PCB News - What is the difference between PCB positive film and negative film?

The difference between PCB positive film and negative film.

PCB positive film and negative film are the opposite manufacturing processes in the final effect.

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, and the bottom layer. 

The effect of the negative film of the PCB board 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 inner 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.

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

Negative film

Generally,we talk about the tenting process.The chemical solution used is acid etched negative film because after the film is made, the necessary circuit or copper surface is transparent, and the unneeded part is black or brown and passes through the circuit.After the process is exposed, the transparent part is chemically cured by the dry film resist when exposed to light. The subsequent development process will wash away the uncured dry film,so only the part of the dry film that has been washed away will be etched during the etching process. Copper foil (black or brown part of the negative film),but the dry film has not been washed off,belongs to the circuit we want (the transparent part of the negative film).After the film is removed, the circuit we need is left. In this process.The middle membrane must cover the holes,and its exposure requirements and membrane requirements are slightly higher,but its manufacturing process is faster.

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 to resist Hardening, the next developing process will wash away the unhardened dry film,followed by the tin-lead plating process, and 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).

What are the advantages of PCB-positive film, and on which occasions is it mainly used?

Negative film is used to reduce the size of the file and reduce the amount of calculation. Where there is copper, it is not displayed, and where there is no copper, it is displayed. This can significantly reduce the amount of data and the burden of a 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 or something. If the power supply is convenient, there are many methods. The positive film can also be easily divided by other methods. It is not necessary to use negative film.

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The above is the difference between PCB positive film and negative film, so have you learned it now?