How to Avoid Electroplating Polarization
2021-09-26
When a metal electrode has both cathodic reaction and anodic reaction properties, the metal electrode is called bipolar electrode. The phenomenon of simultaneous cathodic and anodic reactions on two different surfaces of a bipolar electrode is called bipolar phenomenon.
The simple principle is as follows (taking the most common copper plating as an example): in the electrolytic cell, the current flows from the metal (anode copper ball) into the electrolyte (plating solution) as the anode, and the electrode where the current flows from the electrolyte into the metal is the cathode. (In fact, in the theory of electrochemistry, the professional terms are the first type of conductor (for example: metal) and the second type of conductor (for example: electrolyte). The metal A connected to the (rectifier) separates the electrolytic cell into two cells, so the current between the cathode and anode cannot completely flow from the anode to the cathode through the electrolyte, and must pass through A. Therefore, when the current reaches the surface of A from the anode , at this time, a cathodic reaction occurs on the surface (the difference is wrong? The current flows into the metal from the electrolyte), and an anodic reaction occurs on the other surface of A (the current flows from the metal into the electrolyte). Therefore, , the side facing the sunburst is plated with metal, and the metal A on the other side facing the cathode may dissolve. The principle is as follows, in practice, according to electrochemical theory, a specific anodic or cathodic reaction must reach a certain level the electrode potential (not the voltage) to start the reaction.
Take copper plating as an example: in general, acid copper plating will cause a cathodic reaction (copper ions are reduced to the metal) as long as the voltage difference is around 0.6V. Assuming that a titanium basket in the vertical electroplating tank is in poor contact with the conductive copper bars and there is resistance, then there will be a potential difference between the titanium basket and the two adjacent titanium blues, as long as the potential difference exceeds a certain value. , then the titanium blue becomes A in the above, and becomes a bipolar electrode. It is plated with copper in the direction of titanium blue facing the next door, and the anode is facing the direction of the cathode.
Countermeasures: After understanding the above principles, it is very simple to solve the problem: ensure that all the anodes are at the same potential height relative to the cathodes. That is, one end is grounded, and the other end measures the points of the anode, whether all points are the same potential. Application and PCB electroplating copper, this problem mostly occurs on the anode----titanium blue.
Therefore, the following measures can be taken:
1. Clean the conductive copper bar and the titanium blue hook to ensure a good electrical connection between the titanium blue and the conductive copper bar.
2. Add copper balls in time to ensure close contact between the copper balls and the copper balls.
3. If the clamp of the cathode is not tightly clamped, and one of the substrates is not applied with voltage, the cathode (substrate) becomes a bipolar electrode. At this time, the substrate will be partially dissolved.
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