Plastic Plating-description And Causes Of Coating Defects in The Process Of Plating (1).

Plastic plating-description and causes of coating defects in the process of plating (1).
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1. Pinholes. The pinhole is due to the adsorption of hydrogen on the surface of the plating, which is not released for a long time. So that the plating solution can not moisturize the surface of the plating parts, so that the coating can not be electroprecipitated. With the increase of the thickness of the coating around the hydrogen evolution point, a pinhole is formed at the hydrogen evolution point. It is characterized by a shiny round hole and sometimes a small upward tail. Pinholes are easy to form when there is no wetting agent in the bath and the current density is on the high side.
2. Hemp spot. The pitting is due to the fact that the plating surface is not clean, there is solid material adsorption, or the solid material in the plating solution is suspended, when it reaches the workpiece surface under the action of electric field, it is adsorbed on it, which affects the electroanalysis, and these solid materials are embedded in the electroplating layer to form small bumps (dots). It is characterized by convexity, no shining, no fixed shape. In short, it is caused by dirty workpiece and dirty plating solution.
3. Airflow stripes. The gas flow stripe is due to excessive additives or high cathodic current density or complexing agent, which reduces the cathodic current efficiency and leads to large amount of hydrogen evolution. If the flow of the bath is slow and the cathode moves slowly at that time, the rising process of hydrogen against the surface of the workpiece affects the arrangement of electroprecipitation crystallization and forms a stripe of air flow from bottom to top.
4. Mask plating (exposed bottom). The masking plating is due to the fact that the soft overflow from the pin on the surface of the workpiece has not been removed and the coating can not be Electrodeposited here. The substrate can be seen after electroplating, so it is called exposed bottom (because the soft overflow material is translucent or transparent resin composition).
5. Brittleness of the coating. After cutting and forming after SMD electroplating, it can be seen that there is a crack at the bend of the pin. When the crack between the nickel layer and the matrix, it is judged to be the brittleness of the nickel layer. When the tin layer and nickel layer crack, it is judged to be the brittleness of the tin layer. The brittleness is mostly caused by additives, excessive brightener, or too many inorganic and organic impurities in the plating bath.
6. Airbag. The formation of the airbag is due to the shape of the workpiece and the gas accumulation conditions. Hydrogen accumulates in the "bag" and cannot be discharged to the bath level. The presence of hydrogen prevents the electrodialysis coating. So that there is no coating on the part where hydrogen is accumulated. In electroplating, the airbag phenomenon can be avoided as long as we pay attention to the hook direction of the workpiece. As shown in the figure, when the workpiece is electroplated, when it is hooked perpendicular to the bottom of the plating tank, the air bag will not be produced. When hooked parallel to the bottom of the slot, the air bag is easy to be produced.
7. "tin flowers" bloom in the middle of the blackbody. There is a tin coating on the blackbody, which is because the upward parabola of the gold wire is too high when the tube is soldered, the gold wire is exposed on the blackbody surface during plastic sealing, and the tin is plated on the gold wire, like a flower. It's not the bath.
8. "climb tin". There is a tin layer at the joint between the lead and the blackbody (root), climbing up the blackbody like wall grass, and the tin layer is a dendritic loose coating. This is due to the pre-plating treatment, brushing the SMD frame with a copper brush, and the worn copper powder embedded in the blackbody is not easy to wash off and become a conductive "bridge". As long as the electroplating metal builds a "bridge", it extends, and the dendritic deposit crawls away to connect with other copper powders, and the tin climbing area is getting larger and larger.
9. "Xuzi tin" is at the joint of the lead and the blackbody, there is whisker-like tin on both sides of the lead, and there is a tin coke-like tin pile on the front of the lead at the junction with the blackbody. This is due to the fact that when the SMD frame is silver plated by masking method, the masking device is not tight, and silver is also plated where silver plating is not needed. While in the plastic packaging, there is a part of the silver layer exposed to the blackbody. When the silver layer is pried up before plating, the tin plated on the silver is like a beard or a pile of tin. Overcoming the exposure of silver layer is one of the keys to the technology of silver mask plating.
10. Orange peel-like coating. When the substrate is very rough, or there is corrosion in the pretreatment process, or when the Ni42Fe+Cu substrate is treated before plating, some copper layers have been removed, while in some areas, the copper layer has not been removed, and the whole surface is not smooth. All of the above conditions may cause the state of coating orange peel.