Basic knowledge of FPC flexible circuit board
Soft PCB is generally classified according to the number of layers and structure of the conductor:
1.1 single-sided flexible PCB
Single-sided flexible PCB with only one layer of conductor, the surface may be covered or not covered.
The insulating base material used varies with the application of the product.
Commonly used insulation materials are polyester, polyimide, polytetrafluoroethylene, soft epoxy - glass cloth.
Single-sided flexible PCB can be further divided into the following four categories:
1) one side connection without covering layer
The conductor figure of this kind of flexible PCB is on the insulating substrate, and there is no covering layer on the wire surface.
Like the usual single-sided rigid PCB.
This kind of product is the cheapest kind, often be used at not crucial and have environmental protection application occasion.
The interconnection is realized by soldering, welding or pressure welding.It was used in early telephones.
2) one side connected with covering layer
Compared with the previous type, this type only has an extra layer of coverage on the surface of the wire according to the customer's requirements.
The solder pan should be exposed when covering. Simply do not cover the end area.
Where precision is required, the form of clearance hole can be used.
It is the most widely used one - sided flexible PCB and widely used in automobile instrument and electronic instrument.
3) no overburden double joint
This kind of connection disc interface can be connected on the front and back of the wire.
To this end, a channel hole is opened on the insulating substrate at the welding disc, which can be made by punching, etching or other mechanical methods at the required location of the insulating substrate.
It is used for both sides of mounting elements, devices and occasions requiring soldering. There is no insulating base material in the weld pad area at the access point.
4) double-sided connection with covering layer
This class differs from the previous class in that it has a covering layer on the surface.However, the overburden has access holes, and it is also allowed to be terminated on both sides, and the overburden remains.
This type of flexible PCB is made of two layers of insulation and one layer of metal conductor.
It is used where a covering layer is needed to be insulated from the surrounding devices, and the ends need to be insulated from each other, and both sides need to be connected.
1.2 double-sided flexible PCB
Double-sided flexible PCB with two conductors.
This kind of double-sided flexible PCB has the same application and advantages as single-sided flexible PCB.
It can be divided into a non-metallized hole and no covering layer by having, having and having no covering layer;B no metallized holes and covered;C with metallized holes and no covering;D has metallized holes and a covering layer.Double-sided flexible PCB without overburden is rarely used.
1.3 multi-layer flexible PCB
Soft multilayer PCB can be made into flexible multilayer PCB by using multi-layer pressing technology as rigid multilayer PCB.
The simplest multi-layer flexible PCB is a three-layer flexible PCB formed by two copper shielding layers on both sides of a single-sided PCB.
This three-layer flexible PCB is equivalent to coaxial or shielding conductors in electrical characteristics.
The most commonly used multilayer flexible PCB structure is the four-layer structure, which USES the metallization hole to realize interconnection between layers.
The advantage of multilayer flexible PCB is that the substrate film is light and has excellent electrical characteristics, such as low dielectric constant.The multi-layer flexible PCB made of polyimide film is about 1/3 lighter than rigid epoxy glass cloth multi-layer PCB, but it loses the excellent flexibility of single-side and double-side flexible PCB. Most of such products do not require flexibility.