Unbonded multilayer flexible PCB

Unbonded multilayer flexible PCB is one of the multilayer flexible PCBs. They are circuit boards composed of multiple layers of conductive copper separated by multiple layers of insulating materials. Each layer has a specific function and circuit layout. The main purpose of the multi-layer design of the flexible circuit board is to provide more circuit connections and functions in a limited space.

Common flexible PCB usually have the following layers:

Single layer (Single-sided) flexible PCB: 

This circuit board has only one conductive copper layer and is suitable for applications with simple connections and low cost requirements

Double layer (Double-sided) flexible PCB:

There are two conductive copper layers, separated by insulation material, suitable for medium complexity circuit design.

Multi-layer flexible PCB:

This circuit board has 3 or more conductive copper layers.

What is a unbonded multilayer flexible PCB?

Unbonded multilayer flexible PCB is a type of flexible circuit that consists of multiple layers of copper foil, separated by layers of insulating material, such as polyimide. In the traditional multilayer flexible PCB, all the layers are piled up and bonded together using adhesives. With unbonded multilayer flexible PCBs, the layers are not connected or affixed to one another. The flexibility of unbonded multilayer flexible PCB is higher compared to that of a conventional one.

Characteristics of multilayer flexible PCB

Multilayer flexible PCBs are usually composed of several double-sided flexible circuits and single-layer flexible circuits, so there are no ready-made flexible copper-covered laminates.

A minimum of three layers of flexible conductive material with a flexible insulation layer between them and vias and gold plated holes are connections for the different layers to form a conductive path, external insulating layer.

Common multilayer flex PCBs come as either 4, 6 or 8 layer boards to accommodate more complex designs and higher density requirements. For instance, 4 layer flexible circuit is frequently used in laptop computers while 6-layer flex boards suit a bit more complex electronic devices depending on the application need and design complexity. Nowadays, on the market can hardly be found flexible PCBs with over ten layers being used.

The weight of a multilayer flexible PCB is at least one-third lighter than a rigid FR4 PCB, but due to its multiple layers, it loses the flexibility of single-sided and double-sided flexible PCBs. If flexible circuit boards with 3 or more layers need to maintain maximum flexibility, non bonded multi-layer flexible printed circuit boards are the best choice.

Advantages of unbonded multilayer flexible PCB:

Flexibility: Since there is no adhesive between the layers, these PCBS can be bent and flexed more easily without damaging the conductive path.

Dynamic bending: Unbonded multilayer flexible PCBs are suitable for applications where continuous or repeated bending is required.

Layer structure: Usually consists of alternating layers of conductive material and insulating layers. The layers are connected only at specific points, usually using through-holes or other interconnection methods.

Reduced thickness: No adhesive reduces the overall thickness of the PCB, making it ideal for compact and lightweight applications.

Improved heat dissipation: Enhanced flexibility and no adhesive layer results in better heat dissipation.

Application of Unbonded multilayer flexible PCB

For example, a mobile phone circuit board does not have just one. Side buttons and cameras require separate circuits, so there may be many different circuit boards in a product. Multilayer flexible PCB is actually made by pressing several circuit boards together. In this way, the thin-looking flexible PCB actually has several layers of circuits. Its thickness is even thinner than a single-layer rigid PCB. This is why products such as mobile phones, computers, and digital cameras are becoming thinner and thinner.

Wearable electronic products: Wearable products generally require relatively light weight, so they are very suitable for use on these products.

Medical equipment: The flexibility and reliability of flexible PCBs determine their suitability for medical devices, such as implants and diagnostic equipment.

Automobiles: Electronic products in automobiles often require the use of flexible circuit boards, as well as lighting, PDLC, wipers, and other components.

Consumer electronics: commonly used for foldable and flexible display technologies, such as smartphones, cameras, and tablets.

Aerospace: Suitable for aerospace applications that require weight reduction and flexibility.

Unbonded multilayer flexible PCBs offer enhanced flexibility and dynamic bending capabilities, making them ideal for a variety of advanced applications where traditional multilayer flex PCB or rigid PCB cannot meet the requirements.

Flex Plus (Xiamen) Co., Ltd. is a professional flexible PCB manufacturer in China. Our products cover single sided, double sided, multilayer flex PCB, rigid-flex, sculpturer flex PCB and other types of flexible PCBs, which can meet the needs of customers for all kinds of products.