Buy China Flexible PCB Suppliers - Lightweight and Bendable Circuit Boards from Leading Factory Companies, Factories
Product Description
The Main Functions Are Reflected In
Far-Reaching Impact
It has directly given rise to innovative product forms such as foldable screen mobile phones and wearable devices, and has become an indispensable cornerstone for the high-end development of fields such as automotive electronics, medical equipment, and aerospace. Flexible PCBs have profoundly transformed the design concepts and industrial landscape of electronic products by endowing them with "flexibility" and "deformability" capabilities.
What is Flexible PCB (FPC)?
Flexible PCB, whose full name is flexible printed circuit board, is commonly known as "soft board".
You can imagine it as a kind of "flexible electronic circuit" or "circuit cloth". It is a "relative" of the common green, hard computer motherboard (rigid PCB) we often see, but the core material is completely different.
Core Features (What is it)
- The material is soft: Its substrate is not hard glass fiber but a flexible plastic film such as polyimide, which is heat-resistant and can be repeatedly bent.
- Bendable and foldable: It can be bent, wound and folded in three dimensions to adapt to various narrow or irregular spaces.
- Thin and light: Much thinner and lighter than rigid PCBs.
Main Uses (What to do with it)
- Smartphones / foldable phones: The "flat cables" connecting the screen, camera, buttons and battery are mostly flexible PCBs.
- Wearable devices: Smartwatches, bracelets and health patches that fit the curves of the human body.
- Notebook computers: The "link" connecting the motherboard and the screen.
- Automotive electronics: LED headlights, central control screens, sensors, complex wiring harnesses.
- Precision medical equipment: Endoscope capsules and pacemakers with extremely high space and reliability requirements.
- Aerospace: Satellites and aircraft — reducing weight and adapting to complex cabin layouts.
Normal Types of Flexible PCB
How to Design Flexible PCB?
Flexible PCB is widely used in consumer electronics, automotive electronics, medical equipment and other fields due to its characteristics of being bendable, thin and light, and resistant to bending. Its design needs to take into account the characteristics of flexible substrates, mechanical reliability and electrical performance. The core design points can be decomposed into the following core dimensions.
▶ Substrate selection
- Core base material: Commonly used PI (polyimide) base material (temperature resistance -200°C to 260°C, excellent bending resistance), supplemented by PET (low cost, poor temperature resistance, only suitable for low-requirement scenarios). For the covering film, PI material is preferred as it needs to match the bending characteristics of the base material.
- Thickness matching: The thickness of the flexible substrate (such as 25μm, 50μm PI) should be combined with the bending radius and load-bearing requirements. Electrolytic copper (with good ductility) is preferred for copper foil. The recommended thickness is 12μm or 18μm. Thick copper (≥35μm) should be avoided as it may increase bending stress.
▶ Structural design
- Single/double/multi-layer flexible boards: Single layers are suitable for simple wiring, while multi-layers require an additional bonding layer. For high-frequency/high-bending scenarios, glue-free flexible boards (Rigid-Flex) are preferred.
- Transition between rigid zone and flexible zone: The junction between the rigid zone (FR-4 substrate) and the flexible zone should be chamfered (≥0.3mm) to prevent cracking caused by stress concentration.
▶ Routing rules
- Line width and line spacing: The line width in the flexible zone is ≥0.1mm, and the line spacing is ≥0.1mm. For high-current traces, the width should be widened to prevent heating.
- Routing form: Right-angle/acute angle routing is prohibited (prone to stress). All should use circular arc transitions (fillet radius ≥0.1mm). Wiring in the bending area should be as parallel as possible to the bending direction.
- Avoid single-point connection: The wiring in the bending area should not be fixed at a single point. Auxiliary wiring can be added or copper can be laid to enhance mechanical strength.
▶ Layout optimization
- Keep components away from the bending area: Components are not allowed to be mounted in the flexible area. They should be placed in the rigid area and at least 1mm away from the edge of the flexible area.
- Symmetrical layout: The wiring of multi-layer flexible boards should be symmetrically distributed to reduce the stress difference between layers during bending.
▶ Bending radius control
- Minimum bending radius: Must meet "bending radius ≥5 times the total thickness of the flexible board". For dynamic bending (repeated bending) scenes, the radius needs to be increased to 10 times the total thickness.
- Bending times: The dynamic bending life of a common flexible board is approximately 100,000 times. For high-reliability scenarios, bent-resistant base materials (such as modified PI) should be selected.
▶ Stress relief
- Copper laying design: Grid-shaped copper sheets (instead of solid copper) can be laid in the bending area to reduce the stretching/compression of the copper foil during bending.
- Reinforcing ribs: In areas prone to wear or high stress, polyimide reinforcing ribs (25 to 50μm in thickness) can be added, or the covering film can be thickened locally.
▶ Pad specification
- No pads in the flexible zone: Pads are only arranged in the rigid zone. If welding is required in the flexible zone, a rigid reinforcing plate (FR-4 or stainless steel) needs to be added. The size of the reinforcing plate should cover the outside of the pad by ≥0.5mm.
- Pad shape: Rectangular pads with rounded corners (radius ≥0.1mm) to prevent cracking at the pad edges. The size of the SMD pad should match the pins of the components, with a solder allowance of 0.05 to 0.1mm reserved.
▶ Hole position design
- Through holes: Through holes are prohibited in the flexible zone and must be arranged in the rigid zone. The hole diameter of metallized vias should be no less than 0.2mm, and the copper plating thickness on the hole walls should be no less than 8μm.
- Positioning holes: Should be kept away from the bending area, with a hole diameter tolerance of ±0.05mm. The edges of the holes should be chamfered.
▶ Covering film design
- The covering film must completely cover the flexible area traces. The distance between the edge of the window and the traces should be ≥0.1mm to avoid exposed copper.
- The recommended thickness of the covering film in the bending area is 25μm. If it is too thick, the bending flexibility will be reduced.
▶ Process limitations
- Bending process: Cold bending (at room temperature) is required. Hot bending is strictly prohibited. The bending angle should not exceed 180°, and a rebound allowance should be reserved.
- Surface treatment: For the flexible zone surface, OSP (organic solder mask) or nickel-gold plating is preferred. Tin spraying should be avoided.
- Impedance control: For high-frequency flexible boards (such as 5G and RF scenarios), impedance calculation (such as 50Ω and 100Ω differential impedance) is required. The impedance deviation in the bending area needs to be controlled within ±10%.
- Grounding design: The flexible board should be designed with a complete grounding layer to reduce electromagnetic interference. The grounding layer should be as continuous as possible and avoid disconnection in the bending area.
Core Summary: The core of flexible PCB design lies in "adapting to bending characteristics, distributing stress, and ensuring dual reliability of electrical and mechanical aspects". It prioritizes following the basic principles of "wide traces, arc transitions, component placement far from the bending area, and matching the bending radius", while adjusting the substrate and structure selection in combination with application scenarios (static/dynamic bending, high frequency/large current).
Flexible PCB Manufacturing Processes and Controls
The manufacturing process of flexible PCBs is one of the most delicate and complex fields in electronic manufacturing. The core difficulty lies in dealing with extremely thin, soft, deformable and environmentally susceptible materials. Below is a detailed interpretation of the process details and control points of each link:
- Cutting and cleaning: Cut the roll-shaped PI substrate and copper foil in a constant temperature and humidity environment. Clean immediately after cutting to remove oil stains and particles.
- Dry film application / photoresist coating: Apply a single layer of photosensitive resist (dry film) onto the copper foil.
- Exposure and development: By exposing the film with a line pattern to ultraviolet light and then developing it, the required line pattern is protected, and the unexposed resist is washed away.
- Etching: Use chemical solutions (such as acidic copper chloride) to etch away unprotected copper to form fine copper circuits. The control requirements for the etching factor are extremely high to ensure the accuracy of fine lines.
- Film removal and cleaning: Remove the resist layer protecting the circuit to obtain the exposed inner circuit pattern.
- Surface treatment: Micro-etching or chemical treatment is carried out on the copper circuit to enhance the adhesion with the covering layer.
- Coating alignment and lamination: Align the PI covering film (with an opening to expose the solder pad) or liquid photosensitive covering ink with the inner circuit through a precise optical alignment system, then perform hot-pressing curing. It is essential to ensure that there are no bubbles, no wrinkles and that the alignment is precise.
- Drilling: Due to the softness of the material, a drilling rig with high rotational speed and low feed rate should be used, along with specially designed covers and pads, to prevent burrs at the hole opening, nail heads or material tearing.
- Pre-treatment and electroless copper plating: The hole walls of flexible materials are smooth and not prone to adhesion. First, drilling dirt should be removed and activated with plasma or potassium permanganate solution, then a thin layer of chemical copper is deposited on the hole wall to provide a conductive substrate for subsequent electroplating.
- Outer layer pattern transfer: Similar to the inner layer, through film application, exposure, development, pattern electroplating, thickening of copper holes and circuits, and etching, the outer layer circuits and through hole connections are formed.
- Solder mask and surface treatment: Apply flexible solder mask ink to protect the circuit and expose the pads. The pads undergo surface treatment, such as chemical nickel-gold, OSP or electroplated hard gold (for gold fingers).
- Shape processing: The final shape is cut out through precision die punching or CNC milling machines. The mold clearance and milling cutter parameters must be strictly controlled to prevent delamination and burrs.
- Electrical testing and final inspection: Conduct 100% open and short circuit electrical tests (commonly used flying probe tests) along with strict visual inspection, dimensional measurement and reliability spot checks (such as bending test, solderability test).
⚙️ Tension Control
- Objective: From opening to winding, all conveying rollers and mechanical hands must achieve minimum tension or even zero tension transmission.
- Reason: Any excessive stretching will lead to permanent deformation of the material, inaccurate alignment of the graphics, dimensional deviations, and even microcracks.
🧹 Cleaning and Dust-Proof Control
- Objective: Key processes (exposure, lamination, covering) must be carried out in an environment with a cleanliness level of 1,000 or higher.
- Reason: Tiny dust particles falling on the film or material can cause defects such as circuit notches, short circuits or open circuits.
🌡️ Temperature and Humidity Control
- Objective: Maintain a constant temperature and humidity throughout the workshop (e.g., 22±2°C, 50±5%RH). All hygroscopic materials must be strictly baked before use.
- Reason: After the material absorbs moisture, it may experience plate cracking, delamination and bubbles during high-temperature processes.
🔧 Stress Management
- Objective: To balance the stress of each layer of material in design and process.
- Measures: Design symmetrical stacked structures; adopt a slow cooling process after lamination; carry out stress release baking when necessary; prevent the finished board from warping and curling.
The Application of Flexible PCBs in 2026
Looking ahead to 2026, the application of flexible PCBs (FPCs) and rigid-flex boards will become more extensive and in-depth. The core driving forces for their growth come from the innovation of equipment forms, the demand for performance improvement, and the explosion of emerging markets.
1. Consumer Electronics: The Core of the Form Revolution
Folding/curling/stretching screen devices: Flexible PCBs will continue to serve as the "neural network" for hinges and screens. By 2026, foldable phone forms will be more diverse (such as three-fold and rollable), and requirements for bending reliability, thinness and lightness, and signal integrity of FPCs will reach new heights.
AR/VR devices: Flexible PCBs are the key to achieving high-density wiring and sensor integration in thin and light helmets and smart glasses.
New wearable devices and "electronic skin": Smart bracelets/watches will integrate more health sensors (such as continuous blood glucose monitoring). "Electronic tattoos" or flexible patches used for health monitoring will start to enter the consumer market.
2. Automotive Electronics: The "Blood Vessels" of Intelligence and Electrification
Intelligent cockpits and displays: Large-sized, irregular-shaped, and height-adjustable automotive displays will extensively employ rigid-flex panels and FPCs to achieve complex wiring and high reliability.
ADAS and autonomous driving: An increasing number of cameras, millimeter-wave radars and lidar sensors require lightweight FPCs for high-speed signal transmission.
Battery management system: Inside the battery pack of new energy vehicles, the replacement of traditional wiring harnesses by FPC has become a clear trend. By 2026, the application penetration rate of FPC in BMS will increase significantly.
3. Medical and Health Care: In-Depth from Diagnosis to Treatment
Implantable and ingestible devices: Micro-implantable devices used for cardiac monitoring, nerve stimulation, etc., whose ultimate miniaturization and biocompatibility requirements must rely on highly integrated flexible/rigid-flexible combined circuits.
High-end wearable medical devices: Hospital-grade continuous vital sign monitoring patches will become more widespread, and flexible PCBs are the core to ensure comfort, accuracy and wireless connectivity.
4. Communication and Computing: The Cornerstone of Performance Upgrade
5G-Advanced/6G and millimeter-wave devices: High-frequency communication requires extremely low signal loss. Flexible circuits using new substrates such as liquid crystal polymers will become the preferred solution for millimeter-wave antenna modules and high-speed connectors.
Advanced packaging and chip interconnection: FPC technology will be more widely applied to chip-level interconnection, such as the interposer layer in 2.5D/3D packaging or the rewiring layer in fan-out packaging, to enhance computing power.
5. Robots and Human-Machine Interaction
Bionic and collaborative robots: Flexible sensors and circuits will be integrated into the robot's "fingers" and "skin", endowing it with more sensitive touch and adaptive grasping capabilities.
The integration of flexible electronics and structural components: FPC will be further integrated with structural components to form "structural electronics", meaning that the product casing itself is part of the circuit, achieving ultimate space savings and functional integration.
In conclusion, by 2026, flexible PCBs will become a fundamental and transformative technology that defines the form of the next generation of electronic products, enhances system performance, and empowers emerging intelligent scenarios. Core trends include: Technology Integration (FPC integrating with sensors, antennas, heat dissipation films), Material Innovation (LCP and modified PI substrates), and Market Penetration (from high-end to mid-range consumer electronics and mainstream vehicle models).
Conclusion
Flexible PCB (FPC) is a silent revolution in electronic interconnection technology. It is not only a material that makes electronic devices "softer" and "thinner", but also a fundamental enabling technology that drives product innovation, enhances system performance, and gives rise to brand-new application scenarios. Its future development will continue to follow the direction of "thinner and lighter, more reliable, higher frequency and speed, and higher integration", deeply embedded in every key electronic node of the intelligent society, and its importance will increase day by day.
