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PCB Tech

PCB Tech

PCB Tech

PCB Tech

The difference between positive and negative PCB circuit boards
2021-10-05
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Author:Downs

Printed circuit board negative film: generally we talk about the tenting process, and the chemical solution used is an acid etching negative film because after the negative film is made, the required circuit or copper surface is transparent, and the unneeded part is black. After the circuit process is exposed, the transparent part is chemically cured by the dry film resist being exposed to light. The subsequent development process will wash away the uncured dry film, so only the dry film washed out part is bitten during the etching process. The copper foil (the black part of the negative film), and the dry film has not been washed off, which belongs to the circuit we want (the transparent part of the negative film)

pcb board

The positive film of the circuit board: Generally, the pattern process we talk about is the alkaline etching positive film. After the circuit process is exposed, the transparent part is chemically hardened by the dry film resist being exposed to light. The next development process will wash off 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 in the previous process (development), and then the action of removing the film (removing the dry film hardened by light), and in the next process etching, use alkaline solution to bite off the tin and lead protection Copper foil (the transparent part of the negative), the rest is the circuit we want (the black part of the negative)

Positive film and negative film are actually selected according to the process of each company. Positive film: the process is (double-sided) cutting-drilling-PTH (one-time plating is also called thick copper)-circuit-two copper (pattern plating) and then SES Line (removal film-etching-removal tin) negative film: the process is (double-sided) cutting-drilling-PTH (one-time plating is also called thick copper)-line (not through two copper pattern plating) and then take the DES line (etching -Remove film)

①Distinguish the master film (negative film), working film, positive and negative film, and film surface: film has master film and working film (child film), black film and yellow film, positive film and negative film; ②Generally speaking, the master film For black film, also known as silver salt film, it is mainly used to copy work film (yellow film is also called diazo film), but work film is not necessarily only yellow film. There are also black film for work film, which is mainly used for high-precision HDI. In order to save money, it can be used in the production of one-off low-volume circuit boards. The yellow film is used in the manufacture of ordinary boards and batches of ordinary circuit boards. ③When distinguishing the medicinal film surface, the black and smooth surface is the medicinal film, while the yellow film is the opposite. Generally, you can see which side is the medicinal film by scraping on the film with a scraper or a blade. (Master film: positive medicine surface, sub film: positive medicine surface) ④Pay attention when using yellow film: there are two kinds of smooth surface and matte surface. The second type is prone to oil surface indentation. ⑤The light-transmitting negative film on the film circuit (with copper), the opaque film is the positive film; the positive film is used for pattern plating, the circuit is developed, and the remaining function is anti-corrosion electroplating, mainly coated with lead and tin . The negative film is used for direct etching, and the resist left after development is a circuit, which is directly etched with an acid etching solution.

This is the difference between positive and negative PCB circuit boards