The manufacturing technologies of flex-rigid pcb are different due to different types of PCB. The basic technologies leading to the differences are fine circuit manufacturing technology and micro hole manufacturing technology. With the development of electronic products towards lightweight and miniaturization, multifunctional and compact assembly, the most concerned high-level PCB includes HDI rigid pcb and embedded rigid pcb.
Rlex-rigid pcb is made by stacking the layers of rigid pcb and flex PCB orderly and selectively, and plating through holes responsible for the connection between layers. The figure below shows the basic structure of rigid flexible PCB.
The appearance of flex-rigid pcb can effectively reduce the volume and quality of electronic products by replacing the wiring harness and connector commonly used in electronic products. In addition, rigid and flex PCB can solve the contact and strong heat problems caused by wiring harness and connector, thus greatly improving the reliability of the equipment.
As early as the 1970s, rigid printed circuit boards were made by stacking rigid boards onto flexible boards. Continuous progress and optimization witness many new rigid flexible PCB manufacturing technologies. So far, the most mature and practical flex-rigid pcb manufacturing technology is to use glass fiber epoxy resin (FR4) as external rigid board and solder resist to protect rigid circuit pattern. For the flexible substrate material, a copper coated polyimide (PI) bilayer is used as the flexible core, and a polyimide / acrylic film is used to protect the flexible circuit pattern. Adhesion depends on the low flow prepreg. All of these components are laminated so that rigid and flex PCBs can be made.
Rigid and flex PCB can replace wiring harness and connector, so as to overcome poor contact and heat dissipation problems, so as to improve the reliability of equipment. The flexible part can be bent at any angle, and the whole PCB board has excellent electrical and mechanical properties. Therefore, flex-rigid pcb can be used for 3D assembly, and the degree of freedom of products can be improved with the decrease of equipment volume and quality, so they can be well used in electronic equipment that needs to be bent repeatedly. Flexible substrate material has excellent dielectric stability, suitable for high frequency signal transmission and impedance control, and can withstand radiation, temperature shock and extreme environment, so as to ensure the smooth operation of electronic equipment.
Traditional flex-rigid pcb is difficult to manufacture with relatively low yield and high density, and it is difficult to repair after breakdown. In the process of PCB manufacturing, it is necessary to embed the rigid substrate into the expensive flexible substrate material to keep the scrap rate of raw materials at a high level, and the manufacturing technology is also very difficult. Flexible substrate materials have relatively high coefficient of thermal expansion and high moisture absorption, so large area of flexible substrate materials will lead to dimensional tolerance accumulation, which will further affect the circuit pattern, lamination, drilling, electroplating and through hole cleaning, and lead to low production. However, embedded flexible circuits can effectively reduce and avoid this problem.