For most of us, telling the difference between a flex board and a rigid-flex board design needs to be effortless. Well, it all is until it is not. So let us try this: enumerate all the differences you can think of – can you? I thought not.
However, understanding the distinction between flex and the rigid-flex board can make or break your PCB design. You must navigate all the intricacies and master the ruses involved if you want a functional and efficient PCB for your application. But first things first, what is a flex board design? What is a rigid-flex PCB design?
This article seeks to exhaustively tackle the difference between flex board design and rigid-flex design.
What is a Flex Board Design?
A flexible PCB design, often called a flex board design, comes well patterned (printed circuitry) with components that use flexible-based materials. It can either have or lack a cover-lay material.
Like you, most electronic engineers have gotten accustomed to rigid PCB designs. However, a significant trend shift has increased the flex circuit design. While not necessarily a new concept, you will find most contemporary electronics possessing flex circuits. Your smartwatch, printers, mobile phone, keyboards, etc., represent some of the most common electronic examples with flex PCBs.
Flex board designs in other scenarios also possess stiffeners. Such instances happen when your application area demands it. However, unlike many other people, you need to avoid confusing this with rigid-flex PCB design. The two represent two entirely different things.
What is a Rigid-Flex Board Design?
A rigid-flex PCB implies a board that uses rigid and flexible board technologies when deployed. You will find such a board comprising several layers of flex circuit substrate that get attached to more rigid boards (externally or internally).
Your application area often determines the design type, though the flex substrate by design constantly bends. Because of this, you will find it formed in the flexed curve during fabrication or installation.
Another vital point to consider entails its extra challenging design environment compared to the conventional rigid boards. In most cases, you must design a rigid-flex PCB in a 3D environment that provides more spatial efficiency. As a result, you as the engineer or designer can twist, roll, and fold the flex substrate to realize the intended shape for the anticipated application.
Differences Between Flexible PCB Design and Rigid-Flex PCB Design
Considering that the days of rigid printed circuit boards as the sole PCB design option no longer exist, understanding both the flex and rigid-flex PCB design becomes imperative as an engineer. You have to grasp the details about each and the points of departure for each to successfully design a suitable printed circuit board for your unique application.
So, do you want to design a flexible PCB or a rigid-flex PCB but unsure of where to begin? Consider the following guidelines.
Flex PCB Design Guidelines
Knowing the Bendability of Your Flexible PCB
Flexible circuits offer the unique benefit of bendability for challenging application areas requiring constant flexibility. However, as the designer, you should understand how many times the flex PCB will bend, the extent of the bend, and the number of bend times in the application. Such information determines whether to settle for a static or dynamic flex board.
A static flex board implies a flexible circuit that needs to bend upon installation, though it will only bend or flex not more than a hundred times post-installation. On the other hand, a dynamic flex circuit proves more robust. Unlike the static flex board, it must constantly bend and withstand more than tens of thousands of flexes or bends. You will mostly find dynamic flex circuits applied in military and spacecraft applications.
Another crucial aspect to consider concerning the flexibility or bendability of your flex PCB entails the bend radius. The bend radius implies the minimum bend amount of the flex area. Therefore, you must always identify the bend radius early during the design phase to allow for the design to accommodate any amount of bends without subjecting the copper to any damage. So how do you calculate the bend radius?
Consider the number of layers in your flex PCB to calculate your bend radius. For instance, a single layer needs to have an x6 flex thickness, a double amount of thickness for a double layer, and x24 flex thickness for a multilayer flex board.
Consideration for Laying the Bend Radius
- Avoid 90-degree bends that otherwise cause high strain
- Avoid placing plated through-holes in the bend area
- In multilayer flex circuits, stagger the conductors to achieve greater effectiveness
- Conductors measuring less than ten mils need to get placed in the neutral bend axis because of the absence of compression or tension during flexing
Heat-Forming Flexible Printed Circuit Boards
In most cases, the need for heat-forming requires a steel jig. The steel jig forces the PCB board to lie in one specific way before getting into an oven. Heat-forming has a significant advantage in producing a tighter bend radius. However, you can only use it primarily for a more straightforward installation process as much as the tighter bend radius achieves.
Slots and Cutouts in the Bend Area
You can always minimize the bend area or region when it lacks traces. However, the bend radius needs to get minimized by inserting slots or cutouts. Cutouts reduce the number of materials for the bend. It is also possible to seek a different alternative by removing some flex sections without circuitry. However, it would help if you carried it out lengthwise, also needing a routing afterward.
Understand your Flexible PCB Materials
Most flex PCBs use polyimide as the main material for the core and cover-lay layers. Flex materials provide enhanced properties than rigid printed circuit boards. Another crucial benefit of flex material is its uniform thickness with an enhanced dielectric constant of 3.2 to 3.4. The absence of woven glass reinforcement eradicates Dk variations. Similarly, you will get polyimide with a uniform thickness owing to its unique manufacturing process (cast) – a typical layer has a thickness ranging from 0.5 mils to 4 mils.
It is also important to note that polyimide cores (flex) possess either rolled or electro-deposited annealed copper. The copper comes thin and proves ideal for both static and dynamic applications. One of the most common electro-deposits of copper measures 0.5 and 1 ounce, though the limit is 2 ounces. You tend to get the best mix of the thinnest construction.
Flex material types can come in either adhesive-based materials or adhesive-less materials. Adhesive-based materials use acrylic adhesive to bond the copper to the polyimide. Conversely, the adhesive-less type features the copper cast directly to the polyimide. Adhesives, in general, get used to laminating the layer of copper together with the core (polyimide). But in using an adhesive, you can quickly get cracks forming in the copper plating, especially within the vias. It arises because the acrylic adhesive tends to become soft upon heating. As such, you need to integrate tear-drops and anchors when designing.
Drawbacks of Utilizing Adhesive-Based Materials
- It forms cracks within the copper plating, as explained above.
- Incorporating adhesive thickens the copper-clad laminate though eliminating it also leads to thinner laminates.
- All adhesive-based materials tend to absorb environmental moisture. Because of this, it proves best for a system that exposure to the outside environment.
- The core’s thickness can be reduced post the fabrication process, leading to errors in dimensions.
In trying to address the issues outlined, the idea of adhesive-less construction ensued. Some of the critical features of this material include the following.
Adhesive-less Material Features
- Enhanced flexibility because of reduced flex thickness
- A diminished flex thickness owing to the eradication of the layer of adhesive
- An enhanced controlled impedance, especially on signal attributes
- It is well-suited for application in extreme or harsh environments
- It features a better temperature rating than an adhesive-based material
Another crucial point for you to consider regarding understanding your flex materials for your flex PCB entails its looser outline tolerance to other boards. As a result, flex materials have lesser dimensional stability compared to rigid ones. Further, based on the tolerance profile, it may become necessary to use a laser or hard tool cutting, which may prove too expensive.
Similarly, chemicals within the adhesive can become soft upon heating. Therefore, it becomes essential to enlarge your pads as much as possible. Here you can use anchors, spurs, and tear-drops to achieve stability of the outer layer besides reducing stress in your design.
Monitor the Flex Trace Routing
The layout of your circuitry can break or make your printed circuit board. For instance, when you consider the bend radius dimensions, a larger one becomes preferable to the sharp angles, which otherwise shorten the board’s lifespan. Additionally, it would help if you avoided the I-beaming to reduce the copper circuit-thinning stress effect. Remember, curved traces results to lower stress compared to angled traces. Also, keep your traces at a perpendicular angle to that of the general bend. Further, stagger the traces when you place them in two-plus layered PCBs (bottom and top staggering always works)
Position the Flex Layers in the Stack-Up’s Center
It primarily applies to rigid-flex PCBs where you must place the flexible layer between two rigid layers. However, milling the part becomes necessary to expose the flex part. Such an arrangement offers protection to the flex part from exposure to plating of the outer layer. It is an arrangement that also simplifies the manufacturing process besides enhancing control and impedance in the flex region.
However, it is possible to etch away the flex layer as a segment of a different process. It will allow for extra protection.
Mitigate Risks in the Flex Vias
Vias tend to break peel or sometimes crack in flex PCB designs. However, you can always mitigate this by tear-dropping the vias while incorporating the tabs and the anchors. Further, enlarging the annular rings also come in handy.
Benefits of Flex Circuit Boards
If you want to design and use a flex circuit board, you can enjoy a myriad of advantages. It includes ease-of-use, function, fit, etc. Below, some key benefits of flex PCBs.
Ease of Use
- Flex PCBs have few design constraints, with design flexibility to fit any shape or type of device.
- Its motion range permits printed circuit boards to suit every application.
- The reduced mass of flex PCBs limits risks in rough environments like one with consistent vibrations.
- Flex PCBs also have reduced errors otherwise found in most standard printed circuit board assemblies.
- You also get to enjoy a limited weight aspect when using flex PCBs as no extra cables, connectors, and wires exist.
Cost Reduction
The overall installation costs are low
Flex PCBs eliminate a myriad of steps in production, thereby shortening the total turn-time and reducing the cost.
Rigid-Flex PCB Design Guidelines
As one of the fascinating PCB types in the contemporary world, rigid-flex PCBs fuse both elements of flexible circuits and rigid PCBs. The hybrid’s fabrication process mimics that of a conventional hardboard circuit. However, some layers are flexible circuitry and run along through rigid or hardboards. As a designer, you need to consider that the fabricator will have to incorporate plated through holes to ensure a compelling connection between flexible and rigid regions of the circuitry.
Once you factor in such configurations, you can develop a rigid-flex circuit capable of getting assembled as a hardboard PCB. Further, it will also fold besides fitting into the anticipated electronic product without constraints.
A rigid-flex PCB also proves ideal for dynamic flex situations or applications. It can handle a hundred thousand plus flex cycles without any mishaps if well-designed. What is more? You can integrate both the flexible and rigid substrates into a unit capable of further getting manipulated into a three-dimensional subassembly.
Design Guidelines for Rigid-Flex PCBs
A rigid-flex PCB design closely resembles that of a hardboard or rigid design. However, with an experienced eye, you will notice that the flexible layers extend into the board’s rigid areas. Everything notwithstanding, however, a rigid-flex design will require a similar set of requirements to a rigid PCB when it comes to fabrication. For instance, you must submit the Gerber file, nomenclature, solder mask layers, cover-layer, rout files, etc. However, other distinct points of departure exist as well.
But what should you consider when designing a rigid-flex PCB?
Considerations
Material Layup
Material layup can heavily influence a rigid-flex PCB’s total costs, performance, and manufacturability. As a designer, spending a considerable amount of time determining the best material becomes essential. For instance, resistance, controlled impedance, and other requirements like current-carrying can, in turn, affect both material selection and copper weight.
It would help to always collaborate with us at RayMing PCB and Assembly or any other ideal PCB fabricator for material selection deliberations. For instance, variables like costs vis-à-vis cost implication and performance can influence your rigid-flex design. Another essential aspect to consider entails the accepted standard of 20 or fewer layers for rigid-flex boards. However, you can also have rare occasions to design the PCB with more layers. Further, the rigid sections can vary in layer count, provided the material layup and thickness prove similar.
Component Placement
Plenty has happened recently when it comes to design rules. Fresh rules for component placement on a rigid-flex PCB design allow increased freedom, unlike before. For instance, you can now place components within the flexible area of the PCB. Together with a multilayer approach, such an approach allows for more circuitry buildup in your rigid-flex PCB design. However, with greater freedom comes more challenges of holes and routing that you must contend with.
For instance, you cannot place vias or components near the bend line as the flexible segment of the circuit due to the likelihood of material stress. It is also imperative to utilize more thru-hole plating besides bolstering the pad’s support with extra cover-lay to anchor the PCB pads.
Electromechanical Factors
It would help to think of the potential electromechanical factors that can influence both the rigid and flex parts of the PCB. Here, aspects like the bend radius to thickness ratio become important. Always keep the bend radius at least ten times the flex-circuit material’s thickness. It is also vital to develop a “paper doll” to know the bend areas.
Another crucial aspect entails avoiding any stretching of the flex section of the PCB along its inner bend or outer bend. For instance, enhancing the bend angle over 90 degrees also increases its stretching from one end and compression on another flex circuit point. It would be best to consider the type and thickness of the conductor within the bend area. It is possible to reduce the mechanical stress and thickness by reducing the plating on conductors and utilizing pads-only plating. Additionally, heavy gold, nickel, or copper plating reduces flexibility at the bend region, allowing for mechanical stress and potential fracturing.
Teamwork Aspect
Recent printed circuit board design tools provide aspects that allow for the management of several layer stacks, checking design rules, visualizing the three-dimensional electromechanical designs, and simulation of the flex circuit operations. However, the enhanced aspects of the tools notwithstanding, you must incorporate teamwork (fabricators and your team) exceedingly early in the project’s design phase to become successful.
Differences between Flex Circuit and Rigid-Flex PCB and their Production
| Flex Circuit | Rigid-Flex PCB |
| It only has flexible circuitry and thus only flexible substrate or polymer film containing the conductive circuit. | It incorporates both flex and rigid materials by layering flexible substrates within the rigid material. |
| Moderately low cost of production | The high cost of production |
| The basis for the development procedure of rigidized flex fabrication | Requires an FPC overlay while the FR-4 material loads up during its manufacturing |
| Application areas rest on consumer electronic products like cell phones, etc. | Application areas feature satellites, the military, and other high-quality request areas. |
| A simpler quality control process compared to rigid-flex PCB | A more troublesome quality control process |
| Mostly has a flexible film created from polyester, polyimide, and PTFE | Possesses flexible cement film and a flexible dielectric film |
| Offers high flexibility though with differing longevity based on the type (dynamic and flex) | Lesser flexibility though durable |
IPC Flex Circuit Standards
Quality verification proves an important aspect of the manufacturing process of flex and rigid-flex PCBs. However, various industry standards exist as benchmarks for any new PCB product. As a PCB designer or engineer, you can either test or use other guidelines to check the quality of your flex and rigid-flex PCBs. But why not use the IPC or Association Connecting Electronic Industries guidelines? Below are some of the best IPC guidelines to start acquainting yourself with.
IPC-6013 (December 2013)
It first came to the fore in 2013 and gave the performance and qualification specification for flexible circuits. It supersedes some of the earlier IPC standards, including the first IPC-6013 established in 1998. The IPC standard specifies diverse test methods, including bend, thermal, and impedance examination or testing. It also entails quality assurance like sample test guidelines and coupons for quality conformance and acceptance tests.
IPC-2223
It offers guidance on picking rigid-flex interface and adhesive materials. You also get tips about flex vias and plated thru-hole.
IPC-FC-234
It is a quality assurance standard that offers insights regarding PSAs or pressure-sensitive adhesives for flex PCB assembly. The guide gives information on the types of adhesives available besides suggested processes for their correct use. It also provides their weaknesses, strengths, and limitations.
IPC-2223 (Sectional Design Standard for Rigid-Flex/ Flexible Printed Boards)
It is a quality assurance guideline document commonly used in conjunction with IPC-2221. IPC-2223 outlines the design specification for flex printed circuits and offers information on interconnecting structures and component mounting.
IPC test methods apply to circuit boards. Such circuit board testing comes as an environment and application-specific process. It often proves a solid foundation for designing reliable, flexible circuits. But as a design or engineering beginner, starting with IP-FC-234 and IPC-2223 can prove a decent place to start from. You will have assurances of reliability for your flexible PCB.
Introduction
Printed circuit boards (PCBs) are essential components in most electronic devices and equipment. They provide the foundation to mount and interconnect electronic components using conductive tracks and pads.
There are different types of PCBs designed for various applications and requirements. The two most common categories are rigid PCBs and flexible PCBs (flex PCBs). Rigid-flex PCBs combine rigid and flexible circuits into one board, taking advantage of both technologies.
This article will compare flex board design versus rigid-flex board design. We will explore the key differences between these two PCB technologies, their applications, pros and cons, and design considerations. Gaining a clear understanding of the distinctions can help you select the right option for your project.
What is a Flex PCB?
A flex PCB, also known as flexible printed circuit board, is fabricated on a thin and flexible dielectric substrate. Common materials used for the flexible dielectric base include polyimide or polyester films.
The tracks are photolithographically etched or printed on the flex circuit, allowing the board to conform to different shapes and be dynamically flexed during use. Components can be soldered directly to a flex PCB or connected using various connectors.
Features and Benefits of Flex PCBs
- Can be bent, twisted, and folded to fit mechanically dynamic applications
- Thin, lightweight, and flexible construction for compact and portable devices
- Can be fabricated in different shapes like circles or complex contours
- Can connect circuits positioned across movable joints or hinged sections
- Highly durable to withstand repeated bending cycles
- Allows three-dimensional wiring paths
- Easy to handle and install during assembly
- Generally lower costs compared to rigid boards for low complexity circuits
Flex PCBs are well-suited for the following applications:
- Wearable devices
- Medical equipment
- Consumer electronics like foldable phones
- Automotive camera systems and sensors
- Industrial robotics and machine controls
- Military avionics systems
- Spacecraft mechanisms
Limitations of Flex PCBs
While flex PCBs provide unmatched flexibility, they also come with some limitations:
- Can only support low component densities and less complex circuitry
- More layers and higher component counts lead to thickness, reducing flexibility
- Components with leads or connectors are hard to mount directly
- Prone to damage without proper strain relief in dynamic flexing applications
- Require robust structural support for most applications
- Generally lower current ratings and power handling capabilities
What is Rigid-Flex PCB?
A rigid-flex PCB integrates rigid boards and flexible circuits into a single interconnected assembly. It combines sturdy rigid sections with dynamic flexing interconnects on the same PCB structure.
The rigid portions provide mechanical support and can host higher component densities, while the flexible sections enable three-dimensional wiring paths. Rigid and flex layers are laminated together using adhesive sheets into a multi-layer sandwich structure.
Features and Benefits of Rigid-Flex PCBs
- Combines advantages of both rigid boards and flexible circuits
- Rigid sections support components and provide structure
- Flexible layers enable out-of-plane interconnections
- Folds into a compact three-dimensional assembly
- Eliminates connectors between separate rigid and flex PCBs
- Simplifies system assembly and enhances reliability
- Allows dynamic flexing at hinges and openings
- Reduces overall weight and improves space efficiency
- Lower costs compared to assembling separate rigid and flex boards
Rigid-flex PCBs suit the following types of products:
- Foldable consumer electronics like laptops
- Portable medical instruments
- Aerospace and defense systems
- Wearable and IoT products
- Automotive camera and sensor modules
- Industrial robotics and automation equipment
Limitations of Rigid-Flex PCBs
While rigid-flex PCBs provide the best of both rigid and flex worlds, they also pose some limitations including:
- Relatively more complex design requirements
- Generally higher fabrication costs
- Need for special flex-rigid assembly processes
- Careful layout required to distribute components and routing
- Challenging to repair or modify once assembled
- Often require additional shielding or strain relief provisions
Key Differences Between Flex PCB and Rigid-Flex PCB Designs
Now that we have looked at the basic features of flex PCBs and rigid-flex PCBs, let’s examine some of the key differences between these two design architectures:
Board Materials
The choice of materials is a major differentiator between flex and rigid-flex designs:
- Flex PCBs only use flexible dielectric films like polyimide
- Rigid-flex PCBs incorporate both rigid laminates (FR-4, polyimide) and flex films
Layer Stackup
Another fundamental difference is the layer stackup:
- Flex PCBs contain single or double-sided conductor layers
- Rigid-flex boards have much more complex layer structures with 4-30+ conductive layers
Circuit Complexity
This leads to significant differences in circuit complexity and component mounting:
- Flex PCBs support only simple wiring with low component counts
- Rigid portions on rigid-flex boards allow high density ICs, fine lines, and small via structures
Conductor Thickness
Conductor thickness is vastly different between the technologies:
- Flex PCB conductors are typically 12-35 microns thick
- Rigid-flex boards use 1 oz (35 microns) copper or thicker up to 3 oz or 105 microns
Outline and Form Factor
The outline and form factors enabled distinguish the two design types:
- Flex PCBs can be fabricated in any 2D shape and fit confined spaces when folded
- Rigid-flex PCBs fold into complex 3D structures but can’t freely flex over entire length
Dynamic Flexing
The ability to dynamically flex during use provides a major contrast:
- Flex PCBs can bend repeatedly to conform to contours and motions
- Rigid-flex PCBs only flex at discrete points determined in the design
Cost
There are notable cost differences as well:
- Simple flex PCBs are relatively low cost for basic applications
- Rigid-flex PCBs entail higher fabrication and assembly costs
Reliability Factors
Reliability considerations vary for the two architectures:
- Flex PCBs require robust strain relief for dynamic bending
- Rigid-flex boards need careful pad layouts to avoid cracks
Rigid-Flex PCB Design Guidelines
Rigid-flex PCB design combines both rigid board and flex circuit layout approaches. Here are some key guidelines for reliable rigid-flex PCB design:
Layer Stack Planning
- Plan conductor layer stackup minimizing rigid-flex transitions
- Use symmetric structures around neutral axis to avoid stress
- Add stiffeners on outer layers of the flex area if needed
High-Density vs Low-Density Areas
- Group high component density areas on the rigid portions
- Place low density wiring on the flexible areas
Component Placement
- Distribute components judicially between rigid and flex zones
- Ensure clearance from edges to avoid rigid-flex interface strains
- Avoid placing heavy components on flex areas
Board Outline and Fold Lines
- Optimize board outline for panel utilization and foldability
- Position fold lines along the neutral bend axis
- Allow sufficient flexibility and clearance for dynamic folds
Routing Considerations
- Route critical signals on inner layers in rigid sections
- Limit length of lines routed across the rigid-flex boundary
- Watch for impedance changes at rigid-flex interfaces
Pad and Via Layout
- Avoid placing pads or vias directly at rigid-flex junctions
- Implement tear-drop pad designs on inner layers at transitions
- Space pads slightly away from edges and fold lines
Shielding Flex Areas
- Add ground planes or traces to shield noise in flex regions
- Incorporate shielding on both sides of a flex layer for better effectiveness
Strain Relief and Reinforcement
- Provide adequate strain relief for dynamic and static flex zones
- Consider reinforcing outer flex layers with additional stiffening
By following these guidelines, you can architect reliable and robust rigid-flex PCB designs.
Comparing Pros and Cons of Flex Boards and Rigid-Flex Boards
To summarize the key trade-offs, here is a comparison of the pros and cons for flex board and rigid-flex board implementations:
Flex PCB Pros
- Extremely thin and lightweight
- Can conform to tight spaces and complex shapes
- Low cost for high-volume applications
- Support millions of dynamic flex cycles
- Simple assembly and installation
Flex PCB Cons
- Limited in component density and layer counts
- Prone to wear and tear failures without strain relief
- Require additional structure and enclosures
- Generally lower current ratings and power handling
Rigid-Flex PCB Pros
- Combines advantages of rigid and flex circuits
- Enables complex circuitry in rigid sections
- Simplifies interconnects across form factors
- Folds into compact 3D configurations
- Eliminates connectors between PCBs
- Consolidates multiple PCB assemblies
- Often lower cost than assembling separate boards
Rigid-Flex PCB Cons
- Relatively higher design complexity
- Fabrication is more expensive than rigid or flex alone
- Repair and modification is difficult after assembly
- Needs careful pad layout at rigid-flex interfaces
- Typically requires additional shielding provisions
- Overall production cost can be higher than flex alone
Comparing Applications of Flex Circuits and Rigid-Flex PCBs
The types of products and applications that typically use flex board or rigid-flex board implementations can also highlight their differences:
Typical Flex PCB Applications
- Wearable devices
- Printer head interconnects
- Military radio antennae
- Medical catheters
- Robotics sensor ribbons
- Consumer electronics flex cables
Typical Rigid-Flex PCB Applications
- Aerospace avionics systems
- Servers with backplanes
- Laptop and portable electronics
- Automotive camera modules
- Industrial machine controllers
- Medical imaging instruments
While simple interconnect applications suit flex PCBs, more complex and dense electronic products benefit from selecting rigid-flex PCB technology. However, the choice depends on the specific requirements, trade-offs and costs involved for an application.
Flex Circuit vs Rigid-Flex PCB: Which is Better?
Whether to use a flex PCB or rigid-flex PCB depends on the particular product requirements and constraints. Here are some key considerations when deciding between the two:
Flex PCBs Are Preferred When:
- Only simple wiring interconnections are needed
- Ability to dynamically flex is required
- Very compact and thin circuit is optimal
- Extremely lightweight construction is critical
- Project budgets are tight
Rigid-Flex PCBs Are Preferred When:
- Complex high-density circuits are required
- Component densities and layer counts are high
- Interconnecting varied form factors and shapes
- Static and dynamic flexing regions are needed
- Overall product costs justify additional PCB expenses
- Reliability is critical over flex life
- Noise control and shielding is important on flex areas
Analyzing the trade-offs allows selection of whether rigid-flex PCB or flex PCB architecture fits best for a particular design. The decision depends on balancing the product’s technical requirements against capabilities and costs.
Summary and Key Takeaways
- Flex PCBs provide ultra-thin and dynamic flexible circuits, while rigid-flex PCBs combine rigid board areas with flexing interconnects.
- Flex PCB construction uses only flexible polymer films enabling tight bend radii, while rigid-flex PCBs incorporate both rigid laminates and flex films.
- Flex boards support simpler circuits with low component counts, whereas rigid portions of rigid-flex PCBs allow much higher densities.
- Rigid-flex designs require careful planning for layer stackups, component placement, routing and pad layouts across rigid-flex junctions.
- Flex PCBs suit low-complexity dynamic flexing interconnect applications with cost limitations, while rigid-flex excels where dense circuits must interface across varied form factors.
- The choice depends on balancing flexibility, complexity, density, reliability, form factor, and cost requirements for a particular product design application.
Flex PCB vs Rigid-Flex PCB – Design Selection FAQs
Q1. When is a flex PCB the best choice over a rigid-flex PCB?
A flex PCB is preferable when only simple wiring is needed in a tight space, the circuit needs to dynamically flex in use, an extremely lightweight or low profile is required, or when project budgets are limited. A rigid-flex PCB would be over-designed in these scenarios.
Q2. When is a rigid-flex PCB the right selection over a flex PCB?
If high component densities, layer counts, and complex circuitry are required, a rigid-flex PCB would be the right choice over flex alone. Rigid-flex is also superior when interconnecting PCBs across varied shapes or enabling both static and dynamic flex regions on the same board.
Q3. What are the typical applications suited for flex PCBs?
Common applications using flex PCB technology include wearable devices, medical catheters, robotics, consumer electronics cabling, printer heads, and military antennae. These leverage the dynamic flexing abilities within the design constraints of flex circuits.
Q3. What types of products typically use rigid-flex PCBs?
Typical products that use rigid-flex PCB technology include portable electronics, aerospace systems, server backplanes, laptops, automotive cameras, machine automation controllers, and advanced medical instruments. These require integrating high complexity ICs across multiple form factors and shapes.
Q5. Does rigid-flex PCB technology completely replace the need for flex PCBs?
No. Rigid-flex PCBs provide a hybrid option blending rigid and flex PCB abilities, but don’t fully replace standalone flex PCBs in all scenarios. Simple flex circuitry with only wiring connections will often use dedicated flex boards when the complexity of rigid-flex is unnecessary.
The choice depends on balancing the trade-offs in flexibility, complexity, density requirements and costs when selecting between flex PCB or rigid-flex PCB implementations for a product.
