content is low, the coating is rough and the anode is passivated. Increasing the sulfuric acid content improves the throwing power, but some brighteners tend to decompose. The content of some company specifications is 40 ~ 60g / L, some 55 ~ 65g /, and some 60 ~ 70g / L.

Some companies control the content of copper sulfate in the range of 180-270g/L and the sulfuric acid content in the range of 55-65g/L, achieving very good results, making the copper layer reach the optimum hardness and prolonging the storage period.

At the temperature of 15 °C, the corresponding relationship between copper sulfate + sulfuric acid content and Baume degree is shown in Table 2.

3. Chloride (Cl-), obtained by adding a little hydrochloric acid. Chloride is an indispensable electrodeless anion in acid bright copper plating. An ideal bright copper layer cannot be obtained without chloride ions, but an excessively high chloride ion content will cause pitting of the copper plating layer and affect brightness and flatness. It should be used according to the requirements of additives, such as: 50 to 60 ppm for Mignano, about 50 ppm for Hard, and 80 to 120 ppm for Daiwa.


(5) Preparation method of plating solution

The calculated amount of copper sulfate is first dissolved in 2/3 of the volume of warm water. After the copper sulfate is completely dissolved and cooled, sulfuric acid is slowly added under constant stirring (sulphuric acid is added as an exothermic reaction), and the bath is then filtered and filtered. , After adding the specified additives, test plating can be put into production.

(to be continued)