Do you know what the function of the PCB board aqueduct solution is? The main purpose of the control of the PCB plating solution is to keep all chemical components within the range specified by the process. The chemical and physical properties of the coating are ensured only within the parameters specified in the process. There are many types of processes used for control, including chemical fractionation, physical testing, acid value determination of solutions, specific gravity of 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.
Although the analytical method is reliable for bath control, there is no guarantee that a good coating will be obtained. Therefore, it is also necessary to resort to electroplating tests. In particular, many electroplating baths add organic additives to improve the structure and performance of the coating in order to ensure good electrical and mechanical properties of the coating. These additives are difficult to use by chemical analysis methods, and are analyzed and compared using electroplating test methods, which serve as an important supplement to control the chemical composition of the bath. Additional controls include the determination of additive levels and adjustments, filtration and purification. These need to be carefully “observed” from the Holstein plating bath test panel, and then analyzed, analyzed and inferred from the plate coating distribution state to achieve improvements or improvements in the process. Step purpose.
For example, the parameters of high dispersibility, bright high acid and low copper plating bath are adjusted by the chemical folding method; in addition to chemical analysis, the chemical copper solution is also subjected to pH acid value or ratio and Color measurement, etc. If the chemical composition is within the process range after analysis, it is necessary to pay great attention to the changes of other parameters and the surface state of the substrate to be plated, such as the temperature of the plating solution, the current density, the method of mounting and the influence of the surface treatment state of the substrate on the bath. In particular, it is necessary to control the inorganic impurity-zinc of the bright acid copper plating solution, which exceeds the allowable process specification value, and directly affects the surface state of the copper layer; the tin-lead alloy bath solution must strictly control the content of copper impurities, such as a certain amount will affect the wettability and weldability and protection of the tin-lead alloy coating.
First, PCB plating test
The control principle of the plating bath should include the main chemical composition of the bath. To achieve the correct judgment, advanced and reliable test instruments and analytical methods are required. Some baths also need to use auxiliary means such as measuring their specific gravity and acid value (PH). In order to directly observe the surface state of the coating, most PCB manufacturers now adopt the method of Holstein’s groove test. The specific test procedure is to tilt the test panel by 37° to the same length as the long side, with the anode perpendicular and along the long side. The change in anode-to-cathode distance will have a regular gauge along the cathode, with the result that the current along the test plate is constantly changing. From the state of the current distribution of the test plate, it is possible to scientifically determine whether the current density used in the plating bath is within the range specified by the process. The direct effect of the additive content on the current density and the effect on the surface coating quality can also be observed.
Second, the PCB bending negative test method:
This method is adopted because it masks a wide range, which exposes an angle, and its upper and lower surfaces are adapted to the dielectric effect due to the vertical shape. From this, the current range and the dispersing ability can be tested.
Third, judgment and inference:
Through the above-mentioned test method, it is possible to judge the phenomenon of occurrence in the low current region of the test plate at the time of plating by the actual recording of the test plate, and it can be judged that the additive is required to be added; and in the high current region, the plating is performed. Defects such as rough surface, blackening and irregular appearance may occur, which indicates that the inclusion of inorganic metal impurities in the bath directly affects the surface state of the coating. If the surface of the coating is pitted, it means that the surface tension is to be reduced. The damaged plating layer often exhibits excessive amounts of additives and decomposition in the bath. Such phenomena fully demonstrate the need for timely analysis and adjustment so that the chemical composition of the bath meets the process parameters specified in the process. Excess additive and decomposed organic matter must be treated, filtered and purified using activated carbon or the like.
In short, although the use of computer technology to automatically control one by one through the development of science and technology, but also must be tested by means of assistance, in order to achieve double insurance. Therefore, the commonly used control methods in the past need to be used or further research and development of new test methods and equipment to make the PCB plating and coating process more perfect.
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Post time: Jul-20-2019