PCB Technical - How to control the PCB aqueduct solution is the best

Do you know what the role of PCB aqueduct solution is? The main purpose of PCB plating bath solution control is to keep all chemical components within the specified range of the process. Because only within the parameters specified by the process, the chemical and physical properties of the coating can be ensured. There are many types of process methods used for control, including chemical analysis, physical testing and determination of acid value of solution, specific gravity or colorimetric determination of solution, etc. These process methods are to ensure the accuracy, consistency and stability of the parameters of the bath. The choice of control method is determined by the layer type.

Although the analytical method is reliable for the control of the plating solution, it cannot guarantee a good plating layer. Therefore, it is necessary to resort to electroplating tests. In particular, in order to ensure that the coating has good electrical and mechanical properties, many electroplating tanks add organic additives to improve the structure and performance of the coating. It is difficult for these additives to be effective by chemical analysis methods. The process method of electroplating test is used for analysis and comparison, which is used as an important supplementary means to control the chemical composition of the plating solution. Supplementary control includes the determination of additive content and adjustment, filtration and purification. These need to be carefully "observed" on the test board of the Hoss electroplating bath, and then research, analysis and inferences on the distribution state of the coating on the sample plate to achieve improvement or improvement of the process Step purpose.

For example, the parameters of the electroplating bath with high dispersibility, bright, high acid and low copper are adjusted or adjusted through the analysis data provided by chemical methods; in addition to chemical analysis, the electroless copper solution must also be subjected to pH or acid value comparison. 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 condition of the plated substrate, such as the temperature of the plating solution, the current density, the mounting method and the effect of the substrate surface treatment state on the bath solution. In particular, it is necessary to control the inorganic impurity-zinc of the bright acid copper plating solution. If the value exceeds the allowable process specification, it will directly affect the surface state of the copper layer; the tin-lead alloy bath solution must strictly control the content of copper impurities, if it exceeds A certain amount will affect the wettability, solderability and protection of the tin-lead alloy coating.

1. PCB electroplating test

The control principle of the electroplating bath should include the main chemical composition of the bath. To reach the correct judgment, advanced and reliable test instruments and analytical methods are required. Some bath liquids also need auxiliary means such as measuring its specific gravity, acid value (PH), etc. In order to directly observe the surface state of the coating, most PCB manufacturers now adopt the process method of the Holstein cell test. The specific test procedure is to tilt the test board at 37° to the same length as the long side, and place the anode perpendicular and along the long side. The change of the distance between the anode and the cathode will make a regular distance along the cathode. As a result, the current will continuously change along the test board. From the current distribution state of the test board, it can be scientifically judged whether the current density used in the electroplating bath is within the range specified by the process. The direct influence of additive content on the current density and the influence on the quality of the surface coating can also be observed.

2. PCB bending negative plate test method:

This method is adopted because it can cover a wide range, it exposes a corner, and its upper and lower surfaces can adapt to the dielectric effect due to the vertical shape. From this, the current range and dispersion ability can be tested.

3. Judgment and inference:

Through the above-mentioned test method, the actual record of the test board can be passed. First, the phenomenon that occurs in the low current area of the test board during electroplating can be judged, and it can be judged that additives need to be added; while in the high current area, the plating Defects such as surface roughness, blackening and irregular appearance will appear, which indicates that the inorganic metal impurities in the bath directly affect the surface state of the coating. If there are pits on the surface of the coating, it means that the surface tension should be reduced. The damaged electroplating layer often shows excessive additives and decomposition in the bath. This kind of phenomenon fully shows that it is necessary to analyze and adjust in time to make the chemical composition of the bath liquid meet the process parameters stipulated by the process. The excess additives and decomposed organic matter must be treated, filtered and purified with activated carbon.

In short, even though the development of science and technology now chooses to use computers for automatic control one by one, it must be tested with the help of auxiliary means to achieve double insurance. Therefore, the commonly used control methods in the past need to be used or further researched and developed new test process methods and equipment to make the PCB plating and coating process more perfect.