Description And Reasons of Poor Plating During Electroplating 2/3

Description And Reasons of Poor Plating During PCB Electroplating:

11. Recess plating. There are sparse and dense irregular cavities on the surface of the coating (different from pinholes), which is a “ceiling face” coating. There are two situations that may form a “ceiling face” coating.
(1) Some units use glass bead spray to remove flash. When the sprayed air pressure is too high, the kinetic energy inertia of the glass beads will impact the coated surface into small pits. When the coating is too thin, the pit is not filled, and it becomes a “ceiling face” coating.
(2) The metallographic phase of the base material alloy is not uniform, and there is selective corrosion during the pre-plating process. (The more active metal is etched first to form cavities). If the cavities are not filled up after electroplating, it becomes a “ceiling face” coating.
For example: Ni42Fe base material, if Ni and Fe are not fully mixed uniformly during the metallurgical process, the surface of the material is likely to have uneven alloy metallurgy in some areas after rolling into a material. During the pre-plating process, since Fe is more active than Ni, it is selectively etched preferentially to form pits. If the plating layer cannot be flattened, the pit becomes a “ceiling face” plating layer. Similarly, zinc brass has the same phenomenon. If the copper-zinc metallographic phase is not uniform, zinc will be selectively corroded before copper during pre-plating, making the substrate appear pits, and after electroplating, it will appear like a pit plating layer.

12. Loose dendritic coating. When the plating solution is dirty, the main metal ion concentration is high, the complexing agent is low, the additives are low, the anode and the anode are too close, the current density is too large, and a loose dendritic coating is easily formed in the current area. The loose coating is like foam plastic, and the dendrites are uneven, and the coating can be wiped off with your fingers.

13. Double-layer plating. The formation of double-layer plating mostly occurs when the operating temperature of the plating solution is relatively high. During the electroplating process, the workpiece is lifted out of the plating tank and then re-plated. During this process, if the workpiece is raised for a long time, the plating solution on the surface of the workpiece will precipitate salt frost and adhere to the workpiece due to the evaporation of water. During the re-plating, the salt frost has not had time to dissolve, and the coating is plated on the salt frost surface to form a double-layer coating.

To avoid double-layer plating, you can shake the workpiece in the plating solution for a few seconds before re-plating, let the salt frost dissolve, and then power on re-plating.

14. The coating is blackened. The main reason for the blackening of the coating is the high metal and organic impurities in the plating solution, especially in the low current density area, the coating is darker. In the case of insufficient additives, a black coating will also appear in the middle of the large plated area. The temperature is too low for ions, the activity is small, and the gray-black plating layer will be formed when the current is high. To deal with metal impurities, a corrugated board can be used as the cathode, 01-0.2A/dm2 electrolysis. To deal with organic pollution, 3-5 g/l, activated carbon can be used. Use the granular one and wash it with pure water first.

15. Passive peeling. Ni42Fe alloy is easily passivated. Activation before plating includes two chemical processes, one is oxidation process and the other is oxide dissolution process. If the oxidation process is not sufficient or the oxide is too late to dissolve, there will still be oxide residues on the plated surface, and the coating will peel or be rough.

16. Replacement peeling. If there are two different materials on the same workpiece. For example, the surface of the copper substrate is nickel-plated, and copper is exposed on the cut after cutting and forming. When the copper ions in the strong corrosion tank increase to a limit value, a replacement copper layer is likely to occur on the nickel layer. With replacement copper, the tin layer will peel off after tinning. In this case, you can only update the corrosion potion frequently to avoid replacement peeling.

17. Peeling due to oil pollution. If the oil is not removed in the pre-plating treatment, there will be no plating in the oil-contaminated area during electroplating. Even if the plating is covered, it is pseudo-plating. The plating has no bonding force with the base material.

18. Dark round spot coating. When the workpiece has a large area to be plated, such as the heat sink of a pipe. When there are too many impurities or insufficient additives in the plating solution, a gray-black dark round spot plating layer will be formed in the center of the heat sink, like a plaster. Because the center of the large area is a low current area, impurities are concentrated and precipitated here. Or when the additives are insufficient, the depth capability of the plating solution decreases.

19. The gloss of the coating is uneven, and the thickness is obviously uneven (visually). This is due to the fact that the additives have just been added, and the additives are not fully dispersed, which makes the bath characteristics uneven. After the additives are evenly dispersed, the malfunction disappears naturally.

20. Chemical fiber contamination of the plating solution, visible traces of chemical fiber embedded on the plating layer. This failure can be overcome if the anode bag PP cloth is made with a soldering iron.