What is the difference between positive film and negative film of pcb circuit board?

What is the difference between positive film and negative film of pcb circuit board?

Negative film of pcb circuit board

         Generally speaking, the solution used in the negative film process is an acid-base corrosion process. After the film is formed, the required path or copper surface is completely transparent, and the unnecessary part is black. After the route process is exposed, because the dry film inhibitor is exposed to the sun, the completely transparent part will be chemically hardened, and the following development process will not harden the film and the dry film will be washed away, so during the etching process, Only the dry film is washed away part of the copper deposit (the black part of the negative film), while the preserved dry film is not washed away, this is the pcb circuit board we want (the transparent part of the negative film).

Positive film of pcb circuit board

       Generally speaking, the positive film process is based on the alkaline etching process. On the negative, the required path or copper surface is black, and the unnecessary parts are completely transparent. Similarly, after the route process is exposed, the completely transparent part is hardened by the chemical action of the dry film blocker exposed to the sun, and the subsequent development process will wash away the dry film without hard substrate in the next process. We use alkali The solution will cut off the copper surface (the transparent part of the negative film) that is not maintained by tin and lead, and what is left is the part of the pcb circuit board (black film).

The difference between positive and negative pcb circuit board

① Distinguish screen printing screen (negative film), working film, positive film and negative film and film surface: screen printing screen has master film and working film (child film), black and yellow film, positive film and negative film;

② Negative film is also called black film or carbon film. However, working negatives are not only yellow films, but also black films to make workpieces. It is mainly used to manufacture high-precision HDI boards or to save costs, in small batch production and manufacturing pcb circuit boards in one-time mass production and manufacturing pcb circuit boards.

③ When the film surface is different, the bright side of the black film is the film, while the yellow film is the opposite. Generally speaking, it can be seen that the side is based on the film surface of the graffiti pen or cutter head on the screen printing.

④ Precautions for yellow film application: There are two types of surfaces: smooth and matt. The second type of application is prone to oil indentation.

⑤ The light-transmitting negative film (containing copper) on the film circuit is a positive film; the positive film is used for pattern plating process, the developer drips as a path, the remaining effect is a corrosion-resistant plating process, and the key inlays are lead and tin. In the instant etching process, the film is usually used, the corrosion resistance after the developer is the way, and the acid-base etching solution is used for the instant etching process.