Flex and rigid PCBs are defined by one primary factor: their substrate material. The one in flex PCBs is bendable, while the base in rigid boards is solid and non-flexible.
Each PCB type has its strengths that are ideal for different applications. Flexible PCBs, for instance, are better suited for applications with limited space availability or excessive vibrations, such as in wearables and automotive devices.
On the other hand, rigid boards are ideal for conventional electronics with high space availability because they are more affordable to make.
Let’s compare flex vs. rigid PCBs to determine their differences, similarities, and applications.
Table of Contents
- What is a Flex PCB
- What is a Rigid PCB
- What are the Main Differences Between Flexible and Rigid PCBs
- Are There Similarities between Flexible and Rigid Boards
- What are the Applications of Flex PCB and Rigid PCB
- What are the Differences Between Flex and Rigid PCB Manufacturing and Assembly Processes
- What are Key Considerations for Flex and Rigid PCB Design Processes
- How Much Does Flex vs. Rigid PCB Cost
- What are Future Trends for Flexible versus Rigid PCB
- How To Choose From Flex, Rigid, and Rigid-Flex PCB
- FAQ
What is a Flex PCB
A flex PCB is a circuit board with a bendable substrate material, such as polyimide, polyester, LCP, PEEK, or PEN. These PCBs should have a dynamic bend radius, thin and lightweight construction, and be rugged enough to withstand multiple bending/flexing cycles without snapping.
A flexible PCB
The flexible construction is more resistant to vibrations and gives greater freedom in the design and operation of the board’s application area.
What is a Rigid PCB
As the name suggests, a rigid PCB has a solid, inflexible substrate, which can be FR4, metal, ceramic, Teflon, or Rogers. Since it cannot bend, this board can have more internal copper layers to support denser circuits and provide better mechanical support to the mounted components. Another benefit of rigid PCBs over their flexible counterparts is their lower cost.
A rigid FR4 PCB
What are the Main Differences Between Flexible and Rigid PCBs
Rigid circuit boards have the following characteristics.
- Structural and dimensional stability, which ensures consistent performance under various environmental conditions
- Robustness and durability
- Better thermal management and stability (thicker substrates dissipate heat more efficiently)
- Lower design, manufacturing, and material costs
- Can accommodate multiple layers and high component densities
On the other hand, flexible PCBs provide:
- Dynamic flexing and bendability
- Thin and lightweight constructions
- High-density interconnections in small areas
- Better shock and vibration resistance
- Integration with rigid circuit boards to form rigid-flex circuit boards that are easier to assemble and test.
Here’s a summary of flexible circuits and rigid circuits.
| Comparison Factor | Rigid PCB | Flexible PCB |
| Substrate Materials | FR4, CEM, ceramic, aluminum, Teflon (PTFE), and Rogers | Polyimide, PET, PTFE, LCP, PI composite, polyester, PEEK, and PEN |
| Flexibility | Rigid and non-bendable | Bends, twists, and folds to fit in tight spaces |
| Thickness | Thicker | Thinner |
| Layers | Can have more layers | Fewer layers to enable flexibility |
| Durability and Reliability | Provides mechanical stability but is only durable and reliable in non-moving parts | It is not stable mechanically but highly reliable in moving parts because it is shock and vibration-resistant |
| Weight | Heavy | Lightweight |
| Design and Manufacturing Complexity | Not complex | Complex |
| Thermal Management | Better (thicker substrate) | Needs careful thermal management |
| Interconnect Density | Lower | Higher |
| Space Utilization | Less efficient | More efficient |
| Cost | Low | High |
| Applications | Suitable for most standard electronics | Ideal for custom-shaped and compact electronics, such as wearable devices and smartphones. Car electronics also use flex PCBs due to their shock and vibration-resistant properties. |
Are There Similarities between Flexible and Rigid Boards
Although flexible circuit boards and rigid boards have multiple differences that primarily manifest in their application areas, they have some similarities as well, which include:
- Basic Functionality: Both provide electrical connectivity to the mounted components
- Manufacturing Processes: Some manufacturing steps are similar, such as photolithography or LDI, chemical etching, hole drilling, and hole plating.
- Layer Structure: Whether single, double, or multilayer designs, the structure is more or less the same, but the substrate material differs.
- Solder Mask and Silkscreen: For trace protection and marking/labeling, respectively
- Surface Finishes: Similar protective coatings above bare copper areas
- Design, Inspection, and Testing: Both require CAD tools for circuit design, inspection using AOI or X-ray, and various tests, such as electrical, solderability, contamination, etc.
What are the Applications of Flex PCB and Rigid PCB
Where are Flex PCBs Used
Flex PCBs are preferred in these industries.
- Consumer Electronics: Almost a third of all flexible PCBs manufactured end up in electronic devices like scanners, printers, and smart mobile devices. As these electronics become smaller to the handheld level, flex PCBs will be key inside them because they enable heavy processing power in tiny packages.
- Automotive: Modern cars house various hardware, such as sensors, displays (infotainment and digital clusters), cameras, GPS, etc. These devices need flexible PCBs to withstand the shocks and vibrations inside the vehicle.
- Aerospace: Electrical devices in aerospace and aviation applications are exposed to more intense vibrations and temperatures than when in automotive applications, which makes flexible (or rigid-flex) PCBs the only viable solutions. The lightweight property of these boards is also critical for avionics, satellites, and rockets.
- Telecommunications: Wireless and mobile communication devices feature flexible antennas with flex PCBs, plus flexible interconnections inside for signal transmission to enable compact and lightweight designs.
- Medical Systems: Modern healthcare and fitness electronics have become popular because they provide medical assistance, data collection, or diagnosis directly when on the patient. However one of their key requirements is to conform to the human body shape, which is made easier using flexible PCBs.
- Industrial and Instrumentation Devices: Flexible heaters, sensors, and robotics rely on the flexibility properties of these PCBs to provide reliable electrical connections.
- Lighting and Energy: Use cases include flexible LED strips, solar panels (for portable and wearable solutions), and battery pack connections.
Where are Rigid PCBs Used
Rigid and flexible boards have some common applications, but the former is typically used in these areas.
- Consumer Electronics: Large consumer electronics and home appliances, such as TVs, fridges, microwaves, and washing machines, rely on rigid PCBs for their circuitry because they have no space shortage. These boards also help to lower their cost.
- Computing: The multilayer capability and high component densities in rigid PCBs make them suitable for computer and server motherboards, graphics cards, hard drives, and SSDs.
- Automotive: Although most in-car electronics feature flexible boards, rigid PCBs are common in various ECUs, such as the engine and transmission control units.
- Industrial Systems: Industrial control and automation equipment, like PLCs.
- Medical Equipment: Common in imaging systems like CT scanners, MRI machines, and ultrasound devices.
- Telecommunications: The core systems of cellular base stations and networking equipment (routers, modems, switches, etc.) have rigid boards.
What are the Differences Between Flex and Rigid PCB Manufacturing and Assembly Processes
The first difference in the manufacturing process of Flex and rigid PCBs is in substrate material selection, which we’ve covered in the table above. This extends further to the copper cladding, where the copper used in rigid PCBs is a standard copper foil, while the one in flexible PCBs is thinner and more flexible (rolled annealed copper).
In the actual fabrication process, rigid PCBs are laminated using high temperature and pressure, while flexible boards undergo the same process using only adhesives. This step requires high precision and control to avoid damaging the thin materials. Etching also requires extra care to prevent substrate damage.
Layer stacking and alignment are easier on rigid boards because the materials remain solid. However, flexible layers require high precision because the materials can stretch or shift.
In the drilling stage, rigid boards can be punctured using mechanical or laser drills, but flexible boards can only be drilled using lasers, which don’t exert mechanical stress on the thin stack. Flex PCBs might also require stiffeners on specific sections.
Some considerations to keep in mind are the adhesives, solder mask, and surface finishes used. On flexible boards, you can only use adhesives that retain their flexibility property after drying. The solder mask and surface finishes also need to flex and bend without cracking or peeling.
What are Key Considerations for Flex and Rigid PCB Design Processes
Flex PCBs Design Considerations
The flexible PCB design process requires more considerations:
- Bend radius
- Flex cycles
- Material selection
- Layer count, transitions, and shielding
- Trace width and spacing
- Component placement (placement area and weight distribution)
- Strain relief
- Traces/conductors
- EMI and signal integrity
- Stiffeners (mechanical support)
- Thermal management
- Via features
- Plating and surface-finish requirements
If their flexibility limits their functionality, it might be worth considering a rigid-flex PCB or a flex PCB with more internal layers.
The latter will have a limited bend radius and few flex cycles.
Rigid PCB Design Considerations
With rigid PCBs, you have to consider these design requirements.
- Material selection
- Dimensions
- Copper weight (to suit the required electrical parameters)
- Trace layout, routing, and stacking (multiple layers)
- Mechanical and structural integrity (board thickness, mounting hole locations, etc.)
- Thermal management
- Component placement
- Signal integrity (ground planes, differential pair routing, etc.)
- Testing points
- Surface finishes
How Much Does Flex vs. Rigid PCB Cost
Low-volume flex PCB orders and prototypes are quite costly, with single-layer boards costing around $20–$100 per piece and $500, respectively. But, the economies of scale associated with high-volume orders can lower the cost to $10 or less.
However, complex multilayer flex PCBs (12+ layers) can cost up to $2,000 for prototyping and $50–$500 per piece, depending on the order volume.
Rigid PCBs, on the other hand, cost about $5–$200+ per piece. The actual price of the board differs depending on these factors.
Layer Count
Each layer increases the manufacturing costs and raises the PCB’s price. Rigid types can cost up to $200 per layer for small-volume orders, while flexible boards can reach up to $500 for the same order volume.
Different layers in a rigid-flex PCB design
Order Quantity
When comparing 2-layer flex PCBs, prototypes will cost you $150–$600, while low-volume orders (10–100) cost $30–$300. High-volume orders of 1,000+ boards are the cheapest, going for as low as $15 per piece.
Materials and Board Size
Flex PCBs are typically made of a polyimide substrate, which offers good value for money. A polyester base is more economical, but it has a lower temperature rating.
LCP, PEEK, and PI composite are all costlier than polyimide but offer better performance in terms of durability (with tight tolerances), chemical resistance, and ruggedness, respectively.
Depending on the material, the flexible board can cost the following in medium-volume orders.
- $100–$200 for 50x50mm
- $150–$30 for 50x100mm
- $200–$400 for 100x100mm
- $300–$500 for 150x200mm
Rigid board materials make them significantly cheaper, with FR4, the most common one, costing $1–$10 per square foot (305x305mm). Aluminum is common in high-power applications and costs $10–$20 per square foot.
For high-frequency PCBs, Rogers substrates will require roughly $20–$50 per square foot, while ceramic demands $50–$200 per square foot. In comparison, polyimide (for flex PCBs) costs $5–$20 per square foot, depending on the board thickness and quality.
Other critical cost factors are:
- Board thickness
- Fabrication complexity (heavy copper plating, specialized surface finishes, controlled impedance, etc.)
- Tolerance
- Flexing requirements
- Reliability
- Testing and certifications
- Turnaround time
What are Future Trends for Flexible versus Rigid PCB
The emerging technologies that are impacting flex and rigid PCBs include:
- Advancing Materials: PCB manufacturers are increasingly switching to eco-friendly substrates, such as halogen-free FR4, to reduce the environmental impacts of PCBs and electronics at the end of their service life. Although expensive, materials like metal and ceramic are also being favored over FR4 because they are easy to recycle. Manufacturers are switching to materials with better electrical properties, durability, and flexibility (like graphene) as well, to make more efficient and reliable flexible boards.
- Rigid-Flex Hybrids: Flexible and rigid PCBs have different strengths and weaknesses, but rigid-flex boards combine the benefits of both. These boards are poised to become more common in compact medical devices, wearables, and foldable electronics.
Predictions for Flex PCB and Rigid PCB Market Growth
The PCB market size for all three types (rigid, flexible, and rigid-flex) is expected to almost double by 2033, and this will be primarily driven by the industrial electronics, IT, telecom, defense, aerospace, automotive, and consumer electronics segments.
But the interesting bit is that the flexible PCB market is expected to contribute almost half of that growth, reaching $65 billion out of a combined $144 billion by 2032.
The key factors that will drive this growth include:
- Increasing demand for smaller and lighter electronics, including wearable tech
- IoT, IIoT, and AIoT adoption in smart homes, industries (Industry 4.0), agriculture, etc.
- Automotive tech (ADAS, infotainment systems, and other in-car electronics)
How To Choose From Flex, Rigid, and Rigid-Flex PCB
As you can see, the primary differences between rigid and flexible PCBs come about in the manufacturing, applications, and cost aspects, but the most notable is in the application areas.
Flexibility, lightweightness, and shock/vibration resistance are key flex PCB properties that separate them from their rigid counterparts and make them suitable for wearables, portable electronics, and various automotive hardware.
Rigid PCBs, on the other hand, have a low-cost advantage due to cheaper materials and a less complex manufacturing process, which makes them suitable for regular consumer electronics. These boards can also house multiple layers to form complex circuits for computing applications.
Rigid-flex PCBs provide a hybrid between these two to give the best of both worlds. Therefore, if you need a complex computing device in tiny or vibration-resistant packages, this option is the way to go. Think of smartphones, smartwatches, military, aerospace, automotive, and telecom devices.
We have the capacity to build either option at reasonable costs to suit your application. Contact us with your requirements or project designs to get a quote for flex, rigid, or rigid-flex printed circuit board manufacturing or assembly today!
FAQ
Which is Better: a Rigid or a Flexible PCB?
There is no better or worse option between a rigid and flexible PCB. Surprisingly, each option is designed to be useful in a specific use case.
Therefore, we recommend flexible PCBs if you’re working with compact spaces and rigid PCBs for more durability and cost-effective applications.
What’s the Lifespan of a PCB?
Most PCBs having proper maintenance and repair will serve you well for at least 50 years or more. However, choose a rigid PCB for more lifespan.
Can You Replace a Flex PCB with a Rigid PCB?
No! A flex PCB is mainly used in tighter and more compact spaces. Moreover, they’re designed to function well even in extreme conditions like high temperatures.
Therefore, replacing it with a rigid option will likely render your device ineffective. Similarly, you can’t replace a rigid PCB with a flex one.
