Structure of a PI Heating Film: Materials and Layer Design Explained

Polyimide (PI) heating films are widely used in precision temperature control applications due to their ultra-thin structure, high flexibility, uniform heating performance, and outstanding insulation resistance. Understanding the internal structure of a PI heating element is essential for engineers, procurement specialists, and project developers who need stable and reliable heating solutions.

This article provides a full breakdown of PI heater materials, construction layers, circuit design principles, adhesive types, temperature sensors, and connector options — offering a complete professional-level overview for industrial buyers.

1. Overview of PI Heating Film Structure

A typical PI heating film consists of several engineered layers that perform different functions:

Polyimide (PI) substrate – the primary outer layer that provides insulation and flexibility.
Etched foil heating circuit – the metal layer responsible for generating heat.
Adhesive layer – bonds PI and metal foil together.
Reinforcement zone – added around pads or connectors for durability.
Temperature sensing components – NTC thermistor, RTD, thermostat.
Connector pads or terminals – enable electrical power input.

These layers are laminated through a precise high-temperature, high-pressure process to ensure excellent stability and durability even under harsh environments.

2. Polyimide (PI) Substrate Layer

The outermost layer of the heater is a high-performance polyimide film such as DuPont Kapton® or equivalent. Key characteristics include:

Excellent heat resistance
Outstanding electrical insulation
High tensile strength and dimensional stability
Chemical resistance against oils, solvents, and moisture
Ultra-thin — typically 12.5μm to 50μm

The PI film plays a crucial role in protecting the internal etched circuit while maintaining flexibility. Because PI does not degrade easily, it ensures long-term heater performance with low risk of insulation failure.

3. Etched Foil Heating Circuit Layer

The heart of every PI heating film is its etched metal foil circuit, usually made from:

Copper (most common)
CuNi alloy (higher resistance applications)
Stainless steel (special environments)

Why etched foil?

Etching provides a highly precise heating pattern, enabling engineers to:

Customize heat distribution
Improve temperature uniformity
Increase efficiency
Reduce weight and thickness

Typical circuit thickness:

12μm
18μm
35μm

The etched foil allows fast heat response and accurate temperature control, which is why PI heaters are preferred in advanced electronics and scientific equipment.

4. Adhesive Layer

This layer bonds the metal foil to the PI film. High-temperature adhesives are required because the heater may operate continuously at 80–200°C.

The most commonly used adhesive systems include:

Acrylic adhesive – flexible and cost-effective
Silicone adhesive – excellent temperature resistance
Special PI-based adhesive – for medical or aerospace use

Without proper adhesive selection, heaters may delaminate, resulting in poor performance or shorter life cycles.

5. Insulation and Lamination

The entire heater circuit is laminated using high pressure and temperature. Proper lamination ensures:

No air bubbles
Stable insulation properties
Strong bonding between layers
Resistance to moisture and chemicals

High-quality lamination is the key to long-lasting PI heating films, especially in medical, automotive, and aerospace systems.

6. Reinforcement Layer & Gold Finger Technology

To improve durability at connection points, PI heaters often include:

Extra PI reinforcement layers
Glass fiber reinforcement (for high mechanical stress)
Gold finger pads

Gold finger pads provide multiple enhancements:

Corrosion resistance
Improved conductivity
Resistance to repeated plug/unplug cycles
Compatibility with SMT components

This is why high-end PI heating elements often use PCB-grade SMT and gold finger technology.

7. Temperature Sensing Layer (Optional but Recommended)

To ensure precise temperature control, PI heaters can include built-in sensors such as:

NTC thermistor (10K, 50K, 100K)
PT100 / PT1000 RTD
K-type thermocouple
Thermostat / thermal fuse

These components are typically SMT-mounted directly on the heater, enabling real-time temperature feedback for smart control systems.

8. Connector Interfaces

PI heating films support different connector types depending on application requirements:

JST, Molex, Hirose connectors
SMT plugs
Lead wires with solder pads
Custom metal terminals

Connectors may also include reinforcement to withstand mechanical stress during installation.

9. Customization Flexibility

PI heater structure can be customized in almost any dimension and shape:

Circles, rectangles, U-shape, L-shape
Curved or irregular forms
Punched holes, slots, adhesive areas
Multi-zone heating patterns

Thickness can also be customized between 0.08–0.5 mm depending on the application.

10. Final Summary

The structure of a PI heating film is a highly engineered combination of advanced materials:

Polyimide film for insulation and flexibility
Etched metal foil for uniform heating
High-temperature adhesive layers
Reinforced connectors and SMT components
Optional intelligent sensors

This multi-layer structure gives PI heating films exceptional performance in industries such as medical devices, battery heating, aerospace, industrial sensors, and precision electronics. With their ultra-thin form, long life cycle, and customizable engineering, PI heaters remain one of the world’s most advanced flexible heating solutions.