The main purpose of the PCB plating solution is to maintain all chemical composition within the scope of the process. Because only in the process of the parameters specified in order to ensure that the chemical and physical properties of the coating. There are many types of process methods used in the control, including chemical fractionation, physical test and acid value determination of the solution, the specific gravity of the solution or colorimetric determination. These processes are designed to ensure the accuracy, consistency and stability of the bath parameters. The choice of control method is determined by the type of buildup.
Such as high dispersion capacity, bright high acid and low copper plating bath to determine the parameters of the chemical method is provided by the sub-folding data to adjust or adjust; chemical copper solution in addition to chemical analysis, but also PH acid value or ratio Color determination and so on. If the chemical composition of the analysis within the scope of the process; it is necessary to pay attention to other changes in the parameters and the surface of the substrate surface, such as the bath temperature, current density, the method of loading and substrate surface treatment of the tank on the impact. In particular, to control the bright acid copper plating liquid inorganic impurities - zinc, more than the allowable process of the specified value, it will directly affect the copper surface of the state; electroplated tin-lead alloy bath must strictly control the content of copper impurities, such as more than A certain number, will affect the tin-lead alloy coating wetting and solderability and protective properties.
Although the analytical method is reliable for the bath control, it is not guaranteed to obtain a good plating layer. Therefore, it must also rely on electroplating test. In particular, many plating baths to improve the electrical properties and mechanical properties of the coating, add organic additives to improve the coating structure and performance. These additives by chemical analysis method is difficult to work, the use of electroplating test method for analysis and comparison, it is used as an important means to control the chemical composition of the bath. The supplemental control includes the determination of the additive content and the adjustment, filtration and purification. These are required to be carefully observed by the Huo's electroplating tank test plate, and then analyzed and analyzed and deduced from the distribution of the sample plating to improve or improve the process Step purpose.
First, electroplating test
The control principle of the plating bath should include the main chemical composition of the bath. To achieve the correct judgments, the need for advanced, reliable test equipment and analytical methods, some of the bath also need to use auxiliary means such as: determine the specific gravity, acid value (PH) and so on. In order to directly observe the surface of the coating surface, most manufacturers are using the Hawthorn trough test process. The specific test procedure is to tilt the test plate at 37 ° and the length of the long side, the anode vertical and along the long side. The change in anode to cathode distance will be regular along the cathode for the gauge, and the results are constantly changing along the current of the test plate. From the state of the current distribution of the test plate, you can scientifically determine whether the current density of the plating bath is within the range specified by the process. It is also possible to observe the direct effect of the additive content on the current density and its effect on the quality of the surface coating.
Second, the bending plate test method:
This method is taken because it can cover a wide range, it exposes a corner, because the vertical shape of its upper and lower surface can adapt to the role of dielectric. Which can test the current range, the dispersion of the pros and cons.
Third, judgments and inferences:
Through the above-mentioned test method, you can through the experimental board of the actual record, you can first determine the plating in the test plate in the low current area of the phenomenon, you can determine the need to add additives; and in the high current, There will be rough surface, black and irregular appearance and other defects, indicating that the bath contains inorganic metal impurities directly affect the coating surface state. If the surface of the coating presents pits, it means to reduce the surface tension. The damaged plating layer often shows excessive amounts of additives and decomposition in the bath. This phenomenon is fully explained to timely analysis and adjustment, so that the chemical composition of the bath in line with the process of the required process parameters. The excess additives and decomposition of organic matter must be treated with activated carbon, filtration and purification.
In short, despite the use of computer automatic control, but also must rely on auxiliary means to test, can be double insurance. Therefore, the commonly used control methods in the past need to be used or for further research and development of new test methods and equipment, PCB plating and coating process more perfect.