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Understanding Flex PCBs: What is it, Types, and Applications

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A flex PCB is designed to be bendable. That allows it to be used where space is limited, or where a circuit board needs to conform to a non-planar surface. In view of that, flex circuit boards useful in many different situations. We wrote this post to introduce you to this type of PCB, as well as provide you with insight into its many uses and benefits.

What is a Flex PCB?

A flex PCB (also flexible printed circuit board in full) refers to a type of circuit board that can bend or curve to fit into tight spaces or unique shapes. These PCBs are typically made from flexible plastic substrates. They also use flexible copper conductors to route electrical signals.

A flex PCB board is either designed for static or dynamic applications. Static Flex PCBs are meant for applications where they will not flex during normal use. Dynamic Flex circuit boards, on the other hand, are designed for situations where the board will bend repeatedly during normal use.

Flex PCB structure
Flex PCB structure
Resource: https://www.designworldonline.com

Flex PCB Structure

The materials and layers used in a flex PCB circuit board can vary depending on the specific requirements of the application, but generally, the typical flex PCB structure includes the following: substrate, copper conductors, adhesives, and coverlays.

Flexible PCB Substrate

The flexible PCB substrate is the flexible material that forms the base of the PCB. It’s normally made from plastic materials such as polyimide, polyester, or PTE. Most often, the flex PCB substrate is polyimide.

The properties of polyimide, such as high temperature resistance and dimensional stability, make it a good choice for applications where a PCB may be subjected to high stress and strain.

Flexible PCB Copper Conductor

This is the conductive element that carries electrical signals on the flex PCB . The conductor is usually are made from a thin, flexible strip of copper that can be used for both static and dynamic flex PCB applications.

The copper may be electrically deposited or roll annealed. Based on its thickness and other design features, the flexible PCB copper conductor or layer may allow the board to flex more or less.

Flexible PCB Adhesive

To bind the different layers, an adhesive material is normally used. The flex PCB adhesive can be different materials. These include acrylic and epoxy that come in tape form and pressure-sensitive adhesive.

With ability to form strong bonds, the most common flexible PCB adhesive is the pressures-sensitive type. It’s also easier to apply and, therefore, popular for many different types of the flexible circuit board.

Flexible PCB Coverlay

The flexible PCB coverlay, or cover film, refers to the thin protective layer (about 0.001 inches) that’s applied to the surface of the flex PCB to protect the copper conductors and provide insulation.

The coverlay of flex PCB is likened to the solder mask of rigid PCBs: the two perform a similar function, which is to protect the circuit board from damage by the elements or other materials.

Flex PCB types
Flex PCB types
Resource: https://youtu.be/iC0LzSI2MIg

Flex PCB Types

Several types of flex PCBs can be manufactured: single sided flex PCBs, double-sided flex PCBs, single-layer flex PCBs, multi-layer flex PCBs, and multi-layer PCBs. The flex PCB types, together with their characteristics and applications, are listed below.

1. Single Sided Flex PCB

The single sided flex PCB consists of a single layer of flexible substrate material, with copper conductors on one side. These are the simplest and least expensive types of flex PCB to make.

As such, these flex PCBs are often used in applications where the flexibility of the board is the primary concern, or where space is highly limited, as they can be very thin and fit into tight spaces.

One disadvantage of the single sided flex PCB is its limited routing options, as all of the conductors must be placed on a single layer. This can make it difficult to design complex circuits with many components, or circuits that require a lot of interconnectivity.

2. Double Sided Flex PCB

This is a type of bendable circuit board that has conductive material, usually copper, on both sides of the flexible substrate. The flexible substrate is mostly polyimide, although other materials such as polyester may also be used.

A double-sided flexible PCB may be designed to include vias that connect the conductive material on both sides of the substrate, allowing for more complex circuitry.

The double-sided flexible PCB is commonly used in applications where they can offer the advantage of bendability or reduced weight and volume, but without affecting the need for complex routing or circuitry.

3. Multilayer Flex PCB

As the name suggests, the multilayer flex PCB is made up of multiple layers of conductive material embedded within flexible substrate layers. These are then connected through vias, small holes that are drilled through the substrate to provide electrical connectivity.

The multilayer flexible PCB is generally more complex and more expensive to manufacture than single-layer or double-sided flexible PCBs.

It also requires more design considerations and a stricter manufacturing processes. The structure of these flex PCB types provides many benefits, though, such as higher density of interconnects.

4. Rigid Flex PCB

A rigid-flex PCB is composed of both flexible and rigid substrate materials. These are joined together to create a single unit. Ideally, it combines the flexibility of a flexing PCB with the rigidity of standard non-flexible PCBs.

These flex PCB types can, therefore, be bent or folded to conform to the shape of the device they are being used in, while still providing the necessary rigidity for mounting components or connecting to other circuit boards.

Thin flex PCB (1)
Thin flex PCB
Resource: https://youtu.be/OfvP4pLit-4

Advantages of Flex PCB

With the ability to bend or flex, the flex PCB offers several when compared to PCBs, which make it preferred in many different situations. Some of the main advantages of flex PCBs include:

Space savings: Because they can bend to fit into tight spaces or unique forms, flex PCB boards save space in smaller electronic devices.

Improved reliability: The flexing nature of the flexible PCB reduces stress and prevents cracking, among other forms of damage. That, in turn, means improved reliability when it comes to performance.

Increased durability: The ability of flex PCB boards to bend and flex without breaking can make them more durable and resistant to damage from vibration or shock.

Cost savings: Depending on the application, using a custom flex PCB can help to reduce the overall cost of a product by simplifying the assembly process or reducing the need for connectors or other components.

Using flex PCB circuit boards
Using flex PCB circuit boards
Resource: https://hackaday.com

Flexible PCB Application

The many advantages of flex PCB boards make them suited for many different applications. These range from consumer electronics to more complex needs such as aerospace and medical devices. Here is a list of flex PCB application examples to give you an idea of what you can use this type of board for.

1. Wearable Devices: Flexible PCBs find use in wearable devices such as smartwatches, fitness trackers, and various medical devices. They are lightweight and take the shape of the human body, providing a comfortable and unobtrusive experience.

2. Mobile Devices: This is another important flex PCB application today. Examples include mobile devices such as smartphones and tablets. In these uses, the flex board connects various components, such as the display, the touch screen, and the battery.

3. Medical Devices: In medical devices such as wearable’s or implantable and monitoring equipment, the flex PCB board is quite useful as it can conform to the shape of the body while also offering the dynamic or static flexibility and reduced volume or weight.

4. Aerospace and Defense: Flexible PCBs are also used in aerospace and defense applications, where they are required to withstand harsh environments and high levels of vibration. These uses include weaponry, navigation systems, communication systems, and radar systems.

5. Automotive: This is a very common flex PCB application. Flexible PCBs in automobiles connect sensors, cameras, and other electronic components in tight spaces and high vibration environments without breaking.

6. Consumer Electronics: Flexible PCBs can be found in many different types of consumer electronics, from cameras and gaming consoles to home appliances.

Flex PCB Price

The cost of flexible PCBs is largely influenced by several factors: the type of PCB, number of layers in the PCB, and board size. The materials used also determine the range of a flex PCB price.

The cheapest flex PCB boards include single layer and one-sided designs. Double-sided or multilayer flexible PCBs cost more, owing to their design complexities and material mass.

To get an accurate figure for a flex PCB quote, you may want to contact a PCB manufacturer or supplier with your specific requirements. Note that prices will also be different from one flex PCB supplier to another, so it helps to scout around and compare the options.

Conclusion

The flex PCB offers many advantages. It’s also a necessary PCB design in many applications today. However, it does require special design considerations and manufacturing processes. Therefore, it’s important that you work with an experienced manufacturer or designer to ensure that your specific requirements are met.

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