When a metal electrode has both the cathodic reaction and the anodic reaction at the same time, the metal electrode is called a bisexual electrode. The phenomenon that the cathodic and anode reactions occur simultaneously on two different surfaces of the bipolar electrode is called bipolar phenomenon.
The simple principle is as follows (take 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 electrochemical theory, the technical terms are the first type of conductor (for example: metal) and the second type of conductor (for example: electrolyte). (Rectifier) The connected metal A separates the electrolytic cell into two cells, so the current between the anode and the cathode cannot completely flow from the anode to the cathode through the electrolyte, and must be borrowed from A.” Therefore, when the current reaches the surface of A from the anode At this time, the surface has a cathodic reaction (wrong with the branch? The current flows into the metal from the electrolyte), and on the other surface of A, there is an anodic reaction (the current flows from the metal into the electrolyte). , One side of the rising sun pole is plated with metal, while the metal A on the other side facing the cathode may dissolve. The principle is like this. In practice, according to electrochemical theory, a specific anode or cathode reaction must reach a certain level. The electrode potential (not the voltage) can start to react.
Take copper plating as an example: in general, acid copper electroplating will have a cathodic reaction (copper ions are reduced to the metal) as long as the voltage difference is about 0.6V. Assuming that a titanium basket in the vertical electroplating tank has a resistance due to poor contact with the conductive copper bar, 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 At this time, the titanium blue becomes the A above, and becomes a bipolar electrode. The direction facing the partition wall titanium blue is plated with copper, and the direction facing the cathode is still the anode.
Countermeasures: After understanding the above principles, it is simple to solve the problem: to ensure that all anodes are at a uniform potential height relative to the cathode. That is, one end is grounded, and the other end measures the points of the anode to see if all points are at a uniform 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, a part of the substrate will be dissolved.