The process of printed circuit board from light plate to display line graph is a complex process of physical and chemical reaction. In this paper, the last step -- etching is analyzed.
At present, the typical process of printed circuit board (PCB) processing adopts "graphic electroplating". In the first part of the board to keep the outer copper foil, which is part of the graphics circuit on pre plating a layer of tin resist layer, and then the rest of the copper foil etched by chemical etching method, called.
The type of etch
It is important to note that there are two layers of copper on the plate on the etch. Only one layer of copper must be etched out in the outer etching process, and the rest will form the final circuit. This type of pattern is characterized by plating, copper plating layer only exists in the resist layer below tin.
How to control the process of PCB etching
In the processing technology of the outer circuit of the printed board, there is another way of replacing the metal coating with a photosensitive film as an anticorrosion layer. This method is very similar to the inner etching process, which can be used to refer to the etching in the inner fabrication process.
At present, tin or tin is the most commonly used anti corrosion layer, used in the etching process of ammonia etching agent. Ammonia etching agent is a chemical liquid medicine in common use, and tin or tin no chemical reaction. Ammonia etchant mainly refers to ammonia / ammonia chloride etching solution.
The quality of etch and the existing problems
The basic requirement for the etching quality is that all copper layers except the anticorrosion layer can be completely removed. In a strict sense, the etching quality must include the consistency of line width and the degree of lateral erosion, if it is to be precisely defined. Because of the inherent characteristics of the current corrosion fluid, it is not only downward but also etched in all directions, so the side erosion is almost inevitable.
The structure of etching equipment and the etching solution of different components will affect the etching factor or the degree of side erosion, or it can be controlled with optimistic words. The use of some additives can reduce the degree of side erosion. The chemical ingredients of these additives generally belong to business secrets, and their respective developers are not disclosed to the outside world.
For the etching process of outer layer, many of the problems are reflected on the top of the printed circuit board because of the appearance of "inverted stream". At the same time, it is also the last ring of a long series of processes that have been etched from the sticker to the beginning of the photoreceptor, and then the transfer of the outer layer is successful. The more the link, the greater the possibility of problems. This can be seen as a very special aspect of the production of printed circuit circuits.
Relationship between equipment adjustment and corrosion solution
In the processing of printed circuit, ammonia etching is a more sophisticated and complex chemical reaction process. In turn, it is an easy job. Once the process is up-regulated, it can be produced continuously. The key is to keep a continuous working condition once the machine is open, so it is not suitable to dry and stop. The etching process depends to a great extent on the good working state of the equipment. For now, no matter which etching solution is used, high pressure spray must be used. In order to get more regular line side and high quality etching effect, nozzle structure and spray way must be strictly chosen.
How to control the process of PCB etching
This is a functional reason to put air into the etching box. But if the air is too much, it will accelerate the loss of the ammonia in the solution and reduce the pH value, and the result still reduces the etching rate. Ammonia is also the amount of change that needs to be controlled in the solution. Some users will use pure ammonia into the etching liquid storage tank approach. It must be added a pH meter control system. When the automatically measured PH results are lower than the given value, the solution will be added automatically.
On the problems of different etch States
A large number of problems relating to the etching quality are focused on the etched parts of the upper plate. It is very important to understand this. These problems come from the influence of the colloidal slab produced by the etching agent of the upper plate of the printed circuit board. On the one hand, the colloidal bonding on the surface of copper affects the injection force, on the other hand, it blocks the addition of fresh etching solution, resulting in the decrease of etching speed. It is because of the formation and accumulation of the colloidal slab that the etching degree of the upper and lower shapes of the plate is different. It also makes the etching part of etch machine Naka Sako easy to be etched thoroughly or easy to cause corrosion, because the accumulation is not yet formed, and the etching speed is fast. On the other hand, the accumulation of the plate after the entry is formed and the etching speed is slowed down.