Description And Reasons of Poor Plating During PCB Electroplating:
1. Pinhole. The pinholes are due to the hydrogen adsorbed on the surface of the plated parts, and they are not released for a long time. Make the plating solution unable to wet the surface of the plated parts, so that the plating layer cannot be electrolytically deposited. As the thickness of the coating in the area around the hydrogen evolution point increases, a pinhole is formed at the hydrogen evolution point. It is characterized by a shiny round hole and sometimes a small upward tail. When the plating solution lacks wetting agent and the current density is high, pinholes are easily formed.
2. Pitting. The pitting is caused by the unclean surface of the plated surface, the adsorption of solid matter, or the suspension of solid matter in the plating solution. When it reaches the surface of the workpiece under the action of an electric field, it is adsorbed on it, which affects the electrolysis and embeds this solid matter in the electroplating layer, small bumps (pits) are formed. The characteristic is that it is convex, there is no shiny phenomenon, and there is no fixed shape. In short, it is caused by dirty workpiece and dirty plating solution.
3. Airflow streaks. Air flow streaks are due to excessive additives or high cathode current density or high complexing agent, which reduces the cathode current efficiency, resulting in a large amount of hydrogen evolution. If the plating solution flows slowly and the cathode moves slowly at that time, the hydrogen gas will affect the arrangement of the electrolytic crystals during the process of rising against the surface of the workpiece, forming a bottom-up gas stream streak.
4. Exposure (showing the bottom). Masking is due to the fact that the soft flash on the pins on the surface of the workpiece has not been removed, and the electrolytic deposition coating cannot be carried out here. The base material is visible after electroplating, so it is called exposure (because the soft flash is a translucent or transparent resin component).
5. The coating is brittle. After SMD electroplating, after cutting the ribs and forming, it can be seen that there are cracks in the bends of the pins. When there is a crack between the nickel layer and the substrate, it is judged that the nickel layer is brittle. When there is crack between the tin layer and the nickel layer, it is judged that the tin layer is brittle. The cause of brittleness is mostly additives, excessive brightener, or too much inorganic or organic impurities in the plating solution.
6. Air pocket. The formation of the air pocket is due to the shape of the workpiece and the air-trapping conditions. Hydrogen accumulates in the “pocket” and cannot be discharged to the surface of the plating solution. The presence of hydrogen prevents the electrolysis coating. Make the part where hydrogen accumulates no plating. During electroplating, as long as you pay attention to the hooking direction of the workpiece, the air pocket phenomenon can be avoided. When the workpiece is electroplated when it is hooked perpendicular to the bottom of the plating tank, no air pockets are generated. When hooked parallel to the bottom of the groove, it is easy to produce air pockets.
7. There is a “tin flower” in the center of the plastic-sealed black body. There is tin plating on the black body. This is because when the electron tube is soldered, the upward parabola of the gold wire is too high. The gold wire is exposed on the surface of the black body during plastic packaging, and the tin is plated on the gold wire, like a flower. It is not a problem with the plating solution.
8. “Climbing Tin”. There is a tin layer at the junction (root) of the lead and the black body, which climbs up the black body like a wall-climbing grass. The tin layer is a dendritic loose plating layer. This is because in the pre-plating process, the SMD frame is scrubbed with a copper brush, and the worn-out copper powder embedded in the black body is not easy to wash off, becoming a conductive “bridge”. When electroplating, as long as the electrolytic metal builds the “bridge”, it will extend. The deposits crawled away to connect with other copper powder, and the area of tin crawling became larger and larger.
9. “Whisker tin” is at the junction of the lead and the black body. There is whisker-like tin on both sides of the lead, and there is a coke-like tin pile on the front of the lead and the junction of the black body. This is because when the SMD frame is silver-plated by the mask-plating method, the mask-plating device is not tight, and the silver-plated places are also plated with silver. While in plastic packaging, part of the silver layer is exposed outside the black body. In the pre-plating process, the silver layer is pried up, and the tin-plated on the silver is like whiskers or piles of tin. Overcoming the exposure of the silver layer is one of the keys to silver masking technology.
10. Orange peel-like coating. When the substrate is very rough, or there is over-corrosion in the pretreatment process, or when the Ni42Fe+Cu substrate is treated before plating, some of the copper layer has been removed, while in some areas the copper layer has not been removed, and the entire surface is damaged. Flowers are not smooth. The above conditions may cause the orange peel state of the coating.
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