Biaxially Oriented polyimide film refers to a film that, during the manufacturing process, is first stretched in one direction (Machine Direction, MD) along the polyimide base material, and then stretched again in the perpendicular direction (Transverse Direction, TD) to achieve higher orientation and mechanical enhancement in both primary directions. Compared to uniaxial stretching, biaxially oriented films offer more balanced performance, significantly reduced mechanical anisotropy, and are thus more advantageous in applications that require high strength, dimensional stability, and electrical insulation. Below are the main features and common applications of biaxially oriented polyimide films.

I. Key Features of Biaxially Stretchable Polyimide Film

1. Balanced mechanical properties, higher strength

• High tensile strength, tear resistance, and fatigue resistance are achieved in both MD and TD directions.

• Compared to unidirectional stretching, it is more advantageous in withstanding multidirectional stresses or maintaining stability in complex deformation environments.

• The molecular chains have ordered orientations in both directions, resulting in more uniform thermal shrinkage and expansion distribution within the two-dimensional plane, exhibiting lower anisotropic size change rates.

• Under high-temperature conditions, the film is less prone to warping, wrinkling, or delamination issues.

• Polyimide materials inherently possess high dielectric strength, excellent chemical and solvent resistance, and the bidirectional stretching does not diminish their inherent material properties.

• The anisotropy in dielectric constant and dielectric loss, among other electrical parameters, is relatively smaller.

• The molecular chains align consistently after stretching, resulting in a more even distribution of internal stress. The film surface is typically flatter, and the porosity is lower.

• Enhances uniformity and reliability for subsequent coating, deposition, lamination, metallization, and other processes.

• Due to the reduced deformation differences in all directions by bidirectional stretching, the film performs better in terms of reuse and lifespan in high-precision devices and components.

• Helps to reduce the risk of product failure under thermal cycling or mechanical fatigue conditions.

Section II: Typical Applications of Bilayer Stretchable Polyimide Film

1. High-end Flexible Printed Circuits (FPC) and electronic components

• For flexible printed circuits (FPC) requiring higher reliability and more stable size characteristics, using bidirectional stretchable films can reduce issues like solder joint cracking and trace deformation due to thermal expansion and contraction.

• Suitable for high-density interconnect (HDI), multi-layer flexible circuits, and rigid-flex boards that require higher processing precision.

• Enhanced molecular structure uniformity and surface flatness after bidirectional stretching, which is beneficial for reducing signal loss and crosstalk caused by dielectric non-uniformity, particularly suitable for high-frequency RF or microwave circuits.

• Provide more stable dielectric properties and lower signal attenuation for high-frequency applications such as 5G, millimeter wave, and satellite communication.

• Aerospace demands stringent requirements for material thermal stability, dimensional accuracy, and reliability. Biaxially stretched polyimide film can withstand extreme temperatures, vacuum, and radiation environments, while minimizing structural stress caused by thermal expansion and contraction.

• Materials for spacecraft applications, including multi-layer insulation (MLI) for spacecraft, solar cell backsheet, foldable antennas, or flexible deployment mechanisms.

• Many precision sensors and MEMS devices require high stability in response to environmental changes. Bi-axial stretching offers lower anisotropic deformation, preventing cumulative errors in measurement or structure.

• For applications in high-precision dimension scenarios such as medical testing equipment, optical devices, and laboratory testing equipment.

• Advanced semiconductor packaging (such as COF, CSP, BGA, etc.) requires substrates with high dimensional accuracy, high reliability, and excellent thermal dissipation properties.

• biaxially oriented film effectively mitigates the stress shock of chips during repeated temperature cycles, reducing the probability of device failure.

• Flexible displays or new types of displays require high flatness, light transmittance, mechanical strength, and thermal stability of the substrate.

• Bi-directional stretching significantly reduces creasing and deformation issues during the display module processing, ensuring display quality and yield.

• Laminating or bonding with materials like metal foil, carbon fiber, and glass fiber to create composite structures that meet various mechanical and functional requirements.

• High tensile strength and bidirectional dimension stability provided by the bidirectional stretching enhance the impact and fatigue resistance of the composite materials.

III. Selection and Usage Precautions

1. Balance mechanical performance with cost

• Bi-directional stretching is more complex than uni-directional stretching processes and typically more expensive. Consider both performance requirements and budget when choosing the appropriate film type.

• Different thicknesses and elongation ratios of biaxial films exhibit variations in mechanical properties, dielectric performance, and thermal stability; it is essential to thoroughly verify the film performance data before specific application.

• Some subsequent processes (such as metal sputtering, electroplating, lamination, or high-frequency welding) have special requirements for the film surface characteristics and thermal stability. It is necessary to confirm whether the biaxially stretched products have the relevant surface treatment and thermal stability treatment.

• Although bidirectional stretching can significantly reduce deformation, residual stresses and fatigue effects must still be evaluated in environments of extreme high or low temperatures, or frequent thermal cycles.

• Manufacturers vary in their stretching process control and grade development, so it's necessary to obtain the corresponding technical data sheets and application support to ensure the selected biaxially stretched polyimide film meets actual requirements.