Mar. 03, 2025
Choosing the right flexible PCB material is crucial as it impacts board functionality, production time, and cost. But how to select a suitable substrate? Many designers blindly opt for FR4. Should you just follow the trend? Don't make this mistake. You need to analyze the design requirements before making a choice.
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Different kinds of substrates are available for different applications. One such material used to build FPCs is polyimide. In this article, you will learn all about its properties, types, and applications.
Polyimides (PI) are synthesized polymers of imide monomers comprised of two acyl groups (C=O) linked to nitrogen (N). They belong to the thermosetting and thermoplastic categories.
Due to their excellent mechanical strength and thermal resistance, they have replaced glass and metals in many applications. Because of their good dielectric properties and low coefficient of thermal expansion (CTE), PI is prevalently used in flexible printed circuit board fabrication.
This material is available in many forms, such as films, resin, plastic, adhesive, and insulation.
The properties of the dielectric material can impact heat dissipation, signal integrity, load-bearing capacity, and the overall weight of your board. In this section, we will see how polyimide laminates can be a good choice for your design.
Polyimide substrates have good strength and durability to resist any physical damage when operating in harsh conditions.
Excellent flexibility: This laminate has a film structure, allowing it to bend. That's why they are generally preferred for flexible and rigid-flex designs. In the below graph, you can see that the elongation is directly proportional to the stress.
Good tensile strength: Even though they are flexible, polyimide board materials have commendable tensile strength. This enables them to be stable and support heavier loads.
The graph shows that PI materials are stable even when they are elongated for a longer duration. They are warp-resistant, which helps during the stack-up preparations.
Electronic devices operate in a wide variety of environments; therefore, the material should withstand chemical reactions such as corrosion and ionic contamination. Polyimides are chemically stable, and their long linear-ordered structure makes them solvent resistant.
During the manufacturing and assembly processes, the board materials are exposed to high thermal pressure. After fabrication, PCBs may have to withstand high operating temperatures based on your application.
To mitigate these challenges, you need to choose a substrate that endures high temperatures without any breakdowns. In addition to this, you should also implement thermal strategies such as thermal pads and heat sinks to effectively dissipate the heat.
Polyimide substrates for PCBs are stable across a wide range of temperatures between 400-500°C and have good thermal conductivity. In recent applications, Kapton substrates have been successful in withstanding temperatures from -269°C to 400°C.
PI has a linear and stiff cyclic backbone in comparison to other thermoplastic polymers with coiled and flexible chains. This arrangement allows polyimide to have lower CTE. Hence, they exhibit better thermal stability. Additionally, their glass transition temperature (Tg) is also high (>300°C).
Good electrical characteristics are a basic requirement to avoid signal integrity issues. PI provides suitable insulation with the dielectric constant varying between 2.78 and 3.48 at 1Hz. It also has a lower dielectric loss that ranges from 0.01 to 0.03 at 1Hz. It also exhibits transparency in microwave circuits, and is resistant to radiation.
There are many laminate compositions, and their properties can vary from manufacturer to manufacturer. Here are a few examples with their specifications:
DuPont manufactures this film laminate used for a wide range of applications. The properties of DuPont Kapton HN Film are as follows:
ParameterValueTest method/ standards CTE (linear)20 ppm/°CASTM D-696-91 Thermal conductivity0.12 W/m KASTM F-433-77 Smoke generation DM ' 1NFPA-258 Specific heat1.09 J/g KDifferential calorimetry Shrinkage 0.17 %IPC TM 650, Method 2.2.4A Tg Between 360°C and 410°CVaries depending on test methods Tensile strength231 Mpa at 23°CDuPont Kapton HN polyimide material datasheet
This PI laminate is infused with an E-glass weave. You can use this for normal speed and normal loss applications.
ParameterValue Dissipation factor at 1 GHz0. Dielectric constant at 1 GHz3.78 CFA-resistantYes CTE, X/Y axis lower limit14 ppm/°C CTE, X/Y axis upper limit13 ppm/°C Electrical strength Volt/mil RoHS compliantYes Tensile strength (Cross direction)36.1 Kpsi Tensile strength (Length direction)54.5 Kpsi Thermal conductivity0.4 W/m.kIsola P95 polyimide datasheet
For interpreting the values of the datasheet, read our article on PCB Substrates: Knowing Your Dielectric Material's Properties. Try our PCB Material Selector to explore the types of laminates available.
Before comparing the materials, let's briefly discuss what FR4 is.
FR4 stands for flame retardant, level 4. This is a substrate that comprises an epoxy resin and glass weave. It is a popular choice as the material has good mechanical and electrical properties and is also cost-efficient. The primary difference between polyimide and FR4 is flexibility.
Additionally, FR4 can be fabricated with a standard manufacturing process, whereas PI needs a higher temperature. The choice of substrate depends on the circuit and application requirements.
The below table provides a detailed difference between polyimide and FR4 PCB materials. Knowing these differences will help you make the right decision.
ParametersFR4Polyimide FlexibilityRigidHighly flexible Chemical resistanceGoodBetter Tensile strength70 Mpa231 Mpa Thermal stability-50°C to 110°C-200°C to 300°C Glass temperature135 °C195-220 °C Thermal conductivity2.2-2.5 cal/h.cm °C0.2 W/mK Thermal cyclingGoodBetter DurabilityGoodBetter Elasticity24 Gpa4.0 Gpa Dk at 1GHz2.78 to 3.484.2 Df at 1 GHz0..0 PriceLow-pricedhigh-pricedBoth of them are thermosetting plastics that are heat resistant. However, the significant difference is in their chemical structure. Polyimide has an imide (-CO-N-OC-) group construction in resin form. Hence, we use it in board applications. On the other hand, polyamides have an amide (-CONH-) linkage, which is mostly in thread forms such as nylon. This is not suitable for circuit board construction. However, both these materials have outstanding electrical and physical characteristics.
Polyimide board substrates can be classified into different categories depending on the structure and the additives included.
With no fillers
As the name suggests, this PI version does not contain additives such as brominated flame retardant. These are the pure and oldest kind of polyimide available and fall under the second-generation material. They are still popular as they are more flexible, strong, and thermally stable than other types of PI.
With flame retardants
These are updated versions of the 2nd generation with an added additive of flame retardants. This makes the polyimide PCB material more resistant to accidental fire.
The inclusion of an additive lowers the time and temperature needed for producing the substrate. Hence, bulk production is possible. On the contrary, it reduces its thermal stability.
Many tests and regulations exist to check for the fire safety of a substrate. For instance, Underwriters Laboratory has set UL-94 flammability standards that categorize plastics into classes like V0, V1, V2, HB, etc. As an example, the DuPont' Kapton HN polyimide falls under the UL-94 class V0.
If you are looking for more details, kindly visit Heat Resistance of PI Advanced Materials.
With flow restrictors
The low-flow polyimides are built with flow restrictors and resin. Hence, they are not as flexible as other versions, and this stiffness becomes useful to withstand harsh environments. Choose this type of PI laminate if your design calls for higher durability materials.
Filled type polyimide
This PI is cured with various filler materials to avoid cracks or breakage in the resin during the lamination and drilling processes.
All the above substrates with additives fall under the 3rd generation polyimide category. In addition, 4th generation materials are expected to have improved adhesion properties and overall stability.
The versatility of PI makes it desirable for a wide range of applications in both domestic and advanced usage.
With a constant demand for advanced, compact, and lightweight handheld devices, polyimide flex boards have enormous potential for consumer applications. Examples include computers, laptops, tablets, smartphones, video game consoles, and televisions. The material's durability and thermal stability enable the gadgets to withstand heat and stress generated due to prolonged usage.
Cars and automobiles are built with many electronic devices such as engine control systems, audio systems, antilock braking systems (ABS), etc. These features ensure proper control and operation of the vehicle. Circuit boards in automobiles must withstand vibrations, temperature variation, and wear and tear.
Therefore, the materials used in these electronics should be robust. Polyimide flex PCBs have excellent mechanical strength and can bend to fit into irregular spaces. Hence, they are a popular choice for this application.
For more, see automotive PCB design guidelines.
The medical industry has increasingly relied on electronics for diagnostics and treatment. Equipment such as magnetic resonance imaging, ultrasound technology, and other advanced applications are aiding healthcare staff.
Circuit boards in medical devices can be exposed to contamination and temperature variations. Therefore, choosing a chemically resistant substrate is a prerequisite. To learn about standards, read MedTech PCB design considerations with IPC and Ul standards.
In cases like hearing aids and implants, the circuit needs to be compact and lightweight. Many prefer polyamide flex PCBs for these applications.
In military and aerospace applications, the boards have to operate in extreme environments. Therefore, the mil-grade laminate should have a high glass transition temperature (Tg). It is also ideal to have substrate materials with a low CTE and reduced losses.
A few applications that require advanced circuit boards are power distribution systems, digitized signal processing, flight instrumentation, communication, and navigation systems.
Even though they are not invincible, polyimide circuit board materials exhibit durability and thermal stability, which makes them the right choice for the military and aerospace industries. As this substrate can become brittle with heavy copper, choose a filled PI that is resistant to cracks.
All these advanced applications must comply with IPC standards and other regulations.
Prefer polyimide PCB material if you are working on flex designs that require higher thermal stability. These materials are tailored for operations in harsh environments. It can also be a good alternative for FR4 when there are no cost constraints. If you need anything more on PCB material selection, please comment below. We will be happy to help you out.
IMARC Group's report, titled 'Polyimide Manufacturing Plant Project Report : Industry Trends, Plant Setup, Machinery, Raw Materials, Investment Opportunities, Cost and Revenue' provides a complete roadmap for setting up a polyimide manufacturing plant. It covers a comprehensive market overview to micro-level information such as unit operations involved, raw material requirements, utility requirements, infrastructure requirements, machinery and technology requirements, manpower requirements, packaging requirements, transportation requirements, etc. The polyimide project report provides detailed insights into project economics, including capital investments, project funding, operating expenses, income and expenditure projections, fixed costs vs. variable costs, direct and indirect costs, expected ROI and net present value (NPV), profit and loss account, financial analysis, etc.
The market for polyimide is experiencing steady growth, driven by the electronics and semiconductor industry. The exceptional properties of polyimide (PI), such as high thermal stability, excellent electrical insulation, and mechanical strength, make it indispensable in manufacturing flexible printed circuit boards (PCBs), wire insulation, and as a substrate for semiconductors. The global expansion of the electronics sector, especially in consumer electronics and telecommunications, directly boosts PI demand.
Whereas, the remarkable heat resistance, lightweight nature, and mechanical robustness of polyimide make it ideal for aerospace and automotive applications. These industries increasingly seek materials that can withstand extreme temperatures and harsh environments, ensuring safety and performance. In aerospace, PI is used in wire insulation, engine components, and as a matrix material in composites. According to GITNUX, the global aerospace industry has reached $838 Billion as of . However, in the automotive sector, it finds applications in engine components, gaskets, and insulation materials.
Rising Applications in Healthcare
The healthcare sector is increasingly turning to polyimide (PI) materials owing to their superior biocompatibility, chemical resistance, and thermal stability. These properties are critical in medical applications where materials must endure harsh sterilization processes without losing their integrity or performance. The exceptional characteristics of polyimide make it ideal for use in medical tubing, catheters, and a variety of other medical devices that require durability and reliability. For instance, in the production of catheters, PI ensures flexibility and strength, which are essential for patient comfort and safety during procedures. Additionally, its chemical resistance prevents degradation from exposure to bodily fluids and cleaning agents, thereby extending the lifespan of medical devices. The ability of polyimide to maintain its properties under high temperatures and radiation used in sterilization processes further underscores its suitability for the healthcare industry. This growing adoption is reflected in the medical tubing market. According to the IMARC GROUP, the global medical tubing market reached US$ 13.6 Billion in , and is expected to reach US$ 23.6 Billion by , exhibiting 6.2% during -.
Growing Investments in Renewable Energy Sector
The renewable energy sector is experiencing rapid growth, especially in solar and wind energy, which is significantly driving the demand for polyimide (PI) materials. The exceptional thermal and chemical resistance of polyimide makes it an ideal choice for applications where durability and efficiency are paramount. In the solar energy sector, PI films are extensively used as insulating materials in photovoltaic cells. These films enhance the efficiency of solar cells by improving their electrical insulation and also extend their operational lifespan by protecting them from harsh environmental conditions and thermal stresses. This durability ensures that the solar panels can maintain optimal performance over many years, thereby reducing maintenance costs and improving overall energy output. According to the IMARC GROUP, the global solar panel market reached 259.7 GW in , and is expected to reach .5 GW by , exhibiting a CAGR of 16.8% during -. Similarly, in wind energy, polyimide materials are used in various components of wind turbines, such as insulation for wires and as part of composite materials for blades, which require high strength and resistance to environmental degradation.
The market is also being driven by rising mergers and acquisitions (M&A):
The following aspects have been covered in the polyimide manufacturing plant report:
The report provides insights into the landscape of the polyimide industry at the global level. The report also provides a segment-wise and region-wise breakup of the global polyimide industry. Additionally, it also provides the price analysis of feedstocks used in the manufacturing of polyimide, along with the industry profit margins.
The report also provides detailed information related to the polyimide manufacturing process flow and various unit operations involved in a manufacturing plant. Furthermore, information related to mass balance and raw material requirements has also been provided in the report with a list of necessary quality assurance criteria and technical tests.
The report provides a detailed location analysis covering insights into the land location, selection criteria, location significance, environmental impact, expenditure, and other polyimide manufacturing plant costs. Additionally, the report provides information related to plant layout and factors influencing the same. Furthermore, other requirements and expenditures related to machinery, raw materials, packaging, transportation, utilities, and human resources have also been covered in the report.
Capital Expenditure (CapEx) and Operational Expenditure (OpEx) Analysis:
The report also covers a detailed analysis of the project economics for setting up a polyimide manufacturing plant. This includes the analysis and detailed understanding of capital expenditure (CapEx), operating expenditure (OpEx), income projections, taxation, depreciation, liquidity analysis, profitability analysis, payback period, NPV, uncertainty analysis, and sensitivity analysis. Furthermore, the report also provides a detailed analysis of the regulatory procedures and approvals, information related to financial assistance, along with a comprehensive list of certifications required for setting up a polyimide manufacturing plant.
Profitability Analysis:
Particulars Unit Year 1 Year 2 Year 3 Year 4 Year 5 Total Income US$ XX XX XX XX XX Total Expenditure US$ XX XX XX XX XX Gross Profit US$ XX XX XX XX XX Gross Margin % XX XX XX XX XX Net Profit US$ XX XX XX XX XX Net Margin % XX XX XX XX XXWhile we have aimed to create an all-encompassing polyimide plant project report, we acknowledge that individual stakeholders may have unique demands. Thus, we offer customized report options that cater to your specific requirements. Our consultants are available to discuss your business requirements, and we can tailor the report's scope accordingly. Some of the common customizations that we are frequently requested to make by our clients include:
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