Rigid PCB vs Flexible PCB

In the process of electronic manufacturing, customers often invest time in designing components, shapes, and specifications, overlooking a crucial aspect: PCB selection. This is a pivotal point as using the right type of circuitry can positively impact your entire project. For instance, utilizing IMS PCB is ideal for applications demanding robust heat dissipation capabilities, while opting for high-frequency PCB is essential for applications requiring enhanced signal transmission capabilities. Additionally, the strength and slimness of the circuit board are also vital considerations, involving the choice between employing a more reliable rigid PCB or flexible PCB adaptable to three-dimensional spaces. To assist customers in making the most of FS Technology, this article will emphasize comparing rigid PCB and flexible PCB, aiding you in achieving your project goals effectively.

Rigid PCB vs Flexible PCB

Rigid PCB vs. Flexible PCB: Difference

There isn’t a definitive answer to what type of circuit board is suitable for your project; it requires analysis based on the specific circumstances. If you’re facing difficulty in choosing between rigid and flexible circuitry, here are five distinct aspects to help you gain a deeper understanding of them:

  • Cost
  • Features
  • Design
  • Protection Layer
  • Application Area

Price Comparison

Is the ultimate goal of everything to make a profit? Therefore, prioritizing a price comparison between the two in custom projects is always a prudent approach. When circuit boards have the same specifications, flexible PCB often comes at a higher price—a phenomenon that is widely understandable.

The primary factor causing the cost difference is the variation in required materials. Common materials for rigid PCB manufacturing include phenolic paper laminates, epoxy paper laminates, polyester glass mat laminates, and epoxy glass cloth laminates. In contrast, flexible PCB uses materials like polyester film, polyimide film, and fluorinated ethylene propylene film. Clearly, flexible PCB materials are more expensive.

Furthermore, the manufacturing process for flexible PCB is more complex, involving precise cutting, drilling, circuit formation, and soldering steps. This demands not only advanced manufacturing techniques but also specialized equipment from the manufacturer.

However, it’s important to note that we’re only referring to the bare board manufacturing cost here. The ultimate goal of producing PCB is to achieve functional PCBA boards. Using flexible PCBA can significantly reduce component procurement costs, thus lowering the overall cost of assembly projects. This is because, compared to rigid PCBA boards, flexible PCBA boards in electronics can reduce the usage of connectors, wiring harnesses, and other circuit board components. If you are a price-sensitive customer, we recommend reading “PCB Assembly Cost Driver Analysis and Price Calculation” to make the right decisions.

Feature Comparison

Flexible Features vs Rigid Features

Considering whether you need a rigid board or a flexible board involves observing the advantages and characteristics of both to select the circuit that better suits your project.

Rigid Board:

  • High Density: When examining manufacturers’ PCB manufacturing capabilities, it’s evident that rigid circuits can be built with up to 60 layers, while flexible circuits are typically limited to around 10 layers. This is because achieving bonding and stability between layers in a multi-layer flexible circuit structure poses challenges that might result in interlayer separation or delamination issues.
  • Reliability: As the name suggests, rigid PCB is sturdy and possesses superior physical resistance. Depending on the materials used, they can also be endowed with additional qualities like chemical resistance, flame retardancy, and heat dissipation. Moreover, due to manufacturers’ adeptness with rigid PCB manufacturing techniques, the probability of faults occurring during production is lower.
  • Efficient Assembly: PCBA companies can easily complete assembly processes with rigid boards, facilitating fast turnovers in assembly projects.
  • Design Flexibility: Various performance requirements (electrical, physical, chemical, mechanical, etc.) for projects can be met through standardized rigid circuit design.
 

Flexible Board:

  • Lightweight: Generally, flexible PCB weigh only a fraction of what rigid PCBs do, contributing to overall product weight reduction.
  • Compact Size: This not only manifests on the PCB itself but extends to product design. Flexible PCB can be bent, rolled, twisted, and folded, allowing for better space utilization and conservation in electronics.

Design Comparison

PCB Design Complexity

In PCB design process, the corners during routing can potentially impact electromagnetic interference. Right-angle corners lead to abrupt signal changes, generating high-frequency components that may increase radiation and sensitivity. Hence, FS Technology suggests utilizing soft corners (such as rounded bends) to mitigate this issue. An intermediate angle is 45 degrees, often considered a preferable choice as it maintains geometric simplicity while reducing problems associated with sharp angles.

For flexible PCB, the bend ratio is a critical factor. The bend ratio refers to the ratio of the flexible board’s thickness to its bend radius. If the bend ratio is too small, it implies that the material undergoes excessive strain during bending, potentially causing material fractures or damage. Thus, in flexible circuit design, it’s imperative to determine an appropriate bend radius based on material characteristics and application requirements to prevent mechanical failures.

Protection Layer comparison

Overlays and Solder Masks

Due to the fragility of circuits, applying a protective layer on the surface of the board to prevent abrasion and exposure to moisture-induced chemical corrosion is essential. The choice of material and treatment methods varies due to the differences in form. In rigid PCB, solder-resist ink is used to create solder mask, while in flexible PCB, polyimide is employed to build a cover film. Despite the distinct materials, both aim to safeguard the circuits. 

The use of different materials arises from the potential need for bending or folding in flexible PCB applications, where solder resist ink would become rigid upon curing. The cover film effectively addresses this concern, with thickness ranging from 0.0005” to 0.005”, commonly 0.001” and 0.002”. During the manufacturing process, manufacturers apply a thermosetting adhesive on the surface and use heat and pressure to laminate the polyimide and adhesive cover layers. The application of heat aids the unrestricted movement of the adhesive, allowing it to fill gaps between traces and pads and reducing trapped air between layers. Adhesive movement is crucial as it facilitates overall surface bonding and encapsulation. The adhesive material leads to an extrusion around the holes, known as adhesive squeeze-out, which is a necessary process. After the cover layer lamination process, components, parts, and/or holes in features are manufactured using drilling, milling, or laser cutting.

Application Field Comparison

In modern intricate electronics, a single circuit configuration often falls short of meeting demands. Typically, it’s the combination and interaction of different forms that excel. One such amalgamation is the Rigid-flex PCB that marries rigidity and flexibility, catering not only to rigid requirements but also accommodating layouts in three-dimensional spaces.

Applications dominated by rigid circuits are often cost-effective and ubiquitous, including consumer electronics like TVs, phones, keyboards, and mice. Additionally, industries requiring utmost reliability, like industrial automation, employ rigid PCB— industrial control PCB being a prime example. On the other hand, flexible circuits shine in densely-packed or miniaturized electronics. They find their forte in wearables, Bluetooth earphones, foldable phones, GPS systems, and more. These instances invariably highlight the demand for lightweight and compact solutions.

Rigid PCB and Flexible PCB: Similarities

Similar Manufacturing Process

Rigid vs. Flex PCB Manufacturing

In the PCB manufacturing process, the same approach is used for both types of boards:

 

  • Drilling and plating of holes and vias.
  • Copper trace imaging and etching.
  • Pad planning and profiling.
  • Baking the boards to remove moisture.
  • Both types of boards feature identical component connection configurations.
  • The thickness and hole sizes of these boards are typically the same.

Same Test

The importance of the testing process is self-evident. Apart from conducting functional tests upon completion of the final product, it’s essential to incorporate necessary testing into the production process as well. For FS Technology, regardless of the quantity or the type of boards you use, we adhere to consistent quality control standards and testing to validate quality and expedite progress. Here are some common testing methods:

IPC Standard

As the most official and authoritative non-profit organization, all PCBA companies are proud to implement IPC standards. Some information is listed below. If you need it, you can go to the official website to check:

  • IPC-2221A: Generic Printed Circuit Board Design Standards. Download
  • IPC-2223E: Sectional Design Standard for Flexible/Rigid-Flexible Printed Boards. Download
  • IPC-4101E: Specification for Base Materials for Rigid and Multilayer PCBDownload
  • IPC-4202: Flexible Base Dielectrics for Use in FPC.
  • IPC-4203: Adhesive-coated dielectric films used as overlays for FPC and flexible adhesive-bonded films.
  • IPC-4204: Flexible Metal-Clad Dielectrics for Use in Fabrication of FPC.
  • IPC-6013D: Qualification and Performance Specification for Flexible/Rigid-Flexible Printed Boards. Download

Summarize

AspectRigid PCBFlexible PCB
Physical StrengthGenerally more robust, suitable for larger mechanical stressThinner and flexible, suitable for bending and compact spaces
Bending AbilityTypically poor, not suitable for bending applicationsExcellent bending and flexing capabilities, suitable for flexible designs
Space EfficiencyLess efficient, not suitable for compact designs and limited spacesSuperior space efficiency, suitable for compact and limited spaces
WeightUsually heavier, not suitable for lightweight and portable devicesLightweight, suitable for lightweight and portable devices
CostGenerally lower cost, suitable for mass productionUsually higher cost, suitable for flexible designs and small-scale production
Heat ManagementTypically good, suitable for high-power applications and heat dissipation needsHigh flexibility, usable in high-temperature and heat dissipation applications
Electronic PerformanceRelatively stable electronic performance, suitable for standard applicationsFlexible electronic performance, suitable for specific requirements and custom designs
Design ComplexityLower complexity, suitable for typical circuit layouts and assemblyHigher complexity, suitable for intricate layouts and 3D structural designs
ReliabilityGenerally high reliability, suitable for most application scenariosGenerally high reliability, but dependent on design and material choices
Applicable IndustriesGeneral electronics, industrial, automotive, etc.Mobile devices, medical instruments, electronic textiles, etc.

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