PCB Tech - The respective effects between PCB anode and cathode

Negative film of PCB circuit board: generally it is a tenting process, and the chemical solution used is an acid etched negative film because after the film is made, the required circuit or copper surface is transparent, and the undesired part is black. After the circuit process After exposure, the transparent part is chemically hardened by the dry film resist being exposed to light. The subsequent development process will wash away the uncured dry film, so during the etching process, only the part of the copper that has been washed away by the dry film will be etched. Foil (the black part of the negative), while leaving the dry film not washed off belongs to the circuit we want (the transparent part of the negative)

The positive film of the PCB circuit board: generally we talk about the pattern process, and the chemical solution used is the alkaline etching positive film. If viewed from the negative film, the required circuit or copper surface is black, and the other part is transparent. The same After the ground is exposed through the circuit process, the transparent part is chemically hardened by the dry film resist being exposed to light.

On the copper surface washed away by the dry film in the previous process (development), then the film is removed (removing the dry film hardened by light), and in the next process, the etching is bitten off with an alkaline solution without tin and lead protection The copper foil (the transparent part of the negative), and 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 thickened 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)

1. Distinguish the master film (negative film), the working film, the positive and negative film and the medicated film: the film has the master film and the working film (child film), black film and yellow film, positive film and negative film;

2. Generally speaking, the master film is black film, also known as silver salt film, which is mainly used to copy the work film (yellow film is also called diazo film), but the work film is not necessarily only the yellow film. There are also black films as the work film. It is used in the production of high-precision HDI boards or in the production of one-off small-batch circuit boards in order to save costs. Yellow sheets are used in the manufacture of ordinary boards and batches of ordinary circuit boards.

3. When 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: orthographic positive medicine noodles, sub-film: orthographic negative medicine noodles)

4. Pay attention to the use of yellow films: there are two types of glossy and matte surfaces. The second type is prone to indentation on the oil surface.

5. The 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 board 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.