PCB Technical - The difference in the process of making positive and negative films on PCB circuit boards

When the PCB circuit boardis made, film is required. Depending on the production process, there are two different ways of filming, namely PCB positive film and negative film, and the positive film and negative film are ultimately produced by the opposite manufacturing process.

The effect of PCB positive film: wherever lines are drawn, the copper of the printed board is retained, and where there is no line, the copper is removed. Generally, the signal layer such as the top layer, the bottom layer... is a positive film.

The effect of PCB negative film: wherever lines are drawn, the copper coating on the printed board is removed, and where there is no line drawing, the copper coating is retained instead. The Internal Planes layer (internal power/ground plane) (referred to as the internal electric plane) is used to lay out power lines and ground lines. The traces or other objects placed on these layers are copper-free areas, that is, the working layer is negative.

What is the difference between the output process of PCB positive film and negative film?

PCB circuit board production

Negative film: generally we talk about the tenting process, and the chemical solution used is acid etching

Negative film is because after the film is made, the necessary circuit or copper surface is transparent, and the unneeded part is black or brown. After the circuit process is exposed, the transparent part is chemically affected by the light of the dry film resist Hardening, the next developing process will wash away the dry film that is not hardened, so during the etching process, only the part of the copper foil (black or brown part of the negative film) that has been washed away by the dry film is etched, while leaving the dry film untouched. Wash out the circuit that belongs to us (the transparent part of the negative film). After removing the film, the circuit we need is left. In this process, the film has to cover the holes, and the exposure requirements and the requirements for the film are slightly higher. Some, but its manufacturing process is fast.

Positive film: Generally we talk about the pattern process, and the chemical solution used is alkaline etching

If the positive film is viewed as a negative, the required circuit or copper surface is black or brown, and the other part is transparent. Similarly, after the circuit process is exposed, the transparent part is chemically affected by the light of the dry film resist Hardening, the next developing process will wash away the dry film that is not hardened, and then the tin-lead plating process, the tin-lead is plated on the copper surface washed away by the dry film of the previous process (development), and then the film is removed Action (remove the dry film hardened by light), and in the next process of etching, use alkaline solution to bite off the copper foil (the transparent part of the negative) that is not protected by tin and lead, and the rest is the circuit we want (the negative Black or brown part).

Now most of our PCB circuit boards use positive film, and less use negative film.