Inventory of reasons for poor PCB coating
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.
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 these solid matter in In the electroplating layer, small bumps (pits) are formed. The characteristic is that it is convex, there is no shining phenomenon, and there is no fixed shape. In short, it is caused by dirty workpiece and dirty plating solution.
3. Air 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 is flowing slowly and the cathode is moving slowly, the hydrogen gas will affect the arrangement of the electrolytic crystals during the process of rising against the surface of the workpiece, forming bottom-to-up gas flow stripes.
4. Masking (exposed)
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 exposed (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.