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Definitions and Significance of Parameters Related to Polyimide Films

2025-12-31

1.1 Definitions and Significance of Parameters Related to Polyimide Films

1.1.1 Width

The effective width of the film in the lateral direction. It is constrained by production equipment and also limits user applications.

1.1.2 Thickness

between the two opposite surfaces of the thin film Distance Only when the thickness is uniform and meets the requirements can a qualified product be produced. Copper-clad laminate 。

1.1.3 Density

The mass per unit volume of a thin film. It characterizes the quality of polyimide films.

1.1.4 Tensile strength

At Tensile test Among them, the maximum stress that the specimen withstands until fracture occurs. Tensile stress This refers to tensile strength, which is academically known as tensile strength. In engineering applications, it is often referred to simply as tensile strength. The result is expressed as: MPa Indicates. The English name is: tensile strength

The greater the tensile strength, the higher the rigidity of the film.

1.1.5 Elongation at break

Test specimen The ratio of the displacement at fracture to the original length. With Percentage Indicates ( % )

The lower the elongation at break, the greater the rigidity of the film.

1.1.6 Thermal shrinkage rate

Hot Shrinkage rate It is the ratio of the dimensions before and after contraction. With Percentage Indicates ( % )

The lower the thermal shrinkage rate, the better the thermal stability of the film.

1.1.7 Power-frequency electrical strength

The dielectric strength is the breakdown voltage divided by the thickness of the breakdown sample, which equals the sample’s dielectric strength.

Power frequency Dielectric strength refers to the dielectric strength under the current AC power supply conditions.

The higher the dielectric strength, the less likely the film is to be punctured by high voltage, and the better its insulation performance.

1.1.8 Surface resistivity

Parallel to through Materials On the surface Current Direction of Potential gradient The ratio to the current per unit width of the surface, expressed as Ohm Indicates.

It refers to a physical quantity that characterizes the ease with which charges can move or current can flow on a material's surface.

The higher the resistivity, the better the insulation.

1.1.9 Volume resistivity

Volume resistivity , is Materials The resistance per unit volume.

Volume resistivity The higher it is, the better the electrical insulation performance.

1.1.10 Relative dielectric constant

The dielectric constant is a measure of an insulator's ability to store electrical energy. It refers to the space between two metal plates that is filled with an insulating material. Materials The ratio of the capacitance when a dielectric is present to the capacitance between the same two plates when the medium is air or vacuum. The dielectric constant represents... Dielectric the degree of polarization, that is, to Electric charge The ability to bind charges increases with a higher dielectric constant. The medium filling the space between the two plates of a capacitor affects its capacitance, and the same medium will have the same effect. However, different media have different dielectric constants.

1.1.11 Dissipation factor

Under the action of an electric field, insulating materials, due to... Medium The energy loss caused internally by the hysteresis effect of electrical conductivity and dielectric polarization. Also known as... Dielectric loss , abbreviated as dielectric loss.

Under the action of an alternating electric field, the complementary angle (δ) between the phase angle of the current flowing through the dielectric and the phase angle of the voltage—known as the power factor angle Φ—is referred to as the dielectric loss angle. It is often abbreviated as the dissipation angle.

Dissipation factor It refers to the tangent of the dielectric loss angle, often abbreviated as the tan δ of the dielectric loss angle. The definition of the dielectric loss factor is as follows:

A decline in insulation capability is directly reflected by an increase in dielectric loss.

1.1.12 Long-term heat resistance

The property of a material that enables it to maintain its excellent physical and mechanical properties even under prolonged exposure to heat.

Long-term heat resistance is critical to the quality of flexible copper-clad laminates, which are downstream products of thin films.

1.1.13 Surface tension

Surface tension , is a liquid Surface layer Due to the molecule Gravity The force acting along the surface at any boundary due to imbalance. Tension 。

If the surface tension of the thin film is high, it will be easier to apply adhesive during the production of copper-clad laminates and less likely to peel off.

1.1.14 Water absorption rate

It indicates that the object is in a normal state. Atmospheric pressure Lower water absorption level Physical quantity 。

Low water absorption ensures that the film can be used normally even in humid environments.

1.1.15 Modulus of elasticity

The material is in Elastic deformation Phase, its Stress and strain are directly proportional (i.e., conform to Hooke's Law ), its Proportionality constant It is called the modulus of elasticity. The modulus of elasticity is an important performance parameter for engineering materials, from... Macroscopic From an angle, the modulus of elasticity is a measure of... Object The measure of a material's resistance to elastic deformation, from a microscopic perspective, reflects the strength of bonds between atoms, ions, or molecules. Any factor that influences bond strength can also affect the material's elastic modulus—for example, the nature of bonding itself, and... Crystal structure chemical composition, microstructure, temperature, and so on. In general engineering applications, the elastic modulus is treated as a constant.

The modulus of elasticity can be regarded as an indicator of how easily a material undergoes elastic deformation. The higher its value, the greater the stress required to induce a given amount of elastic deformation in the material—namely, Material stiffness The greater the modulus of elasticity, the smaller the elastic deformation under a given stress. Modulus of elasticity And E It refers to the stress required to produce unit elastic deformation in a material under external force. It is an indicator reflecting the material's resistance to elastic deformation and is analogous to that found in ordinary springs. Rigidity 。

1.1.16 Coefficient of expansion

The coefficient of expansion is a characteristic that represents... Object Thermal expansion properties Physical quantity , which characterizes how an object behaves when heated Length 、 Area 、 Volume A physical quantity that increases in magnitude. An increase in length is referred to as “ Linear expansion An increase in area is called “area expansion,” and an increase in volume is called “volume expansion.” Together, these are collectively referred to as thermal expansion. For objects of unit length, unit area, and unit volume, when the temperature rises... 1 At ℃, the changes in its length, area, and volume are referred to as: Linear expansion coefficient , coefficient of thermal expansion and Coefficient of thermal expansion This is collectively referred to as the coefficient of expansion.

A moderate coefficient of thermal expansion is essential to ensure that the flexible boards produced remain flat and free from deformation.

1.1.17 Glass transition temperature

Polymer by High-elastic state Transform into Glassy state The temperature refers to the amorphous state. Polymer (Including the amorphous regions in crystalline polymers) transitioning from the glassy state to the rubbery state, or vice versa. Transition temperature , is an amorphous polymer Macromolecular chain The lowest temperature for segment-free motion is typically expressed as: Tg Indicates that there is no fixed numerical value and the result often varies depending on the measurement method and conditions. It is an important process parameter for polymers. Above this temperature, the polymer exhibits elasticity; below this temperature, the polymer exhibits... Brittleness It must be taken into account when used in plastics, rubber, synthetic fibers, and the like. However, it does not represent the upper limit of the product’s operating temperature. For example, the operating temperature of rubber must be above its glass transition temperature; otherwise, it will lose its high elasticity.