Introduction of types of FPC,flexible circuit board
Flexible circuit boards are no longer an unfamiliar term in the electronics industry. A mobile phone contains at least 8 flexible circuit boards. However, many purchasers in the electronics industry are still not very clear about the type of FPC flexible circuit board. Let us briefly introduces the types of flexible circuit board FPC for friends inside and outside the industry.
1. Single-layer FPC
Single-layer FPC has a layer of chemically etched conductive pattern, and the conductive pattern layer on the surface of the flexible insulating substrate is rolled copper foil. The insulating substrate could be polyimide, polyethylene terephthalate, aramid fiber ester, and polyvinyl chloride. Single-layer FPC can be divided into the following four sub-categories:
1.1 One-sided connection without cover
The wire pattern is on the insulating substrate, and there is no covering layer on the surface of the wire. The interconnection is realized by soldering, welding or pressure welding, and it is commonly used in early telephones.
1.2 One-sided connection with cover
Compared with the previous category, there is only one more covering layer on the surface of the wire. The pad needs to be exposed when covering, and it can simply not be covered in the end area. It is the most widely used and most widely used single-sided flexible PCB. It is used in automotive instruments and electronic instruments.
1.3 Double-sided connection without cover
The connection pad interface can be connected on the front and back of the wire. A via hole is opened on the insulating substrate at the pad. This via hole can be punched, etched or other mechanical methods at the desired position of the insulating substrate to make.
1.4 Double-sided connection with cover
Different in the former category, there is a cover layer on the surface, and the cover layer has via holes to allow it to be terminated on both sides, and still maintain the cover layer, made of two layers of insulating material and a layer of metal conductor.
2. Double-sided FPC
Double-sided FPC has a conductive pattern made by etching on both sides of the insulating base film, which increases the wiring density per unit area. The metalized holes connect the patterns on both sides of the insulating material to form a conductive path to meet the flexible design and use functions. The cover film can protect single and double-sided wires and indicate the location of components. Depending on the requirements, metallization holes and cover layers are optional, and this type of FPC is rarely used.
3. Multi-layer FPC
Multi-layer FPC is the lamination of 3 or more layers of single-sided or double-sided flexible circuits, through drilling and plating to form metallized holes to form conductive paths between different layers. In this way, no complicated welding process is required. Multilayer circuits have huge functional differences in terms of higher reliability, better thermal conductivity, and more convenient assembly performance.
The advantage is that the substrate film is light weight and has excellent electrical characteristics, such as low dielectric constant. The multi-layer flexible PCB board made of polyimide film as the substrate is about 1/3 lighter than the rigid epoxy glass cloth multilayer PCB board, but it loses the single-sided and double-sided flexible PCB. The flexibility of most of these products does not require flexibility. Multi-layer FPC can be further divided into the following types:
3.1 Finished flexible insulating substrate
This type is manufactured on a flexible insulating substrate, and its finished product is stipulated to be flexible. This structure usually bonds the two ends of many single-sided or double-sided microstrip flexible PCBs together, but the central part is not bonded together at the same time, thus having a high degree of flexibility. In order to have a high degree of flexibility, a thin, suitable coating, such as polyimide, can be used on the wire layer instead of a thicker laminated cover layer.
3.2 Finished soft insulating base material
This category is manufactured on a flexible insulating substrate, and its final product is specified to be flexible. This type of multilayer FPC is made of flexible insulating materials, such as polyimide film, laminated to form a multilayer board, which loses its inherent flexibility after lamination.
4.The combination of software and hardware
Soft-hard board is a combination of FPC and PCB. The production of soft-hard board should have both FPC production equipment and PCB production equipment. First, the electronic engineer draws the circuit and shape of the flexible bonding board according to the demand, and then sends it to the factory that can produce the flexible and rigid bonding board. After the CAM engineer processes and plans the relevant documents, then arranges the FPC production line production station FPC and PCB production lines are required to produce PCB. After these two flexible boards and hard boards come out, according to the planning requirements of electronic engineers, FPC and PCB are seamlessly pressed by a pressing machine, and then go through a series of details. It became a hard and soft board.
The above are several common types of FPC flexible circuit boards, and the common FPC classification method of flexible circuit boards in the industry. In addition to these categories, there is a classification based on the use of flexible circuit boards, such as capacitive screen FPC, button FPC, etc., Jingwan Electronic will give you a brief introduction in the next article.