Difference between single-layer FPC/double-sided FPC/multi-layer FPC
I'll introduce the types of FPC to you.
I. Single-Layer FPC
It has a layer of conductive pattern produced by chemical etching, and the layer of conductive pattern on the flexible insulating substrate surface is calendered copper foil. Insulation substrates can be polyimide, polyethylene terephthalate, aromatic amide fiber ester and polyvinyl chloride. Single-layer flexible printed circuit can be divided into the following four sub-categories.
1. One-sided connection without overburden
The conductor pattern is on the insulating base material, and there is no overlay on the surface of the conductor. Its interconnection is realized by tin welding, fusion welding or pressure welding. It is often used in early telephones.
2. One-sided connection with overlay
Compared with the former, only one layer of overburden is added to the surface of the conductor. When covering, the pad should be exposed. Simply, it can not be covered in the end area. It is the most widely used one-sided flexible PCB in automotive and electronic instruments.
3. Double-sided connection without overburden
Connecting disc interface can be connected on both front and back of the conductor. A path hole is opened on the insulating base material at the welding pad. The path hole can be made by punching, etching or other mechanical methods at the required position of the insulating base material.
4. Double-sided connection with overlay
Different from the former, there is a layer of covering layer on the surface, and the covering layer has access holes, which allow both sides to be terminated, and still maintain the covering layer, which is made of two layers of insulation material and one layer of metal conductor.
II. Double-sided FPC
Two-sided FPC has an etched conductive pattern on both sides of the insulating base film, which increases the wiring density per unit area. Metallized holes connect the graphics on both sides of the insulating material to form conductive paths to meet the flexibility of the design and use functions. The covering film can protect the single and double-sided conductors and indicate the location of the components. According to the requirements, metallized holes and coatings are optional, and this type of flexible printed circuit is rarely used.
3. Multilayer flexible printed circuit
Multilayer FPC is to laminate three or more layers of one-sided or double-sided flexible circuits together, through drilling L, electroplating to form metallized holes, forming conductive paths between different layers. In this way, complex welding process is not needed. Multilayer circuits board have huge functional differences in higher reliability, better heat conductivity and more convenient assembly performance.
Its advantage is that the base film is light in weight and has excellent electrical properties, such as low dielectric constant. Multilayer flexible PCB board made of polyimide film as base material is about 1/3 lighter than rigid epoxy glass cloth multilayer PCB board, but it loses the excellent flexibility of one-sided and double-sided flexible PCB. Most of these products do not require flexibility. Multilayer FPC can be further divided into the following types:
1. Finished Flexible Insulation Substrate
This type is manufactured on flexible insulating substrates, whose products are specified to be flexible. This kind of structure usually bonds the two ends of many single or double-sided microstrip flexible PCBs, but the central part of the PCB is bonded together at the end, so it has high flexibility. In order to be highly flexible, a thin, suitable coating, such as polyimide, can be used on the conductor layer instead of a thicker layer of laminated coating.
2. Finished Products of Soft Insulation Substrate
This type is manufactured on flexible insulating substrates, and the final product specification can be flexible. This kind of multilayer FPC is made of soft insulating materials, such as polyimide film, which is laminated into multilayer plates and loses inherent flexibility after lamination.
