Rigid flex PCBs are well-known and much preferred due to their ability to provide mechanical support as well as flexible connections in a single piece. Wondering what’s the primary reason behind their usage? Well, they are ideal for items that require both rigid and flex connections but have limited space.
If you’re new to the topic or want to learn about this in detail, this blog covers everything you need to know about them. Although rigid-flex PCBs are often more expensive to manufacture than regular stiff or flexible boards alone, considering their overall cost including printed circuit boards, cable and wires, assembly cost, maintenance cost and reliability, it is still the most cost-efficient solution for a lot of electronics applications.
Let’s get acquainted with rigid flex PCB fabrication. Once we learn about that, we’ll also discuss several cost-effective ways to use such designs in your products across many industries.
What Exactly Are Rigid Flex PCBs?
You can define rigid-flex PCBs as a circuit board that combines rigid materials and flexible materials. These materials consist mainly of FR-4 with flexible substrates like polyimide. This combination can give mechanical support and structure to components while allowing dynamic connections and three-dimensional routing.
Talking about its most common usage, flexible circuits can be fitted into stiff support structures without the use of connectors or wires thanks to rigid flex PCB fabrication. As a result, they are ideal for products that require reliability and flexibility in the smallest package or when space is limited.
Industries that use Rigid Flex PCB Usually
Rigid flex PCBs are common in industries where miniaturization, movement, and reliability are factors. Key industries include:
- Consumer Electronics: Also used in laptops, mobile phones, tablets, and handheld electronics where space can be tight but flexible connections are required. Their compact construction makes them suitable for wearable electronics as well.
- Automotive: for use in dashboard displays, sensors, engine control units, and driver assistance components requiring reliability against conditions of heat, vibration, or crowding.
- Medical: It is used in hearing aids, medical instruments, and other devices where flexibility and dependability are of the essence. Dynamic flex portions provide points of attachment to moving parts.
- Aerospace and Defense: Because of space and reliability considerations, widely used in guidance systems, radars, and other avionics. Rigid flex first appeared in the military/aerospace industry.
Main Factors that Increase Rigid Flex PCB Costs
Although rigid flex PCB fabrication technology does confer considerable benefits, the cost of fabrication tends to be higher than that for traditional boards. Some key considerations include:
- Layer Count: Adding layers raises the complexity and materials of fabrication. Layer needs must be carefully assessed to keep costs low.
- Technologies: The technologies used in rigid-flex PCBs will greatly affect the price. Since as stackup, blind and buried vias., etc.
- Stiffener: Stiffeners or extra layers may be needed to prevent the warping of rigid sections. Stiffener materials can be FR-4, polyimide or metal. Select stiffener materials carefully according to your requirements.
- Tolerances: However, tight tolerances like PCB thickness tolerance, plating tolerance, dimension tolerance, impedance tolerances, etc., make fabrication slow and expensive for rigid-flex PCBs.
- Special Materials: Special flexible materials like high reliability polyimide or rigid materials ceramic substrates can drive up the cost quite substantially.
- Batch Size: Prototypes or small runs are going to cost more per unit than large-volume production.
Cost-Reduction Strategies for Rigid Flex PCB Fabrication
Despite the higher costs, several strategies exist to make rigid flex PCB fabrication more affordable:
- Design Optimization: Rigid flex Layouts Simplify wherever possible to avoid unique materials. Standardize designs across product generations.
- Panel Utilization: Panels with several PCBs make better use of materials and reduce costs. Careful panel design minimizes waste. Please note the width of flexible material is 250mm and 500mm normally.
- Standardized Materials: Aim to use industry-standard materials for rigid/flex substrates instead of exotic materials if possible. The most usual rigid PCB material is FR-4 material, and flex PCB material is polyimide material.
- Reduce Layer count: Try to reduce layer count count if possible, especially the count of flex layers, which will increase the price a lot.
- Combine PCBs: Rigid-flex integration of multiple printed circuit boards can save the cost of connectors. Try to combine more circuit boards together and connect by several flexible parts.
- Build Volume: Capitalize on bulk-purchase discounts by building units in large production batches rather than small lots.
- Embed Passives: Embedded components design can be sued. This not only reduces part cost but also assembly time and costs vs. surface mounting the same components on a rigid or flex substrate.
- Board Thinning: Thinning thick, stiff regions means cheaper materials and is easier with rigid-flex fabrication.
- Use Cheaper Materials: With advances in material science, even cheaper flexible and rigid substrates are developed.
- Evaluate Fabrication Partners: Forge strategic alliances with rigid flex PCB specialists to leverage their knowledge and experience in searching for cost reductions.
Rigid flex printed circuit board technology offers numerous benefits. You can use it when dependability, compactness, and flexibility are all significant concerns. Rigid flex PCB fabrication costs slightly more than regular boards regarding unit cost with the same dimensions and layer counts.
However, as mentioned at the start of the article, careful design and collaboration with specialists keep the price low. Planning to opt for rigid flex PCB fabrication? Opt for the best partner in terms of design, materials, volume, and fabrication. Consider Rigid Flex PCB fabrication which allows it to be economically integrated into a wide range of new electrical goods.
Common Applications of Rigid Flex PCBs
When done wisely, rigid Flex PCB fabrication enables several additional innovative use cases. It can also help you develop products where reliability and flexibility are important factors:
Using embeddable flexible circuits, rigid flex PCB fabrication allows wearables to attach themselves to the unique shapes and sizes of the human body. This allows for more comfortable, ergonomic designs in wearable tech. Rigid areas serve as mounting points and for strength, while the flex elements are connected to your sensors and components in a dynamic design.
Internet of Things (IoT) Devices:
With smaller and more space-locked IoT devices, rigid flex offers flexible antenna connections as well as 3D routing while still providing a fixed frame for processors and wireless modules. The rigid flex PCB fabrication fits the envelope shape precisely. The result is improved RF performance and durable but inconspicuous product packaging.
Rigid flex printed circuit boards provide reliable connections for products that must combine the seamless integration of electronic controls or displays with mechanical actuators. The rigid regions attach to motors or mechanical controls and the dynamic flex circuitry connects with electronic components and sensors.
Backplanes and Test Fixtures:
Rigid flex PCBs are an excellent choice for those applications which require interconnected printed circuits to be precisely aligned and highly reliable, such as backplanes or test fixtures. These stiff portions allow precise alignment of the printed circuit board, while flex circuits achieve dynamic interconnects without any cables. As a result, the mechanical assemblies are robust and compact.
For products requiring many high-density interconnections with limited space, rigid flex PCBs provide connections between several layers of stacked-up rigid circuit boards. This eliminates the need for individual connectors, simplifies assembly, and saves space. The rigid sections ensure precision alignment, while the flexible portions make high-density stacking connections possible.
Rigid-flex PCBs provide a conformal solution for mounting and interconnecting sensors in applications involving various curved surfaces or dynamic structures. The stiff sections provide support and position the sensors, and the flexible regions fit to 3D surfaces. This makes it possible to embed flexible sensor arrays into structures.
Factors in Cost-optimized Rigid Flex PCB Design and Production
To successfully implement a cost-optimized rigid flex printed circuit board design, engineers should follow these steps:
- Conceptual Prototyping: Formal design can be preceded by exploration of the design space through simplified prototyping and simulations.
- Set Goals for Optimization: Focus on finding trade-offs in cost, manufacturability, or performance.
- Research Design Standards: Apply existing design guides for the industry to proven rigid flex constructions.
- Select Manufacturer Early: early involvement of a qualified rigid flex vendor will influence design for manufacturability.
- Solicit Cost Reduction Ideas: Take advantage of the manufacturer’s expertise and find ways to cut down on fabrication costs.
- Pursue Cross-Discipline Collaboration: Make sure the system is optimized by consulting specialists in enclosure design, mechanical design, and electrical design.
- Build Prototypes to Verify: To ensure that design performance, manufacturability, and cost targets are met before full production, build prototypes incrementally.
If these best practices are adhered to, engineers can create cost-optimized rigid flex PCBs that utilize the synergies of integrated flex/rigid technology while driving down total system cost.
- Choose Reliable Manufacture: Since rigid flex PCB fabrication is very complex, very advanced equipment and very skilled engineers and production staff are needed, so we should find a reliable supplier for our rigid-flex circuit board manufacturing.
In addition to space savings, rigid flex PCB fabrication provides opportunities to enhance reliability in electronics products through these design approaches:
Dynamic Flex Interconnections:
Rigid flex PCBs have flexible circuits, which make a motion and vibration more accommodating than soldered connections or cables. It relieves mechanical stress and failure for dynamic components and assemblies.
With noise isolation like a coaxial cable, critical signals routed on inner flex layers surrounded by ground planes are also transmitted. This reduces interference, allowing for more reliable signaling.
Improved Thermal Management:
The use of rigid and flexible materials permits heat sinks, thermal vias (which draw heat away from a hot component), and other materials to be placed wherever they are needed. This allows for cooler running temperatures, improving reliability.
The encapsulated construction of rigid flex printed circuit boards eliminates exposed interconnections. This in itself increases resistance to environmental threats such as moisture, dust, and more.
If a certain number of PCB assemblies can be integrated into one rigid-flex board, then this reduces the total interconnections relative to using connectors. This raises overall reliability.
Tips in Rigid Flex Design and Manufacturing
To design and fabricate cost-effective and reliable rigid flex circuit boards, both designers and manufacturers should pay attention to the following points:
Design for Manufacturing:
Design for manufacturability is also promoted through early cooperation with manufacturers. Rigid flex PCBs more easily attain the targeted quality and reliability.
With rigid flex PCBs, test points and fixtures are combined with the access needed to simplify reliability testing during production.
Reduced Hand Soldering:
Rigid flex vs hand soldering means you can use assembly tools and processes suitable for high-volume production. This improves repeatable quality.
While rigid flex PCBs can enhance reliability in many ways, designers should also be aware of unique potential failure modes:
Flex regions should not have their specified bend radius repeatedly bent beyond. Otherwise, conductor cracks or insulation failures can occur. Careful mechanical modelling helps mitigate this.
Where rigid and flex sections meet can be subject to stresses capable of causing plated through hole vias to crack. Via structures should be reinforced.
All rigid and flexible materials do not adhere equally well. Incompatible material selections result in lower bond strength and even possible delamination.
Over time, atmospheric moisture can infiltrate the polymer materials used for flex circuits. This will result in reduced insulation resistance and outgassing problems.
It is not only possible through careful design, process control, and protective coatings to exploit the natural advantages of integrated rigid-flex PCBs in achieving higher levels of reliability; attention paid to mechanical testing can also help prevent unique failure modes.
De-risking the application: develop a comprehensive validation plan centered on proving how well an optimized rigid flex PCB design works in demonstrating its reliability. Areas to emphasize during qualification include:
- Thermal Cycling: Thermomechanical risks are exposed when evaluating functionality under temperature cycling.
- Vibration and Shock: Because rigid-flex constructions may have unique vibration modes and resonances, testing is necessary.
- Humidity-Temperature: At high temperatures, moisture exposure reveals possible absorption and connection problems in the material later on.
- Flexural Fatigue: Measuring flex circuit robustness against required bend cycles and radii avoids conductor cracking.
- Drop/Bend/Twist: Abusive non-operational handling tests point to potential problems for products that are subjected to grueling mechanical treatment.
- Environmental Testing: Test resistance to dust, splashing liquids, or harmful chemicals (especially at flex/rigid interfaces).
- Electrical Testing: During testing, perform a detailed root-cause analysis of all electrical failures.
- Standards Compliance: Designs are validated against the industry-established performance and reliability requirements.
In conclusion, using testing and process reviews to conduct a complete design validation plan, engineers can be assured that the rigid-flex PCB fabrication design meets reliability targets before high-volume production. This reduces the risk of implementing rigid-flex technology for mission-critical or safety applications.