Rigid-Flex PCB Manufacturing, Design & Applications

Rigid-Flex PCB

From automotive to aerospace, industrial to medical and beyond, rigid-flex printed circuit boards (PCBs) are finding their way into an ever-growing number of applications. Thanks to their unique construction, which combines both rigid and flexible Printed Circuit Board (PCB) materials, rigid-flex PCBs offer designers a wide range of benefits over traditional all-rigid or all-flexible PCBs.

What is a Rigid-Flex PCB?

Rigid-flex printed circuit boards are boards that use a combination of flexible and rigid board technologies. Most rigid flex boards consist of multiple layers of flexible circuit substrates attached to one or more rigid boards externally and/or internally, depending upon the design of the application. The flexible substrates are designed to be in a constant state of flex and are usually formed into the flexed curve during manufacturing or installation.

Both rigid and flexible PCBs serve to guide the movement of electrical current, connecting electronic components in various consumer and non-consumer products. Rigid PCBs are relatively stronger than flexible PCBs but flexible circuit boards offer durability in flexibility.

The rigid-flex PCB is a hybrid board that combines the features of rigid and flexible PCBs to make a highly effective board that maximizes functional efficiency for various applications. It offers benefits from the use of both rigid and flexible material, providing an extra boost of reliability and a wider range of PCB capabilities.

Material of Rigid-Flex PCBs

The performance of flex-rigid PCBs depends on that of substrate material of them that primarily contains flexible dielectric film and flexible adhesive film. As a leading type of flexible substrate material, flexible dielectric film mainly includes polyester (Mylar) that is usually used in low-end products, polyimide (Kapton) that is the commonest type, and fluoropolymer (PTFE) which is usually used in military and aerospace products.

As those three types of flexible materials are compared, polyimide features the highest dielectric constant with excellent electrical and mechanical properties and high-temperature resistance but is expensive and easy to absorb moisture. Similar with polyimide in terms of performance, polyester, however, features bad high-temperature resistance. Polytetrafluoroethylene is primarily used in high-frequency products with low dielectric constant.

Rigid-Flex Product Types

Rigid-Flex PCBs product

Single-Sided Flex: Single-sided flexible material with or without shield(s) or stiffener (one conductive layer).
Double-Sided Flex: Multilayer flexible material with or without shield(s) or stiffener (more than two conductor layers) plated through holes and HDI.
Multi-layer Flex: Multi-layer flexible material with or without shield(s) or stiffener (more than two conductor layers) plated through holes and high-density interconnect (“HDI”).
Multi-layer Rigid and Flex: Multi-layer rigid and flexible material combinations (more than two conductor layers) with plated through holes and HDI.

Rigid-Flex PCB Manufacturing Process

Rigid-Flex PCB Manufacturing Process

Material Preparation (Pre-Clean)

Production panels chemically cleaned, prior to application of circuit forming photoresist film, to ensure proper film adhesion. Conveyorised process utilizing thin core handling equipped systems to prevent damage to ultra-thin material cores.

Circuit Pattern Exposure

Photoresist coated panels, overlayed with circuit artwork patterns, exposed with collimated UV light to transfer circuit image(s) to production panels. Both sides exposed simultaneously if required.

Etch Process

Circuit patterns chemically etched using specialized thin core handling equipped conveyorized systems. Both sides of panels etched simultaneously if required.

Drilling Process

High speed, high precision, small hole capable, drilling systems create required circuit hole patterns in production panels. Laser based systems available for ultra small hole requirements.

Copper Plating Process

Fully automated electrolytic copper plating systems deposit required additional copper within plated through holes to form layer to layer electrical interconnects.

Coverlay Application

Polyimide Coverlays aligned and tacked into place on production panels prior to Coverlay lamination process.

Coverlay Lamination

Coverlays laminated to production panels under heat, pressure and vacuum to ensure proper adhesion.

Stiffener Application

Localized additional stiffeners (if required by specific design) aligned and applied prior to additional lamination process under heat, pressure and vacuum.

Electrical Test

100% netlist driven electrical test per IPC –ET-652. Simultaneous testing of all circuits for continuity and isolation. Both grid and flying probe test systems utilized.

Final Fabrication

Individual parts die cut from production panel using high precision male / female punch and die sets. Other methods include laser cutting, mechanical routing, steel rule dies and chemically milled dies depending upon specific design requirements.

Rigid-Flex PCB Design Guidelines

Rigid-Flex PCB Design

While the advantages of rigid-flex PCBs are well-documented, there are several design guidelines that need to be followed when it comes to manufacturing these PCBs. These include:

1. Determine The Number of Layers

Rigid-flex PCBs are made of alternating layers of flexible and rigid PCB Material. It is therefore important to figure out the exact layer count that is required. It is prudent to consult your electronics contract manufacturer early to ensure that all the requirements can be met.

2. Heat Sinking

Due importance needs to be given to having a heat dissipation mechanism in place. In the absence of it, the device performance can be impacted, and it may also result in damage to the device. The PCB needs to facilitate heat sinking.

3. Material Layup

Layup of materials is yet another crucial factor. This includes checking for:

● Minimum bend radii needed
● The UL flammability rating
● Impedance control
● RoHS certification
● Mechanical considerations, and more.

Material layup, in turn, impacts both cost as well as manufacturability.

Rigid-Flex PCB Applications

Rigid-flex Printed Circuit Boards (PCBs) are becoming increasingly popular for a variety of applications. Their flexibility and durability make them ideal for use in products that are subject to mechanical stress or vibration. They can also be used in space-constrained products, such as cell phones, wearables, and other electronics that need to be compact. Rigid-flex boards can also be used in medical devices and aerospace applications. In addition, rigid-flex PCBs can be used to create complex circuit designs that would be difficult or impossible to produce using traditional rigid PCBs.

Conclusion

Rigid-flex PCBs offer a number of advantages over traditional rigid PCBs and flex PCBs, making it the perfect solution for many applications. They are more durable, have higher electrical performance, and offer greater design flexibility. If you’re considering using rigid-flex PCBs in your next project, Please contact Unitepcb, we are an experienced printed circuit board manufacturer. We will provide you with the best products.

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