When designing thermal management solutions for your products, you will find that thermal interface materials such as thermal paste, thermal gel, and thermal pads are ideal choices for heat dissipation. A suitable thermal interface material not only provides efficient heat dissipation to achieve stable product operation but also extends the product’s service life. However, you may have noticed that there are so many types of thermal interface materials, and the various specifications of different models can be confusing. Reading this article will help you make an informed choice.
What is a Thermal Interface Material?
Thermal interface materials are used to fill the gap between heat sinks and heat-generating components. Thanks to their high thermal conductivity, when components operate and generate heat, these materials efficiently transfer thermal energy to the heat sink, thereby facilitating cooling. Thermal pads, thermal pastes, and thermal gels are all common thermal interface materials. You can apply them for cooling in electronics, industrial equipment, automotive systems, and medical devices to achieve reliable continuous operation and extended service life. However, different thermal interface materials possess distinct characteristics and suitability; you should select the most appropriate one for your project.
Selecting the Appropriate Type of Thermal Interface Material
Different thermal interface materials will offer different levels of heat dissipation for your products, and some may prove unsuitable for your specific application. Information on common thermal interface materials is provided here for your quick reference.
Thermal Gel
Thermal gel is a thixotropic thermal interface material with high thermal conductivity(3 ~ 8W/m·K). It requires application and curing during use, making the process somewhat complex. However, it is readily portioned and can be efficiently processed automatically using equipment such as automated dispensing systems. Thanks to its curing properties, thermal gel is less prone to drying out or leaking. Within its operating temperature range(-50 ~ 150℃), it offers a longer service life than thermal paste and requires less frequent maintenance. Once cured, the thermal gel has excellent adhesion and elasticity, providing superior resistance and mitigation against vibration, noise, and impact. This makes it an excellent choice for thermal management in automotive and industrial applications.
Thermal Pad
Thermal pads are pre-formed flexible sheets supplied by manufacturers, which can be precisely cut to match the shape and size of your surfaces. Compared to thermal paste, their installation process is simpler, making them very suitable for high-volume processing. However, their thicker bonding line results in poor performance on complex or rough surfaces compared to thermal paste, thermal gel, and thermal putty. They offer extended service life, requiring less frequent maintenance and replacement. They are available in various types, such as silicone-based thermal pads, silicone-free thermal pads, and graphite thermal pads, and different thicknesses (0.2–20mm) to meet diverse application requirements.
Silicone Thermal Pads and Silicone-Free Thermal Pads
Thanks to their cost-effectiveness and elasticity, silicone thermal pads are more commonly used. They offer different thicknesses and thermal conductivities (1–15 W/m·K) and thickness options (0.2–20 mm). However, their silicone substrate may release silicone oil or emit silicone vapour during use. You can select Silicone-free thermal pads for enhanced safety in silicone-sensitive applications. However, their thermal conductivity(1–6 W/m·K) is lower than that of silicone pads.
Ultra-Soft Thermal Pads
Ultra-soft thermal pads are softer and more moist than standard variants, offering you superior adhesion to enclosure surfaces, heat sinks, and components. They achieve exceptional conformability even on rough or irregular surfaces, while offering easier installation and a longer service life (approximately 3 to 10 years) compared to thermal paste. Their outstanding flexibility also provides shock absorption and cushioning for components, delivering enhanced protection.
Conductive Thermal Pads
Most thermal pads, such as silicone thermal pads and ultra-soft thermal pads, are insulating. However, to meet your more professional requirements, conductive thermal pads are also available. These offer high thermal conductivity (6 to 13W/m·K) and can achieve electrical conductivity of up to approximately 20,000 S/cm. It is highly suitable for you to use in high-frequency equipment (such as 5G communication, Wi-Fi, and Bluetooth modules) to provide thermal dissipation for heat-generating components while utilising their conductivity for grounding and shielding, thereby achieving superior electromagnetic compatibility.
Carbon Fibre Thermal Pads
Carbon fibre thermal pads are manufactured from lightweight, durable carbon fibre material. They offer superior thermal conductivity (16–50 W/m·K) and enhanced durability for your product. Furthermore, as they do not use silicone materials, they prevent silicone contamination of components. Additionally, they have electromagnetic interference suppression capabilities, resulting in a more stable and precise device operation.
Graphite and Graphene Thermal Pads
Graphite and graphene thermal pads are more advanced thermal interface materials. They are very thin and fill minute gaps with outstanding compliance, offering reduced drying and pumping out during high-frequency use. Should you require a suitable thermal pad for applications involving more extreme temperatures, these will prove satisfactory (operating within a range of approximately -40°C to 400°C). They can handle exceptionally high thermal loads, with graphene thermal pads having thermal conductivities between 70 and 130 W/m·K, while graphite thermal pads can achieve thermal conductivities as high as 1950 W/m·K.
Thermal paste
Thermal paste is a thermally conductive interface material possessing a degree of fluidity, yet it requires no curing during installation and can be directly pressed between components and heat sinks. It can achieve an extremely low bond line thickness, thereby maximising thermal contact area for superior heat dissipation. However, it has a relatively short lifespan (approximately 12 months) and is prone to spillage and drying out during use. This necessitates timely replacement and maintenance. Consequently, if low maintenance requirements are your priority, thermal paste is not the appropriate solution.
Thermal Tape
Thermal tape, similar to thermal pads, is also pre-formed. However, it typically has double-sided adhesive layers, offering enhanced tackiness. It combines thermal conductivity with a securing function, enabling its use in structurally compact projects. In applications less susceptible to vibration and lower temperatures, additional mechanical fastening of thermal tape may not be required. However, owing to its lower thermal conductivity (1–5 W/m·K), it is best suited for products with modest heat dissipation requirements. If you are seeking higher thermal conductivity with good adhesion, thermal gel may be a more right choice. Thermal paste also offers silicone-free options, allowing you to select for silicone-sensitive products.
Thermal Putty
Thermal putty is a thixotropic, paste-like thermal interface material that can effectively cover surface irregularities with minimal stress during application. It maintains prolonged wettability in use, offering you a longer service life (2-8 years) than thermal grease. Furthermore, thermal paste is more suitable than thermal grease for larger components and gaps between heat sinks or enclosures (0.1 ~ 4mm). However, its application is more complex than thermal pads and requires additional investment in dispensing robots or manual dispensing equipment for high-volume processing. Nevertheless, it eliminates the need for mixing and curing, offering a simpler application process than thermal gel.
Thermal Conductive Potting Encapsulant
Thermal Conductive Potting Encapsulant(potting compound) is used for encapsulating electronic components. It also has a degree of thermal conductivity, thereby aiding in heat dissipation while protecting the components. Other thermal interface materials are typically applied by adhesive bonding or coating between the enclosure or heat sink and components. In contrast, thermal conductive potting compounds fill and encapsulate all elements within the housing, achieving an exceptionally robust bond upon curing. It can be used to bond components, delivering enhanced mechanical strength and protecting them from vibration and impact. It also provides sealing properties, guarding against dust, moisture, oil contamination, corrosion, and similar hazards. This multifunctionality results in a lower thermal conductivity (0.8–2.0 W/m·K). If sealing is your primary consideration, it is a good choice.
Phase Change Material
Unlike other thermal interface materials, phase change materials undergo solid-liquid transitions, and absorb heat during the transformation process (from solid to liquid) and release heat (from liquid to solid), thereby maintaining near-constant component temperatures. Consequently, they are the first choice for highly temperature-sensitive products such as medical equipment, effectively minimising operational temperature fluctuations. The thermal conductivity of phase change materials ranges between 2 and 8.5 W/m·K, and their excellent latent heat capacity enables superior thermal management performance. However, their best operating temperature lies between -55 and 125°C, with phase transitions occurring only at a fixed temperature of approximately 45 to 60°C. This imposes limitations on product applications. Furthermore, compared to thermal pastes, they entail higher initial costs.
Determine Parameter Requirements for Thermal Interface Materials
Thermal Conductivity
Firstly, thermal conductivity directly reflects the heat dissipation performance of thermal interface materials. It is advisable to select the most suitable option to prevent unsatisfactory cooling results due to excessively low conductivity. Whilst excessively high thermal conductivity does not impair heat dissipation, it may incur higher costs. Some suppliers offer specialised thermal simulation services, and you may contact them to obtain an accurate assessment.
Thermal Resistance
Beyond thermal conductivity, thermal resistance also warrants consideration. Thermal resistance denotes the capacity of a thermal interface material to impede heat transfer under steady-state thermal power conditions. Consequently, thermal interface materials with lower thermal resistance achieve superior heat dissipation performance. This property is influenced by factors such as material thickness, porosity, and ambient temperature. Within your budget constraints, you may wish to explore options offering lower thermal resistance.
Thermal Impedance
Thermal resistance is measured under steady-state heat transfer conditions, whereas thermal impedance reflects the instantaneous ability of thermal interface materials to resist load fluctuations. When selecting thermal interface materials for products with frequent power variations—such as servers, switchgear, and lighting—thermal impedance must also be considered. Lower thermal impedance indicates that the thermal interface material can deliver more stable temperature control for your product.
Selecting the Correct Rhermal Interface Material Thickness
Thermal interface materials in paste form, such as thermal grease, thermal paste, thermal gel and thermal potting compound, require you to determine the quantity based on product and supplier guidelines and control the thickness during application. For preformed thermal interface materials like thermal pads and thermal tape, you must select the most suitable thickness during procurement. Excessive or insufficient thickness renders the material unusable or compromises performance, leading to material wastage. You’d better measure accurately before making your selection.
The Thermal Interface Material is too Thin
Insufficient thickness fails to fill gaps between the housing(or heat sink) and component, allowing low-thermal-conductivity air to intrude. This not only creates a small thermal contact area but also compromises thermal interface performance. Stacking thermal pads or tapes to achieve thickness is not allowed, as it increases porosity.
The Thermal Interface Material is too Thick
On one hand, overly thick thermal interface material may not fit between components and heat sinks. You cannot alter their thickness post-installation, as damaged thermal interface material will have a reduced lifespan and may fail. On the other hand, excessive thickness increases thermal resistance and thermal impedance, reducing heat dissipation efficiency.
Select Thermal Interface Materials according to the Operating Environment
Operating Temperature
The optimum operating temperatures for thermal interface materials vary. You must consider your product’s operating environment and select materials permitted for use within that range. Thermal pads typically operate between approximately -60°C and 200°C, thermal tapes between -40°C and 120°C, thermal pastes, thermal putties, and thermal gels between -50°C and 150°C, and phase change materials between -55°C and 125°C. Specific variations exist between different product models. Utilising these materials under extreme temperature conditions may result in reduced lifespan and diminished thermal dissipation performance.
Component Surface Roughness
Due to variations in hardness and form, thermal interface materials have differing adhesion properties to surfaces. Thermal pastes, thermal putties, thermal gels, and phase change materials are suitable for rough surfaces. Thermal pads and thermal tapes, however, are better suited for relatively flat surfaces.
Select According to the Budget
Budget should also be considered during selection. Thermal tape and potting compounds are comparatively inexpensive due to their lower thermal conductivity. However, as potting compounds need larger quantities, this may ultimately incur higher costs. Beyond initial expenditure, thermal paste necessitates more frequent maintenance due to its shorter lifespan. In the long term, it may prove more costly than thermal pads and thermal paste. Furthermore, thermal paste, thermal gel, and thermal compound necessitate the additional purchase of expensive automated equipment for high-volume processing. You should know these costs comprehensively before making your selection.
Other Requirements
Insulation and Conductivity
Most thermal interface materials are insulating. You may consult product specifications or enquire with suppliers for confirmation. This enables safe application across diverse electronic devices, mitigating risks such as short circuits. For specialised requirements, conductive thermal pads offering partial conductivity may be selected.
Silicone Sensitivity
Certain silicone-sensitive devices may be damaged by silicone oil leaching from thermal interface materials or by volatilised silicone vapour, potentially leading to costly repairs and replacements. Thermal interface materials such as thermal pads and thermal pastes offer silicone-free alternatives, which you may select to enhance product reliability.
Resistant to Electromagnetic Interference
Should your product require both thermal dissipation and electromagnetic shielding, carbon fibre thermal pads and graphene thermal pads can simultaneously conduct heat while suppressing electromagnetic interference. This effectively counters electromagnetic interference from other devices while also minimising the electromagnetic interference your equipment may cause to others.
FAQs
Can Thermal Interface Materials be Reused?
To maintain optimal performance, most thermal interface materials—such as thermal paste, thermal tape, and thermal gel—are not designed for reuse. You may reuse certain thermal pads without adhesive layers, provided there is no damage or deformation. However, using new materials will result in a better thermal dissipation performance.
Which Thermal Interface Material Offers the Highest Thermal Conductivity?
Thermal paste has higher thermal conductivity, reaching approximately 14 W/m·K at its peak. Graphite thermal pads can achieve thermal conductivities as high as 1950 W/m·K. However, when selecting materials, you must consider not only thermal conductivity but also thermal resistance and suitability. For example, on highly rough component surfaces, thermal paste can deliver better heat dissipation performance compared to thermal pads with the same thermal conductivity.
Can Thermal Interface Materials be Mixed?
Within a single device, you may use different thermal interface materials for different heat-generating components. However, on any given component, you should select a single thermal interface material. Unless explicitly stated by the supplier, these materials should not be layered.
Can Thermal Paste be Substituted for Thermal Gel?
Both thermal paste and thermal gel can achieve satisfactory heat dissipation performance. However, thermal gel offers superior adhesion and a longer service life compared to thermal paste. If these characteristics meet your requirements, it may serve as a suitable alternative to thermal paste.
Is Thermal Interface Material Necessary?
Components accumulate significant heat during continuous operation. If the gap between them and the heat sink is filled with air, this results in low thermal conductivity. This impedes heat transfer, leading to poor heat dissipation performance. Using thermal interface material not only replaces air but also achieves higher heat dissipation efficiency.
What is the Lifespan of Thermal Interface Materials?
On the one hand, thermal interface materials have different shelf lives (approximately 6–24 months), which you can verify in the instruction manual and use within this period. On the other hand, different thermal interface materials and variants have different service lives that are also influenced by the operating environment. You may consult the manual or contact the supplier for this information.
Final Thoughts
Selecting the correct thermal pad can enhance the reliability of your product. After reading this article, you will be better equipped to make an informed choice. GALLOP INNOTEK can guide you in selecting the right product for your needs. Should our current range not fully meet your requirements, bespoke solutions are also available. Please do not hesitate to contact us for a tailored proposal.
