Thermally conductive potting compounds: λ values explained
When power electronics overheat, even the best heat sink is useless unless the heat can escape from the encapsulated component. Thermally conductive potting compounds with a high λ value do just that. They protect electronics from environmental influences and at the same time dissipate heat loss in a targeted manner. But what exactly does the λ value mean, which fillers increase thermal conductivity, and when is it worthwhile to use thermally conductive potting compounds?
Table of Contents
- Why thermal conductivity is crucial for casting compounds
- What is the λ value (lambda)?
- Practical tip: λ value versus thermal resistance
- Comparison: Standard potting vs. thermally conductive
- Fillers and their effect
- Applications
- Selection criteria: Determining the correct λ value
- Processing tips
- Frequently asked questions (FAQ)
- Conclusion
Why thermal conductivity is crucial for casting compounds
Modern electronic assemblies operate in increasingly smaller spaces with rising power densities. LED drivers, DC/DC converters, battery management systems, and motor controllers generate heat loss that must be dissipated. Standard epoxy- or silicone-based potting compounds offer excellent protection against moisture, chemicals, and mechanical stress, but they tend to have an insulating effect on heat.
The consequences of insufficient heat dissipation are measurable. A higher operating temperature significantly accelerates the aging of electronic components. A commonly used rule of thumb states that in many cases, a temperature increase of 10 K can halve the service life. However, the exact effect depends on the component and the dominant failure mechanism.
In addition, hotspots occur when heat is not distributed evenly. Power components must be throttled (derating), which prevents systems from reaching their full performance. In critical applications such as e-mobility battery packs or high-performance LED modules, overheating can lead to failures or safety risks.
Thermally conductive potting compounds solve this problem by containing thermally conductive fillers. These form heat conduction paths in the polymer matrix and enable heat to be transferred from the component to adjacent structures such as housings, carriers, or cooling surfaces. Modern formulations thus combine the protective function of classic potting compounds with active thermal management.
What is the λ value (lambda)?
The λ value, also known as thermal conductivity, describes how well a material conducts heat. The physical unit is watts per meter and Kelvin (W/m·K). A higher λ value means better heat conduction.
Typical λ values for comparison:
- Copper: approx. 390 W/m·K (very good heat conductor)
- Aluminum: approx. 235 W/m·K
- Standard epoxy resin: approx. 0.2 to 0.3 W/m·K
- Standard silicone: approx. 0.15 to 0.25 W/m·K
- Thermal conductive potting compound: approx. 0.5 to 3.0 W/m·K (typical range)
- High-performance thermal paste: significantly higher depending on the system
Thermal conductivity is determined using standardized test methods. Different methods are used depending on the material system and testing laboratory, for example, steady-state or transient methods. It is important to note that λ values can only be meaningfully compared in the context of test methodology, temperature, sample condition, and curing conditions .
Important for practical application: Manufacturer specifications for λ values are only directly comparable to a limited extent if the test methods, temperature, sample geometry, or curing conditions differ.
Practical tip: λ value versus thermal resistance
The λ value is a material property, but it does not say anything about the actual cooling effect in the component. The decisive factor is the thermal resistance Rth of the entire potting layer:
Rth = d / (λ × A)
Here, d is the layer thickness and A is the heat transfer area. A 5 mm thick layer with λ = 1 W/m·K is less effective at dissipating heat than a 2 mm thick layer with λ = 0.8 W/m·K. Therefore, optimize not only the material, but also the geometry.
In addition to λ, layer thickness and surface area, interfaces, air pockets (voids) and geometric effects also influence the actual thermal resistance. In practice, effective heat dissipation is therefore often poorer than an ideal 1D calculation would suggest.
λ value is not everything
- Thermal conductivity of the material (λ)
- Coating thickness of the casting compound
- Effective contact area
- Contact resistances at interfaces
- Air pockets / bubbles
- Component geometry and heat distribution
- Temperature profile during operation
Comparison: Standard potting vs. thermally conductive
The differences between conventional and thermally conductive potting compounds go beyond the λ value. Comparison of typical property profiles:
| property | Standard casting compound | Thermally conductive potting compound |
|---|---|---|
| Thermal conductivity λ | 0.2 to 0.3 W/m·K | 0.6 to 3.0 W/m·K (typical) |
| filler content | 0 to 20% by weight | 40 to 75 percent by weight |
| Viscosity (uncured) | 1,000 to 10,000 mPa·s | 10,000 to 80,000 mPa·s |
| Shore hardness (cured) | Shore A 30 to 80 | Shore A 50 to 90 or Shore D 30 to 60 |
| density | 1.0 to 1.2 g/cm³ | 1.8 to 2.8 g/cm³ |
| processing | Pouring, dosing, vacuum optional | Homogenization important, degassing often recommended, adapted dosing technology useful |
| Price (relative) | lower | higher |
The high filler content of thermally conductive potting compounds poses challenges. Viscosity increases significantly, which makes venting and dispensing more difficult. The higher density often requires adapted dispensing systems. Depending on the formulation and storage conditions, segregation or sedimentation may also occur.
The risk of sedimentation depends heavily on viscosity, thixotropy, particle distribution, and storage time. Not every system shows critical demixing in the practical window. Nevertheless, thorough homogenization before processing remains mandatory.
In return, significantly improved heat dissipation is achieved, while electrical insulation properties generally remain good, provided that electrically insulating fillers are used.
Fillers and their effect
The thermal conductivity of a casting compound depends directly on the type, quantity, shape, and distribution of the fillers used. Polymer matrices such as epoxy, silicone, or polyurethane are poor heat conductors on their own. Only the fillers create continuous heat conduction paths.
Aluminum oxide (Al₂O₃)
Aluminum oxide is one of the most commonly used fillers for thermally conductive potting compounds. It offers good value for money and, at high fill levels, often enables λ values in the range of approximately 0.8 to 1.5 W/m·K. The particles are electrically insulating, chemically inert, and available in different grain sizes. The packing density can be improved by combining different particle sizes (bimodal or multimodal distributions).
Boron nitride (BN)
Hexagonal boron nitride is often referred to as "white graphite" and exhibits pronounced thermal anisotropy. Heat is conducted much more efficiently along certain crystal planes. Depending on the formulation, this allows higher λ values to be achieved, often with favorable electrical properties for certain electronic applications.
Disadvantages include significantly higher material costs and more demanding processing. Plate-shaped particles can become oriented, which affects the actual thermal conductivity in different directions.
Aluminum nitride (AlN)
Aluminum nitride is a very high-performance ceramic filler with high intrinsic thermal conductivity. Potting compounds containing AlN can achieve high λ values while remaining electrically insulating. The limiting factors are usually the higher costs and sensitivity to moisture in the processing chain.
Metallic fillers (e.g., silver, aluminum)
Metallic fillers can greatly increase thermal conductivity, but often lead to electrical conductivity or at least significantly reduced insulation. Such systems are usually unsuitable for classic insulating potting applications, but can be useful in special applications with EMC or grounding requirements.
Applications
Thermally conductive potting compounds are used wherever electronics need to be both protected and cooled.
LED lighting and high-performance LEDs
LED modules are sensitive to increased junction temperatures. This affects brightness, color location, and service life. Thermally conductive potting compounds can protect LED assemblies while improving heat transfer to cooling structures. Depending on the design, flexible silicone systems or harder resin systems are used.
Power electronics and frequency converters
IGBT modules, MOSFET circuits, and DC/DC converters generate relevant heat loss during operation. Thermally conductive potting compounds help reduce hot spots and improve temperature distribution. They also offer protection against moisture, dirt, and mechanical stress.
E-mobility: Battery management systems and charging electronics
Automotive applications place high demands on temperature range, vibration resistance, media resistance, and long-term stability. Thermally conductive potting compounds are used in BMS electronics, sensor technology, and charging electronics, among other things. Depending on the specifications, additional requirements such as flame retardant classifications or special approvals may be relevant.
Power supplies and power sources
Switch-mode power supplies combine high component density with continuous thermal load. Thermally conductive potting can conduct heat specifically to metal housings or base plates while protecting the assembly from environmental influences. Pot life, flow behavior, and degassing are particularly important for complex geometries.
Selection criteria: Determining the correct λ value
Higher thermal conductivity always sounds better at first. In practice, however, a higher λ value often goes hand in hand with higher costs, more difficult processing, and, in some cases, higher mechanical hardness. The choice of material should therefore be based on thermal considerations.
-
What thermal power P (in watts) must be dissipated? The starting point is data sheets, simulations, or measurements during operation. -
Define permissible temperature difference
What temperature difference ΔT between the component and the cooling structure is permissible? Typically, depending on the application, this is a few tens of Kelvin. -
Calculate maximum thermal resistance
Rth = ΔT / P (unit: K/W) -
Estimate the required λvalue
λ = d / (Rth × A)
Where d is the layer thickness in meters and A is the heat transfer area in square meters. A safety factor (e.g., 1.3 to 1.5) is useful to account for tolerances, voids, and aging.
sample calculation
An LED module generates 10 W of heat loss. The heat is to be dissipated via a casting layer 5 mm thick and 50 cm² in area. Permissible temperature difference: 30 K.
- Rth = 30 K / 10 W = 3 K/W
- λ = 0.005 m / (3 K/W × 0.005 m²) = 0.33 W/m·K
- With a safety factor of 1.4, this results in λ ≥ 0.46 W/m·K.
In many cases, a casting compound with λ = 0.8 W/m·K would be sufficient here, provided that the contact quality, geometry, and heat dissipation in the overall system are suitable.
Additional selection criteria
- Chemical resistance (e.g., to coolants, oils, cleaning agents)
- Temperature range and temperature change resistance
- Shore hardness and mechanical decoupling (vibration, shock)
- Electrical insulation characteristics (e.g., dielectric strength, CTI depending on application)
- Processability (pot life, mixability, deaeration, dosability)
- Adhesion to relevant substrates
- CTE and stress build-up during temperature changes
- Approvals and regulatory requirements (e.g., UL, REACH, RoHS, application-specific approvals)
- Rework requirements / Disassembly
Processing tips
The high viscosity and high filler content of thermally conductive potting compounds require adapted processing techniques. Even a material with a good λ value can perform poorly in practice if it is not processed cleanly due to voids or incomplete wetting.
Mixing and homogenizing
Fillers can separate or settle during storage and transport. Thorough homogenization is important before processing. In two-component systems, both components should first be homogenized individually before being mixed. Suitable stirring technology improves filler distribution and reduces batch variations during processing.
vacuum degassing
Air pockets significantly impair effective heat conduction, as air has very low thermal conductivity. Degassing after mixing can significantly improve the quality of the potting. For larger volumes or critical assemblies, vacuum potting may also be advisable.
Dosage and flow characteristics
Thermally conductive systems are often significantly more viscous than standard potting compounds. For highly filled materials, adapted pumping and dosing systems are often advantageous. For complex assemblies, the material should be applied in such a way that air can escape in a controlled manner. Moderate temperature control can improve flow behavior, but depending on the system, it can also shorten the pot life.
curing
Reactive resin systems can generate significant exothermic heat, particularly when used for larger casting volumes. The high filler content influences the heat balance and reaction process. In some cases, it may be advisable to use stepwise curing or slower systems.
Silicone casting compounds generally exhibit significantly lower exothermicity than many epoxy systems, which can be advantageous for larger casting volumes in terms of processing.
Aftercare and quality control
After curing, the quality of the encapsulation should be checked, for example by visual inspection for bubbles, hardness testing, weight or density checks, and thermography under load to verify heat dissipation. For safety-critical applications, additional electrical and mechanical tests are recommended.
Frequently asked questions (FAQ)
Can I remove a thermally conductive potting compound again later?
This is only possible to a limited extent. Soft silicone systems are often easier to remove mechanically than hard epoxies. However, fully cured, highly filled systems can often only be removed with considerable effort and may damage components. If rework is planned, this should be taken into account when selecting the material.
How much does a higher λ value really improve cooling?
A higher λ value improves heat conduction in the material, but does not automatically improve overall cooling performance. Other decisive factors include layer thickness, contact quality, air bubbles, geometry, and subsequent heat dissipation in the system. The thermal resistance of the entire heat path is a key factor.
Why does thermally conductive potting compound cost significantly more than standard potting compound?
The main cost drivers are thermally conductive fillers and the higher formulation and processing costs. High fill levels increase viscosity and density and place higher demands on mixing, degassing, and dosing technology.
Can I process a thermally conductive potting compound with standard equipment?
This is sometimes possible for small quantities and simple geometries. For highly filled systems, good homogenization, suitable dosing technology, and degassing where possible are important in order to achieve reproducible results without air pockets.
Is a high λ value always the best choice?
No. Higher λ values often mean higher costs, higher viscosity, and more difficult processing. In many applications, a cleanly processed system with a moderate λ value is the more economical and technically adequate solution.
Conclusion: Measurably improve thermal performance
Thermally conductive potting compounds are more than just an upgrade. They enable electronic designs that would not function reliably thermally with standard potting. The λ value describes the material's capability, but the actual cooling effect depends on the entire thermal path.
Aluminum oxide-filled systems offer good value for money for many applications. Boron nitride and aluminum nitride-based systems are particularly interesting when higher thermal performance or special electrical properties are required.
The processing requires more care than standard potting. Homogenization, degassing, and adapted dosing technology are crucial for reproducible results. The benefits are measurable: lower component temperatures, longer service life, higher system performance, and better reliability.
When selecting a material, the rule is: as much thermal conductivity as necessary, not as much as possible. A clear thermal analysis prevents over-engineering and keeps costs within reasonable limits.
Technical support provided by SILITECH
Would you like to select a thermally conductive potting compound or optimize an existing system? SILITECH supports you in the preselection, sampling, and technical classification for your application.
- Selection based on temperature, mechanics, and media resistance
- Classification of λ values in the context of application
- Processing instructions (mixing, degassing, dosing)
- Sampling for testing and validation
Thermally conductive potting compounds for your application
Our materials specialists will help you select the ideal thermally conductive potting compound—with thermal calculations, samples, and processing advice. SILITECH offers potting systems for electronics, LEDs, e-mobility, and industrial applications.
Contact & AdviceThermally conductive potting compounds: λ values explained
When power electronics overheat, even the best heat sink is useless unless the heat can escape from the encapsulated component. Thermally conductive potting compounds with a high λ value do just that. They protect electronics from environmental influences and at the same time dissipate heat loss in a targeted manner. But what exactly does the λ value mean, which fillers increase thermal conductivity, and when is it worthwhile to use thermally conductive potting compounds?
Table of Contents
- Why thermal conductivity is crucial for casting compounds
- What is the λ value (lambda)?
- Practical tip: λ value versus thermal resistance
- Comparison: Standard potting vs. thermally conductive
- Fillers and their effect
- Applications
- Selection criteria: Determining the correct λ value
- Processing tips
- Frequently asked questions (FAQ)
- Conclusion
Why thermal conductivity is crucial for casting compounds
Modern electronic assemblies operate in increasingly smaller spaces with rising power densities. LED drivers, DC/DC converters, battery management systems, and motor controllers generate heat loss that must be dissipated. Standard epoxy- or silicone-based potting compounds offer excellent protection against moisture, chemicals, and mechanical stress, but they tend to have an insulating effect on heat.
The consequences of insufficient heat dissipation are measurable. A higher operating temperature significantly accelerates the aging of electronic components. A commonly used rule of thumb states that in many cases, a temperature increase of 10 K can halve the service life. However, the exact effect depends on the component and the dominant failure mechanism.
In addition, hotspots occur when heat is not distributed evenly. Power components must be throttled (derating), which prevents systems from reaching their full performance. In critical applications such as e-mobility battery packs or high-performance LED modules, overheating can lead to failures or safety risks.
Thermally conductive potting compounds solve this problem by containing thermally conductive fillers. These form heat conduction paths in the polymer matrix and enable heat to be transferred from the component to adjacent structures such as housings, carriers, or cooling surfaces. Modern formulations thus combine the protective function of classic potting compounds with active thermal management.
What is the λ value (lambda)?
The λ value, also known as thermal conductivity, describes how well a material conducts heat. The physical unit is watts per meter and Kelvin (W/m·K). A higher λ value means better heat conduction.
Typical λ values for comparison:
- Copper: approx. 390 W/m·K (very good heat conductor)
- Aluminum: approx. 235 W/m·K
- Standard epoxy resin: approx. 0.2 to 0.3 W/m·K
- Standard silicone: approx. 0.15 to 0.25 W/m·K
- Thermal conductive potting compound: approx. 0.5 to 3.0 W/m·K (typical range)
- High-performance thermal paste: significantly higher depending on the system
Thermal conductivity is determined using standardized test methods. Different methods are used depending on the material system and testing laboratory, for example, steady-state or transient methods. It is important to note that λ values can only be meaningfully compared in the context of test methodology, temperature, sample condition, and curing conditions .
Important for practical application: Manufacturer specifications for λ values are only directly comparable to a limited extent if the test methods, temperature, sample geometry, or curing conditions differ.
Practical tip: λ value versus thermal resistance
The λ value is a material property, but it does not say anything about the actual cooling effect in the component. The decisive factor is the thermal resistance Rth of the entire potting layer:
Rth = d / (λ × A)
Here, d is the layer thickness and A is the heat transfer area. A 5 mm thick layer with λ = 1 W/m·K is less effective at dissipating heat than a 2 mm thick layer with λ = 0.8 W/m·K. Therefore, optimize not only the material, but also the geometry.
In addition to λ, layer thickness and surface area, interfaces, air pockets (voids) and geometric effects also influence the actual thermal resistance. In practice, effective heat dissipation is therefore often poorer than an ideal 1D calculation would suggest.
λ value is not everything
- Thermal conductivity of the material (λ)
- Coating thickness of the casting compound
- Effective contact area
- Contact resistances at interfaces
- Air pockets / bubbles
- Component geometry and heat distribution
- Temperature profile during operation
Comparison: Standard potting vs. thermally conductive
The differences between conventional and thermally conductive potting compounds go beyond the λ value. Comparison of typical property profiles:
| property | Standard casting compound | Thermally conductive potting compound |
|---|---|---|
| Thermal conductivity λ | 0.2 to 0.3 W/m·K | 0.6 to 3.0 W/m·K (typical) |
| filler content | 0 to 20% by weight | 40 to 75 percent by weight |
| Viscosity (uncured) | 1,000 to 10,000 mPa·s | 10,000 to 80,000 mPa·s |
| Shore hardness (cured) | Shore A 30 to 80 | Shore A 50 to 90 or Shore D 30 to 60 |
| density | 1.0 to 1.2 g/cm³ | 1.8 to 2.8 g/cm³ |
| processing | Pouring, dosing, vacuum optional | Homogenization important, degassing often recommended, adapted dosing technology useful |
| Price (relative) | lower | higher |
The high filler content of thermally conductive potting compounds poses challenges. Viscosity increases significantly, which makes venting and dispensing more difficult. The higher density often requires adapted dispensing systems. Depending on the formulation and storage conditions, segregation or sedimentation may also occur.
The risk of sedimentation depends heavily on viscosity, thixotropy, particle distribution, and storage time. Not every system shows critical demixing in the practical window. Nevertheless, thorough homogenization before processing remains mandatory.
In return, significantly improved heat dissipation is achieved, while electrical insulation properties generally remain good, provided that electrically insulating fillers are used.
Fillers and their effect
The thermal conductivity of a casting compound depends directly on the type, quantity, shape, and distribution of the fillers used. Polymer matrices such as epoxy, silicone, or polyurethane are poor heat conductors on their own. Only the fillers create continuous heat conduction paths.
Aluminum oxide (Al₂O₃)
Aluminum oxide is one of the most commonly used fillers for thermally conductive potting compounds. It offers good value for money and, at high fill levels, often enables λ values in the range of approximately 0.8 to 1.5 W/m·K. The particles are electrically insulating, chemically inert, and available in different grain sizes. The packing density can be improved by combining different particle sizes (bimodal or multimodal distributions).
Boron nitride (BN)
Hexagonal boron nitride is often referred to as "white graphite" and exhibits pronounced thermal anisotropy. Heat is conducted much more efficiently along certain crystal planes. Depending on the formulation, this allows higher λ values to be achieved, often with favorable electrical properties for certain electronic applications.
Disadvantages include significantly higher material costs and more demanding processing. Plate-shaped particles can become oriented, which affects the actual thermal conductivity in different directions.
Aluminum nitride (AlN)
Aluminum nitride is a very high-performance ceramic filler with high intrinsic thermal conductivity. Potting compounds containing AlN can achieve high λ values while remaining electrically insulating. The limiting factors are usually the higher costs and sensitivity to moisture in the processing chain.
Metallic fillers (e.g., silver, aluminum)
Metallic fillers can greatly increase thermal conductivity, but often lead to electrical conductivity or at least significantly reduced insulation. Such systems are usually unsuitable for classic insulating potting applications, but can be useful in special applications with EMC or grounding requirements.
Applications
Thermally conductive potting compounds are used wherever electronics need to be both protected and cooled.
LED lighting and high-performance LEDs
LED modules are sensitive to increased junction temperatures. This affects brightness, color location, and service life. Thermally conductive potting compounds can protect LED assemblies while improving heat transfer to cooling structures. Depending on the design, flexible silicone systems or harder resin systems are used.
Power electronics and frequency converters
IGBT modules, MOSFET circuits, and DC/DC converters generate relevant heat loss during operation. Thermally conductive potting compounds help reduce hot spots and improve temperature distribution. They also offer protection against moisture, dirt, and mechanical stress.
E-mobility: Battery management systems and charging electronics
Automotive applications place high demands on temperature range, vibration resistance, media resistance, and long-term stability. Thermally conductive potting compounds are used in BMS electronics, sensor technology, and charging electronics, among other things. Depending on the specifications, additional requirements such as flame retardant classifications or special approvals may be relevant.
Power supplies and power sources
Switch-mode power supplies combine high component density with continuous thermal load. Thermally conductive potting can conduct heat specifically to metal housings or base plates while protecting the assembly from environmental influences. Pot life, flow behavior, and degassing are particularly important for complex geometries.
Selection criteria: Determining the correct λ value
Higher thermal conductivity always sounds better at first. In practice, however, a higher λ value often goes hand in hand with higher costs, more difficult processing, and, in some cases, higher mechanical hardness. The choice of material should therefore be based on thermal considerations.
-
What thermal power P (in watts) must be dissipated? The starting point is data sheets, simulations, or measurements during operation. -
Define permissible temperature difference
What temperature difference ΔT between the component and the cooling structure is permissible? Typically, depending on the application, this is a few tens of Kelvin. -
Calculate maximum thermal resistance
Rth = ΔT / P (unit: K/W) -
Estimate the required λvalue
λ = d / (Rth × A)
Where d is the layer thickness in meters and A is the heat transfer area in square meters. A safety factor (e.g., 1.3 to 1.5) is useful to account for tolerances, voids, and aging.
sample calculation
An LED module generates 10 W of heat loss. The heat is to be dissipated via a casting layer 5 mm thick and 50 cm² in area. Permissible temperature difference: 30 K.
- Rth = 30 K / 10 W = 3 K/W
- λ = 0.005 m / (3 K/W × 0.005 m²) = 0.33 W/m·K
- With a safety factor of 1.4, this results in λ ≥ 0.46 W/m·K.
In many cases, a casting compound with λ = 0.8 W/m·K would be sufficient here, provided that the contact quality, geometry, and heat dissipation in the overall system are suitable.
Additional selection criteria
- Chemical resistance (e.g., to coolants, oils, cleaning agents)
- Temperature range and temperature change resistance
- Shore hardness and mechanical decoupling (vibration, shock)
- Electrical insulation characteristics (e.g., dielectric strength, CTI depending on application)
- Processability (pot life, mixability, deaeration, dosability)
- Adhesion to relevant substrates
- CTE and stress build-up during temperature changes
- Approvals and regulatory requirements (e.g., UL, REACH, RoHS, application-specific approvals)
- Rework requirements / Disassembly
Processing tips
The high viscosity and high filler content of thermally conductive potting compounds require adapted processing techniques. Even a material with a good λ value can perform poorly in practice if it is not processed cleanly due to voids or incomplete wetting.
Mixing and homogenizing
Fillers can separate or settle during storage and transport. Thorough homogenization is important before processing. In two-component systems, both components should first be homogenized individually before being mixed. Suitable stirring technology improves filler distribution and reduces batch variations during processing.
vacuum degassing
Air pockets significantly impair effective heat conduction, as air has very low thermal conductivity. Degassing after mixing can significantly improve the quality of the potting. For larger volumes or critical assemblies, vacuum potting may also be advisable.
Dosage and flow characteristics
Thermally conductive systems are often significantly more viscous than standard potting compounds. For highly filled materials, adapted pumping and dosing systems are often advantageous. For complex assemblies, the material should be applied in such a way that air can escape in a controlled manner. Moderate temperature control can improve flow behavior, but depending on the system, it can also shorten the pot life.
curing
Reactive resin systems can generate significant exothermic heat, particularly when used for larger casting volumes. The high filler content influences the heat balance and reaction process. In some cases, it may be advisable to use stepwise curing or slower systems.
Silicone casting compounds generally exhibit significantly lower exothermicity than many epoxy systems, which can be advantageous for larger casting volumes in terms of processing.
Aftercare and quality control
After curing, the quality of the encapsulation should be checked, for example by visual inspection for bubbles, hardness testing, weight or density checks, and thermography under load to verify heat dissipation. For safety-critical applications, additional electrical and mechanical tests are recommended.
Frequently asked questions (FAQ)
Can I remove a thermally conductive potting compound again later?
This is only possible to a limited extent. Soft silicone systems are often easier to remove mechanically than hard epoxies. However, fully cured, highly filled systems can often only be removed with considerable effort and may damage components. If rework is planned, this should be taken into account when selecting the material.
How much does a higher λ value really improve cooling?
A higher λ value improves heat conduction in the material, but does not automatically improve overall cooling performance. Other decisive factors include layer thickness, contact quality, air bubbles, geometry, and subsequent heat dissipation in the system. The thermal resistance of the entire heat path is a key factor.
Why does thermally conductive potting compound cost significantly more than standard potting compound?
The main cost drivers are thermally conductive fillers and the higher formulation and processing costs. High fill levels increase viscosity and density and place higher demands on mixing, degassing, and dosing technology.
Can I process a thermally conductive potting compound with standard equipment?
This is sometimes possible for small quantities and simple geometries. For highly filled systems, good homogenization, suitable dosing technology, and degassing where possible are important in order to achieve reproducible results without air pockets.
Is a high λ value always the best choice?
No. Higher λ values often mean higher costs, higher viscosity, and more difficult processing. In many applications, a cleanly processed system with a moderate λ value is the more economical and technically adequate solution.
Conclusion: Measurably improve thermal performance
Thermally conductive potting compounds are more than just an upgrade. They enable electronic designs that would not function reliably thermally with standard potting. The λ value describes the material's capability, but the actual cooling effect depends on the entire thermal path.
Aluminum oxide-filled systems offer good value for money for many applications. Boron nitride and aluminum nitride-based systems are particularly interesting when higher thermal performance or special electrical properties are required.
The processing requires more care than standard potting. Homogenization, degassing, and adapted dosing technology are crucial for reproducible results. The benefits are measurable: lower component temperatures, longer service life, higher system performance, and better reliability.
When selecting a material, the rule is: as much thermal conductivity as necessary, not as much as possible. A clear thermal analysis prevents over-engineering and keeps costs within reasonable limits.
Technical support provided by SILITECH
Would you like to select a thermally conductive potting compound or optimize an existing system? SILITECH supports you in the preselection, sampling, and technical classification for your application.
- Selection based on temperature, mechanics, and media resistance
- Classification of λ values in the context of application
- Processing instructions (mixing, degassing, dosing)
- Sampling for testing and validation
Thermally conductive potting compounds for your application
Our materials specialists will help you select the ideal thermally conductive potting compound—with thermal calculations, samples, and processing advice. SILITECH offers potting systems for electronics, LEDs, e-mobility, and industrial applications.
Contact & Advice