Wet film is a material used for manufacturing PCB. By covering a layer of photosensitive adhesive on copper foil and exposing it to a specific UV light source, different PCB structures can be manufactured. Wet film can help engineers manufacture high-precision and high-quality PCB during exposure, development, and etching processes. The main materials for wet film of PCB include photosensitive adhesive, steel mesh printing screen, copper foil, sponge strip, and bottom plate. Firstly, stick the copper foil together with the base plate and apply photosensitive adhesive to the copper foil. Then, use steel screen printing to print the pattern onto the photosensitive adhesive, exposing it to a UV light source. During the exposure process, the photosensitive adhesive will be excited by light, which can then serve as an isolation during the development and etching processes. Sponge strips are used to maintain the horizontal state of the PCB. Characteristics 1. Good adhesion and coverage The wet film itself is a blue viscous liquid synthesized from photosensitive resin, with the addition of photosensitive agents, pigments, fillers, and solvents. The pits and scratches on the substrate are in good contact with the wet film, and the wet film is mainly bonded to the substrate through the action of chemical bond, so that the wet film has excellent adhesion with the copper foil of the substrate. The use of screen printing can achieve good coverage, which provides conditions for the processing of high-density fine wire PCB. The wet film has good contact and coverage with the substrate, and adopts negative contact exposure, which shortens the optical path and reduces the energy loss of light and errors caused by light scattering. This makes the resolution of wet film generally below 25um, improving the precision of graphic production, while in actual production, the resolution of dry film is difficult to reach 50um. 2. Low cost The thickness of the wet film is controllable, generally thinner than the dry film, and the packaging cost is also lower. Relatively speaking, the cost of the wet film is slightly lower. The qualification rate of wet film in the production process of fine line inner layer is greatly improved, saving 20% of material cost compared to dry film. The speed of wet development should be 30% faster, the etching speed can also be increased by 10% -20%, and the speed of film fading can also be increased, thereby saving costs. 3. Eliminate burrs on board edges The edges of dry film boards are prone to fuzzing and film breakage, which can affect the qualification rate of the board during production. The edges of wet film boards do not exhibit film breakage or fuzzing. Comparison between wet film and dry film The operation of dry film is convenient, especially with the use of automatic film sticking machines, which can be produced on a large scale. However, the price of dry film is relatively expensive, but it can cover holes with high accuracy. Wet film is cheaper than dry film, but it cannot be used on automatic lines. In theory, it is better to make thin wires for wet film, but it cannot cover the holes. It is difficult to control the oil film entering the holes, and a blocking point needs to be set. In theory, the accuracy of wet film is higher than that of dry film. However, due to the thin wet film, it is easy to clamp the film during graphic electroplating, making it difficult to make high-precision boards and requiring secondary drilling.
