PCB horizontal electroplating technology introduction

I. Overview

With the rapid development of microelectronics technology, the manufacturing of circuit board manufacturing has developed rapidly in multi -layered, accumulated, functionalized and integrated directions. Promote the design and design of the circuit graphics with a large number of tiny holes, narrow spacing, and detailed guide lines in the design of the print circuit, which makes it more difficult to print circuit board manufacturing technology, especially the longitudinal ratio of multi -layer plates exceeds 5: 1 and the accumulation A large number of blind holes adopted in the layer plate make the conventional vertical electroplating process cannot meet the technical requirements of high -quality and high -reliability interconnection. The main reasons need to be analyzed from the principle of electroplating the current distribution state. Through the actual electroplating, the distribution of the current in the hole presents the waist drum shape. The edge of the hole cannot ensure the standard thickness of the copper layer that the copper layer in the central part of the hole needs. Sometimes the copper layer is extremely thin or non -copper layer, which will cause irreparable losses in severe cases, resulting in a large number of multi -layer boards scrapped. In order to solve the quality of mass production in mass production, deep -hole plating problems are currently solved from the aspects of current and additives. In the high -vertical and horizontal -to -printed circuit board electroplating process, most of them are under the auxiliary effect of high -quality additives, combined with moderate air stirring and cathode movement, and under the condition of relatively low current density. Increasing the electrode reaction control area in the hole, the role of the electroplating additive can be displayed. In addition, the cathode movement is very conducive to the improvement of the deep plating ability of the plating fluid. The formation speed of the crystal nucleus is compensated to each other with the growth rate of the grain, so as to obtain a high tough copper layer.

However, when the vertical and horizontal ratio of the hole continues to increase or has deep blind holes, these two processing measures seem weak, so the horizontal plating technology is generated. It is the continuation of the development of vertical electroplating technology, that is, a novel electroplating technology developed on the basis of the vertical electroplating process. The key to this technology is to create an adaptive, supporting horizontal electroplating system, which can make the plating solution that can be highly decentralized. With the cooperation of improving the power supply method and other auxiliary devices, it shows that it is more excellent than the vertical electroplating method. Functional effects.

2. Introduction to the principle of horizontal plating

The horizontal electroplating method and principle of vertical plating are the same, and they must have yin and yang poles. After power -on, the electrode reaction is generated to generate the electrolyte's main ingredients, so that the positive ion with the electrical ion moves to the electrode reaction area. The positive phase of the reaction area moves, so the metal sedimentary coating and gases are generated. Because the process of metal in the cathode deposition is divided into three steps: that is, the metal hydration ion spreads to the cathode; the second step is to gradually dehydrate when the metal hydraulic ions are gradually dehydrated and adsorbed on the cathode surface; third Step is to adsize metal ions on the surface of the cathode to receive electrons and enter the metal lattice. From the actual observation to the operating slot, the unable to observe the alien electron transmission response between the electrode of the solid phase and the liquid phase plating fluid. Its structure can be explained by the two electro -layer principles in the electroplating theory. When the electrode is cathode and in a polarized state, it is surrounded by water molecules and a positive charged cation. Nearby, the outer layer of Helmholtz, which is located on the center point near the cationic center point, is about 1-10 nanometers from the electrode. However, due to the total amount of positive charges carried by the cation on the outer layer of Heimhoz, the positive charge is not enough to neutralize the negative charge on the cathode. The plating fluid far away from the cathode is affected by the flow, and the cation concentration of the solution layer layer is higher than the aion concentration. Because the static power effect is smaller than the outer layer of Hemhzhitz, and it is also affected by thermal movement, the discharge of cations is not as close and neat as the outer layer of the Hemhzhitz. This layer is called the diffusion layer. The thickness of the diffusion layer is inversely proportional to the flow rate of plating fluid. That is, the faster the flow rate of the plating liquid, the thinner the diffusion layer, but the thickness, and the thickness of the general diffusion layer is about 5-50 microns. It is farther away from the cathode. Because the current of the solution generated will affect the uniformity of the concentration of the plating solution. The copper ions in the diffusion layer are transported to the outer layer of Heimhoz by the diffusion and the migration of ions. However, the copper ions in the main plating solution are transported to the cathode surface by the actual effect and ion migration. During the horizontal plating process, the copper ions in the plating solution are transported to near the cathode by three ways to form a dual electrocomputer.

The generation of plating solution is the flow of the externally internal with mechanical stirring and pump stirring, swinging or rotating of the electrode itself, and the flow of electroplating fluid caused by temperature difference. The more closer to the surface of the solid electrode, the influence of the friction resistance to make the flow of the plating fluid getting slower and slower. At this time, the convection rate of the solid electrode surface is zero. From the electrode surface to the flow layer formed between the stream plating liquid, the flow layer is called the flow interface layer. The thickness of the flow interface layer is about ten times that of the thickness of the diffusion layer, so the transportation of ions in the diffusion layer is hardly affected by the flow.

Under the influence of electricity, the ions in the electroplating fluid are static power and the ion conveyor is called ion migration. The rate of its migration is as follows: U = Zeoe/6πrη. Among them, U is an ion mobility, the number of charges of ionic ions, EO is the charge of an electron (that is, 1.61019c), E as potential, R radius of hydraulic ions, and the viscosity of plating fluid. According to the calculation of the equation, the larger the potential E, the smaller the viscosity of the electroplating fluid, and the faster the rate of ion migration.

According to the theory of electrical deposition, when electroplating, the printed circuit board on the cathode is a non -ideal polarized electrode. Copper ions adsorbed on the cathode surface are used to obtain electrons and restored to copper atoms, so that the concentration of copper ions near the cathode is reduce. Therefore, a copper ion concentration gradient is formed near the cathode. This layer of plating fluid with a low concentration of copper ions than the concentration of the main plating is the diffusion layer of the plating solution. The copper ion concentration in the main plating solution is high, which will spread to places with lower copper ions near the cathode, which will spread to continuously supplement the cathode area. Printing circuit board is similar to a plane cathode, and the relationship between the size of the current and the thickness of the diffusion layer is COTTRLLL equations:

Among them, i is current, the number of copper ions is the number of copper ions, F is Faraday frequency, A is the cathode surface area, D is the copper ion diffusion coefficient (D = KT / 6πrη), CB is the copper ion concentration in the main plating, and the CO is the cathode pole. The concentration of surface copper ions, D are the thickness of the diffusion layer, K is Boshiman constant (K = R / N), T is temperature, R is the radius of the copper -water ion, and the viscosity of the plating fluid. When the copper ion concentration of the cathode surface is zero, its current is called the extreme diffusion current II:

It can be seen from the above formula that the size of the limit diffusion current determines the copper ion concentration of the main plating liquid, the diffusion coefficient of the copper ion, and the thickness of the diffusion layer. When the concentration of copper ions in the main plating solution, the diffusion coefficient of copper ions is large, and the thickness of the diffusion layer is thin, the larger the limited diffusion current.
According to the above formula, to reach a higher extreme current value, appropriate process measures must be taken, that is, the heating process method is adopted. Because the elevated temperature can make the diffusion coefficient larger, the increase rate can make it a thin and uniform diffusion layer. From the above theoretical analysis, increasing the copper ion concentration in the main plating solution, increasing the temperature of the plating solution, and increasing the flow rate can increase the extreme diffusion current, and achieve the purpose of accelerating the electroplating rate. The horizontal electroplating is based on the acceleration of the convection rate of the plating solution and forms a vortex, which can effectively reduce the thickness of the diffusion layer to about 10 microns. Therefore, when the horizontal plating system is used for electroplating, its current density can be as high as 8A/DM2.

The key to printed circuit board electroplating is how to ensure the uniformity of the thickness of the copper layer of the inner wall of the inner wall of the substrate. To obtain the balance of the thickness of the coating, it is necessary to ensure that the two sides of the printed board and the plating fluid in the pores should be fast and consistent to obtain a thin and uniform diffusion layer. To reach the spread layer of Bojuyi, in terms of the current structure of the horizontal plating system, although many spray torches are installed in the system, the plating can be quickly sprayed into the printed board to accelerate the flow of the plating fluid in the hole in the pores. The speed causes the flow rate of the plating fluid to be fast. Establishing eddy currents in the upper and lower holes of the substrate, which reduces the diffusion layer and is relatively uniform. However, when the plating fluid suddenly flows into the narrow pores, the plating fluid at the entrance of the pores will also have a reverse return. In addition, the impact of the current distribution, which often causes the electroplating of the hole in the entrance. Due to the thickness of the copper layer, the inner wall of the passing hole constitutes a copper coating of the dog's bone shape. According to the state of flowing in the pores in the pores, that is, the size of the vortex and return flow, the state analysis of the quality of the electroplated pores can only be determined by the process test method to determine the uniformity of the control parameter to achieve the thickness of the electrophus plating of the circuit board. Because the size of the vortex and backflow is still unable to know the theoretical calculation method, only the measured process method is adopted. It is learned from the measured results that to control the uniformity of the thickness of the copper coated layer of the hole, it is necessary to adjust the controllable process parameters according to the vertical ratio of the passing hole of the circuit board, and even choose a high -decentralized electroplating copper solution. Then add appropriate additives and improve power supply methods, and use reverse pulse current for electroplating to obtain copper plating with high distribution capacity.

In particular, the number of micro -blind holes in the accumulation plate increases, not only the horizontal electroplating system is used for electroplating, but also ultrasonic vibration to promote the replacement and circulation of plating fluid in the micro -blind hole. The data can be adjusted to correct the controlled parameters to get satisfactory results.

3. Basic structure of horizontal plating system

According to the characteristics of horizontal electroplating, it is the electroplating method of plating the printing circuit board from vertical form to a parallel plating fluid. At this time, the printed circuit board is cathode, and the horizontal plating system of the current supply method uses conductive clips and conductive rolling wheels. To talk about the convenience of the operating system, the supply method of rolling wheel conductivity is more common. In addition to the cathode, the conductive roller in the horizontal plating system also has the function of transmitting and printed circuit boards. Each conductive roller is equipped with a spring device, which can adapt to the needs of the electroplating of the printed circuit board (0.10-5.00mm) of different thickness. However, when electroplating, the parts in contact with plating liquid may be plated with a copper layer, and the system cannot run for a long time. Therefore, most of the current horizontal electroplating systems are designed to switch the cathode into anode, and then use a set of auxiliary cathode to dissolve the copper electrolyte on the coated wheel. For maintenance or replacement, the new electroplating design also takes into account the areas that are prone to loss for easy disassembly or replacement. The anode is an insoluble titanium basket that can adjust the size of the array, placed in the upper and lower positions of the printed circuit board, respectively. The interior has a diameter of 25mm spherical, phosphorus content is 0.04-0.06 % soluble copper, cathode, and anode. The distance between is 40mm.

The flow of plating fluid is a system composed of pumps and nozzle, so that the plating liquid flows quickly in front of the closed groove, and it can ensure the average nature of the flowing liquid flow. The plating solution is vertically sprayed to the printed circuit board, and the printed circuit board surface forms wall jet vortex. Its purpose achieves the rapid flow of plating fluids on both sides of the printing circuit board and the flooding of the hole to form a vortex. In addition, the filter system is installed in the groove, which is used in the field of 1.2 microns to use the granular impurities generated during the electroplating process to ensure the clean and pollution of the plating solution.

When manufacturing horizontal plating systems, it is also necessary to consider the convenient operation and automatic control of process parameters. Because in the actual electroplating, with the size of the size of the circuit board, the size of the size of the pores, and the different copper thickness required, the speed of transmission, the distance between the printing board, the size of the pump horsepower, the spraying peony The setting of process parameters such as direction and current density requires actual testing and adjustment and control to obtain the thickness of the copper layer that meets technical requirements. Computers must be controlled. In order to improve the consistency and reliability of the quality of production and the quality of the sub -product, the front and rear treatment of the printed circuit board (including the plating holes) in accordance with the process procedures, forming a complete horizontal plating system, which meets the development and listing of new products. need.

Fourth, the development advantage of horizontal plating

The development of horizontal electroplating technology is not accidental, but the need for high -density, high -precision, multi -function, multi -function, high vertical and horizontal -to -multi -layer -to -multi -layered circuit board products. Its advantage is that it is more advanced than the vertical plating process used now, the product quality is more reliable, and it can achieve large -scale production. It has the following advantages compared to the vertical electroplating process:

(1) Adapt to a wide range of size, no need to carry out hand -mounted, realize all automated operations, which is not harmful to improving and ensuring that the operation process has no damage to the surface of the substrate, and is extremely beneficial to the large production of large -scale production.

(2) In the process review, there is no need to leave the position of the clamp to increase the practical area and greatly save the loss of raw materials.

(3) Horizontal electroplating is controlled by the whole process to make the substrates be ensured that the surface of the surface of the circuit board and the coating of the coating of the circuit board per block is uniform.

(4) From the perspective of management, the electroplating groove can fully realize automated operations from cleaning and electroplating fluid, which will not cause management out of control due to artificial errors.

(5) It is known from the actual production. Due to the use of multiple horizontal cleaning of horizontal electroplating, it greatly saves the amount of cleaning water and reducing the pressure of sewage treatment.

(6) Because the system uses a closed operation to reduce the direct impact of the pollution of the operating space and the evaporation of calories on the process, it has greatly improved the operating environment. In particular, due to reducing the loss of calories during baking, the useless consumption of energy saves energy and greatly improves production efficiency.

5. Summary

The emergence of horizontal electroplating technology is completely to meet the needs of high vertical and horizontal pores. However, due to the complexity and particularity of the electroplating process, there are still several technical problems in the design and development level electroplating system. This needs to be improved in practice. Nevertheless, the use of horizontal electroplating systems is a great development and progress for the printing circuit industry. Because the use of this type of equipment in manufacturing high -density and multi -layer boards shows great potential, it can not only save manpower and operating time, but also produces the speed and efficiency than traditional vertical electroplating lines. In addition, reduce energy consumption and reduce wastewater wastewater for waste liquids required, and greatly improve the process environment and conditions of the process, and improve the quality of the electroplating layer. The horizontal plating line is suitable for large -scale output 24 -hour uninterrupted operation. The horizontal plating line is slightly more difficult than the vertical plating line when debugging. Once the debugging is completed, it is very stable. Adjust the plating solution to ensure long -term stable work.