Electric vehicle thermal management is often discussed in terms of cooling. Battery packs, power electronics, and electric motors all generate heat that must be removed under certain operating conditions.
But in cold environments, the opposite problem becomes equally important: how can heat be delivered efficiently, uniformly, and within a limited installation space?
Thick film heaters are one option for addressing this challenge. Their potential value comes not simply from generating heat, but from integrating a resistive heating circuit with a substrate designed for a particular thermal application.
This article looks at how thick film heating works, where it may fit into EV thermal systems, and what engineers should evaluate before selecting a heating element.
- Why EV Thermal Systems Need Active Heating
Lithium-ion batteries are sensitive to operating temperature. At low temperatures, charging capability and available power may decrease. Charging a cold battery under unsuitable conditions can also increase the risk of lithium plating, depending on cell chemistry, state of charge, and charging conditions.
Preheating can help bring a battery closer to its required operating range before charging or high-power operation.
However, heating an EV battery is not as simple as increasing heater wattage.
Engineers must consider:
The battery's initial temperature and target temperature
The thermal mass of the battery pack
The required warm-up time
Temperature differences between cells and modules
Heat losses to the enclosure and surrounding environment
Available electrical power and control requirements
A heater that produces sufficient total energy may still create uneven temperature distribution if heat transfer and installation are poorly designed.
- How Thick Film Heating Works
A thick film heater typically uses a resistive heating pattern formed on a suitable substrate. When electrical current passes through the resistive circuit, electrical energy is converted into heat.
Depending on the design, the substrate may be integrated with a metal structure or another thermally functional component. This can provide a direct heat-transfer path to the target component or a heat-transfer medium.
The final performance depends on more than the resistive material itself. Substrate properties, circuit layout, insulation, mounting pressure, interface materials, and temperature sensing all influence the thermal result.
This is why thick film heaters should be evaluated as part of a thermal assembly rather than as isolated heating elements.
- Potential Applications in Electric Vehicles
Battery preheating
A thick film heating element may be incorporated into a battery thermal-management assembly to help warm the pack before charging or operation.
The important design question is how uniformly the heat reaches the intended areas. Engineers should assess the location of the heating element, the contact between surfaces, and temperature differences across the battery module.
High-voltage coolant heating
In liquid-based thermal-management systems, a heater can transfer energy to coolant, which then distributes heat through a circuit.
In this configuration, performance depends on the interaction between electrical heating, coolant flow, heat-transfer surfaces, and temperature control. Flow rate and local hot spots must be considered alongside nominal power.
Cabin and auxiliary heating
Electric vehicles cannot rely on engine waste heat in the same way as conventional combustion vehicles. Dedicated electric heating may therefore be required for cabin comfort or other auxiliary thermal functions.
Thick film technology can be considered where compact construction and integration with a heat-transfer structure are useful. Whether it is suitable depends on the required output, operating environment, and system architecture.
- Thick Film vs. Silicone and Polyimide Heaters
Different heater technologies solve different installation problems. Choosing one based on a single specification can lead to a poor design decision.
Technology
Potential advantages
Typical design consideration
Thick film heater
Can integrate a resistive circuit with a functional substrate or heat-transfer structure
Substrate design, heat-transfer path, insulation, and assembly requirements
Silicone rubber heater
Flexible, conformable, and suitable for heating curved or irregular surfaces
Contact quality, mechanical attachment, and surface temperature distribution
Polyimide (PI/Kapton) heater
Thin, lightweight, and useful where installation space is limited
Mechanical protection, electrical insulation, and heat-transfer interface
PTC heater
Self-regulating behavior may be useful in suitable designs
Temperature characteristics, system-level control, power requirements, and packaging
These are general characteristics, not guarantees for every product. Actual performance depends on the specific heater construction and operating conditions.
For example, a flexible silicone heater may be a better fit when it needs to conform to a battery enclosure. A PI heater may be preferable when thickness and weight are critical. A thick film design may be worth evaluating when the heating circuit can be integrated with a substrate or thermal structure.
The goal is to select the technology that best fits the heat-transfer path and system constraints.
Five Engineering Factors to Check Before Selecting a Heater
Thermal load
Estimate the energy required to raise the target component from its initial temperature to the desired operating temperature.
A simplified starting point is:
Q = m × c × ΔT
Where:
Q is the required thermal energy
m is the mass of the component
c is its specific heat capacity
ΔT is the required temperature change
This calculation provides an initial estimate, not the complete heater rating. Real systems also lose heat to the environment and surrounding structures.
- Power and voltage
The available voltage, target power, current limits, and electrical architecture must be compatible with the heating circuit.
High-voltage operation also requires appropriate insulation, dielectric testing, spacing, and protection according to the system's applicable requirements.
- Heat-transfer interface
The heater may generate the expected amount of heat while the target component warms too slowly because the interface introduces excessive thermal resistance.
Engineers should evaluate substrate contact, mounting pressure, interface materials, coolant flow where applicable, and the thermal properties of adjacent components.
- Temperature sensing and control
A temperature sensor should measure a location relevant to the control objective. Measuring only the heater's own surface may not accurately represent the temperature of the battery, coolant, or other target.
Sensor placement, response time, control logic, and independent overtemperature protection should be considered during system design.
- Environmental and lifecycle requirements
Automotive applications may involve vibration, humidity, thermal cycling, chemical exposure, and repeated power cycles.
The heater and its assembly should be evaluated against the actual operating environment, including electrical insulation, sealing, mechanical durability, and reliability requirements.
- Why Heater Integration Matters More Than Nominal Wattage
Consider two heating assemblies with the same rated power. One transfers heat efficiently to the target surface, while the other has poor contact and significant heat loss.
The two assemblies can produce very different warm-up times and temperature distributions despite having identical electrical ratings.
This is why thermal design should consider the complete energy path:
Electrical input → resistive heating element → substrate → interface → target component
For liquid heating, the path also includes heat transfer from the assembly into the coolant and transport through the fluid circuit.
A successful design must account for each stage rather than treating rated power as the only performance indicator.
- When Should Engineers Consider a Custom Thick Film Heater?
A custom design may be worth evaluating when standard components cannot meet the required geometry, power distribution, mounting conditions, or thermal performance.
Before requesting a design, engineers should define:
Available installation dimensions
Operating voltage and target power
Target temperature and warm-up requirements
Substrate and mounting preferences
Temperature sensor and control requirements
Environmental and electrical safety requirements
Expected operating cycles and service life
Providing these details early helps narrow the design options and makes prototype evaluation more meaningful.
Conclusion
Thick film heaters can be a useful option for EV thermal management when the heating circuit, substrate, and heat-transfer structure can be designed to work together.
They are not a universal replacement for silicone heaters, polyimide heaters, or PTC solutions. Their suitability depends on the application, thermal interface, electrical requirements, and packaging constraints.
For engineers, the key question is not simply how much power a heater can generate. It is how effectively that energy reaches the intended component under real operating conditions.
For more information, see FLD's thick film heater product page or read the related guide on thick film heaters for EV thermal management.
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