The Difference Between Positive and Negative PCB Board

The negative film of the circuit board: the tenting process. The chemical solution used is an acid etching negative film because after the 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 hardened due to the dry film resist being exposed to light. The subsequent development process will wash away the uncured dry film, so only the dry film will be etched during the etching process. The copper foil (the black part of the negative film), while leaving the dry film not washed off belongs to the circuit we want (the transparent part of the negative film).

The positive film of the circuit board: 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. After the circuit process is exposed, the transparent part is chemically hardened due to 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-stripping tin).

Negative film: the process is (double panel) 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 mainly used for high-precision HDI boards or used in one-off small-batch circuit board production in order to save costs. Yellow sheets are used in the manufacture of ordinary boards and batches of ordinary circuit boards.

3. 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 is developed, and the remaining function is anti-corrosion electroplating, mainly plated with lead 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.

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

5. 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.

XPCB Limited is a manufacturer specializing in the production of high-precision double-sided, multi-layer and impedance, blind buried vias, and thick copper circuit boards. The products cover HDI, thick copper, backplanes, rigid-flex combined, buried capacitance and buried resistance. , Golden Finger and other types of circuit boards, which can meet the needs of customers for various products.