How Polyimide (PI) Heating Films Work: Technical Explanation

Polyimide (PI) heating films — also known as Kapton heaters or flexible etched-foil heaters — are one of the most advanced thin-film heating solutions in the world. This article provides a full technical explanation of how PI heating films work, including their structure, materials, thermal behavior, and electrical heating principles.

1. Overview: How PI Heating Films Work

PI heating films generate heat through electrical resistance. When current flows through the etched metal circuit embedded between polyimide layers, it produces uniform heat across the entire surface.

The core principle follows the Joule heating law:

Q = I² × R × t

Where:

Q = heat energy
I = electrical current
R = resistance of the foil circuit
t = heating time

The etched-foil circuit is carefully designed so that resistance is evenly distributed, creating precise temperature uniformity.

2. Internal Structure of a PI Heating Film

A standard PI heating element contains the following layers:

Polyimide top layer (insulation)
Adhesive layer
Etched copper or Cu-Ni alloy foil circuit
Adhesive layer
Polyimide bottom layer

2.1 Etched-Foil Heating Circuit

The heating circuit is produced through chemical etching, similar to PCB manufacturing. This allows engineers to design extremely precise heating paths.

Foil thickness: 12µm–35µm
Material: Copper or Copper-Nickel alloy
Pattern: serpentine or spiral

This pattern ensures uniform heat distribution and fast thermal response.

2.2 Polyimide Film Layers

Polyimide is chosen for its:

high dielectric strength
high-temperature resistance
chemical stability
mechanical flexibility

Polyimide film thickness typically ranges from 12.5µm to 50µm.

3. Electrical Working Principle

The electrical circuit in PI heating films operates based on controlled resistance.

3.1 Resistance Determines Heat Output

The heating power is calculated by:

P = V² / R

P: heat power (W)
V: voltage (V)
R: electrical resistance (Ω)

Engineers adjust:

foil width
foil length
foil thickness
material type

…to achieve the desired power output.

3.2 Rapid Thermal Response

PI heating films can reach operational temperature within seconds because:

the etched foil is extremely thin
PI has excellent thermal conductivity
low thermal mass allows quick heat transfer

3.3 Uniform Temperature Distribution

The serpentine etching design ensures the heat spreads evenly. This eliminates hot spots and protects the device from overheating.

4. Temperature Control System

PI heating films can integrate advanced temperature sensing and control systems.

4.1 SMT Thermistor

SMT NTC thermistors soldered directly to the heater surface enable:

Real-time temperature feedback
Precise closed-loop control
±1–2°C accuracy

4.2 Thermostat / Thermal Fuse

Provides high-temperature protection.

4.3 PT100 / PT1000 Sensors

For laboratory and medical-grade precision heating.

4.4 Digital Control

Many PI heaters integrate with:

MCU control boards
PID temperature controllers
PWM power control

5. Advantages of PI Heating Film Technology

5.1 Extremely Thin and Flexible

Thickness of 0.1–0.3mm makes PI heaters ideal for compact spaces.

5.2 High Temperature Resistance

Operational range: -200°C to +200°C.

5.3 Excellent Electrical Insulation

PI film withstands high voltage and high dielectric environments.

5.4 Lightweight and Durable

Perfect for drones, aviation, and wearable devices.

5.5 Precise and Stable Heating

Better uniformity than silicone or wire-wound heaters.

6. Engineering Design Considerations

Engineers must consider several parameters:

6.1 Voltage

5V / 12V for electronics
24V / 48V for industrial systems

6.2 Watt Density

Typically 0.2–1.5 W/cm² depending on application.

6.3 Temperature Control

SMT thermistors, thermostats, PT sensors.

6.4 Adhesive Selection

High-temperature acrylic or silicone adhesives.

6.5 Safety Standards

IPC, ISO9001, UL, KC, CE compliance.

7. Applications Requiring PI Heating Film Technology

EV batteries and drone batteries
Camera lens anti-fog heating
Medical laboratory devices
3D printers and extrusion heads
Telecom base stations
Optical sensors and scientific instruments
Industrial temperature control modules

8. Conclusion

Polyimide heating films operate based on precise electrical resistance heating, made possible by etched foil technology and the unique characteristics of PI material. Their thinness, flexibility, and stability make them indispensable in modern high-performance electronics and industrial applications.

FAQ: How PI Heating Films Work

1. How does the etched foil generate heat?

Through controlled electrical resistance, according to Joule heating law.

2. Why is Polyimide used?

Because it withstands extreme temperatures, chemicals, and electrical stress.

3. Can PI heaters integrate sensors?

Yes — SMT thermistors, thermostats, and PT sensors.

4. Do PI heaters heat evenly?

Yes, the etched serpentine pattern ensures excellent uniformity.