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4 Layer Rigid-flex PCB

Jarnistech > Rigid-flex PCB > 4 Layer Rigid-flex PCB

Rigid-flex printed circuit boards have attracted noteworthy interest in recent years, owing to their unrivaled blend of both flexibility and rigidity. This characteristic presents a multitude of benefits in numerous electronic applications. Significantly, the 4 Layer Rigid-Flex PCB emerges as a multipurpose solution delivering amplified design flexibility, elevated reliability and conveys the ability to conserve space. This discourse delves into the intricacies of the 4 Layer Rigid-Flex PCB, thoroughly inspecting its structure, exploring the manufacturing process, and highlighting the advantages they offer in modern electronics.

What is 4 Layer Rigid-Flex PCB?

A 4 Layer Rigid-Flex PCB, alternatively known as a four-layer rigid-flexible printed circuit board, typifies a distinctive class of PCB that synergistically fuses the merits of both rigid and flexible circuits in one comprehensive board. This groundbreaking design coalesces parts of rigid PCB with parts of the flexible PCB, therefore granting the board the ability to bend or flex whilst ensuring maintained electrical continuity throughout.

The term “4 layer” indicates the quantity of layers present in the PCB stack up. In this instantiation, the PCB is composed of four strata of conductive traces and planes that are encapsulated by insulating layers. The conductive layers function as avenues for electrical signals to traverse throughout the board, whereas the insulating layers contribute mechanical stabilization and demarcation between the conductive entities.

The rigid sections of the PCB are made from traditional rigid PCB materials like FR4, while the flexible sections usually employ a polyimide or similar flexible substrate. The rigid and flexible sections are bonded together to create a cohesive board structure.

Understanding Rigid-Flex PCB Construction

Comprehending the structure of rigid-flex PCBs is pivotal in identifying their inherent attributes and advantages.

Layer Arrangement and Stack-Up:

Rigid Layers: Comprising standard rigid PCB materials like FR4, the rigid segments of the PCB impart mechanical backing and accommodate components.

Flexible Layers: The flexible sections use flexible substrates such as polyimide. These layers allow the PCB to bend and flex without breaking or compromising electrical connectivity.

Adhesive layer: Adhesive layers are used to bond the rigid and flexible layers together, creating a cohesive structure. These layers are imperative to provide dual functions – electrical seclusion and mechanical steadiness.

Conductive Traces and Planes:

Rigid Layers: Conductive traces and planes on the rigid layers are typically created using copper, etching processes, and patterned plating techniques. These traces and planes provide electrical connectivity between components and connections.

Flexible Layers: Similar to rigid layers, the flexible strata equally have conductive traces. However, these traces are crafted to flex and endure recurring bends without any crevices or delamination. The traces may use thinner copper foils to enhance flexibility.

Via Technology:

Through-hole Vias: Through-hole vias are used to establish electrical connections between different layer of the PCB. These vias traverse both the rigid and flexible strata, to provide consistent continuity across the entirety of the board.

Blind/Buried Vias: In certain instances, the utilization of blind or buried vias might be necessary to establish interconnections amidst specified layers without crossing the complete depth of the board. They allow for more compact and efficient designs.

Coverlay and Solder Mask:

Coverlay: It is a protective layer of flexible material applied over the flexible sections, encapsulating and protecting the conductive traces. It provides insulation, moisture resistance and protection against environmental factors.

Solder Mask: The solder mask is applied to both rigid and flexible sections to protect the copper traces during soldering processes. It also enhances electrical insulation and prevents solder bridging.

Rigid-flex PCB construction requires careful planning and design considerations to ensure the proper alignment of rigid and flexible sections, appropriate bending areas, and controlled impedance characteristics. Understanding these construction aspects is crucial for achieving reliable and durable rigid-flex PCB in various applications.

4 Layer Rigid-Flex PCB Stack-up Tips

When considering the layer stack-up for a robust rigid-flex PCB, it is crucial to account for the stresses that the flex board may experience due to bends and curves.

Rigid-Flex PCB 4L Stack-up

4 Layer Rigid-flex PCB Stack-up

To establish an optimized stack-up, adhere to the following guidelines:

Position the flexible section symmetrically at the center of the rigid PCB layers. By maintaining symmetry, you ensure balanced mechanical properties and mitigate the risk of excessive stress concentration in specific areas.

Ensure that traces routed on the flexible sections of the PCB run perpendicular to any bending lines. This orientation prevents premature fatigue and wear of the copper. Perpendicular alignment helps distribute the stress evenly, enhancing the longevity of the flexible circuitry.

Employ curved traces instead of employing 45 or 90-degree straight traces commonly used in rigid PCB. In the case of flex PCB, bending the copper in an arc formation minimizes the risk of fatigue. Curved traces accommodate the flexing motion without subjecting the copper to excessive strain.

When dealing with a two-layer flex portion, stagger the traces to avoid their alignment directly on top of each other. This arrangement prevents thickness build-up, where one layer’s copper intersects with another layer’s copper. By staggering the traces, you maintain a consistent thickness profile, optimizing the structural integrity of the PCB.

By following these recommendations, a professional PCB design engineer can develop a robust layer stack-up for a rigid-flex PCB, effectively addressing the stresses associated with bends and curves.

Manufacturing Process for 4 Layer Rigid-Flex PCB

Design and Engineering:

PCB Design: The design phase involves creating the PCB layout using specialized software, considering the placement of components, routing of traces, and differentiation between rigid and flexible sections.

Design Verification: The design undergoes meticulous scrutiny and validation to ascertain conformance to the prescribed specifications, manufacturing competencies, and reliability criteria. This stage is crucial for instituting any mandatory modifications.

Material Preparation:

Material Selection: The appropriate materials are selected for rigid and flexible layers based on the specific requirements of the design, such as FR4 for rigid layers and polyimide for flexible layers.

Material Cutting: The selected materials are cut into the desired panel sizes to accommodate multiple PCBs during the manufacturing process.

Inner Layer Processing:

Inner Layer Imaging: The inner layers of the PCB stack-up undergo imaging, where a photosensitive material is applied and then exposed to ultraviolet light using the design artwork to define the trace patterns.

Etching and Cleaning: Unwanted copper is etched away using a chemical solution, leaving behind the desired copper traces. The board is thoroughly cleaned to remove any residue.

Lamination and Layer Alignment:

Layer Stacking: The inner layers, along with insulation layers and adhesive layers, are stacked according to the pre-defined stack-up configuration. Alignment pins or registration holes ensure precise layer registration.

Lamination: The stacked layers are subjected to heat and pressure in a lamination press, bonding them together into a single solid panel.

Drilling and Plating:

Drilling: Holes for component mounting and electrical connections are drilled into the panel using precise CNC drilling machines. These holes are typically plated through to establish electrical continuity between layers.

Plating: Copper plating is performed to create conductive pathways within the drilled holes, ensuring electrical connectivity between the layers. The panel is then plated with a thin layer of copper to form the outer conductive traces.

Outer Layer Processing:

Outer Layer Imaging: Photosensitive material is applied to the outer layers, and the design artwork is used to expose and define the trace patterns.

Etching and Cleaning: Unwanted copper is etched away, leaving behind the desired copper traces on the outer layers. The board is thoroughly cleaned to remove any residues.

Solder Mask and Silkscreen:

Solder Mask Application: A solder mask is applied to the entire board, protecting the copper traces and ensuring proper soldering during assembly. Openings for component pads and vias are created.

Silkscreen Printing: Component and reference designators, logos, or other markings are printed on the board using a silkscreen process, aiding assembly and identification.

Surface Finishing:

Surface Finish Application: The exposed copper surfaces are coated with a surface finish to protect them from oxidation and ensure good solderability. Common options include immersion gold, HASL (Hot Air Solder Leveling), or OSP (Organic Solderability Preservative).

Routing and Profiling:

Trimming and Routing: The panel is cut into individual PCBs using routing machines, separating them from the larger panel. Additional routing may be performed to create unique board shapes or features.

Profiling: The PCB are profiled to their final dimensions, removing excess material and creating smooth board edges.

Testing and Inspection:

Electrical Testing: Each PCB undergoes electrical testing to verify its functionality and ensure all connections are intact.

Visual Inspection: A thorough visual inspection is performed to check for any manufacturing defects, such as misaligned traces, solder mask issues, or other irregularities.

Assembly and Soldering:

Components are mounted on the PCB using automated or manual assembly processes. Soldering techniques, such as reflow soldering or wave soldering, are applied to establish electrical connections between components and the PCB.

Final Testing and Quality Control:

Functional Testing: The fully assembled PCB is subjected to functional testing to verify its proper operation and adherence to specifications.

Quality Control Measures: Strict quality control measures are implemented throughout the manufacturing process to ensure the final product meets the required standards.

Advantages of 4 Layer Rigid-Flex PCB

4 Layer Rigid-Flex PCB offer several advantages over traditional rigid PCBs or flexible PCBs. Here are some key advantages:

●Space Saving and Compact Design
●Increased Reliability
●Enhanced Durability
●Improved Signal Integrity
●Simplified Assembly and Reduced Manufacturing Steps
●Design Flexibility
●Weight Reduction
●Improved Thermal Management

These advantages make 4 Layer Rigid-Flex PCB a preferred choice for various applications, including medical devices, aerospace systems, automotive electronics, wearable devices, and other compact electronic systems that require reliability, durability, and space optimization.

Why Choose JarnisTech

A Reliable 4L Rigid-flex PCB Supplier in China

JarnisTech is a leading manufacturer and designer of high-quality rigid-flex printed Circuit Boards (PCB), catering to both standard and custom specifications. Our UL certified production facility is equipped with state-of-the-art machinery, enabling us to meet diverse requirements and deliver quick turnaround times.

We take pride in offering a comprehensive range of 4 layer rigid flex PCB that conform to international quality standards, ensuring our products remain competitive in the market. With our wealth of industry experience and a skilled team of professionals, we have gained recognition as one of China’s preferred manufacturers of flexible printed circuit boards.

As a dependable associate, we depend on our rigorously-tested standard methodologies to manufacture 4-layer rigid-flex PCB. Composed employing FR4+Polyimide substances, these boards sport widths/spaces measuring 8/8mil while the finish thickness is approximately 0.2mm for the flex portions and is 1.0mm for the rigid sections. The thickness of the board oscillates between 0.5mm to 3.0mm (0.02″ to 0.12″), and options for copper thickness span from 0.5 OZ to 6 OZ. Customers are generously provided with the latitude to choose from a spectrum of solder mask colors, encompassing white, black, blue, green, and red, in addition to the prestigious Taiyo PSR4000 white solder mask. Further, surface finishes including Immersion Gold, HASL, and OSP can be employed to augment the overall durability and visual appeal.

4 Layer Rigid-Flex PCB – JarnisTech
Model:Rigid-flex board-4L
Surface treatment:immersion gold
Width/space:8/8 mil
Finish thickness:0.2mm(flex),1.0mm
Min Hot:0.8mm
Board Thickness:0.5mm~3.0mm (0.02″~0.12″)
Copper thickness:0.5 OZ, 1.0 OZ, 2.0 OZ, 3.0 OZ, up to 6 OZ
Outline:Routing, punching, V-Cut
Solder mask:White/Black/Blue/Green/Red, Taiyo PSR4000 white
Legend/Silkscreen Color:Black/White
Surface finishing:Immersion Gold, HASL, OSP
Max Panel size:18″*24″
Packing:Vacuum/Plastic bag

At JarnisTech, our utmost pride lies in delivering streamlined, comprehensive solutions for flexible printed circuits, with an unwavering commitment to complete customer gratification. Catering to diverse industries, our offerings encompass not only flexible printed circuit boards but also extend to rigid printed circuit boards. Reach out to us today to discover how we can assist you with your specific requirements.


The innovation of the 4 Layer Rigid-Flex PCB marks a substantial progression in PCB technology, mending the disparity between customary rigid PCB and flexible PCB. Its distinctive construction, which integrates both rigid and flexible advantages, offers a plethora of benefits such as optimization of space usage, reliability, durability and design flexibility.

As the relentless development in electronic devices calling for all the more compact and resilient options, the 4 Layer Rigid-Flex PCB emerges as a substantial alternative for an array of industries such as aerospace, automotive, healthcare, and consumer electronics. With the insistent advancement in spheres of material science, fabrication techniques, and design strategies, the future is anticipated to unfold even higher prospects and breakthroughs pertaining to 4 Layer Rigid-Flex PCB.

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