Thermal management in an electric vehicle is no longer limited to cooling.

Battery packs, coolant circuits, passenger compartments, and other thermal systems may all require controlled heating during cold-weather operation or preconditioning. The challenge is not simply to generate heat, but to deliver the required heat quickly, efficiently, and within a controlled temperature range.

This is where thick film heater technology becomes particularly interesting.

Unlike a conventional wire or foil heater, a thick film heater uses a printed resistive heating circuit integrated with a substrate. Depending on the design, the substrate can also serve as part of the thermal and mechanical structure.

For EV applications, this approach can provide a useful combination of:

• High power density
• Fast thermal response
• Compact construction
• Controlled heating patterns
• Good thermal coupling with metal components
• Flexible integration into liquid or surface heating systems

Research into EV thick film heaters has also moved beyond basic heater development toward thermal-flow simulation, channel design, temperature control, and structural optimization.

The important point, however, is that thick film heating is not a universal replacement for every other heater technology. Its advantages become more apparent when the application has specific requirements for power, heat transfer, space, and integration.

From a Heating Element to an Integrated Thermal Component

One of the most important differences between thick film heaters and conventional flexible heaters is the relationship between the heating element and the substrate.

A typical thick film heater is produced by applying a resistive material to a substrate through a printing process, followed by a curing or firing process appropriate to the material system.

The result is more than a simple resistive circuit.

The substrate can become part of the thermal path:

Electrical input → Printed heating circuit → Substrate → Thermal interface → Target component or fluid

This structure changes how the heater should be designed.

For a flexible silicone or polyimide heater, engineers often focus on heater flexibility, thickness, bonding, and surface conformity.

For a thick film heater, the design discussion can go further into:

• Substrate material
• Heating circuit geometry
• Heat-spreading behavior
• Power distribution
• Thermal interface
• Flow channel design
• Temperature sensing
• Electrical insulation
• Mechanical mounting

This makes thick film heaters particularly suitable for applications where the heater needs to function as part of a larger thermal assembly rather than as a separate flexible heating pad.

Where Thick Film Heaters Fit in an EV Thermal Management System

The best way to understand the value of thick film technology is to look at the thermal system rather than the heater alone.

1. Battery Preheating

Battery temperature has a direct influence on charging, discharging, and overall vehicle operation.

During cold conditions, the battery may need to be heated before high-power charging or before the vehicle demands significant power.

A thick film heater can be integrated into a thermal path to provide controlled heat to:

• Battery cooling plates
• Coolant circuits
• Battery modules
• Thermal management assemblies

For liquid-cooled battery systems, the heater may be designed as part of a coolant heating assembly rather than heating the battery cells directly.

This approach allows heat to be transported through the existing thermal management loop.

2. High-Voltage Coolant Heating

One particularly relevant application is the heating of coolant used by the battery or cabin thermal management system.

A thick film heating element can be integrated with a metal structure containing a fluid path. Electrical energy is converted into heat at the printed heating layer, and the heat is then transferred through the substrate and into the flowing coolant.

This architecture has already been demonstrated in automotive high-voltage coolant heater systems. BorgWarner, for example, has described thick-film heating elements used in high-voltage coolant heaters for battery conditioning and cabin heating.

For this type of application, heater performance cannot be evaluated by electrical power alone.

The thermal design of the heater, substrate, fins, flow channels, and coolant all affect the final result.

3. Cabin Heating

EVs do not have the same waste-heat source available from an internal combustion engine.

As a result, cabin heating becomes an important part of overall vehicle thermal management.

Thick film heater technology can be used in systems designed to transfer heat into air or coolant, depending on the vehicle architecture.

The advantage is not simply that the heater generates heat.

The more important consideration is whether the heating system can deliver the required thermal output while maintaining appropriate temperature control and system efficiency.

4. Auxiliary Thermal Management

The same design principles can also be applied to other components that require controlled heating.

Potential applications include:

• Defrosting systems
• Sensor heating
• Fluid lines
• Thermal management components
• Auxiliary battery heating
• Power electronics thermal management

The specific heater construction should always be determined by the required temperature, power, mounting conditions, electrical requirements, and thermal path.

What Actually Determines Thick Film Heater Performance?

It is tempting to compare heaters using a single number such as rated power.

For engineering applications, that is rarely enough.

A 3 kW heater does not automatically produce the same thermal performance as another 3 kW heater.

The actual result depends on how the generated heat reaches the target.

A useful way to think about the system is:

Electrical power → Heat generation → Heat spreading → Heat transfer → Thermal load

Each stage introduces potential losses or temperature differences.

Heating Pattern

The resistance pattern determines how heat is distributed across the active area.

A poorly designed pattern can create local hot spots while leaving other areas underheated.

For applications such as battery thermal management, this can be particularly important because the goal is often not simply to reach a high temperature, but to achieve controlled and reasonably uniform heating.

Substrate

The substrate plays an important role in heat spreading and mechanical integration.

Depending on the application, engineers may consider metal or ceramic substrates and evaluate:

• Thermal conductivity
• Thickness
• Mechanical strength
• Electrical insulation requirements
• Thermal expansion
• Environmental resistance

Thermal Interface

The heater may generate the required electrical power, but poor contact between the heater and the target can significantly reduce effective heat transfer.

Mounting pressure, interface materials, surface flatness, and contact area therefore become part of the heater design.

Temperature Sensing

Sensor location also matters.

A sensor placed too far from the heating area may respond slowly. A sensor located near a local hot spot may cause the control system to reduce power before the rest of the target has reached the desired temperature.

For this reason, temperature sensing should be considered during the heater layout stage rather than added after the heater has already been designed.

Power Density Is Only Part of the Design

High power density is often presented as one of the major advantages of thick film heaters.

But higher power density does not automatically mean better thermal performance.

The real engineering question is:

Can the generated heat be transferred to the target without creating excessive local temperature rise?

This becomes particularly important in liquid heating applications.

The SAE study on EV thick film heaters examined the interaction between the heating board, fluid flow, fins, and flow-channel structure. Its results demonstrate why thermal-fluid design and heater design need to be considered together.

For a liquid heating system, for example:

Heater power → Substrate temperature → Heat transfer surface → Coolant → Battery

Changing the coolant flow rate or channel geometry can change the thermal behavior even when the electrical input remains unchanged.

Therefore, a thick film heater should be designed around the complete thermal path, not just the resistance value.

Thick Film Heater vs. Other EV Heating Technologies

Thick film heaters should not be treated as a universal replacement for silicone, PI, or PTC heaters.

Each technology solves a different engineering problem.

For example, a thin PI heater can be a better choice when installation space is extremely limited.

A silicone heater can be more practical when the heating element needs to conform to a curved or irregular surface.

A thick film heater becomes more attractive when the application benefits from a rigid thermal structure, high heat transfer capability, concentrated heating power, or integration with a metal component.

The correct choice depends on the thermal architecture.

Designing a Thick Film Heater for an EV Application

Before selecting or customizing a heater, engineers should define the actual thermal requirements.

Start with the Thermal Load

Determine:

• What needs to be heated?
• What is its mass?
• What is the starting temperature?
• What is the target temperature?
• How quickly must it be heated?
• What heat losses occur during operation?

This provides the basis for estimating the required heating power.

Then Define the Electrical Requirements

The heater should be designed around the actual system requirements, including:

• Operating voltage
• Rated power
• Resistance
• Control method
• Electrical isolation
• Connector and terminal design

For high-voltage EV systems, insulation and electrical safety requirements must be considered as part of the overall heater assembly.

Define the Thermal Interface

Next, determine how the heater will transfer heat.

For surface heating, this may involve direct contact with a metal plate or thermal interface material.

For coolant heating, the design may involve:

Heating element → metal substrate → thermal transfer structure → coolant

The interface should be considered during the early design stage.

Consider Temperature Distribution

Average temperature is not enough.

Local hot spots, edge effects, and cold areas can all affect system performance.

The heating circuit can therefore be divided into different zones when the application requires more controlled heat distribution.

Why Customization Matters in EV Thick Film Heating

A standard heater may provide the required electrical power but still fail to meet the actual thermal requirements of an EV system.

For OEM and Tier 1 applications, the heater may need to be customized around the existing mechanical and thermal architecture.

Typical customization parameters include:

• Heater dimensions
• Substrate material
• Heating pattern
• Resistance
• Voltage
• Power
• Heating zones
• Sensor position
• Terminal configuration
• Mounting holes
• Thermal interface
• Insulation structure

This is particularly important when the heater is integrated into a battery thermal management assembly or coolant heating system.

The goal is not simply to manufacture a heater with a specified wattage.

The goal is to develop a heater that fits the mechanical structure, electrical system, and thermal path of the application.

When Should Engineers Consider Thick Film Heating?

Thick film technology is worth considering when several of the following requirements exist:

• High heating power is required in a compact area
• Rapid thermal response is important
• The heater can be integrated with a metal substrate
• Heat needs to be transferred directly to a thermal structure or fluid
• The heating pattern needs to be customized
• Space is limited at the system level
• The heater needs to become part of a larger thermal assembly

It may not be the best solution when the primary requirement is extreme flexibility or ultra-thin installation.

That distinction is important.

Good heater design starts with the application, not with the heater technology.

Building the Heater Around the Thermal System

The biggest advantage of thick film heater technology is not simply the heating element itself.

It is the possibility of integrating the heating function more closely with the thermal structure.

For EV applications, this can mean moving from:

“Where can we install a heater?”

to:

“How should the heating function be integrated into the thermal system?”

That change in design thinking is important as EV thermal systems become more compact and increasingly integrated.

Battery conditioning, coolant heating, cabin heating, and other thermal functions can share common thermal-management architectures. In such systems, the heater needs to be evaluated together with the heat exchanger, coolant path, sensors, controls, and mechanical structure.

This is where thick film technology can offer a meaningful engineering advantage.

Conclusion

Thick film heaters are not simply a higher-performance version of conventional electric heaters.

Their real value lies in the ability to integrate a printed heating circuit with a structural and thermal substrate, creating opportunities for compact, high-power, and application-specific thermal solutions.

For EV thermal management, this makes thick film heating particularly relevant to applications such as battery preheating, high-voltage coolant heating, cabin thermal management, and other systems where controlled heat transfer is important.

At the same time, heater selection should always be based on the complete thermal system.

Power density, temperature distribution, heat-transfer path, electrical requirements, thermal interface, sensing, and mechanical integration all need to be considered together.

For applications where these requirements align, a custom thick film heater can become more than a heating element—it can become an integrated part of the vehicle's thermal management architecture.

FLD develops custom thick film heaters for EV and industrial thermal management applications, with heater geometry, power, voltage, substrate, heating zones, and connection configurations designed around customer requirements.

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