One, single-layer FPC

It has a layer of chemically etched conductive pattern, and the conductive pattern layer on the flexible insulating substrate is calendered copper foil.The insulating substrate may be polyimide, polyethylene terephthalate, aramid fiber ester, and polyvinyl chloride.Single-layer FPC can be divided into the following four categories:

1. One side connection without covering layer

Wire graphics on the insulation substrate, wire surface without a covering layer, its interconnection is to use tin welding, welding or pressure welding to achieve, commonly used in the early telephone.

2. One side connection with covering layer

Compared with the previous class, there is only one more covering layer on the wire surface.Cover the need to expose the welding disk, simple can not cover the end area.It is one of the most widely used soft PCB, which is used in automobile instrument and electronic instrument.

3. Double-sided connection without covering layer

The connection plate interface can be connected on the front and back of the wire, and a passage hole can be opened on the insulating substrate at the welding plate. The passage hole can be made by punching, etching or other mechanical methods at the required position of the insulating substrate.

4. Double-sided connection with covering layer

In the former category, there is a covering layer on the surface, and the covering layer has access holes, allowing both sides to be connected, and still maintaining the covering layer, which is made of two layers of insulating materials and one layer of metal conductor.

Two, two-sided FPC

Double-sided FPC has a conductive pattern etched on both sides of the insulating base film, which increases the wiring density per unit area.Metallized holes connect the two sides of the insulating material graphically to form a conductive path to meet the flexural design and use function.While the covering film can protect the single and double-sided wire and indicate the placement of components.As required, metallized holes and cladding are optional, and this type of FPC is rarely used.

Three, multi-layer FPC

Multi-layer FPC is to layer three or more layers of single-sided or double-sided flexible circuits together, through drilling hole and electroplating to form metallized holes, and form a conductive path between different layers.This eliminates the need for complex welding processes.Multilayer circuits have great functional differences in higher reliability, better thermal conductivity and more convenient assembly performance.

It has the advantage of light weight and excellent electrical properties, such as low dielectric constant.The multilayer soft 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 excellent flexibility of single-side and double-side soft PCB, most of these products do not require flexibility.Multi-layer FPC can be further divided into the following types:

1. Flexible insulation substrate products

This type is manufactured on flexible insulating substrates and the finished product is specified to be flexible.This structure usually binds the two ends of many single-sided or double-sided microstrip flexible PCBS together, but the central part of the PCB is not bonded together, resulting in a high degree of flexibility.For high flexibility, a thin, suitable coating, such as polyimide, may be used on the conductor layer instead of a thicker laminated overlay.

2. Finished soft insulation substrate

This type is manufactured on a soft insulating substrate and the finished product can be flexed.This kind of multilayer FPC is made of soft insulating materials, such as polyimide film, which is pressed into a multilayer plate and loses its inherent flexibility after lamination.