PCB Tech - The key to PCB printed circuit board electroplating

The key to PCB plating is how to ensure the uniformity of the copper layer thickness on both sides of the substrate and the inner wall of the via. To obtain the uniformity of the plating layer thickness, it is necessary to ensure that the plating solution flow rate on both sides of the printed board and the through holes is fast and consistent to obtain a thin and uniform diffusion layer. To achieve a thin and uniform diffusion layer, according to the current horizontal electroplating system structure, although many nozzles are installed in the system, the plating solution can be sprayed to the printed board quickly and vertically to accelerate the flow of the plating solution in the through hole The speed causes the flow rate of the plating solution to be very fast, forming eddy currents on the upper and lower surfaces of the substrate and in the through holes, so that the diffusion layer is reduced and more uniform. However, usually when the plating solution suddenly flows into a narrow through hole, the plating solution at the entrance of the through hole will also have a reverse flow phenomenon. Coupled with the influence of the primary current distribution, it often causes the plating of the hole at the entrance., The thickness of the copper layer is too thick due to the tip effect, and the inner wall of the through hole constitutes a copper plating layer in the shape of a dog bone. According to the state of the flow of the plating solution in the through hole, that is, the size of the eddy current and the reflow, and the state analysis of the quality of the conductive plated through hole, the control parameters can only be determined by the process test method to achieve the uniformity of the PCB plating thickness. Because the size of the eddy current and the backflow still cannot be known by theoretical calculation methods, only the measured process method is used. From the measured results,

it is known that to control the uniformity of the thickness of the copper electroplating layer of the through-hole, the controllable process parameters must be adjusted according to the aspect ratio of the PCB through-hole, and even a copper electroplating solution with high dispersibility must be selected and added Appropriate additives and improved power supply methods, namely the use of reverse pulse current for electroplating, can obtain copper coatings with high distribution capabilities.

In particular, the number of micro-blind holes in laminates has increased. Not only must the horizontal plating system be used for electroplating, but also ultrasonic vibration must be used to promote the replacement and circulation of the plating solution in the micro-blind holes. To adjust the controllable parameters based on the data, satisfactory results can be obtained.

According to the characteristics of horizontal electroplating, it is an electroplating method in which the PCB placement method is changed from a vertical type to a parallel plating liquid surface. At this time, the PCB is the cathode, and some horizontal electroplating systems use conductive clamps and conductive rollers for current supply. From the convenience of the operating system, it is common to use the roller conductive supply method. The conductive roller in the horizontal electroplating system not only serves as the cathode, but also has the function of transferring the PCB. Each conductive roller is equipped with a spring device, the purpose of which can be adapted to the electroplating needs of PCBs of different thicknesses (0.10-5.00 mm). However, during electroplating, all parts in contact with the plating solution may be plated with a copper layer, and the system will not work for a long time. Therefore, most of the currently manufactured horizontal electroplating systems design the cathodes to be switchable to anodes, and then use a set of auxiliary cathodes to electrolytically dissolve the copper on the plated rollers. For the sake of maintenance or replacement, the new electroplating design also considers the parts that are prone to wear and tear to facilitate removal or replacement. The anode adopts an array of adjustable size insoluble titanium baskets, which are placed on the upper and lower positions of the PCB. They are filled with a spherical shape of 25 mm in diameter and a phosphorus content of 0.004-0.006% soluble copper, between the cathode and the anode. The distance is 40mm.

The flow of the plating solution is a system composed of pumps and nozzles, which makes the plating solution flow alternately and rapidly in the closed plating tank back and forth, up and down, and can ensure the uniformity of the plating solution flow. The plating solution is sprayed vertically to the PCB, forming a wall-punching jet vortex on the PCB surface. The ultimate goal is to achieve rapid flow of plating solution on both sides of the PCB and through holes to form eddy currents. In addition, a filter system is installed in the tank, and the filter screen used is 1.2 micrometers to filter out the particulate impurities generated during the electroplating process to ensure that the plating solution is clean and pollution-free.

When manufacturing a horizontal electroplating system, the convenience of operation and the automatic control of process parameters must also be considered. Because in the actual electroplating, with the size of the PCB size, the size of the through-hole aperture and the required copper thickness, the transmission speed, the distance between the PCBs, the size of the pump horsepower, the direction of the nozzle and the current density The setting of high and low process parameters requires actual testing, adjustment and control in order to obtain the copper layer thickness that meets the technical requirements. It must be controlled by a computer. In order to improve the production efficiency and the consistency and reliability of the quality of high-end products, the through-hole processing (including plated holes) of the PCB is formed according to the process procedures to form a complete horizontal electroplating system to meet the needs of new product development and listing.

The above is the knowledge about horizontal electroplating. When high-speed PCB design and manufacturing meets with horizontal electroplating, more needs will be met.