PCB News - Flexible circuit board double-sided / [technology] single-layer FPC / double-sided FPC / multi-layer FPC difference

Flexible circuit board double-sided / [technology] single-layer FPC / double-sided FPC / multi-layer FPC difference

Electronic products must use PCB, and the market trend of PCB boards is almost the vane of electronic work.
With the development of high-end and miniaturized electronic products such as mobile phones, notebook computers and PDAs, there is an increasing demand for flexible PCBs (FPCs). PCB manufacturers are accelerating the development of thinner, lighter and denser FPCs. Let us introduce the types of FPC.

One, single-layer FPC

It has a layer of chemically etched conductive patterns, 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 cellulose ester and polyvinyl chloride.

A single-layer FPC can be divided into the following four sub-categories:

1. Single-sided connection without masking The wire pattern is on the insulating substrate, and there is no masking layer on the surface of the wire. The interconnection is realized by soldering, welding or pressure welding, which is commonly used in early telephones.

2. Single-sided connection with a masking layer Compared with the previous type, only a masking layer is added on the surface of the wire. When covering up, the pads should be exposed, and it can simply be left uncovered in the end area. It is the most widely used and most widely used single-sided flexible PCB. It is used in car meters and electronic instruments.

3. Double-sided connection without masking layer. The connection pad interface can be connected on the front side of the wire and discordant. A via hole is opened on the insulating substrate at the pad. This via hole can be positioned in the required position of the insulating substrate. It is made by punching, etching or other mechanical methods.

4. There is a masking layer in different places before the double-sided connection. There is a masking layer on the surface, and the masking layer has via holes, which allows it to be terminated on both sides, and still maintains the masking layer. It consists of two layers of insulating materials and a layer of metal conductors. production.

Two, double-sided FPC

The 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 pattern on both sides of the insulating material to form a conductive path to satisfy the flexibility of the planning and application function.

The masking film can protect single and double-sided wires and indicate the location of the component. According to requirements, metallized holes and masking layers are optional, and this type of FPC is rarely used.

Three, multi-layer FPC

Multi-layer FPC is to laminate 3 or more layers of single-sided or double-sided flexible circuits together, and form metallized holes by drilling and electroplating to form conductive paths between different layers.

In this way, there is no need to use a messy welding process. Multilayer circuits have huge functional differences in terms of higher reliability, better thermal conductivity, and easier assembly performance.

The advantage is that the base film is light in weight and has excellent electrical properties, such as low dielectric constant.

The multi-layer flexible PCB board made of polyimide film as the base material is about 1/3 lighter than the rigid epoxy glass cloth multi-layer PCB board, but it loses the single-sided and double-sided flexible PCB. Most of these products do not require flexibility.

Multi-layer FPC can further distribute the following types of dividends:

1. Flexible insulating substrate products This category is manufactured on flexible insulating substrates, and the product rules are flexible. This structure usually bonds the double-sided ends of many single-sided or double-sided microstrip flexible PCBs together, but the central part of them is not bonded together, and then has a high degree of flexibility. In order to have a high degree of flexibility, a thin, suitable coating, such as polyimide, can be used on the wire layer to replace a thicker laminated masking layer.

2. Flexible insulating substrate products This category is manufactured on a flexible insulating substrate, and its products can be flexible at the end of the rule. This type of multilayer FPC is made of flexible insulating materials, such as polyimide film, laminated to make a multilayer board, which loses its inherent flexibility after lamination.