PCB Technical - Four steps of PCB inner layer processing

The inner layer processing of printed circuit board can be divided into four steps: pretreatment, dust-free room, etching line and automatic optical inspection.

(1) In the process of processing printed circuit board, the copper foil substrate is first cut into the size suitable for processing and production, and then the pretreatment is carried out. Generally speaking. Pretreatment has two functions: first, it is used to clean the cut substrate to avoid the adverse effect of grease or dust on the subsequent pressing film; second, brush grinding, micro etching and other methods are used to roughen the surface of the substrate, so as to facilitate the combination of the substrate and the dry film. Generally, cleaning solution and micro etching solution are used for pretreatment.

(2) In the transfer of circuit graphics in the dust-free room, the processing process of printed circuit board requires a very high degree of cleanliness of the studio. Generally, film pressing and exposure should be carried out at least in the class 10000 dust-free room. In order to ensure the high quality of circuit graphics transfer, it is also necessary to ensure the indoor working conditions during processing. The indoor temperature is controlled at (2111) degree Celsius and the relative humidity is 55% - 60%. The purpose is to ensure the dimensional stability of the substrate and negative. Only when the whole production process is carried out under the same humidity and humidity, can the substrate and negative film not swell and shrink. Therefore, the production areas in the current processing plants are equipped with central air conditioning to control the temperature and humidity.

Before the substrate is exposed, a layer of dry film needs to be pasted on the grave board during the processing. This work is usually achieved by a film pressing machine, which can automatically cut the film according to the size and thickness of the substrate. The dry film generally has a three-layer structure. The film pressing machine pastes the film onto the substrate at the appropriate temperature and pressure, and then it will automatically tear off the plastic film on the side that is combined with the board.Because the photosensitive dry film has a certain shelf life. Therefore, the substrate should be exposed as soon as possible after film pressing.

In the process of processing, the exposure is carried out by exposure machine. The inside of the exposure machine emits high-intensity UV lines (ultraviolet rays). Used to irradiate the substrate covering the film and film. Through image transfer, the image on the negative will be reversed and transferred to the dry film after exposure. So as to complete the corresponding exposure operation port.

(3) The etching line includes developing section, etching section and stripping section. The etching section is the core of this production line. Its function is to corrode the exposed copper which is not covered by dry film.

(4) After automatic optical inspection, the substrate with inner layer must be strictly inspected. Then the next processing step can be carried out, which can greatly reduce the risk. In this addition stage, the inspection of the identification board is carried out by AOI machine to test the appearance quality of bare board. When working, the processing personnel first fix the plate to be inspected on the machine, AOI uses laser locator to accurately position the lens to scan the whole board surface. Then the obtained pattern is abstracted and compared with the missing pattern to determine whether there is a problem in PCB circuit making. At the same time, AOI can also indicate the type of problem and the specific location of the problem on the substrate.