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Research on the plasma cleaning of the printed plug surface by plasma cleaning equipment:
The printed plug on the printed circuit board is a pin used for electrical connection in the PCB, which plays an important role in electrical conduction. Since the normal gold surface should be bright golden, the surface of the printed plug will be discolored during the production process, commonly known as the oxidation of the gold surface, which affects the electrical conduction, and will cause the failure of the electronic system in serious cases. However, the traditional cleaning method has no obvious effect on the surface of the printed plug. Therefore, cleaning the surface of the printed plug is a problem that plagues the PCB process.
The purpose of gold plating on the PCB printed plug surface is that gold can reduce contact resistance. Because it is a plug-in, gold plating can increase wear resistance and also prevent oxidation. But after the gold plating, the gold surface will always change color, and visually observe it as dark yellow or reddish brown spots. The normal gold surface should be bright golden.
Analysis of the reasons for the discoloration of the golden surface:
Gold surface oxidation is just a common name. Strictly speaking, gold will not be oxidized, because gold is a relatively stable metal element and does not react with other substances in the atmosphere, so it will not be exposed to various corrosive gases. Invasion and chemical changes occur. The reasons for the discoloration of the PCB printed plug surface are mainly reflected in the following two aspects:
At the beginning of electroplating, the surface of the substrate gathers nuclear separation points, and as time increases, the gold will eventually spread continuously in the horizontal and vertical directions and gradually spread on all the surfaces of the substrate. The gold crystal nucleus deposited on the surface of the substrate will inevitably form a gap in the horizontal direction. If this gap forms a micro-hole of the gold plating layer leading to the base metal, the base metal copper will migrate to the surface of the plating layer through the gap of the gold plating layer. There is a potential difference between copper metals. This potential difference will cause the base metal to be corroded when encountering corrosive media. When corrosives accumulate on the surface of the gold layer, the color will change.
The copper surface cannot be cleaned completely before gold plating, and the copper matrix is rough due to excessive pickling, which leads to an increase in the plating gap, and the copper is easily diffused to the gold surface, and then it is corroded by corrosive gases and causes discoloration.
In the electroplating process, if the maintenance of the plating solution is not done well, it will have serious consequences for the quality of the plating. For example, if metal impurities are brought into the plating solution, the dispersion ability of the plating solution will decrease, the current efficiency will be reduced, and the gold plating will be affected. Adverse effects. Poor cleaning after plating and operator's hand sweat contamination are also causes of discoloration of the gold layer.
Analyzing the thickness of the gold plating layer on the surface of the board cleaned by the plasma cleaning equipment and the gold plating layer on the board surface that has not been plasma treated by the plasma cleaning equipment, there is no difference in thickness, that is, the plasma has no effect on the gold plating layer.
The board processed by the plasma of the plasma cleaning equipment did not find the circuit corrosion under the encapsulation, that is, the plasma of the plasma cleaning equipment did not damage the encapsulation during the processing.
Test the binding force analysis of the treated and untreated board and the reinforcement, the binding force of the plasma-treated board and the reinforcement is increased instead, the reason may be that the high temperature in the plasma machine of the plasma cleaning equipment also played a role in curing Function, so that the binding force is enhanced.
Solderability test, the solderability test was performed on the printed plug, and the result was normal. In summary, the plasma will not bring adverse effects to the board in cleaning applications, that is, it can be used in practice.
Compared with traditional cleaning methods, plasma cleaning equipment plasma can clean the gold surface more effectively. It not only has a short action time, saves manpower and time, and has high cleaning efficiency, but also the use of gas is low in price, has cost advantages, and strengthens it. Encapsulation and gold surface have no effect, so plasma cleaning is an excellent gold surface cleaning method.
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