Keywords: Flex Circuits Board, Rigid Flex PCB

New technologies having roots in the past are seemingly encountered sometimes in electronics. Approximately to around 50 years back, the Rigid Flex PCB technologies found their use to fulfill the need of replacing wiring harnesses in spacecraft. Rigid-flex technologies were used in the first commercially available mobile computer.

Few of the applications using rigid-flex PCBs include satellites, wearable technologies, laptop computers, test equipment, and medical devices today.

Rigid-Flex PCB

Rigid circuit and flexible circuit substrates are laminated together With a rigid-flex PCB. The boundaries of the unique properties of flex circuits and traditional rigid PCBs are crossed by Rigid-flex PCBs.

A flexible polyimide such as copper and Norton or Kapton laminated together are used to make Flex circuits. These incorporate lamination using pressure, acrylic adhesive, and heat.

Components can’t be mounted on both sides of the rigid board in conventional PCBs. Connecting cables or connectors are not used between the sections in a rigid-flex design due to the integration that occurs between Flex Circuits Board and the rigid circuits board. Instead, the system is connected together electrically in the flex circuits.

Several things are accomplished by the lack of connecting cables and connectors:

• More space to accommodate other components
• Controlled impedance gets accommodated
• The transmission of a signal without loss is improved in the circuit 
• Weight Reduction
• Connection issues such as cold joints are eliminated

Zones have been created by dividing every rigid-flex PCB. Each zone contains different layer counts and different materials. As compared to the flexible zones, more layers are present in the rigid zones. In transition zones, the materials get shifted from FR-4 to polyimide.

Often, the complex designs transit from rigid to flex and again to rigid many times. Keeping holes away from the transition zone is required by the overlapping rigid-flex materials as these intersections occur. The integrity is maintained this way.  Apart from this, aluminum or stainless steel stiffeners are included in the rigid-flex designs to offer additional support for components and connectors.

Rigid-Flex PCB Manufacturing

As compared to developing traditional circuit boards, designing the Rigid-Flex designs are very complex and challenging.

With designing PCB layout, the manufacturing process begins with the assistance of PCB designing software. For creating required PCB designs, it is easy to learn the software and anyone with no or negligible technical experience can start working with them.

Rigid-Flex PCBs are manufactured by stacking up the flexible and rigid substrate materials layers orderly with plated through holes. This offers a proper connection between layers.

The intense contact and heat issues that occurred by harnesses and connectors are eradicated by the strength and reliability of Rigid-Flex designs.

Rigid-Flex PCBs have been in existence for a long. Over time, the process of board manufacturing has enhanced. Recently glass fiber epoxy resin (FR4) is used in the Rigid-Flex PCB manufacturing process as an external rigid board. For securing the rigid pattern of the circuit, a solder mask is put on the rigid layer. And polyimide (PI) double-layer board is used to make up the material of the flexible substrate. Copper covers this double-layer board. The flexible pattern of design is secured by the acrylic film.

Rigid-flex circuits manufacturing includes the following steps:

• Base material Preparation
• Circuit pattern generation
• The copper laminate Etching
• Précised mechanical drilling
• Through-hole plating
• The boar Protection using a cover plate

Exceptional electrical performance and mechanical support are offered by the Rigid-Flex board and the flexible material facilitates its bending capacity into any shape. Making the board a perfect match for high-frequency transmission of signal and impedance control, the flexible material of the substrate shows excellent dielectric stability and offers flexibility.

Ensuring size tolerance, plating, effective circuit pattern, accumulation, layer up, and drilling, flexible material of the substrate exhibits a large thermal expansion coefficient and high moisture absorbing capacity. 

Material for the Design of Rigid-Flex PCB

Before starting a design, you’ll want to consult your PCB manufacturer. The choice of overlays, the count, copper type, and bend radius may vary based on whether the PCB is meant for stable bend or dynamic bend.

An environment where the PCB will be bent constantly is used to install a dynamic bend rigid-flex PCB. Therefore, using not more than 2 layers is recommended and the bending radius must always be maintained at a level of 100 times the thickness of the material.

Meanwhile, having up to 10 to 20 layers is possible for a rigid-flex PCB to be used in stable-bend installations. The repeated bending force is not used. This indicates that a small radius of bending, which is 10 multiples of its thickness can be used.

Rigid-Flex PCB Pros

The benefits of both flex and rigid circuits are offered by Rigid-Flex designs. Few advantages offered by manufacturers and consumers are as follows:

• Dynamism: Greater flexibility, repeatability, and high precision with packaging designs are offered by the boards.
• Mechanical Stability: Multiple flexible substrate layers construct the rigid-flex design. Offering both flexibility and stability for installation in difficult places, these layers are attached to a single or more than one rigid board.
• Bear Extreme Environment:  Vibration and shock issues are found in Heavy electronic components during the electrical project's execution. However, you need not worry about these troubles while soldering the electrical component with the rigid-flex PCBs. This is because the extreme environment, heat, high temperature, shock, and radiation can be bear by these boards.
• Reliability of Connection: Secure and safe connections with other electrical components are ensured by the greater board polarity and stability.

Rigid-Flex PCB Applications & Examples

• Scores of applications make use of the Rigid-Flex designs. Here board flexibility is essential without having to compromise with the design rigidity.
• Military, industrial and commercial applications make use of these. Smart devices like cell phones, digital cameras, etc make use of these. The pacemakers in the medical industry make use of these for flexible capabilities, space, and weight reduction.
• Offering high reliability and reducing the connection issues, these boards support fragile as well as delicate wiring. In rigid-flex designs, few solder joints are required to enable more connection reliability and in measuring, testing, and automobile applications enable high connection reliability.
• Manufacturing these boards is very economical as less assembly and the logistical cost are involved. As, for computer servers and bar code scanners applications, this is a perfect fit as they are of small size and low weight.

Wrap Up

This article will be of great help to those keen about acquiring detailed knowledge about the Rigid Flex PCB. Hope you might have expanded your knowledge by now.