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Rigid PCB Vs. Flexible PCB: 5 Differences

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Thin flex PCB
Thin flex PCB
Resource: https://youtu.be/OfvP4pLit-4

When making the choice between rigid PCB vs. flexible PCB, businesses must consider their application requirements. That’s because each type of PCB has its own unique advantages and limitations, and these can affect the overall performance of the final product. This article is an insight into 5 major flex PCB vs. rigid PCB differences, and what they mean for your application needs.

Flexible PCB Definition

Starting with the flexible PCB definition, here is what you need to know: A flexible printed circuit board, and which is usually shortened to flex PCB board, is a type of circuit board made of flexible and thin materials, such as polyimide or other plastic, that allow it to bend and fold.

Owing to these qualities, flexible PCBs are used in applications that require high durability and flexibility, since they offer various benefits such as reduced space requirements and resistance to shock and vibration.

Furthermore, you can easily customize a flex PCB board to fit your specific design requirements. This makes it a great solution in many different situations where space constraints and design flexibility are critical.

Rigid PCB Definition

Rigid PCB is used to mean a type of circuit board that is made of a solid, inflexible substrate material. In terms of structure, it consists of a conductive layer of copper traces patterned onto the surface of an insulating material, such as FR4.

The insulating layer, also known as the base material, provides mechanical support for the copper traces and the electronic components that will be mounted on the board.

Unlike flexible PCBs, rigid PCBs may also include other layers such as solder masks, which protect the copper traces from oxidation and silkscreens, which provide labels and other information about the components.

An example application of flexible PCB
An example application of flexible PCB
Resource: https://www.hackster.io

Rigid PCB vs. Flexible PCB

How do rigid and flex PCB boards differ. In this section to compare rigid vs. flexible PCB, we take a look at 5 main ways that the two types of circuit boards are different. These include the types of materials used, thickness, assembly and manufacturing, application, and cost

Rigid PCB vs. Flexible PCB: Material

One of the main differences between rigid and flex PCB is in the types of materials used. Owing to special requirements, the materials for flex PCB are generally thin, flexible plastic substrates, such as polyimide or polyester.

In terms of material, rigid PCBs are typically fiberglass reinforced epoxy laminates. Unlike flexible PCB types, rigid boards cannot bend or flex. However, they offer superior stability, which is ideal for some applications that require strong and stable platforms for electronic components.

Other rigid and flex PCB material differences include the type protective layer. Rigid PCB use solder mask, while flex PCBs use a coverlay that’s mostly a polyamide. Some flex boards also use stiffeners. Flex PCB stiffener is a rigid or semi-rigid material such as FR4 or polyimide that’s used for the non-flexible sections of the board.

Rigid PCB vs. Flexible PCB: Thickness

Needless to say, PCBs are generally thicker than flexible PCB boards due to the differences in substrate materials and design requirements. However, both types of PCBs can be designed with varying thicknesses to meet specific application needs.

Rigid PCBs are typically made of a solid substrate material, such as FR4, and have a uniform thickness throughout the board. This can range from a fraction of a millimeter to several millimeters, depending on the number of layers.

On the other hand, flexible PCBs are made of a thin, flexible substrate material. The typical flexible PCB thickness lies between 0.5 to 5 mils. Thinner flexible PCBs are often used in applications where weight and flexibility are important, such as in wearable devices or medical implants.

Rigid PCB vs., Flexible PCB: Assembly and Manufacturing

The flex PCB manufacturing process requires specialized equipment and steps than a rigid PCB. It also takes longer to fabricate these PCB types that rigid boards, owing to the special requirements to ensure various flexibility and quality aspects.

The flexible PCB assembly process can also be more challenging due to the flexibility of the substrate material as well as its lesser thickness. And this includes both the steps and the types of machines use to place the components.

Rigid PCB vs. Flexible PCB: Application

The application of flexible PCB boards is most common in wearable electronics, medical implants or wearable devices, and automotive systems. These are situations that require circuit boards that can resist high vibrations and bend to fit tight spaces or installation surfaces.

Rigid PCBs are generally used where structural integrity is paramount. They also fit applications that require high current and voltage levels, as they can be made with thicker copper traces and multiple layers to handle the requirements.

In some cases, a combination of rigid and flexible PCBs may be used in the same application. For example, a flexible PCB can be used to connect two rigid PCBs together or to provide flexibility in a system that requires both rigid and flexible components.

Rigid PCB vs., Flexible PCB: Cost

The flexible PCB process, both during manufacture and assembly, is more specialized and detailed. That, including the higher cost of the most common flex PCB material, polyimide, can end up increasing the cost per unit.

However, that being said, the cost difference between rigid PCB vs. flexible PCB boards is highly dependent on the specific requirements of the application. In some cases, the material savings when manufacturing flexible PCBs ends up reducing the overall costs. Furthermore, these PCB types cost less to install.

The rigid or flexible PCB cost will, therefore, depend on a variety of factors. These need to be carefully evaluated on a case-by-case basis to determine the most cost-effective solution for a particular application.

Overall, the choice between a rigid or flexible PCB will depend on the specific requirements of the application, including factors such as space constraints, mechanical requirements, and electrical performance.

Conclusion

Flexible PCBs can conform to irregular shapes and flex without the risk of breakage. They are also lightweight and well-suited for applications where weight and size are critical factors. Your decision between rigid and flexible PCBs will, thus, depend on your application’s specific needs. Note that you may also opt to combine both types of PCBs in a single design, such as using a flexible PCB to connect two rigid PCBs in a complex assembly.

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