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The Differences Between Rigid, Flex, and Rigid-Flex Printed Circuit Boards

Printed circuit boards (PCBs) connect electrical components together using discrete wiring, resulting in a complete and functional unit. PCBs can be as simple as one or two layers of copper circuits, but are far more likely to have many layers of circuitry. The layers are necessary for the designer to “route” all of the circuits between the components – where one, two, or even eight layers of circuitry may not be enough to complete their design and make all of their connections.

While all circuit boards perform the same basic function as a substrate for the electronic components, the design and materials of their construction are the key distinguishing points. Circuit boards are custom-tailored to their particular application.

The three main types of PCBs are rigid boards, flexible circuits (or flex), and rigid-flex. This blog post will provide a clearer understanding of the differences and similarities between each type of PCB.

Rigid PCB vs. Flex PCB

The most notable difference between rigid PCBs and flex PCBs can be inferred from their names. Rigid PCBs are inflexible, while flex PCBs can be bent or otherwise shaped to fit inside the designated system. Flexible circuits, when designed correctly, can also be flexed for hundreds of thousands of cycles repeatedly without failure. The increased versatility of flex boards typically comes at a higher cost, but they are essential for applications with limited space requirements, such as consumer electronics, medical devices, space and automotive applications.

Rigid circuit boards are very popular largely due to their low cost. In conventional electronics, and particularly in consumer electronics, with greater space availability, manufacturers can save significantly by using rigid circuit boards. However, flexible PCBs are beginning to siphon market share from rigid circuit boards due to their versatility, among other advantages, such as:

  • Flexibility. Flexible circuits can be bent, folded, and even creased to fit the end application, giving the designer the ability to have the circuitry fit the device, rather than the end device being built around the electronics and circuit boards. Flexible circuits are ideal for wearable electronics, for example.
  • Connectivity. Flexible circuits provide greater connectivity between other circuit boards, electronic components and the user interface in electronic packaging. They can even provide connectivity in dynamic flex applications where the flexible circuit needs to flex continuously over the life of the device, so they are used extensively in laptop computers, foldable electronics, and display connectivity.
  • Reduced weight. A lower-weight circuit board results in a lighter end product, which is essential in today’s electronics market where small, lightweight devices are preferred by electronic device designers and consumers. Flexible circuits are ideal for unmanned vehicles and drones, due to their very light weight.
  • Durability. While rigid PCBs are typically thicker and fairly strong, flex PCBs absorb shocks and vibrations much more effectively than rigid PCBs. This contributes directly to long-term reliability, product life and functionality. Flexible circuits are used extensively in medical electronics, missile guidance systems, weapons, satellite and other applications requiring excellent environmental survivability.
  • Resistant. While rigid PCBs are at risk of damage or warping from heat, chemicals, or radiation, flex PCBs are much more resistant to these detrimental environments. This explains their wide application in today’s automotive electronics.

With the differences between rigid and flexible PCBs in mind, we will now compare these PCB types with their hybrid counterpart, the rigid-flex PCB.

Dynamic Flex - rigid flex pcb

Rigid-Flex PCB vs. Rigid and Flex PCB

As its name suggests, the rigid-flex PCB is a hybrid of both rigid and flex PCBs, and features the great qualities of both while eliminating many of their individual limitations. A rigid-flex PCB incorporates flexible materials in conjunction with rigid materials by layering flexible circuit substrates inside of the rigid circuit board materials, ultimately combining the versatility of flexible circuits with the stability, strength and circuit routing densities of rigid PCBs. This hybridization opens up a spectrum of possibilities for much more complex and mechanically challenging designs.

Rigid-flex PCBs are a means to streamline the electronic design, by eliminating flexible cables, connectors and discrete wiring. The electrical performance of a rigid flex PCB is enhanced compared to its counterparts, because the circuits are integral to the overall construction. All of the electrical and mechanical connections are internally contained within the rigid-flex PCB, providing the electronics designer with much improved service reliability and electrical performance.

While they do typically arrive at a higher cost than their flex and rigid board counterparts, the reliability, weight reduction, strength and space-saving advantages of rigid-flex boards are often ideal in certain applications, and outperform any other electronic packaging techniques. Ultimately, rigid-flex PCBs provide the best benefits of rigid and flex PCBs in one solution. Applications where rigid flex PCBs excel are:

  • High-reliability applications. If an assembly will be exposed to excessive or repeated shock, or high vibration environments, connectors with flexible cables are more likely to fail. Rigid flex PCBs provide great reliability even when subjected to extreme vibration and shock applications.
  • High-density applications. Within a small enclosure, it’s sometimes impossible to accommodate all of the cables and connectors that an electronic PCB design would require. Rigid flex boards can fold into very small, and very thin profiles, offering substantial space savings in these instances.
  • Five or more rigid boards. If your application will ultimately involve five or more rigid boards connected to one another with flex cables, an integrated rigid flex solution is often the optimal and most cost-effective choice.

mri machine uses rigid flex pcbs

Rigid-Flex PCB Capabilities at Printed Circuits

The applications of rigid-flex PCBs are extensive, and their implementation is growing across industries ranging from automotive, medical, military, and many more.

Based in Minneapolis, Printed Circuits is centrally located in one of the world’s largest flexible circuit manufacturing hubs. With more than 40 years of manufacturing experience in advanced circuitry, we pride ourselves on the quality and precision of our rigid-flex products and services. For more information about rigid, flex, or rigid-flex PCBs for your application, contact us today to learn more.

How to Choose the Right Rigid Flex PCB Manufacturer

How you package your electronic device is one of the more critical decisions you can make as a designer.

There are times when a conventional hardboard is the best, most robust solution at the lowest possible cost. Then there are times when a flexible circuit will provide you with greater creative control in your design – allowing the function to follow your desired form factor.

But, there are certain cases where neither a conventional hard board nor a flexible circuit is the ideal fit for a given electronic application. Conventional hard boards provide you with increased routing density – but no flexibility. Flexible circuits are flexible, but have limited routing density relative to hard boards, usually just a few layers or less, and often limited by stiffener placement as well.

To get the most routing density and still get some level of flexibility/folding of your design, rigid flex is the best packaging solution.

Rigid flex printed circuit boards (PCBs) serve as an innovative and versatile solution for more complex circuit designs. These boards combine the characteristics of both flexible and rigid circuit boards, meaning that they can be folded to fit into a space or device, or used in applications where they must be folded repeatedly (known as “dynamic flex”). In either case, the rigid portions of the circuit provide high circuit densities as well as a stable and rigid surface on both sides of the board for your components. This combination is ideal for ensuring structural integrity even throughout highly demanding environmental conditions.

rigid flex pcb

Some applications where rigid flex circuits excel over conventional hard board and flexible circuits:

  • High vibration environments – where traditional connectors and flex cabling will fail in time
  • High shock environments – the flexible circuits are buried within the hard boards, for the ultimate in packaging reliability, withstanding tens of thousands of g’s without failure
  • Ultralight packaging – rigid flex circuits can be built with very thin, ultralight components providing you with circuit density AND lightweight design
  • Lower cost – when your design includes four or more hardboards connected with connectors and/or flexible cables, a rigid flex design can often cost less (see our rigid flex cost estimator)

Once you have decided to investigate rigid flex packaging for your design, it is time to locate a fabricator who can work closely with you to make your concept a reality. Unlike with conventional hard boards or flexible circuit designs, the relationship between the rigid flex designer(s), the fabricator and even the assembler is MUCH more collaborative. Remember, your board will be for a three-dimensional application, requiring mechanical engineering skills. It also may have electrical requirements with dissimilar materials, requiring electrical engineering skills.

Mechanical engineers, electrical engineers, PCB layout engineers, CAD engineers, assembly line engineers and your fabricator’s front-end engineering department work together to produce a successful rigid flex PCB product.

Material selection, physical stack up, signal integrity requirements and design rule constraints all become more critical in rigid flex design. As there are many factors to consider, it is crucial to select a PCB manufacturer who will carefully analyze your application so that your needs are adequately met.

Here are some starter guidelines on how to successfully partner with the right rigid flex manufacturer for your needs.

How to Find the Right Rigid Flex PCB Manufacturer

When selecting a rigid flex PCB manufacturer, consider these essential factors:

  • Experience and expertise. Manufacturing rigid flex PCBs successfully increasingly requires higher-end equipment and software that analyzes and predicts material movement. Therefore, selecting a manufacturer with ample proof of each of these resources is crucial. Additionally, while many PCB manufacturers offer rigid, flex, assembly, and rigid flex boards, it is important to partner with one with an extensive expertise in rigid flex to ensure they have the necessary skills and knowledge to meet your project requirements and standards.
  • Capabilities for PCBs with UL 94 V-0 flame ratings. Another way to assess a potential rigid flex PCB partner is to find out whether they offer boards with UL 94 V-0 ratings. This is especially important for medical and industrial applications, or anyone whose insurance carrier requires UL certification as a condition of coverage. Additionally, UL ratings are notoriously difficult to obtain with rigid flex constructions, and it saves a lot of time and effort if your manufacturer can provide pre-approved, UL-certified rigid flex PCBs.
  • Impedance requirements. Modeling and manufacturing impedance-controlled circuits on rigid flex boards is more demanding than doing so for flexible circuits or hard boards. Impedance circuits that transverse the flexible areas of the part and the rigid sections need to be modeled for both structures. Dielectric values supplied by material manufacturers can be inaccurate, and online free modeling software usually returns erroneous values, and can only model simple trace to plane structures. If impedance is important or critical to your design, you need to find a supplier who will work with you in the beginning to model the requirements in your board, and one that has the software to help you model your requirements. It is also important to choose someone who will test your boards at the end of your build to make sure they match the impedance values that you want. Controlled impedance, without testing the results, is not really controlled at all.

At Printed Circuits, we specialize in providing rigid flex PCB solutions. To further expand our product offerings and capabilities, we obtained UL 94 V-0 flame ratings for an extensive, representative sampling of our constructions. By doing so, we can offer cost-effective, fully-compliant boards without the expense and time required to get individual certification. We have the software, material libraries, experience, and expertise to help you achieve the impedance values you want for your design, and then have the test facilities to verify that we met your requirements.

Inside a Clinac® Radiation Machine

Cost Factors to Consider

While experience and dedication to quality are among the most critical factors in selecting a rigid flex provider, cost should also be considered.

In general, it is well-known that rigid flex PCBs are more expensive than either hard boards or flexible circuits. The raw materials (such as no flow prepreg, adhesiveless flexible laminates) and specialized construction components for specific operating requirements (such as thicker flex dielectrics for impedance layers) are key contributors to the higher cost involved. However, there are constructions and methods that you can use to limit those costs.

The Printed Circuits team created a guide—Valu Builds for Rigid Flex—to help you navigate the process of designing and selecting cost-effective PCBs. It provides the lowest cost, as well as the most robust and stable rigid flex design guidelines. Additionally, you can check out our Rigid Flex Cost Estimator to receive a cost estimate of your rigid flex design before you start. It will give you a quick go/no go estimate on what your design might cost in low volume production. While not an exact quote, this tool is designed to make it simple to determine whether a rigid flex PCB is feasible for your project.

Contact Printed Circuits for Your PCB Needs

If you have determined that a rigid flex PCB would be a great choice for your project, there are several factors to consider before partnering with a manufacturer, including experience, available resources, manufacturing capabilities, and cost requirements.

At Printed Circuits, we understand that when customers opt for rigid flex solutions, they are looking for excellent quality and great long-term value, which is why we have spent decades refining our equipment, engineering support, and technology to optimize it for rigid flex packaging solutions. Since 1997, we have served the medical, aerospace, military, and industrial and commercial industries with high reliability rigid flex PCBs.

Our highly-collaborative design process begins with design assistance services to help you create the design that suits your needs. Our technicians and state-of-the-art equipment then build your circuit to your exact specifications. We are certified to the military performance specification MIL-PRF-31032, MIL-P-50884, ISO 9001:2015, ITAR, and the JCP 4532 standard, so you can trust us to provide high-quality PCBs.
Contact us or request a quote today to see how our rigid flex PCB solutions can suit your unique project and design needs.