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6/01/2021

Dielectric Film as TIM in Power Electronic Applications

Aismalibar says

The omnipresent trend in electronics is towards smaller designs with  increasing performance requirements. 

As a consequence , there is the need to dissipate the heat generated by electronics quickly, effectively and inexpensively.

In this article we introduce an electrically insulating heat conducting dielectric as TIM. The aim is to offer an efficient solution for the growing thermal management challenges.

Table of Contents

Dielectric Film as Tim

Above all, a well-designed thermal management system guarantees a longer service life for the electronic components used. By this, it ensures a higher performance and quality of the entire electronic application.

That is to say, simply transferring the heat generated by components to the ambient air is no longer sufficient.

Instead, it is important to have additional cooling of the electronic components. A method to achieve this additional cooling is by using an external, active or passive heat sink.

Therefore, Aismalibar proposes the implementation of a dielectric film as TIM. To clarify, it is an electrically insulating heat conducting dielectric film to be used as Thermal Insulating Material of Printed Circuit Boards.

Currently, it is very common to use the housing of the application as a cooling element for the electronics. 

Additionally, the protection against accidental contact through dielectric breakdown has an additional safety-related significance. The aim is to guarantee personal protection against an electrical shock.

Examples are power connected devices for Lighting and Medical or future 800 V battery environments in electric cars.

Schematic representation of a cooling situation in power electronics using the example of an IMS circuit board with LEDs, which is coupled to an aluminum heat sink via a TIM
Figure 1: A cooling in power electronics using the example of an IMS circuit board with LEDs coupled to an aluminum heat sink via a TIM.

Dielectric Film benefits

Dielectric film as TIM prevents or minimizes air inclusions in order to enable efficient heat transfer from the heat source to the heat sink.

A technically and cost-saving solution for the thermal and insulation challenges in power electronics is BONDSHEET Cured. An electrically insulating heat conducting dielectric film by Aismalibar.

BONDSHEET Cured consists of a base of glass fabric with the addition of mineral fillers.

This thermal interface prepreg with a glass transition temperature of 120 °C achieves a thermal conductivity of 2.2 W / mK. Its dielectric strengths reach 4 kV (70 µm dielectric) or 6 kV (100 µm dielectric).

This means that, by utilizing a thin film thickness (70 or 100 µm), it is possible to achieve a low thermal resistance Rth of 0.315 or 0.45 K cm2 / W.

This efficiently dissipates the heat generated by the power electronics to the cooling element for spreading and dissipation to the ambient air.

Application areas

The main areas of application of the heat-conducting dielectric film as TIM are in power electronics. 

To clarify,  it is where there is the need to optimize the heat transfer between two flat metal surfaces. An optimization in terms of heat conduction and electrical insulation.

Currently the dielectric C stage cured sheets find  successful  applications in:

· Solar inverters

· Wind turbines

· Commercial vehicles transmission controls

· LED lighting industry

Future projects include: 

· Electric cars, especially in power train,  

· Battery management, including the on-board charging electronics.

Industrial power electronics, like in welding machines and robot drives, also use heat-conducting dielectric films. This is to efficiently dissipate the  heat from the control electronics.

Application example of a liquid-cooled, highly compact MOSFET assembly for power electronics.
Figure 2: Application example of a liquid-cooled, highly compact MOSFET assembly for power electronics. (Image: IQ evolution)

Here, too, the task of the film is to efficiently dissipate heat with maximum insulation dielectric strength. The purpose is to optimally connect PowerMOSFETs to the liquid-cooled micro coolers from IQ-evolution.


Extensive tests, in fact, demonstrate that for this application the heat conducting dielectric shown achieves the best technical-commercial combination of heat dissipation and dielectric strength compared to alternative TIM techniques.

BONDSHEET Cured: Dielectric film as TIM by Aismalibar

The basis of BONDSHEET Cured, a dielectric film as TIM, is to utilize a unique glass fabric reinforcement with the addition of ceramic fillers in a proprietary process.

In addition to the pure material properties of these fillers, ( Al2O3, AlN and BN among others), Aismalibar enhanced the particle size and shape as well as the distribution. In this way it ensures that the starting glass fabric has homogeneous heat-conducting properties.

Image 3: The thermal conductive film BONDSHEET CURED for further processing is cut, sawed, punched or routed to accomplish the customer required shape.
Image 3: The thermal conductive film BONDSHEET CURED for further processing is cut, sawed, punched or routed. To accomplish the customer required shape.

Moreover, the heat conducting film is totally customizable according to different needs and requirements. Once adapted to the customer specifications, Aismalibar delivers it as the final product.

BONDSHEET Cured dielectric film in any format

At the customer’s request, the producer can, in fact,  cut the BONDSHEET CURED film in house in any rectangular or square format. Then it delivers the product in stacks of several hundred individual films for manual or automated further processing at the customer’s facility.

BONDSHEET CURED is also an ideal high thermal interface material for the use with automatic pick and place machines. It is perfect for automated insertion.

Figure 4: Example of the electrically insulating heat-conducting C stage sheet, contoured according to customer specifications, in order to achieve an optimal mechanical adaptation of the circuit board to the heat sink.
Figure 4: Example of the electrically insulating heat-conducting C stage sheet, contoured according to customer specifications. In order to achieve an optimal mechanical adaptation of the circuit board to the heat sink.
For samples and prototypes, the manufacturer contours the sheet according to customer specifications with rounded corners and holes (as shown in Figure 4). This way the film is directly insertable between the heat sink and the circuit board during the customer's end product assembly into a unit.
The utilization of the heat-conducting film does not imply any oils, pasters or silicons. The assembly/ dissassembly of the electronics module is, therefore, easily and neatly (for example, when servicing).
In the situation of high-volume series production, punching the film with a customer-specific punching tool is the most cost-efficient manufacturing process. 70 or 100 µm thick are available through the Barcelona warehouse.
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Outlook on future developments

Aismalibar develops thermally conductive dielectrics that meet or increase the high technical requirements for thermal conductivity and dielectric strength.

In addition, the optimized processability is essential for high-volume series productions such as in the automotive sector.

One example is the “Dual Thermal Coating” (DTC) process.  This consists of  two layers directly to a metal carrier (copper or aluminum) without glass.

By applying the heat-conducting or insulation layer directly to a metal carrier, the result is a very thin product.

Image 5: Copper substrate coated with two thermally conductive polymer resins, supplied as a B-stage over a polymerized C stage layer
Image 5: Copper substrate coated with two thermally conductive polymer resins, supplied as a B-stage over a polymerized C stage layer

To sum up, the result is a highly compact power module with optimized electrical and thermal properties. Subsequently, this leads to long storage life before further production processes, meeting high requirements of the electronics industry.

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