PCBs are used in electronic products, and the market trend of PCBs is almost the vane of the electronics industry. With the development of high-end, miniaturized electronic products such as mobile phones, notebook computers and PDAs, the demand for flexible PCB (FPC) is increasing, and PCB manufacturers are accelerating the development of thinner, lighter and denser FPCs.
There is 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 may 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 an insulating substrate, the surface of the conductor is uncovered, and the interconnection is achieved by soldering, welding or pressure welding, which is commonly used in early telephones.
2). Single-sided connection with covering layer
Compared with the previous class, it only has a layer of cover on the surface of the wire. The pad needs to be exposed when covering, and it can be easily covered in the end area. It is the most widely used and widely used one-sided flexible PCB, and is used in automobile instruments and electronic instruments.
3). Double-sided connection without covering layer
The land interface can be connected to the front and back of the wire, and a via hole is formed in the insulating pcb substrate at the pad. The via hole can be punched, etched or otherwise mechanically prepared at a desired position of the insulating substrate. to make.
4). Double-sided connection with covering layer
In the different types of the former, the surface has a covering layer, and the covering layer has a passage hole, which allows both sides to be terminated, and still maintains the covering layer, and is made of two layers of insulating material and a layer of metal conductor.
The double-sided flex pcb has a conductive pattern formed by etching on both sides of the insulating base film, which increases the wiring density per unit area. The metallized holes connect the patterns on both sides of the insulating material to form a conductive path to meet the design and use functions of the flexibility. The cover film protects the single and double-sided wires and indicates where the components are placed. Metallized holes and overlays are optional, as required, and there are fewer FPC applications.
The multi-layer flex pcb laminates three or more layers of single-sided or double-sided flexible circuits together, and forms a metallized hole through the vias/holes and plating to form a conductive path between the different layers. This eliminates the need for complex welding processes. Multilayer circuits have tremendous functional differences in terms of higher reliability, better thermal conductivity, and more convenient prototype pcb assembly performance.
This has the advantage 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. Multi-layer FPCs can be further divided into the following types:
1). Flexible insulation substrate finished product
This type is manufactured on a flexible insulating substrate and the finished product is specified to be flexible. This construction typically bonds the two ends of a plurality of single-sided or double-sided microstrip flexible PCBs together, but the central portions are bonded together to provide a high degree of flexibility. For a high degree of flexibility, a thin, suitable coating, such as polyimide, can be used on the wire layer instead of a thicker laminate overlay.
2). Soft insulating substrate finished product
This type is manufactured on a soft insulating substrate, and the finished product is specified to be flexible. Such multilayer FPCs are laminated to a multilayer board using a soft insulating pcb material such as a polyimide film, which loses its inherent flexibility after lamination.