Guide

Rigid-Flex PCB: Types, Features, and Applications

Rigid-Flex PCB

Introduction of Rigid-Flex PCB

We are living in a fast and rapidly changing 21st century predominantly known by the introduction of new technologies almost every 2-3 years. Electronics as a domain has been there for a while now and since it has a huge role in making the 21st century tech savvy, there is no denying the fact that electronics itself is undergoing modifications to keep up with the demands of technological advancements. The basis of 21st-century electronics lies in its smart devices, their assembly and their incorporation in not-so-smart environments. In the initial epochs of technological evolutions, there was no need for a number of varieties and types present for each and every device, but now times have changed. To introduce novelty in devices, the need for advanced electronic components is inevitable. PCB (Printed Circuit Board) is one of the basic components in electronics used for innovations, prototyping of ideas and inventing new devices.

During the initial phases of the electronics boom, only one type of PCB was used; nowadays, it is called as Rigid PCB. But as times started to change, so did the requirement for more advanced PCB boards. And now with electronics in full bloom, we have multiple types of PCB boards. And one of among them is called as Rigid Flex PCB. Rigid-flex PCB is a kind of printed circuit board that combines both rigid area and flexible area together on one single PCB board. It is important to be familiar with the basic types of PCBs first according to their flexibility.

rigid flex PCB

rigid flex PCB

Types of PCB According to Flexibility

1. Rigid PCB: A rigid printed circuit board is a type of PCB that is rigid in nature and is not bendable; hence, it is not flexible. The stiffness of a rigid PCB comes from the core materials used in its making- glass fiber and epoxy resin commonly termed as substrate. Glass fiber is chosen as its core material carefully to make the board unbreakable and very solid. These types of PCBs were primarily used during the formative years of the electronic era and are now usually used at places where there is a need for stable assembly of electronic circuits.

2. Flexible PCB: Flexible PCB boards are flexible in nature due to the use of flexible core materials such as polyimide which allow the boards to bend and be non-rigorous in nature. Flexible PCBs are not used for their core strength as they get damaged quite easily in comparison to rigid PCBs. These are used in environments where there is a shortage of space, installations need to be done on curved surfaces and where there is a requirement for bending and flexibility of board.

3. Rigid-Flex PCB: The most sought-after item in the electronics market is Rigid-Flex PCB. It is a type of PCB that uses both rigid and flexible board technologies. It is a hybrid model of the other two types of PCB boards. It uses the main features of both rigid and flexible and incorporates both into one. Rigid flex PCBs have the strength and unbreakable nature of rigid PCBs but the flexibility and bendability of flexible PCBs. It is used where there is a critical need for a product or circuit with promising strength along with bending properties.

Types of Rigid Flex PCB

Rigid – Flexible printed circuit board is a sandwiched structure (dual-side) with rigid laminates forming the outer layers of the sandwich and the flexible substrate in the middle. For the rigid laminate, rigid materials like glass fibre and FR-4 are used to introduce the core strength it and substances like polyimides suffice the role of flexible core materials. These PCBs are designed in 3D ensuring their smooth bending and flexibility. These are very lightweight boards, apt for use in portable electronic devices like smartwatches, mobile phones, tablets and laptops. The flexibility property allows them to fit into any small and thin gaps present. They are convenient to use on bent surfaces and toward the edges.

A. On the number of flexible layers
  1. Rigid flex PCB with only one flexible layer: Single Layer PCBs are those PCBs in which the conducting material mostly copper is present on only one side of the PCB board. One side is used for conducting purposes and the other side is used for mounting the components on board. This kind of rigid-flex PCB is very cost-effective and thereby mostly used by consumer electronics and cost-sensitive products.
  2. Rigid flex PCB with two flexible layers: This kind of rigid-flex circuit board is very commonly used because it is easier to produce. For example, 4-layer rigid-flex PCBs with two flexible layers in the middle.
  3. Rigid flex PCB with multi-flexible layers: Multi-layer PCBs are those PCBs with a number of rigid and flexible layers present, with three or more flexible layers. If each layer is a dual side, then for each pair of rigid layers, there exists one flexible layer of polyimide (PI), forming a sandwich-like structure.
  4. HDI Rigid Flex PCB: In some cases, rigid-flex PCB is designed with small trace and drills, such as blind and bruised vias, stacked vias and staggered vias These are introduced to optimise the connectivity in multi-layer flexible layers by allowing the use of conducting vias. Vias are nothing but conducting strips to make vertical connections possible in a multi-layer PCB. They are quite expensive but they maintain the integrity of multi-layered boards. There are many types of this type of board based on the positioning of vias such as through-hole via, blind via, buried via, etc. This kind of rigid-flex circuit board is usually used in very complex applications.
B. On the basis of flexibility:
  1. Static Rigid Flex PCB: This kind of rigid flex PCB will only need to be bent once to fix the applications. For this kind of board, lower standard flexible material can be used to save costs. We can even use semi-flex FR-4 material as a substitution.
  2. Dynamic Rigid Flex PCB: These are primarily designed for the increased flexibility and bending of PCBs such and so that they can undergo repeated multiple bending repetitions called Flex Cycles. They are used in places that are highly susceptible to bends and folds.
  3. 3D Rigid Flex PCB: 3D PCBs are mainly invented to accommodate a circuit in a tightly enclosed space and these are designed in a similar fashion such that they can fit into the space perfectly. This type of PCB can not withstand any compromise made while choosing the appropriate flexible substances as it has to undergo heavy folds and sit into weird shapes and positions.
Rigid flexible PCB

Rigid flexible PCB

Features of Rigid-flex PCB

Rigid-Flex PCBs are significantly known for their hybrid model of combining the prime features of rigid-type PCBs and flexible-type PCBs into one. In addition to that, there are other features also associated with these boards and they are:

1. Flexibility and rigidity: It has both flexibility and strength in its core due to which it is versatile in nature and can be used at any place where there are high mechanical stress conditions and also where it is difficult to maintain posture and stiffness.

2. Thin structure: Due to its thin structure, it can easily be moulded into any 3D shape fitting into any place in question and also can fill in thin gaps present.

3. Lightweight: It is very lightweight as compared to rigid PCBs and that is why it is preferred to be used in portable electronics such as smartphones, smart watches, step counters and similar smart devices.

4. Complex PCB designs: It makes the use of complex PCB designs possible as it supports the mounting of components on both rigid as well as flexible surfaces in case of a single conducting surface of a layer and also since it can be folded in any shape, this in turn becomes a possibility.

5. Signal transmission: It allows increased connectivity between multiple layers due to which the signal integrity is maintained with reduced signal loss and minimal interference values.

6. Shock resistant: It can withstand electrical shocks, vibrations and high mechanical stress due to its rigid core strength.

Applications of Rigid Flex PCB

1. Military: Due to its reliability and rigorous core strength, it has become a trusted electronics component among military devices and operations.

2. Medical Electronics: Used in medical electronic equipment such as health monitors, diagnostic equipment, sensing devices, wearable tracking devices, medical implants like pacemakers, surgical instruments, laboratory equipment, etc.

3. Everyday Electronics: It is basically an electronic component and is used in every field where electronics have been introduced such as control systems, automation devices and vehicles, daily use devices like fitness trackers, smart devices, laptops, etc.

4. Internet of Things: Smartwatches having step counters, heart rate measuring devices, pressure meters and other features incorporated in them is possible because of these boards as smart watches are very small in structure and space is a restriction and these boards come handy in such devices as they provide flexibility.

5. Robotics: Heavily employed in the Robotics domain due to its efficiency, ruggedness, reliability and flexibility to fit and mould into any shape and position.

6. Satellites and Aerospace: It is used in communication devices and satellites as it provide high signal integrity, high signal transmission and low interference.

Conclusion

Rigid-flex PCBs are widely used in many applications because of their features of 3D usage and their lightweight. There are different types as well according to their design. It is obvious that rigid-flex circuit boards will be more and more widely used.

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