Introduction of Basic Materials for Rigid-Flex Circuits
Feb 12,2020

PCB design trend is to lightweight small direction development. In addition to high-density circuit board design, there are soft and hard the three-dimensional connection assembly of the binding plate is such an important and complex field. Soft and hard laminates are also called rigid and flexible laminates. With the development of FPC,this new product has been widely used in various fields gradually. Therefore, the flexible circuit board and the traditional hard circuit board, through many processes, according to the relevant work requirements are combined to form circuit boards with FPC characteristics and PCB characteristics at the same time. It can be used for some among the products with special requirements, there are both a certain flexible area and a certain rigid area, which can save the inner space of the product, can reduce the volume of finished products, improve the product performance.

Materials for flexible plates

As the saying goes:” if you want to do well, you have to do well “, so it is very important to be well prepared when considering the design and production process of a hard and soft composite board. However, this requires a certain degree of expertise and understanding of the characteristics of the required materials, and the materials selected for the soft and hard binder directly affect the subsequent production process and its performance.

Base Material: FCCL(Flexible Copper Clad Laminate)

Polyimide(PI): kapton (12.5um/20um/25um/50um/75um). Flexibility good, high temperature resistance (long-term use temperature of 260°C, short-term resistance of 400°C), high moisture absorption, good electrical characteristics and mechanical properties, good tear resistance. Good weather and chemical resistance, good flame retardancy. Wide application of Polyimide(PI).The widest 80% of this is made by Dupont.

PET:polyester (25um/50um/75um). Cheap, flexible, tear resistant. Tensile strength good mechanical and electrical properties, good water resistance and moisture absorption. However, the shrinkage rate after heating is large, and the resistance to high temperature is not enough good. Not suitable for high temperature tin welding, melting point 250°C.




The main function of the covering film is to protect the circuit from moisture, pollution and welding. covering film thickness from1/2 mil to 5 mils (12.7 to 127um).

Conductive Layer

The conductive layer is divided into several ways, namely, the Rolled Annealed Copper, the Electrodeposted Copper, and the Silver Ink. Among them, the structure of electrolytic copper crystal is rough, which is not conducive to the yield of fine lines. Calendering copper crystal structure is smooth but poor adhesion to the base film. can distinguish point decomposition and calendering copper foil from appearance. The electrolytic copper foil is copper-red and the copper foil is grayish-white.


Auxiliary materials and stiffeners:

A hard material on a soft plate that is additionally pressed in order to weld components or add reinforcement for installation. Reinforcement film can be FR4, resin plate, pressure adhesive, steel sheet aluminum sheet reinforcement, etc.


Low Flow PP

Semi-curable sheet with non-flow/low flow glue lamination for soft and hard laminates (rigid and flex connection), usually very thin pp. there are generally 106(2 mil),1080(3.0 mil/3.5 mil),2116(5.6 mil) these specifications.

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