Let you know what is a flexible circuit board

FPC: English spelling Flexible Printed Circuit, which means flexible printed circuit board, referred to as soft board. It is made of conductive circuit patterns by using photo-imaging pattern transfer and etching process on the surface of a flexible substrate, and the surface and inner layers of double-sided and multi-layer circuit boards are electrically connected to the inner and outer layers through metallized holes. , The surface of the circuit pattern is protected and insulated by PI and adhesive layer.

Tengchuangda circuit: It is mainly divided into single-sided board, hollow board, double-sided board, multi-layer board, and rigid-flex board.

PCB: English spelling Printed Circuit Board, which means steel printed circuit board, referred to as hard board.

03Characteristics of flexible circuit boards

⒈Short: The assembly time is short, all the lines are configured, and the connection work of redundant cables is omitted;

⒉ Small: The volume is smaller than that of PCB (hard board), which can effectively reduce the volume of the product and increase the convenience of carrying;

⒊ Light: lighter weight than PCB (hard board) can reduce the weight of the final product;

4 Thin: Thinner thickness than PCB (hard board) can improve softness and strengthen the assembly of three-dimensional space in a limited space.

Advantages of flexible circuit boards

A flexible printed circuit board is a printed circuit made of a flexible insulating substrate, which has many advantages that rigid printed circuit boards do not have:

1. It can be bent, wound, and folded freely, and can be arbitrarily arranged according to the spatial layout requirements, and can be moved and stretched freely in three-dimensional space, so as to achieve the integration of component assembly and wire connection;

2. The use of FPC can greatly reduce the volume and weight of electronic products, which is suitable for the development of electronic products in the direction of high density, miniaturization and high reliability. Therefore, FPC has been widely used in aerospace, military, mobile communications, laptop computers, computer peripherals, PDA, digital cameras and other fields or products;

3. FPC also has the advantages of good heat dissipation and solderability, easy assembly and connection, and low comprehensive cost. The design of soft and hard combination also makes up for the slight deficiency of the flexible substrate in the component carrying capacity to a certain extent.

04FPC main raw materials

The main raw materials are: 1. Base material, 2. Cover film, 3. Reinforcement, 4. Other auxiliary materials.

1. Substrate

1.1 Adhesive substrate

The adhesive substrate is mainly composed of three parts: copper foil, adhesive and PI. There are two types of single-sided substrates and double-sided substrates. The material with only one copper foil is a single-sided substrate, and the material with two copper foils is a double-sided substrate. surface substrate.

1.2 Adhesive-free substrate

The adhesive-free substrate is a substrate without an adhesive layer. Compared with the ordinary adhesive substrate, the middle adhesive layer is missing, and it is only composed of copper foil and PI, which is thinner than the adhesive substrate. , better dimensional stability, higher heat resistance, higher bending resistance, better chemical resistance and other advantages, have now been widely used.

Copper foil: At present, the thickness of commonly used copper foil has the following specifications, 1OZ, 1/2OZ, 1/3OZ, and now a thinner copper foil with a thickness of 1/4OZ is introduced, but this material is currently being used in China, and it is making ultra-fine roads. (Line width and line spacing are 0.05MM and below) products. As customer requirements become higher and higher, materials of this specification will be widely used in the future.

2. Cover film

It is mainly composed of three parts: release paper, glue and PI. In the end, only the glue and PI remain on the product. The release paper will be torn off during the production process and will not be used again (there are foreign objects on the protective glue).

3. Reinforcement

It is a specific material for FPC and is used in a specific part of the product to increase the support strength and make up for the "soft" feature of FPC.

The commonly used reinforcing materials are as follows:

▶FR4 reinforcement: the main components are glass fiber cloth and epoxy resin glue, which is the same as the FR4 material used in PCB;

▶Steel sheet reinforcement: the composition is steel, which has strong hardness and support strength;

▶ PI reinforcement: The same as the cover film, it consists of PI and adhesive release paper, but the PI layer is thicker, and can be produced in proportions from 2MIL to 9MIL.

4. Other auxiliary materials

▶Pure adhesive: This adhesive film is a heat-curable acrylic adhesive film composed of protective paper/release film and a layer of adhesive, mainly used for layered boards, flexible and rigid boards, and FR- 4/Steel sheet reinforcement board, play a role in bonding.

▶Electromagnetic protective film: paste it on the board surface for shielding.

▶Pure copper foil: only composed of copper foil, mainly used for hollow plate production.

Type of 05FPC

FPC types have the following 6 distinctions:

A. Single panel: only one side has lines.

B. Double-sided: There are lines on both sides.

C. Hollow plate: also known as window plate (finger face opening window).

D. Layered board: lines on both sides (separate).

E. Multilayer board: more than two layers of lines.

F. Rigid-flex board: a product that combines soft board and hard board.

06FPC process flow

In the future, FPC will continue to innovate from three aspects, mainly in:

1. Thickness; the thickness of FPC must be more flexible and needs to be thinner;

2. Folding resistance; bending is an inherent characteristic of FPC, and the folding resistance of future FPC must be stronger;

3. Process level: In order to meet various requirements, the process of FPC must be upgraded, and the minimum aperture and minimum line width/line spacing must meet higher requirements.