What is a flexible circuit board? What is an FPC board? In fact, a flexible circuit board is called a FPC. It is a PCB board made of a soft insulating substrate. It is suitable for high density, high reliability, and miniaturization of today's electronic products. The need to develop in a lightweight direction also meets the stringent economic requirements and the need for market and technology competition.
FPC flexible circuit board basics
Soft PCBs are usually classified as follows according to the number of layers and structure of the conductor:
1.1 single-sided flexible PCB
A single-sided flexible PCB with only one layer of conductor and a surface with or without a cover.
The insulating substrate material used will vary with the application of the product.
Commonly used insulating materials are polyester, polyimide, polytetrafluoroethylene, and soft epoxy-glass cloth.
Single-sided flexible PCBs can be further divided into the following four categories:
1) No cover layer single-sided connection
The wire pattern of such a flexible PCB is on an insulating substrate, and the surface of the wire has no cover layer.
Like a normal single-sided rigid PCB.
These products are the cheapest and are often used in applications where environmental protection is not critical.
The interconnection is achieved by soldering, welding or pressure welding. It is commonly used in early telephones.
2) Covered single-sided connection
Compared with the previous class, this type only has a layer of cover on the surface of the wire according to customer requirements.
The pad needs to be exposed when covering, and it can be easily covered in the end area.
If precision is required, it can be in the form of a clearance hole.
It is the most widely used and widely used single-sided flexible PCB, and is widely used in automotive instruments and electronic instruments.
3) Uncovered double-sided connection
This type of land interface can be connected to both the front and the back of the wire.
To this end, a via hole is formed in the insulating substrate at the pad, which can be formed by etching, etching or other mechanical means at a desired position of the insulating substrate.
It is used for two-sided mounting elements, devices, and where soldering is required. There is no insulating substrate in the pad area of the via, and such pad areas are typically removed chemically.
4) Covered with double-sided connection
This type differs from the former class in that it has a layer of cover on the surface. However, the cover layer has via holes, which also allows both sides to be terminated and still maintain the cover layer.
This type of flexible PCB is made of two layers of insulating material and a layer of metal conductor.
It is used when the cover layer and the surrounding devices are required to be insulated from each other, and they are insulated from each other, and the ends need to be connected to both the front and the back.
1.2 double-sided flexible PCB
Double-sided flexible PCB with two layers of conductors.
The application and advantages of this type of double-sided flexible PCB are the same as those of a single-sided flexible PCB. The main advantage is that the wiring density per unit area is increased.
It can be divided into: no metallized holes and no cover layer: a no metallized holes, no cover layer; b no metallized holes, with a cover layer; c with metallized holes, no cover layer ;d has metallized holes, with a cover layer. Double-sided flexible PCBs without overlays are less useful.
1.3 multi-layer flexible PCB
Flexible multilayer PCBs, such as rigid multilayer PCBs, use multilayer lamination technology to create multilayer flexible PCBs.
The simplest multi-layer flexible PCB is a three-layer flexible PCB formed by coating two layers of copper shielding on both sides of a single-sided PCB.
This three-layer flexible PCB is equivalent in electrical characteristics to a coaxial wire or a shielded wire.
The most commonly used multilayer flexible PCB structure is a four-layer structure in which interlayer interconnections are realized by metallized holes, and the middle two layers are generally a power supply layer and a ground layer.
The advantage of a multilayer flexible PCB is that the substrate film is lightweight and has excellent electrical properties such as a low dielectric constant. Multilayer flexible PCB board made of polyimide film is about 1/3 lighter than rigid epoxy glass cloth. However, it loses single-sided, double-sided flexible PCB. Flexibility, most of these products are not required for flexibility.
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