Decoding the development of electroplating power supply and the research and development of new technologies

　　I. Introduction

　　Electroplating is the process of reducing metal ions to metal by electrochemical methods, and forming a smooth and dense metal coating that meets the requirements on the surface of metal or non-metal products. The properties of the coating after electroplating largely replace the properties of the original substrate, playing a decorative and protective role. With the development of the decoration industry and the increase in demand for film protection, people have higher and higher requirements for electroplating quality. However, there are still some defects in the current electroplating technology, such as long processing time, poor uniformity of coating thickness, easy defects in the coating, and large internal stress. These defects limit the application and development of electroplating technology and cannot adapt to current production, especially the needs of precision manufacturing. The type of power supply used in electroplating production has a great influence on the quality of the coating. Pulse electroplating is a new electroplating technology. This article briefly introduces the pulse power supply technology in electroplating power supply.

　　2. Development of electroplating power supply

　　2.1 Basic principles of electroplating

　　The electroplating power supply is a device used to generate current in electroplating. The current passing through the plating tank is a necessary condition for electroplating. The metal coating on the plated part is formed by electrochemical reaction when the current flows through the plating tank.

　　From the basic principle of electroplating, it can be seen that the quality of the coating can be improved from two aspects: ① adjusting the electroplating solution; ② improving the electroplating power supply. In reality, the method of improving the electroplating power supply is widely used. This can be seen from the development and evolution of the electroplating power supply.

　　2.2 Development stages of electroplating power supply

　　Electroplating power supply has gone through four stages of development:

　　(1) DC generator stage This power source consumes a lot of energy, has low efficiency and loud noise. It has been eliminated.

　　(2) The silicon rectifier stage is a successor to the DC generator. The technology is very mature, but it has low efficiency, large size, and inconvenient control. At present, many companies still use this electroplating power supply.

　　(3) The thyristor rectifier stage is the mainstream power supply that currently replaces the silicon rectifier power supply. It has the characteristics of high efficiency, small size, and easy regulation. With the maturity and development of the core device - thyristor technology, this power supply technology is becoming more and more mature and has been widely used.

　　(4) Transistor switching power supply , i.e. pulse power supply stage Pulse electroplating power supply is the most advanced electroplating power supply today. Its appearance is a revolution in electroplating power supply. This power supply has the characteristics of small size, high efficiency, superior performance, stable ripple factor, and is not easily affected by output current. Pulse electroplating power supply is the direction of development and has begun to be used in enterprises.

　　3. Research and analysis of pulse plating and pulse power supply

　　3.1 Pulse plating

　　Pulse plating is a new electroplating technology. Its characteristics are determined by the special effects of pulse current on the electrode process dynamics, the most important of which is the effect on the mass transfer process. In DC plating, the metal ions plated in the plating solution are gradually consumed in the solution near the cathode surface. This causes a difference in the concentration of the plated metal ions and the ions in the solution. This difference increases with the increase of the current density used. When the concentration of the ion in the liquid layer near the cathode drops to 0, the so-called limiting current density is reached, and the mass transfer process is completely controlled by diffusion.

　　During pulse plating, due to the existence of the off time, the consumed metal ions use this time to diffuse and replenish near the cathode. When the next on time comes, the metal ion concentration near the cathode is restored. Therefore, a higher current density can be used. Therefore, the difference between the mass transfer process during pulse plating and the mass transfer process during DC plating causes the peak current to be higher than the average current, which makes the speed of seed formation much higher than the speed of crystal growth, making the coating crystallization refined and tightly arranged. The pores are reduced and the resistivity is low.

　　In addition, the adsorption and desorption mechanisms of various substances on the cathode surface under continuous cathode polarization potential during DC electroplating are very different from those under intermittent high cathode polarization potential under pulse conditions. This results in the same solution formula and additives having very different effects when the power waveform is different.

　　3.2 Pulse power supply

　　Pulse power supply is divided into digital pulse power supply and analog pulse power supply. The so-called digital pulse power supply is a power supply that uses a microprocessor and digital circuit to control the DC chopping in the pulse power supply and realizes digital display and digital regulation. It is the most advanced electroplating power supply today. Due to its combination with computer technology, its control is more convenient and flexible. It is currently the development direction of electroplating power supply. The principle of digital pulse power supply

　　Compared with the traditional analog pulse power supply, the digital pulse power supply has the following advantages:

　　(1) The driving waveform is regular, which greatly improves the output waveform after chopping, which is very beneficial to improving the quality of electroplating;

　　(2) Digital control is adopted, which is intuitive and simple;

　　(3) The waveform adjustment range is wide, and the adjustment step can be as low as 0.1ms;

　　(4) The temperature drift coefficient is small and can operate stably and continuously for a long time.

　　In current applications, high-power switch tubes IGBTs are commonly used to chop the DC power supply to achieve the purpose of pulse output. The square wave drive signal sent by the digital controller controls the on and off of the IGBT. By changing the signal of the digital controller, the output pulse width and frequency can be adjusted.

　　Digital pulse plating is essentially a kind of on-off DC plating. The difference is that digital pulse plating has three independent parameters (pulse average current density I, on-time and off-time BEDEquation.DSMT4) that can be adjusted, while general DC plating has only one parameter (current or voltage) that can be adjusted. Therefore, the use of digital pulse plating provides a powerful means for controlling the coating outside the tank. A large number of practices have confirmed that digital pulse plating is a new electroplating technology with high economic benefits that can improve both the quality of the coating and the deposition rate. Figure 3 shows the current waveform of the digital pulse power supply.

　　4. Relationship between coating content and pulse frequency

　　When the current pulse width remains unchanged, the metal content in the coating gradually decreases as the pulse frequency increases.

　　Under the condition that the average current density I remains unchanged, it can be known from the following formula:

　　The lower the frequency, the greater the peak current, that is, within the pulse width, the metal ions near the cathode will be sharply reduced. Since the deposition speed of the matrix metal is faster in a shorter time, the speed of being transported to the cathode and embedded in the coating cannot catch up with the deposition speed of the matrix metal. Therefore, in order to improve the quality and efficiency of the coating, the frequency and pulse width of the pulse power supply can be appropriately adjusted according to different coating metal solutions to achieve changes in the peak current.

　　V. Conclusion

　　A large number of practices by electroplating workers at home and abroad have confirmed that digital pulse electroplating is a new electroplating technology that can improve both the quality of the coating and the deposition rate. Intelligent pulse power supply is a good way to improve the electroplating process. As long as the corresponding parameters such as pulse width, frequency, temperature, etc. are set according to the requirements of different coating metal solutions, the intelligent pulse power supply can automatically complete the electroplating of the workpiece.