With the upgrading and rapid expansion of the global electronic product market, the miniaturization, high-precision, and ultra-fine circuit printing technology of electronic products is entering a period of rapid development. In order to meet the ever-increasing demand of the market, especially in the field of ultra-fine circuit technology, the traditional backward etching technology is being replaced by advanced vacuum etching technology.

1. Definition of PCB Etching 

The surface of the copper clad board is etched with chemical water to remove the unnecessary copper conductors, leaving the copper conductors to form a circuit pattern. This subtraction process is the mainstream of current printed circuit board processing.

2. Etching Solution and Etching Operating Conditions 

Etching solution

At present, the mainstream is the acid copper chloride etching solution of copper chloride and hydrochloric acid, and the alkaline copper chloride etching solution of copper chloride and ammonia water.

Etching operating conditions

The etching operating conditions are the control of process parameters such as temperature, pressure, time, and solution concentration, so that the etching process is in the best state.

3. Etching Equipment

The difference of etching equipment is mainly reflected in the conveying method and spraying method.

Conveying methods are divided into: fixed, vertical, and horizontal.

Fixed type: The early equipment was a tank, after storing the etching solution, the PCB was immersed in it.

Disadvantages: low board placement efficiency and low etching efficiency; line width/spacing is above 0.5mm.

Vertical type: The PCB is hung vertically from the fixture and enters the etching machine, and the solution is sprayed on the board surface on both sides of the etching chamber. Due to the complexity of the etching equipment and the mediocre etching effect, this technology has not been developed.

Horizontal: Use the roller to transfer the PCB. There is a gap between the rollers, and nozzles are installed up and down, and spraying is used for etching.

Advantages: The transfer speed is relatively stable, and the etching is relatively uniform. High efficiency, both sides can be etched at the same time. It is the current mainstream transmission method.

Spray method

In order to spray the solution to every part of the PCB surface and accelerate the flow of the solution on the board surface, we need to move the nozzle.

4. "Pool Effect"

At present, the mainstream horizontal conveying spray type can realize the maximum degree of production automation and reduce the cost, but this method is not perfect, and it will cause the "pool effect" and make the etching results different.

The "pool effect" is: when the PCB is horizontally transferred, the etching liquid on the edge of the board is easy to flow away. It is easier to exchange new and old etching solutions. At the center of the plate, it is easy to form a "pool", and the flow of etching liquid is restricted. Therefore, the etching effect of the middle part of the PCB will be worse than other positions.