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 What is the Polyimide Flex PCB ?

What is the Polyimide Flex PCB ?


polyimide flex pcb , often referred to as PI, is a preferred material for flex PCB substrates. Its yellow-transparent appearance and relative density of 1.39 to 1.45 make it unique. Polyimide films exhibit exceptional resistance to high and low temperatures. electrical insulation, adhesion, radiation resistance, and dielectric properties. These characteristics enable polyimide to perform reliably in a temperature range of -269°C to 280°C . with short-term resistance up to 400°C . Its tensile strength remains robust, ensuring durability under various conditions. It is especially suited for high-temperature electrical insulation. and as a base material for flexible printed circuits. making it an essential component in advancing flex PCB technology.

what is polyimide

Advantages of Polyimide in Flex PCBs


Polyimide (PI)



Glass Transition Temperature (Tg)




Continuous Operating Temperature




Tensile Strength (MPa)




Thermal Expansion (ppm/°C)




Dielectric Constant




Dielectric Strength (kV/mm)




High Temperature Resistance

Polyimide can withstand continuous operating temperatures up to 260°C and short-term exposure to 400°C, making it ideal for applications in aerospace and automotive industries.

Superior Mechanical Properties

It exhibits high tensile strength (231 MPa), low thermal expansion (20 ppm/°C), and excellent dimensional stability, ensuring reliability under stress, vibration, and impact.

Outstanding Electrical Insulation

With a dielectric constant of 3.5 and dielectric strength of 280 kV/mm, polyimide minimizes signal loss and crosstalk, suitable for high-frequency and high-speed data applications.

Chemical Resistance

polyimide flex pcb resists acids, alkalis, and organic solvents, making it suitable for harsh chemical environments.

Lightweight and Thin

Polyimide’s lightweight and thin nature allows for reduced weight and size in portable electronic devices and aerospace components.


Its inherent flexibility makes polyimide an ideal choice for flexible printed circuit boards, allowing them to bend and conform to various shapes without losing functionality.

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Types of Polyimide PCB Materials and Models

Kapton (DuPont)

  • Kapton HN: Standard grade for a wide range of applications
  • Kapton FN: Features a fluoropolymer coating for added properties
  • Kapton MT: High thermal conductivity

Upilex (Ube Industries)

  • Upilex R: High glass transition temperature (280°C)
  • Upilex S: Exceptional thermal stability (500°C+)
  • Upilex VT: Enhanced mechanical properties

AP (Kaneka)

  • AP-8525: High-temperature resistance
  • AP-8535: Improved mechanical strength and flexibility


  • VTEC PI-1388: Excellent chemical resistance
  • VTEC PI-1390: High dielectric strength


  • Duraflex PIF: Known for flexibility and durability

Highlights Polyimide Flex PCB Materials

Kapton HM offers superior thermal performance and flexibility. making it suitable for extreme environments. Isola P95, with its high thermal stability and dielectric properties. That preferred for high-temperature and high-voltage applications. Both materials are excellent choices for demanding flex PCB applications. but the choice depends on the specific requirements of the application.

PropertyKapton HMIsola P95
Density1.42 g/m³1.43 g/m³
Glass Transition Temp (Tg)428℃ (802℉)260℃(500℉)
Tensile Strength1000 psi (6.9 MPa)800 psi (5.5 MPa)
Elongation at Break200%150%
Dielectric Constant3.33.4
Dielectric Strength4000 V/mil4000 V/mil
Moisture Absorption0.02%0.02%
Flame RetardantUL 94 V-0UL 94 HB
Chemical ResistanceExcellentExcellent
Temperature Range“-269℃ to 400℃ (-452℉ to 752℉)“-269℃ to 260℃ (-452℉ to 500℉)
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Design Guidelines for Polyimide Flex PCBs

Material Selection

  • Polyimide Types: Choose the appropriate type (e.g., Kapton HM, Isola P95) based on thermal, mechanical, and electrical requirements.
  • Thickness: Consider the required thickness for flexibility and durability.

Layout Design

  • Bend Radius: Ensure the bend radius is at least 10 times the thickness of the PCB to avoid cracking.
  • Trace Routing: Avoid sharp angles and stress points; use curved traces.
  • Layer Stack-up: Use appropriate layer configurations to balance flexibility and performance.

Manufacturing Considerations

  • Adhesive Systems: Select adhesives compatible with polyimide to maintain flexibility and integrity.
  • Via Design: Use staggered vias to maintain mechanical strength.
  • Coverlay: Apply polyimide coverlay for additional protection and flexibility.

Testing and Quality Control

  • Flexibility Maintenance: Handle carefully to maintain flexibility and avoid damage.
  • Component Placement: Place components away from high-flex areas to reduce stress.
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Understanding the Differences Between Polyimide and FR4 in Flex PCBs

Due to polyimide flex pcb’s superior properties in flexible circuit boards. its cost is significantly higher. Therefore, many customers compare FR4 and Polyimide to optimize costs. Understanding the differences between these materials is crucial for making cost-effective decisions.

PropertyPolyimide (PI)FR4 (Fiberglass Reinforced Epoxy)
Thermal StabilityHigh (up to 260)Moderate (up to 130)
Mechanical StrengthHigh (Tensile Strength: 231 MPa)Moderate (Tensile Strength: 124 MPa)
Dielectric Constant3.54.7
Dielectric Strength280 kV/mm20 kV/mm
Chemical ResistanceExcellentModerate
Moisture AbsorptionLow (0.02%)Higher (0.1-0.3%)
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In this article, we’ve explored the significant advantages of Polyimide in flexible PCBs. highlighting its high thermal stability, exceptional flexibility, and superior mechanical and chemical resistance. We’ve compared popular Polyimide materials like Kapton HM and Isola P95. and discussed their specific applications and performance characteristics. Additionally, we’ve outlined design guidelines for utilizing Polyimide in flex PCBs. to ensure optimal performance and cost-effectiveness. Understanding these insights can help in making informed decisions. about material selection for various electronic applications.

For professional assistance and to optimize your PCB designs, visit Gesflex Circuit. Our team is ready to help you achieve the best results for your projects.

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