Polyimide (PI) Film Insulation Guide: Thicknesses, Thermal Tests, Adhesive Types & Roll Specs

Polyimide (PI) flexible films represent the upper boundary of thin-gauge organic electrical dielectric materials. Engineered via aromatic dianhydride and diamine polycondensation, PI films maintain exceptional mechanical flexibility, mechanical tear resistance, and dielectric integrity at continuous operating temperatures ranging from -269°C up to +240°C (Class C thermal endurance).

Unlike rigid thermoset composite laminates (such as polyimide-glass thick boards or epoxy laminates), flexible PI films are utilized as wire wrapping, transformer inter-layer insulation, flexible printed circuit (FPC) base substrates, and pressure-sensitive adhesive tapes. This technical guide from RDS Composite details commercial film gauge thicknesses, dielectric breakdown standards, adhesive layer options, and standard supply roll dimensions.

1. Standard Film Thickness Gauges & Mechanical Limits

PI films are manufactured via precision casting and biaxial orientation. Standard thickness callouts are specified in either micrometers (μm), millimeters (mm), or mil (1/1000 inch):

2. Dielectric Strength & Thermal Endurance Test Protocols

PI film provides high electrical breakdown insulation retention even under extreme thermal stress. Key laboratory test parameters include:

3. Adhesive Layer Configurations: Silicone vs. Acrylic

For pressure-sensitive adhesive (PSA) tape applications, bare PI film is back-coated with specialized high-temperature adhesive systems:

• Bare Uncoated PI Film: Pure polyimide film without adhesive. Maximum temperature endurance (240°C+); specified for direct oil-immersed transformers, FPC copper laminating, and spiral wire wrapping.
• Cross-linked Silicone Adhesive Coating: Applied at 30 μm to 40 μm wet thickness. Retains tackiness and peel adhesion up to 260°C continuous (300°C short-term peak); clean removal without adhesive residue after PCB wave soldering masking.
• Thermosetting Acrylic Adhesive Coating: Higher initial room-temperature bond strength against metals and plastics; continuous thermal rating up to 155°C (Class F). Highly resistant to solvent degradation.

4. Supply Roll Widths, Slitting Tolerances & Packaging Specs

RDS supplies flexible PI film in master jumbo rolls or custom precision-slit narrow tape coils according to the following commercial parameters:

1. Master Roll Widths: Standard effective widths are 500 mm, 1,000 mm, and 1,040 mm (custom slitting available from 5.0 mm up to 1,000 mm width).
2. Slitting Width Tolerance: Precision rotary shear slitting delivers narrow width tolerances of ±0.15 mm with clean, burr-free slit edges to prevent longitudinal tear propagation during automatic high-speed wrapping.
3. Roll Core Specifications: Wound on standard 3-inch (76.2 mm) inner diameter rigid plastic or heavy-walled cardboard cores; standard roll length ranges from 33 m (adhesive tapes) up to 1,000 m – 3,000 m (master film rolls).

To compare flexible polyimide films with rigid thermoset boards and insulation laminates, explore our master navigation page: Epoxy & Composite Board Specifications Guide.