PCB Fabrication

PCB filming methods and skills

by:A-TECH      2021-04-01
Paste film When pasting the film, first peel off the polyethylene protective film from the dry film, and then paste the dry film resist on the copper clad board under heating and pressurizing conditions. The resist layer in the dry film becomes soft after being heated, and its fluidity increases. With the help of the pressure of the hot pressing roller and the action of the binder in the resist, the film is completed. The filming is usually done on a filming machine. There are many models of filming machines, but the basic structure is roughly the same: the film can be applied continuously or single-posted. Pay attention to the alignment of the dry film on the upper and lower dry film feed rollers during continuous film pasting. When single-posting, the size of the film should be slightly smaller than the board surface to prevent the resist from sticking to the hot press roller. The continuous film production efficiency is high and it is suitable for mass production. Small batch production can adopt the single-posting method to reduce the waste of dry film. The three elements that must be mastered when applying the film are pressure, temperature, and transmission speed. Pressure: For the newly installed laminating machine, first adjust the upper and lower hot pressing rollers to be axially parallel, and then use the method of gradually increasing the pressure to adjust the pressure, adjust according to the thickness of the printed board to make the dry film easy to stick and stick firmly , No wrinkles. After the pressure is adjusted, it can be fixed and used without frequent adjustment. The general line pressure is 0.5-0.6 kg/cm. Temperature: It varies slightly according to the type, performance, ambient temperature and humidity of the dry film. The film coating is relatively dry, the ambient temperature is low, and the humidity is low. The film temperature should be higher, and vice versa. If the film temperature is too high, the image of the dry film will become brittle, and the plating resistance will be poor. If the film temperature is too low, the dry film will not adhere firmly to the copper surface, and the film will tend to warp or even fall off during the development or electroplating process. The temperature of the film is usually controlled at about 100°C. Transmission speed: It is related to the film temperature. The higher the temperature, the faster the transmission speed, and the lower the temperature, the slower the transmission speed. Usually the transmission speed is 0.9 to 1.8 m/min. In mass production, under the required conveying speed, it is difficult for the hot pressing roller to provide enough heat, so it is necessary to preheat the board to be filmed, that is, the film can be filmed after a little cooling after drying in an oven. In order to adapt to the production of fine wire printed boards, a wet filming process has been developed. This process uses a special filming machine to form a water film on the surface of the copper foil before applying the dry film. The function of the water film is to improve the dry film. The fluidity of the film; removes the air bubbles remaining on the parts such as scratches, blisters, pits and fabric depressions; in the process of heating and pressing the film, the water increases the viscosity of the photoresist, which can greatly improve the dry film and the substrate Adhesiveness, thereby improving the pass rate of fine wires. According to reports, the pass rate of fine wires can be increased by 1-9% by using this process. The intact film should have a smooth surface, no wrinkles, no bubbles, no dust particles and other inclusions. In order to maintain the stability of the process, the film should be exposed after 15 minutes of cooling and recovery period.
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