In the production of LCD screens, the PCB circuit board occupies an extremely important position, so what exactly did the PCB circuit board use to make him occupy such a position in the production of LCD screens?
1. High density
In order to adapt to the fine pitch of surface mount components and the development of multi-lead technology, the wiring density of PCBs is gradually increasing. 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-pitch components has greatly improved PCB mounting density. Compared with the traditional plug-in printed board, the surface mount printed board area is reduced by 60%, the weight is reduced by 80%, and the circuit logic density is increased by more than 5 times.
2. Small aperture
In surface mount PCBs, most of the metallized holes are no longer used to insert fixed components, but to realize the through connection of various layers of circuits. As the assembly density of components increases, the wiring density on the board is greatly increased, and the aperture is also increasingly reduced. Diameter of metallized through hole—generally
0.60~0.30mm, and develop in the direction of 0.30~0.10 mm.
3. There are many levels
With the continuous improvement of the integration and assembly density of electronic components, the miniaturization and ultra-miniaturization of electronic components, PCB boards are not only suitable for single-layer and double-panel, but also widely used in multi-layer boards with high wiring density. There are 68 layers and 4 layers in the LCD module.
4. The PCB circuit board has excellent transmission characteristics
With the development of high-frequency working circuits, higher requirements are put forward for high-frequency performance such as PCB characteristic impedance, surface insulation resistance, dielectric constant, and dielectric loss, and higher requirements are put forward for PCB substrates.
5. High flatness and smoothness
Since the components are directly mounted on the printed circuit board, the surface of the circuit board needs higher flatness and smoothness. The rough surface and uneven texture of the fiber cloth can lead to poor bonding of surface mount components, poor soldering, and even failure to fall off. Since the warpage of the PCB not only directly affects automatic surface mounting and soldering positioning, but also causes micro cracks in chip components and points due to deformation, which leads to circuit failure. Therefore, it is generally required that the warpage of the PCB before static soldering should be allowed to be less than 0.3%. And it is required to choose a substrate with good dimensional stability, low warpage, and excellent comprehensive performance in the process of material selection, assembly and manufacturing.
6. Good stability
During component mounting, the thermal expansion of the PCB creates stress on the electrode of the component, causing component damage or solder joint failure. Therefore, the thermal expansion coefficient of the substrate is one of the important factors that must be considered in PCB design and material selection. The expansion coefficient of the PCB is required to be as small as possible, and the expansion coefficient of the components and the PCB must 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 reinforcing materials, and the surface is covered with electrolytic copper foil and pressed. The liquid crystal display module adopts 0.5 mm, 1.0 mm, 1.2 mm, 1.6 mm, 2.0 mm and other printed circuit board thicknesses.
