What is the difference between PCB positive film and negative film

What is the difference between PCB positive film and negative film

1. The difference between PCB positive film and negative film:

PCB positive film and negative film are manufacturing processes whose final effect is opposite.

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. The signal layer such as the top layer, the bottom layer... is the 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 the power and ground wires. The traces or other objects placed on these layers are copper-free areas, that is, the working layer is negative.

    2. What are the differences between PCB positive and negative output processes?

Negative film: Generally it is the tenting process we talk about, 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 is washed away by the dry film is bitten, and the dry film is left 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, the chemical solution used is alkaline etching

If the positive film is viewed as a negative film, 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 unhardened dry film, followed by 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 the 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).

    3. What are the advantages of PCB positive films, and in which occasions are they mainly used?

Negative film is used to reduce the file size and reduce the amount of calculation. It is not displayed where there is copper, and it is displayed where there is no copper. This can significantly reduce the amount of data and the burden of computer display in the ground power layer. However, the current computer configuration is no longer a problem for this point of work. I think it is not recommended to use negative film, which is prone to errors. If the pad is not designed, it may be short-circuited.

There are many ways to split the power supply if it is convenient. The positive film can also be easily divided by other methods. It is not necessary to use the negative film.