The difference between positive and negative PCB circuit boards

Negative film of circuit board: Generally, it is the tenting process we talk about. The drug solution used is acid etching negative film because after the negative is made, the line or copper surface is transparent, and the part that is not black. After exposure through the line process, the transparent part will be hardened by chemical action due to the dry film resistance agent under light, and the following development process will be the dry film without hardening Then, in the etching process, only the dry film is eaten and part of the copper foil is washed away (the black part of the negative), while the dry film is not washed away and belongs to the line we want (the transparent part of the negative).

Printed circuit board positive: generally we talk about the pattern process, the use of liquid for alkaline etching positive if the negative, to the line or copper surface is black, and do not part of the transparent, the same through the line process exposure, the transparent part due to dry film resistance by light chemical hardening, the next development process will not harden the dry film , followed by the tin lead plating process. The tin lead is plated on the copper surface where the dry film has been washed off in the previous process (developing), and then the film is removed (removing the dry film hardened by light). In the next process etching, the copper foil without the tin lead protection is bitten off with an alkaline solution (the transparent part of the negative), and the rest is the line we want (the black part of the negative).

Positive and negative film is actually according to the company's process to choose, positive: process is (double panel) opening - drilling -PTH (a plating also called thickened copper) - line - two copper (graphic plating) and then go SES line (film - etching - tin) negative film: Process is (double panel) opening - drilling -PTH(a plating also called thickening copper) - line (without two copper graphic plating) and then go DES line (etching - film).

(1) To distinguish the film (negative) parent film, working film, positive and negative film surface: film has parent film and working film (sub-film), black film and yellow film, positive film and negative film;

(2) Generally speaking, the mother film for black film, also known as silver salt tablet, is mainly used to copy the work film (yellow film is also known as diazo tablet), but the work film is not necessarily only yellow, there are also black pieces to do the work film, which is mainly to do high precision HDI board or in order to save money in a one-time small batch circuit board production, Yellow tablets are used in the manufacture of ordinary boards and ordinary PCB circuit boards.

(3) When the drug film surface is differentiated, the smooth surface of the black film is the drug film, and the yellow film is on the contrary. Generally, it can be seen that the side is the drug film surface by scraping the pen or blade on the film. (Parent: positive character positive medicine face, child: positive character negative medicine face).

(4) Note when using yellow tablets: there are two kinds of smooth surface and dumb surface, and the second kind is easy to appear oil surface indentation when using.

(5) Film line (with copper) on the negative light, light is positive; Positive for the use of graphic plating, development is off the line, leaving the role of corrosion resistance plating, the main plating is lead tin. The negative film is used for direct etching, and the corrosion resistance left after development is a circuit, which is etched directly with acid etching solution.