In the production of LCD screen, PCB circuit board occupies an extremely important position, so what does the playing method of PCB circuit board use to make it occupy such a position in the production of LCD screen?
In order to adapt to the fine spacing of surface mount components and the development of multi lead technology, the wiring density of PCB increases gradually. At present, the line width and line spacing of PCB components with lead spacing of 0.762mm>0.635mm → -0.508 mm3+0.381mm>0.305mm have been reduced to 0.15-0.1 mm. The application of multi lead and fine spacing components has greatly improved the installation density of PCB. Compared with the traditional plug-in PCB, the surface mount PCB area is reduced by 60%, the weight is reduced by 80%, and the circuit logic density is increased by more than 5 times.
In surface mount PCB, most of the metallized holes are no longer used to insert fixed components, but to realize the through connection of each layer of circuit. With the increase of the assembly density of components, the wiring density on the board is greatly increased, and the aperture is also decreasing. The diameter of metallized through-hole is generally 0.60~0.30mm, and develops towards 0.30~0.10 mm.
With the continuous improvement of the integration and assembly density of electronic components and the miniaturization and ultra miniaturization of electronic components, PCB is not only suitable for single-layer and double-sided boards, but also widely used in multilayer boards with high wiring density. There are 68 layers and 4 layers in LCD module.
With the development of high-frequency working circuit, higher requirements are put forward for high-frequency performance of PCB, such as characteristic impedance, surface insulation resistance, dielectric constant, dielectric loss and so on, and higher requirements are put forward for PCB substrate.
Since the components are directly installed on the printed circuit board, the surface of the circuit board needs higher flatness and smoothness. The rough surface and concave convex texture of the fiber cloth will lead to poor fitting, poor welding and even failure to fall off of the surface mounting components. As the warpage of PCB not only directly affects the automatic surface mounting and welding positioning, but also causes micro cracks in chip components and points due to deformation, resulting in circuit failure, it is generally required that the warpage of PCB before static welding should be less than 0.3%, and it is required to select substrates with good dimensional stability, small warpage and excellent comprehensive performance in the process of material selection, assembly and manufacturing.
During component installation, the thermal expansion of PCB generates stress on the electrode of the component, resulting in component damage or solder joint failure. Therefore, the thermal expansion coefficient of substrate is one of the important factors that must be considered in PCB design and material selection. The expansion coefficient of PCB shall be as small as possible, and the expansion coefficient of components and PCB shall be matched. The substrate of the printed circuit board is made of epoxy resin or epoxy phenolic resin as the adhesive, cotton fiber cloth, paper and glass fiber cloth as the reinforcement, and the surface is covered with electrolytic copper foil and pressed. The LCD module adopts the thickness of 0.5mm, 1.0mm, 1.2mm, 1.6mm, 2.0mm and other printed circuit boards.