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PI Stiffener Flexible PCB: A Game-Changer in Flex Circuit Design

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Item Flexible PCB
Max Layer 8L
Inner Layer Min Trace/Space 3/3mil
Out Layer Min Trace/Space 3.5/4mil
Inner Layer Max Copper 2oz
Out Layer Max Copper 2oz
Min Mechanical Drilling 0.1mm
Min Laser Drilling 0.1mm
Aspect Ratio(Mechanical Drilling) 10:1
Aspect Ratio(Laser Drilling) /
Press Fit Hole Ttolerance ±0.05mm
PTH Tolerance ±0.075mm
NPTH Tolerance ±0.05mm
Countersink Tolerance ±0.15mm
Board Thickness 0.1-0.5mm
Board Thickness Tolerance(<1.0mm) ±0.05mm
Board Thickness Tolerance(≥1.0mm) /
Impedance Tolerance Single-Ended:±5Ω(≤50Ω),±7%(>50Ω)
Min Board Size 5*10mm
Max Board Size 9*14inch
Contour Tolerance ±0.05mm
Min BGA 7mil
Min SMT 7*10mil
Surface Treatment ENIG,Gold Finger,Immersion Silver,Immersion Tin,HASL(LF),OSP,ENEPIG,Flash Gold;Hard gold plating
Solder Mask Green Solder Mask/Black PI/Yellow PI
Min Solder Mask Clearance 3mil
Min Solder Mask Dam 8mil
Legend White,Black,Red,Yellow
Min Legend Width/Height 4/23mil
Strain Fillet Width 1.5+0.5mil
Bow & Twist /
Table of Contents
Primary Item (H2)

In the realm of flexible printed circuit boards (PCBs), introducing Polyimide (PI) stiffeners has been revolutionary. These stiffeners have become a cornerstone in enhancing the durability and functionality of flexible PCBs, particularly in applications where flexibility and mechanical stability are paramount. Let's delve into PI stiffener flexible PCBs, exploring their benefits, applications, and why they're increasingly becoming the go-to solution for complex electronic designs.

What is a PI Stiffener?

A PI stiffener is a reinforcement made from polyimide material attached to specific areas of a flexible PCB to provide additional mechanical support. Unlike traditional rigid PCB materials, PI stiffeners offer a unique combination of flexibility and rigidity, making them ideal for reinforcing flex circuits without compromising their inherent bendable nature.

The Role of PI Stiffeners in Flexible PCBs

  • Enhanced Mechanical Support

PI stiffeners are strategically placed to bolster areas of the flex PCB that require extra support, such as connector sites or component mounting areas. This targeted reinforcement helps prevent damage during assembly, handling, and operation, thereby extending the lifespan of the PCB.

  • Improved Assembly Process

Adding PI stiffeners simplifies the assembly process by providing a stable foundation for soldering components. This stability is crucial for automated assembly processes, where precision and reliability are vital to minimizing defects and ensuring high-quality outcomes.

  • Design Flexibility

PI stiffeners allow designers to push the boundaries of flex circuit applications. With the ability to customize the shape, size, and placement of stiffeners, designers can create more complex and innovative PCB layouts that meet the specific needs of their projects.

Benefits of Using PI Stiffeners

Polyimide (PI) stiffeners are crucial in enhancing the mechanical stability of flexible printed circuit boards (PCBs) while maintaining their inherent flexibility. These stiffeners are made from polyimide, a high-performance polymer known for its excellent thermal stability, mechanical properties, and chemical resistance. 

  • Thermal Resistance: PI stiffeners can withstand high temperatures, making them ideal for applications undergoing rigorous soldering or operating in high-temperature environments. This characteristic ensures the stiffener does not degrade or lose its mechanical properties under thermal stress.
  • Chemical Resistance: Polyimide resists most solvents and chemicals, including those commonly used in PCB manufacturing and cleaning processes. This resistance ensures that the stiffener maintains its integrity and does not contribute to the contamination or degradation of the PCB.
  • Mechanical Stability: While flexible PCBs are prized for their ability to bend and flex, certain areas may require additional support to prevent damage. PI stiffeners provide targeted reinforcement, enhancing the mechanical stability of these areas without significantly impacting the overall flexibility of the PCB.
  • Electrical Insulation: PI materials are excellent electrical insulators. When used as stiffeners, they contribute to the overall electrical performance of the PCB by preventing short circuits and electrical interference, thereby ensuring the reliability of the electronic device.
  • Flexibility: PI stiffeners retain flexibility despite their role in providing mechanical support. This allows them to be used in applications where the PCB needs to bend or flex during use or installation without compromising the structural integrity of the stiffened areas.
  • Durability: PI stiffeners are known for their durability and resistance to wear and tear. This makes them suitable for applications where the PCB may be subject to repeated flexing, vibration, or other physical stresses.
  • Lightweight: Polyimide is a lightweight material, which means that adding PI stiffeners to a flexible PCB does not significantly increase its weight. This is particularly important in aerospace, wearable technology, and other applications where every gram counts.
  • High-Frequency Performance: PI materials have favorable dielectric properties, making PI stiffeners suitable for high-frequency applications. They do not significantly affect the impedance of the PCB, ensuring that signal integrity is maintained.
  • Customization: PI stiffeners can be customized in terms of thickness, shape, and size to meet the specific requirements of each application. This allows for precise control over the mechanical properties of the PCB in critical areas.

Applications of PI Stiffener Flexible PCBs

PI stiffener flexible PCBs find their place in a wide array of industries, including:

  • Consumer Electronics: In devices like smartphones, tablets, and wearables, the PCB must conform to compact and complex shapes.
  • Automotive: For applications that require durable and flexible electronics, such as in-vehicle infotainment systems.
  • Medical Devices: The flexibility of the PCB allows for innovative device designs without sacrificing durability or reliability.
  • Aerospace: In applications where the PCB must endure extreme conditions without failing.


PI stiffener flexible PCBs represent a significant advancement in electronic design, offering an optimal balance between flexibility and mechanical stability. As technology continues to evolve, the role of PI stiffeners in enabling more sophisticated, reliable, and flexible PCB designs will undoubtedly grow. Whether in the latest wearable tech or critical medical devices, PI stiffener flexible PCBs are set to play a pivotal role in tomorrow's electronics.

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