The Differences between PET and Pl Material of Flexible PCB

Introduce

• Polyimide (PI): A class of polymers characterized by imide monomers. PI materials are known for their excellent thermal stability, mechanical properties, and chemical resistance. They are used in applications requiring durability and reliability under extreme conditions.
• Polyethylene Terephthalate (PET): A thermoplastic polymer made by polymerizing ethylene glycol and terephthalic acid. PET is recognized for its good strength-to-weight ratio, thermal properties, and chemical resistance, albeit at levels generally lower than those of PI.

physical properties

Polyimide (PI) Physical Properties

• Thermal Resistance: PI materials are exceptional in their ability to withstand extreme temperatures. They can operate continuously in environments ranging from -269°C to +400°C, with some special formulations capable of enduring even higher temperatures for short periods. This high thermal resistance makes PI ideal for applications that experience rapid temperature fluctuations or are exposed to high heat.
• Mechanical Flexibility and Durability: Despite its thinness, PI exhibits excellent mechanical strength, making it resistant to tearing and puncturing. Its flexibility is a standout feature; PI can be repeatedly bent and flexed without losing its structural integrity, making it perfect for applications requiring tight bends or constant motion, such as in wearable technology or foldable electronics.
• Electrical Properties: PI has a high dielectric strength, low dielectric constant, and low dissipation factor, making it an excellent insulator even at high frequencies. These electrical properties are crucial for minimizing signal loss and cross-talk in high-speed and high-density electronic applications.
• Dimensional Stability: PI maintains its shape and size over a wide range of temperatures and mechanical stresses. This dimensional stability is critical in applications where precise alignment of components is required, such as in semiconductor manufacturing and complex multi-layer Flex PCBs.

Polyethylene Terephthalate (PET) Physical Properties

• Thermal Resistance: PET’s thermal resistance is lower than that of PI, with an operational range typically up to 150°C. This makes it suitable for consumer electronics and other applications where extreme temperature conditions are not a concern. PET’s melting point is around 250°C to 260°C, limiting its use in high-heat applications.
• Mechanical Flexibility and Durability: PET is flexible and has good tensile strength, but it is generally less durable than PI when subjected to repeated flexing. It is suitable for static applications or where the Flex PCB does not need to be flexed frequently after installation.
• Electrical Properties: While PET also exhibits good electrical insulation properties, its performance is not at the same level as PI, particularly at higher temperatures or frequencies. However, for many standard applications, PET’s electrical properties are sufficient.
• Dimensional Stability: PET has reasonable dimensional stability, but it can be prone to shrinking or warping at higher temperatures or under mechanical stress. This aspect needs to be considered in applications where precise component placement and stability over time are important.

Chemical properties

Polyimide (PI)

• Chemical Resistance: Polyimides exhibit outstanding resistance to a wide range of chemicals, including hydrocarbons, esters, ethers, alcohols, and many acids and bases. This resistance is attributable to the PI’s aromatic backbone, which provides stability and resilience against chemical attack. This makes PI an excellent choice for applications in chemically harsh environments, such as industrial processes, aerospace, and automotive applications where exposure to fuels, lubricants, and hydraulic fluids is common.
• Moisture Absorption: PI materials have very low moisture absorption rates, which ensures that their physical and electrical properties remain stable even in high humidity environments. This low absorption rate minimizes swelling and potential hydrolytic degradation, preserving the integrity and performance of PI-based components over their operational life.
• Solvent Resistance: PI is generally resistant to solvents, including alcohols, ketones, and aromatic hydrocarbons. This solvent resistance allows for easier handling and processing in manufacturing environments where solvents are used for cleaning or as part of the production process.
• Gas Permeability: Polyimides have low gas permeability rates, particularly for oxygen and nitrogen, which is beneficial for applications requiring barrier properties, such as packaging and encapsulation of sensitive electronic components.

Polyethylene Terephthalate (PET)

• Chemical Resistance: PET exhibits good resistance to dilute acids and bases, many solvents, and alcohols, making it suitable for a range of packaging and consumer electronics applications. However, it is less resistant to strong acids, bases, and certain solvents (e.g., acetone) than PI, which can lead to hydrolysis and degradation under certain conditions.
• Moisture Absorption: PET absorbs more moisture than PI, although it still maintains good performance in many environments. The moisture absorbed can lead to hydrolytic degradation at elevated temperatures, affecting its mechanical and electrical properties. Therefore, PET’s performance in very humid environments or in applications involving direct contact with water may be a consideration.
• Solvent Resistance: While PET is resistant to many common solvents, it is more susceptible to attack by strong solvents than PI. This susceptibility can limit PET’s use in applications where exposure to aggressive solvents is likely.
• Gas Permeability: PET has higher gas permeability compared to PI, particularly for gases like CO2 and O2. This characteristic is advantageous in packaging applications where breathability is required but may be a disadvantage in applications requiring airtight seals.

Production Processes

PI: The production of PI involves a two-step polymerization process: the formation of polyamic acid followed by cyclodehydration to form the imide. This process allows for the creation of films, fibers, and coatings that maintain their properties under extreme conditions.
PET: PET is produced through a polycondensation reaction between ethylene glycol and terephthalic acid or its esters. The process can be adjusted to control the polymer’s crystallinity, impacting its thermal and mechanical properties.

Application Differences

Aerospace and Automotive:

PI: Preferred for its thermal stability, chemical resistance, and mechanical durability. Used in high-temperature applications, such as engine compartments and aerospace components.
PET: Less commonly used due to its lower thermal and mechanical performance.

Consumer Electronics:

PI: Chosen for high-end electronics where durability and high-temperature performance are required.
PET: Widely used in everyday consumer electronics, displays, and flexible circuits where extreme conditions are not encountered.

Medical Devices:

PI: Selected for implants and devices requiring sterilization and biocompatibility.
PET: Used in non-implantable medical devices and disposables where cost and moderate performance criteria are met.

Environmental and Industrial Monitoring:

PI: Ideal for sensors and devices in harsh chemical and thermal environments.
PET: Employed in applications with less stringent environmental requirements.