What is a PCB reinforcement board? Explore its type, use and thickness

Do you know what PCB reinforcement is? They are widely used in flexible and rigid-flexible combined circuit boards. Although flexible PCBs have excellent adaptability and can be bent, folded, and twisted to meet complex design requirements, their flexibility poses challenges when assembling components on the circuit board, making interconnection integration more difficult. This is where PCB reinforcement comes into play, it provides targeted structural support and enhances the function of the circuit board.

What are the reinforcing bars in the PCB?

First of all, we need to understand that PCB reinforcement is not an inherent part of the circuit board, but a layer of material added to strengthen or strengthen the PCB. Usually, it is used in areas that require rigidity or structural support. Importantly, it helps to solve the manufacturing and operating problems faced by flexible circuits, and ultimately improve their overall performance and reliability.

3 types of PCB reinforcement bars

According to the different reinforcement materials, it can be divided into 3 types：

1. Polyimide (PI) reinforcement

Polyimide reinforcement is a professional solution for flexible circuit design and is widely used in applications that require precise thickness and lightweight characteristics, such as ZIF (zero insertion force) connector applications. Their main advantage is that they provide targeted reinforcement while maintaining circuit flexibility. In addition, PI flexible PCB reinforcement ribs ensure reliable connector bonding and optimal electrical performance, which is essential for precision and adaptable applications.

2. FR-4 reinforcement

For flexible circuits with complex component configurations, FR-4 reinforcement boards are the standard reinforcement method. Its main purpose is to avoid circuit bending near sensitive areas to protect precision solder joints from mechanical stress. FR-4 reinforcement board has a wider thickness range and more general applications, mainly used in consumer electronics products and industrial equipment.

3. Special metal reinforcement: aluminum and stainless steel

Aluminum reinforcement is an excellent heat dissipation material, suitable for applications that require efficient thermal management. Stainless steel reinforcement bars are especially useful in space-constrained designs, providing excellent component area support beyond traditional FR-4 options. These metal reinforcement bars are more expensive and take longer to manufacture, but they have great advantages for electronic professional applications that require extraordinary mechanical strength and thermal properties.

Common uses of PCB reinforcement boards

PCB board reinforcement has a variety of important uses in flexible circuit design：

• Mechanical reinforcement: They provide key support for areas where PTH and SMT components need to be assembled.
• Thickness maintenance: Flexible circuit reinforcement ribs help maintain a consistent circuit thickness.
• Component support: Provide support for various PCB components and connectors.
• Flexible constraints: According to the design requirements, the reinforcing bars can limit the flexible part to a predetermined rigid area.
• Processing improvements: They make it easier to operate thin and precise circuit boards.
• Enhanced stability: Through strategic reinforcement placement, certain areas of the flexible circuit can be kept flat and stable.
• Connector compatibility: They help meet zero insertion force (ZIF) connector specifications.
• Reduce stress: Reinforcing bars can increase the bending radius at the intersection of rigid and flexible joints, thereby reducing the stress during repeated bending operations.

How to connect the reinforcement to the flexible PCB?

There are two main methods for attaching reinforcing bars to flexible printed circuit boards: thermal bonding and pressure sensitive adhesive (PSA). They each have different functions and applications, as shown in the figure below：

The difference between rigid-flexible binding board and rigid-flexible board

Are you confused about the difference between rigid flexible board and rigid flexible board PCB? Many people want to know if they are the same, but the answer is no. They have different designs and functions：

The rigid flexible circuit is basically a flexible PCB reinforced by FR4 reinforcing bars to support mechanical assembly, but there are no electrical circuits on the rigid parts. In contrast, rigid-flexible combined PCB is a complex hybrid circuit that combines rigid and flexible substrates to form a single laminated structure. There are electrical lines and interconnections in both rigid and flexible components.

Rigid-flexible binding plates are mainly used for mechanical reinforcement, while rigid-flexible binding plates provide comprehensive electrical connections and structural integration, so they are suitable for more complex electronic applications involving electrical performance and structural adaptability.

Typical reinforcement thickness

Choosing the right reinforcement thickness is essential because it affects the flexibility, performance, and reliability of the circuit board. The thickness of the reinforcing bars in the PCB varies depending on the application and the type of material used：

• Polyimide reinforcing plate: usually thinner to maintain flexibility, the layer thickness ranges from 25µm to 125µm (0.025mm to 0.125mm). They also offer a customized thickness range from 0.025mm to 0.25mm for flexible PCB designs.
• FR4 stiffeners: These stiffeners are designed with rigidity in mind and usually have a wider thickness range (0.08mm to 3.18mm).
• Metal reinforcement: For heavy-duty support, the thickness of aluminum or stainless steel reinforcement is usually between 0.1mm and 0.45mm to maintain strong mechanical strength in certain areas.

conclusion

PCB reinforcement is an advanced solution in modern flexible circuit design, which helps to enhance the overall function, simplify the assembly process, and create more reliable products.