Specification
Multilayer flexible PCB commonly use the following three types of substrate materials:
Polyimide (PI) Substrate
With high heat resistance (over 300 °C) and excellent mechanical strength, PI is the most widely used material for FPCs. Its dielectric constant is approximately 3.2–3.535.
Polyester (PET) Substrate
PET offers a lower cost, but has limited heat resistance (below 120 °C). Its dielectric constant is around 3.0–3.435.
Polyethylene Naphthalate (PEN) Substrate
The performance of PEN lies between PI and PET, with a dielectric constant of about 3.0–3.2.
Features of Multilayer Flexible PCB (FPC)
Multilayer Flexible Printed Circuit Boards (FPCs) are characterized by high density, light weight, flexibility, and high reliability. These features make them ideal for compact and complex electronic systems.
High Density
Multilayer flexible PCBs, especially HDI (High-Density Interconnect) flex PCBs, enable high-density circuit layouts by fabricating fine conductor patterns on multiple substrate layers. This structure meets the stringent requirements of modern electronic devices for miniaturization and complex circuit design.
Light Weight and Flexibility
The substrate materials used in multilayer FPCs are highly flexible and lightweight, allowing the circuit board to bend, fold, and twist in multiple dimensions. This flexibility enables efficient use of space within electronic assemblies and supports compact, lightweight product designs.
Enhanced Flexibility and Design Freedom
The multilayer FPC design allows circuits to move and adjust freely in three-dimensional space, adapting to various installation and mechanical constraints. This feature improves the mechanical adaptability and operational flexibility of electronic devices.
High Reliability
Through precise manufacturing processes and careful material selection, multilayer FPCs offer stable electrical performance and superior reliability. Their robust design minimizes the likelihood of electrical faults and ensures consistent functionality in demanding environments.
Structure of Multilayer Flexible PCB (FPC)
The structure of a Multilayer Flexible Printed Circuit Board (FPC) typically comprises several key layers, each serving a distinct function to ensure electrical performance, flexibility, and durability.
Substrate Layer
The substrate is the fundamental structural layer of the FPC, commonly made from polyimide (PI) or polyester (PET) materials.
PI offers superior heat resistance and insulation properties, making it suitable for applications requiring high thermal stability.
PET is more cost-effective, with excellent flexibility and processability, but lower heat resistance-ideal for general consumer electronics.
Copper Layer
The copper layer serves as the conductive pathway of the FPC and is typically made of electrolytic copper foil or rolled annealed (RA) copper foil, with a thickness ranging from 12 μm to 35 μm.
Electrolytic copper foil is economical and suitable for low-flex applications.
Rolled copper foil provides high ductility and is ideal for designs requiring frequent bending and flexing.
Coverlay (Protective Layer)
The coverlay protects the copper circuitry from moisture, dust, and mechanical damage. It is usually composed of the same material as the substrate (PI or PET) with a thickness between 0.0125 mm and 0.05 mm.
Openings or windows can be designed in the coverlay to allow for soldering and electrical connections where needed.
Adhesive Layer
The adhesive layer bonds different materials together within the FPC structure. Common adhesive types include acrylic and epoxy resin, chosen for their heat resistance, chemical resistance, and flexibility. The adhesive thickness generally ranges from 0.01 mm to 0.05 mm.
Solder Mask Layer
The solder mask layer protects the soldering pads and conductive traces during assembly. It prevents solder bridging and provides electrical insulation. Typical solder mask inks are green, blue, or transparent, depending on design and visual requirements.
Surface Treatment Layer
The surface treatment enhances solderability and electrical contact performance at connection points. Common surface finishes include ENIG (Electroless Nickel Immersion Gold), OSP (Organic Solderability Preservative), immersion tin, or immersion silver, depending on cost and performance requirements.
Applications of Multilayer Flexible PCB (FPC)
Multilayer Flexible Printed Circuit Boards (FPCs) are widely used across numerous industries due to their light weight, high flexibility, and excellent electrical performance. The main application areas include the following:
Multilayer FPCs play a critical role in modern automotive electronics, including navigation systems, air conditioning controllers, instrument panels, safety systems, and infotainment modules.
Their ability to fit into tight spaces and conform to complex shapes provides superior adaptability, reliability, and vibration resistance, essential for harsh automotive environments.
In devices such as smartphones, tablets, laptops, wearable devices, and game consoles, multilayer FPCs enable ultra-thin, lightweight, and flexible designs.
Their foldable and bending characteristics make electronic products more compact, portable, and durable, supporting the ongoing trend toward miniaturization and multifunctionality.
FPCs are increasingly used in implantable and portable medical equipment, such as pacemakers, nerve stimulators, hearing aids, and sleep monitoring devices.
Their biocompatible materials, small size, and flexibility allow them to meet the stringent requirements for high integration, light weight, and reliable performance in medical applications.
In industrial applications such as sensor networks, PLCs (Programmable Logic Controllers), and robot control systems, multilayer FPCs provide excellent heat resistance, high wiring density, and durable connectivity.
Their ability to perform reliably under high-temperature and high-vibration conditions makes them ideal for industrial automation and precision equipment.
5.FPCs are widely applied in routers, switches, wireless base stations, and optical transceivers, where high wiring density and stable signal transmission are essential.
They help achieve compact designs and high-speed performance, meeting the demands of modern communication and data transmission systems.
Production time
After the flex PCB design stage is completed, the next step is prototype fabrication.
For a 4-layer flexible PCB prototype, the typical production time is approximately 10 days.
As the number of layers increases, the manufacturing complexity also rises - resulting in a longer production cycle.
Factors such as material availability, surface treatment requirements, and special process demands (e.g., impedance control or stiffener bonding) may also influence the overall lead time.
Customized product
Most of our products are customized based on the original Gerber files provided by our customers.
After receiving the original Gerber files, we convert them into working Gerber files for production use.
During this conversion process, we adjust certain parameters-such as hole diameter, trace width, and trace spacing-to optimize manufacturability and ensure smooth production.
Package and warranty
All our products are vacuum-packaged with desiccant to ensure optimal protection during storage and transportation.
The shelf life of vacuum-packaged circuit boards varies depending on the surface treatment process, typically ranging from 3 to 12 months. The details are as follows:
Shelf Life for Different Surface Treatment Processes
ENIG (Electroless Nickel Immersion Gold)
Can be stored for up to 12 months under vacuum packaging with desiccant protection.
Lead-Free HASL (Hot Air Solder Leveling)
When no special storage adjustments are made, the shelf life is typically about 3 months.
OSP (Organic Solderability Preservative)
Has a shelf life of 3–6 months under vacuum packaging with desiccant protection. However, if stored improperly (e.g., without desiccant or with insufficient vacuum sealing), the shelf life may shorten to around 3 months.
Immersion Gold (Chemical Gold Plating)
Shelf life can reach 6–12 months, provided that sealed packaging and desiccant are used.
Company advantage
1. We guarantee a response within 24 hours to all customer inquiries and complaints.
2. Our factory offers 1-day sample production for 2-layer boards and provides rapid manufacturing services for small and medium orders, ensuring short lead times and on-time delivery.
3. We support multiple payment options, including EUR, USD, RUB, and CNY, through PayPal, T/T, and other convenient methods.
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