High-Quality China Rigid Flex PCB Suppliers | Single & Double-Sided, Multi-Layer Rigid Flex PCB Factory Manufacturers, Quotes
Product Description
What is Rigid Flex PCB?
Core Components & Structure
A typical rigid-flex PCB consists of three key parts, layered and bonded together through specialized processes:
Made of traditional rigid substrate materials (e.g., FR-4, a glass-reinforced epoxy resin). These parts provide mechanical stability to support electronic components (such as chips, resistors, capacitors) and ensure structural integrity.
Composed of flexible substrates (common materials include polyimide, PI, or polyester, PET). These parts are thin, lightweight, and can be repeatedly bent, folded, or twisted, allowing the board to adapt to irregular shapes or dynamic environments (e.g., parts that need to open/close or vibrate).
The rigid and flexible sections share internal conductive copper layers (signal traces, power lines, ground planes) that are seamlessly connected. This eliminates the need for wires, connectors, or solder joints between separate rigid and flex boards, reducing failure risks.
Key Advantages
Compared to standalone rigid PCBs or flex PCBs, rigid-flex PCBs offer distinct benefits:
They can be folded to fit into tight, complex enclosures (e.g., foldable phones, wearables), reducing the overall size and weight of electronic devices.
Fewer connectors and solder joints mean fewer potential points of failure (e.g., loose connections from vibration or aging), which is critical for high-reliability applications like aerospace equipment.
Integrating multiple rigid and flex parts into one board streamlines the manufacturing process, reducing assembly time and human error.
Continuous copper traces minimize signal loss and electromagnetic interference (EMI), ensuring stable signal transmission—essential for high-frequency devices.
Common Applications
Rigid-flex PCBs are indispensable in industries where space, reliability, and flexibility are paramount:
- Consumer Electronics: Foldable smartphones, smartwatches, laptops, cameras, and earbuds (e.g., the hinge area of foldable phones uses flexible sections to connect rigid display and battery boards).
- Aerospace & Defense: Satellites, aircraft avionics, and military equipment (they withstand extreme temperatures, vibration, and space constraints).
- Automotive: In-vehicle infotainment systems, sensor modules, and advanced driver-assistance systems (ADAS) (adapt to the curved or confined spaces of car interiors).
- Medical Devices: Portable monitors, implantable devices (e.g., pacemakers), and diagnostic equipment (offer biocompatibility, miniaturization, and durability).
The Type of Rigid Flex PCB
The classification dimensions of Rigid-Flex PCB are numerous. The core classification can be based on structural form, flexible area characteristics, number of layers, and adaptability to application scenarios, etc. Different categories correspond to different process difficulties and usage requirements. The following are the mainstream classification methods and detailed explanations in the industry.
This is the most commonly used classification method. The core basis is the connection mode and layout characteristics of the rigid and flexible areas, which directly determine the installation compatibility of the PCB.
- Single flexible zone rigid-flexible combined PCB: The entire board has only one continuous flexible zone, with both ends or one end connected to the rigid board. The flexible zone is mainly used to achieve "folding" or "turning" functions, such as the flat cable connecting the laptop screen to the main unit and the circuit board of some headphones. It has a simple structure and low cost, and is the most common basic model in consumer electronics.
- Multi-flexible zone rigid-flexible combined PCB: It contains two or more independent flexible zones and forms a complex structure through the series connection of multiple rigid boards. It is suitable for equipment that requires multi-directional bending and decentralized layout, such as industrial sensor modules (multiple detection units are connected to the main control rigid board through flexible areas) and lens module circuit boards for multi-camera mobile phones.
- Three-dimensional rigid and flexible combined PCB: The flexible area can achieve bending and twisting in three-dimensional space, while the rigid area is distributed in different spatial planes and seamlessly connected through the flexible area. It is mostly used in equipment with extremely compact space and irregular shapes, such as the fuselage control board of unmanned aerial vehicles and the integrated circuit boards in car instrument panels, which can maximize the utilization of three-dimensional space.
The main distinction is whether the flexible part can be repeatedly bent to adapt to static installation or dynamic working scenarios.
- Static rigid-flex combined PCB: The flexible area is only bent and shaped once during assembly, maintaining a fixed form during subsequent use and not subject to repeated deformation. For instance, the frame of a foldable phone is connected to the circuit board. After assembly, the flexible area remains in a fixed folded state for a long time. The core requirement is the structural stability after shaping.
- Dynamic rigid-flex PCB: The flexible area needs to withstand long-term and repeated bending, twisting and other dynamic actions, which requires extremely high fatigue resistance and copper layer adhesion of the flexible substrate. Typical applications include the paper feed mechanism circuit board of printers and the opening and closing components of wearable devices (such as foldable watches), which need to meet the requirement of no failure after tens of thousands of bends.
Similar to ordinary PCBs, they are classified by the number of layers of conductive circuits. The more layers there are, the higher the integration degree and the more complex the process.
- Single-layer rigid-flex PCB: It contains only one layer of conductive copper foil, and the flexible and rigid areas share this layer of circuit. It has the simplest structure and the lowest cost, but its function is single. It is only suitable for low-complexity circuits, such as the control boards of simple toys and the connection lines of small remote controls.
- Double-layer rigid-flexible combined PCB: It consists of two layers of conductive copper foil, with interlayer conduction achieved through vias in the middle. The flexible area uses a flexible substrate, and the rigid area is equipped with a FR-4 core board. Taking into account both cost and practicality, it is widely used as a peripheral module for smart phones and tablet computers.
- Multi-layer rigid-flex PCB: The number of layers is ≥4, usually composed of alternating superposition of "rigid layer - flexible layer - rigid layer", and it has a power layer, ground layer and signal layer inside. It has a high degree of integration and can achieve complex signal transmission and power management. It is suitable for high-end electronic devices, such as satellite circuit boards in aerospace and precision detection mainboards in medical equipment.
Specialized types designed for extreme environments or special needs, with additional customized requirements for materials and processes.
- High-frequency rigid-flex combined PCB: It adopts flexible substrates with low dielectric constant and low loss (such as PTFE-modified polyimide), reducing attenuation and interference during signal transmission, and is suitable for high-frequency scenarios such as 5G equipment, radar systems, and satellite communication equipment.
- High-temperature resistant rigid-flex combined PCB: The flexible substrate and adhesive are made of high-temperature resistant materials (such as special PI), which can operate stably within a temperature range of -55 °C to 200 °C or even wider. It is widely used in peripheral equipment of aero engines and industrial high-temperature sensors.
- High-density interconnect (HDI) rigid and flexible combined PCB: By using micro-vias and fine line width and line spacing technologies, it enhances the line density and reduces the board size, making it suitable for miniaturized devices such as smartwatches and implantable medical devices (such as auxiliary circuit boards for pacemakers).
How to Design Rigid Flex PCB?
The design and production of rigid-flex combined PCBs need to take into account both the structural stability of rigid PCBs and the bending adaptability of flexible PCBs. During the design stage, potential risks in subsequent production and use should be avoided. In the production stage, special process links need to be controlled to ensure the reliability and consistency of the product. The following are detailed design and production key points:
Boundary definition: A transition zone (usually 0.5-1mm) should be reserved at the boundary between the rigid zone and the flexible zone to prevent components, vias, and copper foils from crossing the boundary and to avoid cracking due to material differences during bending. The edges of the flexible zone need to be rounded (radius ≥1mm) to reduce stress concentration.
Flexible zone location & bending: The flexible zone should avoid high-stress areas. In dynamic bending scenarios, the bending radius should meet the requirement that "the minimum bending radius of the inner copper foil is ≥ 10 times the thickness of the flexible substrate, and that of the outer copper foil is ≥ 15 times". Static bending only requires one-time shaping, and the radius can be appropriately reduced. Avoid overlapping and bending in the flexible zone.
Component layout: Heat-generating components (chips, resistors) should be concentrated in the rigid area far from the flexible zone. Heavy-duty components (interfaces, sensors) must be fixed in rigid areas with reserved heat dissipation space and fixing holes.
Line direction adaptation: In the flexible zone, the line direction is preferred to be horizontal (parallel to the bending direction) to reduce tensile/compressive damage. Avoid dense thin lines and sharp angles; line width and spacing should be slightly larger than rigid areas (minimum recommended ≥0.1mm).
Stacking structure: For multi-layer rigid-flexible boards, the flexible layer should adopt a symmetrical structure (e.g., "rigid layer - flexible layer - flexible layer - rigid layer") to prevent warpage. Rigid core materials are prohibited in the flexible zone; adhesives should use flexible materials (such as acrylic).
Via & grounding: Metallized vias are prohibited in the flexible zone (keep ≥1mm away from boundary). Set up independent ground layers to reduce signal interference.
Flexible substrate: For dynamic bending, choose polyimide (PI) with high fatigue resistance; for static scenarios, lower-cost polyester (PET) can be selected. High-frequency equipment requires low-loss PI (such as PTFE-modified PI).
Copper foil & coverlay: Rolled copper foil (excellent ductility and bending resistance) is preferred for flexible areas, while electrolytic copper foil can be used for rigid areas. The surface of the flexible zone should be covered with a flexible coverlay (PI film), extending 0.2-0.3mm beyond the copper foil for insulation.
Key Points of Manufacturing
The production of rigid-flexible combined PCBs integrates the processes of rigid and flexible PCBs, and requires additional control over the connection links between rigidity and flexibility. The core points are as follows:
• Substrate cleaning: The surface of the flexible PI substrate is prone to adsorbing impurities. It is necessary to remove oil stains and oxide layers through plasma cleaning or chemical treatment to enhance the adhesion between the copper foil and the substrate. Rigid FR-4 substrates need to be dried and dehumidified to prevent air bubbles from forming during lamination.
• Precise lamination: During lamination, temperature, pressure and time need to be controlled. The bonding parameters of the flexible zone and the rigid zone should be set differently to prevent deformation of the flexible substrate or delamination of the rigid zone. The stepwise lamination method is adopted. First, the flexible layer is laminated, and then it is laminated with the rigid layer to ensure a tight interlayer bond.
• High-precision exposure: Flexible substrates are prone to stretching. Special fixtures should be used for fixation during exposure to prevent line deviation. The ultraviolet parallel light exposure machine is adopted to ensure the accuracy of the line pattern, especially to control the line width error in the flexible zone within ±0.02mm.
• Etching process optimization: Alkaline etching solution is used to treat the copper foil in the flexible zone. The etching speed is slightly lower than that in the rigid zone to prevent excessive etching from causing line breakage. After etching, it is necessary to clean it in time to avoid the residual liquid from corroding the substrate.
• Flexible zone contour cutting: The flexible zone contour is processed by laser cutting (CO₂ laser or ultraviolet laser), with a smooth cut and no burrs, avoiding the tearing of the base material caused by mechanical cutting. When cutting, the laser power needs to be controlled to prevent damage to the internal circuits.
• Rigid zone forming: The rigid zone can be formed by CNC milling, and the edges need to be deburred and chamfered. The boundary between the rigid zone and the flexible zone needs to be ground a second time to ensure a smooth transition and reduce stress concentration during bending.
• Surface treatment: Rigid areas can undergo surface treatments such as tin spraying, gold plating, and OSP to enhance soldering performance. The surface of the flexible zone is only protected by a covering film. High-temperature treatments such as tin spraying are prohibited to prevent deformation of the base material.
• Full-process inspection: During production, interlayer adhesion (through peel test) and line conductivity (flying probe test) need to be inspected. The finished products need to undergo bending tests (dynamic bending requires simulating tens of thousands of cycles) and high and low temperature environment tests to ensure stability and reliability in usage scenarios.
Rigid Flexible PCB Capability Specification
| Parameter / Feature | Standard Specification | Advanced Specification | ||
|---|---|---|---|---|
| RIGID FLEX PCB | Flex Layers | Lamination structure ≤4L；Book structure ≤10L | Lamination structure ≤4L；Book structure ≤12L | |
| Max. Panel Size (Shipping) | 210mm × 480mm | 460mm × 480mm | ||
| FPC Dielectric Thickness | 2 MIL, 3 MIL, 4 MIL | 1 MIL | ||
| PTH Rigid-Flex Transition Area | ≤ 1.2 mm | ≤ 1.0 mm | ||
| Pattern Spacing (Rigid to Transition) | ≥ 1.2 mm | ≥ 0.9 mm | ||
| Rigid-Flex Structure | Typical structure, Flying tail structure, Multi-flex book structure, Two-flex lamination structure, Single-sided asymmetric structure, Asymmetric structure, etc. | |||
Frequently Asked Questions (FAQ)
Q1 What is the difference between a flex PCB and a rigid-flex PCB?
A flexible PCB (FPC) is built entirely from flexible substrates like polyimide, making the whole board pliable. A rigid-flex PCB is an integrated hybrid containing both rigid FR-4 sections (for mounting heavy or dense components) and flexible sections (for dynamic bending or compact folding) joined without separate cable connectors.
Q2 How do rigid-flex PCBs improve electronic product reliability?
By integrating rigid and flexible substrates into a unified circuit board, rigid-flex PCBs eliminate vulnerable solder joints, wire harnesses, and physical pin connectors. This drastically minimizes electrical connection failures caused by shock, continuous vibration, and environmental stress.
Q3 What are the standard bending radius rules for rigid-flex designs?
For dynamic bending applications, the minimum bend radius should be at least 10 times the flexible substrate thickness for inner copper foils and 15 times for outer copper foils. For static (one-time assembly) bends, a tighter radius can be utilized safely.
Q4 Which substrate materials are best suited for rigid-flex circuit boards?
Polyimide (PI) is the most preferred flexible core material due to its exceptional fatigue resistance and thermal stability. FR-4 is standard for rigid sections. For high-frequency microwave applications, PTFE-modified polyimide or low-loss specialized substrates are used.
Q5 Are vias allowed in the flexible section of a rigid-flex PCB?
Plated through-hole (PTH) and micro-vias are strictly prohibited in the flexible bending zone to prevent trace cracking under mechanical stress. All vias must remain in the rigid sections and maintain at least 1.0mm spacing from the rigid-flex transition interface.
Q6 Can rigid-flex PCBs be used for high-density interconnect (HDI) applications?
Yes. Modern rigid-flex manufacturing supports HDI technology, including micro-vias, laser drilling, and ultra-fine trace line/spacing (down to 1 mil dielectric thickness), making them ideal for compact wearables, pacemakers, and high-density mobile devices.
