The etching process is one of the basic steps in PCB production. Simply put, the substrate copper is covered by a corrosion resistant layer, and the copper that is not protected by the corrosion resistant layer reacts with the etchant to be bitten off, ultimately forming the design circuit graphics and solder pads. Of course, the principle of etching can be easily described in a few words, but in reality, the implementation of etching technology is still quite challenging, especially in the production of micro circuits, where there are very small line width tolerance requirements and no errors are allowed in the etching process. Therefore, the etching results should be just right, and cannot be widened or excessively etched.

Further explaining the etching process, PCB manufacturers prefer to use horizontal etching lines for production to achieve maximum automation and reduce production costs. However, horizontal etching is not perfect, and the "pool effect" that cannot be eliminated causes different etching effects on the upper and lower surfaces of the board. The etching rate at the edges of the board is faster than that at the center of the board, sometimes, This phenomenon can cause significant differences in the etching results on the board surface.

That is to say, the "pool effect" can cause greater corrosion on the circuit at the edge of the board than on the circuit at the center of the board, and even careful circuit correction (appropriately widening the circuit width at the edge of the board) to compensate for different etching rates may fail, as obtaining ultrafine circuits requires very precise control of etching tolerances.

This situation leads to a significant change in etching rate. Located on the top of the circuit board, near the edge of the board, the etching solution is easier to flow out of the board, and new and old etching solutions are easier to exchange, thus maintaining a good etching rate. At the center of the board, it is relatively easy to form a "water pool" situation, which restricts the flow of the etchant. It is relatively difficult for the solution rich in copper ions to flow out of the board surface. As a result, compared to the edge or bottom of the board, the etching efficiency decreases and the etching effect deteriorates. In fact, it is unlikely to avoid the "pool effect" in practice, as the chain type horizontal transmission roller will prevent the discharge of etching solution, resulting in the accumulation of etching solution between the rollers. This phenomenon is more obvious when producing large plates or ultra-fine lines, even if special production process control and compensation methods are used, such as spray systems that can be independently adjusted horizontally in the transmission direction Adding oscillating spray pipes and adding corrective re etching sections cannot solve this problem well without significant technological investment. Therefore, achieving the goal of avoiding the "pool effect" does not have to go back to the starting point and start anew.