2 layer flex pcb
All electronic products use PCBs, and the market trend of PCBs is almost a weathervane for the electronics industry. With the development of high-end and miniaturized electronic products such as mobile phones, laptops and PDAs, the demand for flexible PCBs (FPCs) is increasing. PCB manufacturers are accelerating the development of thinner, lighter and denser FPCs. I will introduce the types of FPCs to you.
1.Single-layer FPC
It has a layer of chemically etched conductive pattern, and the conductive pattern layer on the surface of the flexible insulating substrate is a rolled copper foil. The insulating substrate can be polyimide, polyethylene terephthalate, aramid fiber ester and polyvinyl chloride. Single-layer FPC can be divided into the following four subcategories:
(1)Single-sided connection without covering layer
The conductor pattern is on the insulating substrate, and there is no covering layer on the surface of the conductor. Its interconnection is achieved by soldering, fusion welding or pressure welding, which is often used in early telephones.
(2)Single-sided connection with covering layer
Compared with the previous category, there is only one more covering layer on the surface of the conductor. When covering, the pad needs to be exposed, and it can be simply uncovered in the end area. It is the most widely used and most widely used single-sided flexible PCB, used in automotive instruments and electronic instruments
(3)Double-sided connection without covering layer
The connection pad interface can be connected on both the front and back sides of the wire, and a via hole is opened on the insulating substrate at the pad. This via hole can be punched, etched or made by other mechanical methods at the required position of the insulating substrate.
(4)Double-sided connection with covering layer
The difference between the previous type and the previous type is that there is a covering layer on the surface, and the covering layer has a via hole, which allows both sides to be terminated and still maintains the covering layer. It is 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 metallized hole connects the patterns on both sides of the insulating material to form a conductive path to meet the design and use functions of flexibility. The covering film can protect single-sided and double-sided wires and indicate the location of component placement. According to the requirements, the metallized hole and the covering layer are optional, and this type of FPC is less used.
3.Multilayer FPC
Multilayer FPC is to laminate 3 or more layers of single-sided or double-sided flexible circuits together, form metallized holes by drilling and electroplating, and form conductive paths between different layers. In this way, there is no need to use complex welding processes. Multilayer circuits have huge functional differences in higher reliability, better thermal conductivity and more convenient assembly performance.
Its advantages are that the substrate film is light in weight and has excellent electrical properties, such as low dielectric constant. Multilayer soft PCB boards made of polyimide film as the substrate are about 1/3 lighter than rigid epoxy glass cloth multilayer PCB boards, but they lose the excellent flexibility of single-sided and double-sided soft PCBs. Most of these products do not require flexibility. Multilayer FPC can be further divided into the following types:
- Flexible insulating substrate finished products
This type is made on a flexible insulating substrate, and its finished products are specified to be flexible. This structure usually bonds the two ends of many single-sided or double-sided microstrip flexible PCBs together, but the center part is not bonded together, so it has high flexibility. In order to have a high degree of flexibility, a thin, suitable coating, such as polyimide, can be used on the conductor layer instead of a thicker laminated cover layer.
- Finished products on soft insulating substrates
This type is made on a soft insulating substrate, and the finished product is not specified to be flexible. This type of multi-layer FPC is made of soft insulating materials, such as polyimide films, laminated into multi-layer boards, and loses its inherent flexibility after lamination.