Rigid-Flex Printed Circuit Board: All You Need To Know

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Oakley Mae

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About Rigid-Flex Printed Circuit Board, We all know that choosing the best PCB type depends on your understanding of its design, benefits, and applications.

One PCB type that stands out and has many applications in electronics is the rigid-flex PCB. 

Surprisingly, a rigid-flex printed circuit combines the best features of rigid and flexible-board technology.

These flexible boards make them easy to install and perfect for small spaces. 

But what are their applications, and how is the fabrication process?

This article provides all rigid-flex PCB-related information. 

Table of Contents

What Is A Rigid-Flex PCB?

These boards combine the features and technology of rigid and flexible printed circuit boards.

In most cases, we’ll have multiple flexible circuit substrate layers attached to single or multiple rigid boards.

Surprisingly, the attachment could happen either internally or externally based on your design and intended application. 

Normally, the flexible substrate is created into the flexed curve during installation and manufacturing and will maintain its constant flex state for a long time.

However, rigid-flex PCBs undergo design in 3D space, making them more difficult to design than normal boards.

Without the 3D space, you won’t be able to fold, roll, or twist the board substrate to achieve your desired shape. 

Advantages of Rigid-Flex Printed Circuit

A printed circuit board

(A printed circuit board)

Employing rigid-flex, especially in portable electronics, will offer you the best of both worlds.

Apart from offering flexibility, these PCBs provide strength and stability that guarantees maximum durability.

Let’s consider the advantages of rigid-flex circuit boards below: 

Reduced Packaging

As mentioned, rigid-flex PCBs combine flexible and rigid PCBs into a single integrated unit. Therefore, you won’t need many wired connections; they’re usually eliminated. 

We noted that rigid-flex material would take only about 10% of weight and size compared to wired connections. Therefore, you can create lighter and smaller designs.

For example, a single rigid-flex PCB can fit in an area where several rigid boards and connectors won’t fit. 

Furthermore, these PCBs offer a tighter bend feature that offers interconnect solutions you’ll never find in other solutions. 

Higher Reliability

The only alternative to using rigid-flex PCBs is multiple rigid circuits. Unfortunately, with multiple rigid PCBs, you’ll require a lot of interconnects.

Surprisingly, this involves using connectors, contact crimps, and solder joints, which take up much space and might easily fail if you accidentally drop your device.

This could be dangerous, especially in industries like military and medical applications that require reliability and precision. 

Luckily, we have rigid-flex PCBs that offer higher reliability to vibrations and shocks to cover problems that could arise from using rigid PCBs.

Moreover, these PCBs have limited interconnect points, thus maintaining high performance even when you drop them.

Finally, the fact that rigid-flex PCBs are lightweight eliminates the likelihood of possible failures. 

Higher Capabilities

Generally, rigid-flex circuit boards are designed with flexible areas that offer a wide range of capabilities compared to rigid PCBs having wire interconnections.

To begin with, these PCBs can comfortably handle designs and transmission loads that need controlled impedance and high-speed signals.

Moreover, they offer high shielding levels for RF and EMI interference from external sources. 

Furthermore, rigid-flex PCBs work reliably and effectively even in harsh environments and applications. Also, they come with good chemical, UV, and corrosion resistance features.

Finally, they can function well in high temperatures of 200°C while at the same time effectively emitting the generated heat.

It Saves Costs

Besides rigid-flex PCBs having an easier assembly, they consume fewer components and materials. Therefore, expect a high-cost saving in your project.

Moreover, rigid-flex PCBs are always developed into lighter and smaller packages. Any customers purchasing them will only pay for the materials that go into the final assembly. 

Furthermore, most rigid-flex circuits can be designed with almost every connector and component.

Surprisingly, many customers have expressed satisfaction with how these circuit boards are easy to install or assemble.

They only have one way of installation, thus reducing any assembly or installation errors.

Rigid-Flex Printed Circuit Fabrication Issues

While manufacturing and designing rigid-flex PCBs, you need to consider some factors to account for the final circuit board’s size variations.

The flexible polyimide core usually shrinks after you etch away the bonded copper foil. Therefore, you must account for such variations during the design and manufacturing. 

Also, the final assembly will require you to bend the flex portions into shape.

Consequently, you might stress the flex laminations, thus causing stress fractures.

Rigid-Flex Printed Circuit Board Applications

A digital camera

(A digital camera)

Rigid-flex PCBs find application in many areas. Surprisingly, even some devices you’re using now use these circuit boards.

For example, you’ll find them in high-performance applications like medical devices and televisions. 

Moreover, they’re common in low-tech bendable applications like LED lighting and kitchen cabinets. We also noted their application in smart jackets, cell phones, and digital cameras.

Generally, since they’re flexible, we use them in tight and small spaces to minimize layout flaws. 

Rigid-Flex PCB Fabrication Process

PCB manufacturing

(PCB manufacturing)

Before starting the rigid-flex fabrication process, you must create a PCB design layout.

Generally, the rigid-flex process combines flexible and rigid board manufacturing technologies by stacking up their respective layers. 

Check out the PCB fabrication process below:

Base Material Preparation

The first step is to prepare the base material or laminate. Therefore, you must clean the laminate, which has the copper layer, whether or not it has an adhesive coating.

Pattern Generation

Next, you’ll have to generate the patterns. This is possible through photo imaging or screen printing

Etching Process

This step involves etching all the lamination sides with the circuit pattern. To do this, spray them with an etchant solution or dip them in an etch bath. 

Mechanical Drilling Process

For this step, you use precision drilling techniques and systems to drill circuit pads via patterns and circuit holes useful in the production panel. Therefore, we recommend the laser drilling technique. 

Copper Plating Process

This process involves depositing copper in the circuit holes. Consequently, you create an electrical interconnection between the circuit board layers. 

Cover Lay Application

Next, you imprint cover lay materials on the rigid-flex circuit board surface with screen printing. In most cases, you use polyimide film and adhesive. 

Cover Lay Lamination

You must ensure proper cover lay adhesion by laminating it under the required pressure, vacuum, and heat limits.

Applying Stiffener

If you need stiffeners on your circuit board, this is the time to do it. Also, you can carry out an additional lamination process after this. 

Board Cutting

This process involves cutting circuit boards from the production panel using specialized blanking knives or hydraulic punching methods. 

Electrical Testing and Verification

Circuit board testing

(Circuit board testing)

Finally, you test the boards to ensure they meet design specifications for quality, continuity, performance, and isolation. Therefore, we recommend using grid testing systems or flying probes. 

FAQ

What’s the difference between rigid, flex, and rigid-flex PCBs?

Rigid PCBs are the most common boards having an unbendable board. They’re green and reinforced with glass. On the other hand, flexible PCBs have the flexibility that enables them to bend and fold into various shapes.

Therefore, they can endure vibrations and disperse heat with ease. Finally, we have rigid-flex PCBs that combine the features of rigid and flexible PCBs. 

Which materials are used to develop rigid-flex PCB?

First, we use substrate materials like woven fiberglass, epoxy resin, polyimide, and polyester. Moreover, we apply copper materials as the conductor materials.

Furthermore, we include adhesives to improve the board’s service life. Finally, we apply cover layers and coats to offer a protective coating.

Are rigid-flex PCBs worth it?

Generally, using rigid-flex PCB is worth it and even better than traditional options. Surprisingly, you can bend and fold these PCBs to fit in smaller and tighter spaces. Also, the cost of using these PCBs is lower than that of traditional boards. 

Conclusion

As we have highlighted, rigid-flex circuit boards combine the features and technologies of rigid and flexible boards.

Generally, they’re flexible and thus easy to install in small and tight spaces.

Moreover, they find applications in high-performance applications like medical devices and televisions. 

Furthermore, you’ll find them in low-tech bendable applications like smart jackets.

Finally, these circuit boards are reliable and offer a cheaper approach than traditional ones.