PCB Blog - Flexible PCB Stacked Layer Structure Design

Flexible pcb stacked layer structure refers to the flexible circuit board in the different layers of the material stacking method. Generally speaking, the flexible pcb stacked structure usually includes the following layers:

1. steel plate or polyimide film (PI): used to provide rigidity and stability of the FPC.

2. copper foil layer: used to conduct electricity and transmit signals.

3. Surface treatment layer: Provides superior electrical performance and corrosion resistance through treatments such as chemical or gold plating.

4. Coating: Used to isolate electrical and mechanical interference between circuit layers.

5. Thin Film Circuit Board Layer: Used to assemble the circuit structure, usually with polyimide film material.

Common Flexible PCB Stacked Layer Structures:

Flexible pcb stacking structure according to different application requirements, usually divided into single-layer, double-layer, multi-layer and rigid-flex combination structure. The following are some typical FPC stacking forms:

Single-layer FPC: consists of a layer of conductive copper foil and a layer of substrate, the copper foil is engraved with a circuit pattern, and coated with a protective film.

Structure: substrate + copper foil + cover film

Characteristics: Simple structure and low manufacturing cost, suitable for applications with relatively simple circuits.

Double-layer flexible pcb: consists of two layers of conductive copper foil with a substrate sandwiched in the middle, and the two layers of copper foil are connected through guide holes.

Structure: Covering film + Copper foil + Substrate + Copper foil + Covering film

Features: Supports more complex circuit design, improves circuit density and connection stability.

Multi-layer FPCs: comprised of multiple layers of copper foils and substrates alternately laminated with adhesive bonding between the layers and connected through vias.

Structure: Cover film + Copper foil + Substrate + (Adhesive + Copper foil + Substrate) x N + Cover film

Features: Suitable for high-density, high-performance complex circuit design, widely used in advanced electronic equipment. 

Rigid-Flex Combination FPC: Combines a flexible pcb with a rigid circuit board in the same circuit, containing a flexible area and a rigid area.

Structure: Rigid part consists of multi-layer PCB, flexible part consists of multi-layer FPC, and the two parts are connected by adhesive layer and guide hole.

Characteristics: Both mechanical stability and flexibility, to meet the needs of complex three-dimensional wiring and high reliability of the connection.

flexible pcb

Flexible pcb stacked design key points

1. Select the appropriate material and thickness: according to the product bending needs, conductive requirements and working environment, reasonable choice of substrate, copper foil thickness and bonding layer material and thickness. For high-frequency bending scenarios, it is recommended to choose calendered copper foil and thin substrates to ensure the flexibility and durability of the circuit board.

2. Reasonable design of perforations and routing: In multi-layer structures, perforations are used for cross-layer connections, and the design needs to ensure the firmness and stability of the perforations, and try to avoid the perforated area from bending to prevent breakage. Cabling design needs to take into account the stability of signal transmission, try to avoid cross-interference and signal reflection, especially in high-speed signal transmission applications.

3. Considering the adaptability of the manufacturing process: the design of the stacked structure needs to take into account the requirements of the actual manufacturing process, avoiding too many complex layer design, in order to reduce the production difficulties and manufacturing costs. Production process, the need to maintain the uniformity of each layer of material to ensure the overall consistency and reliability of the flexible pcb.

Flexible PCB Lamination Inspection Requirements

After the completion of the stacked layer, you also need to check to ensure that the number of flexible pcb placed on each layer, thickness, graphics, etc. are in line with the requirements. Specific inspection requirements are as follows:

1. check the quality and quantity of each layer of material to meet the requirements.

2. check the thickness of each layer of material to meet the requirements. 3. check the graphics of each layer of material to meet the requirements.

3. check whether the graphic of each layer of material meets the requirements. 4. check whether the graphic of each layer of material meets the requirements.

4. Check whether there is electrical and mechanical interference between the materials of each layer.

5. check whether the overall quality and performance of the FPC meet the requirements.

The design of the flexible pcb stacking structure is the key link to ensure the performance and reliability of the flexible circuit board. Strict stacking inspection to ensure that the quality and fit of each layer of material meets the standard is a necessary step to guarantee the overall quality of the flexible pcb. In the future, with the continuous improvement of performance and reliability of electronic products, the design and quality management of FPC stacked layer structure will continue to be the focus of the industry, and promote flexible electronic technology to a higher level.