A wrong choice of thermal management materials can have a detrimental effect on your electronic components. What is thermal paste? Understanding its function, properties, and applications is of great importance for your industry. This article can help you learn more.
What is Thermal Paste for?
Thermal paste, also called thermal compound, is a paste-like thermal conductive medium. The purpose of heat sink thermal paste is to enhance the heat transfer efficiency between electronic components and heat sinks. It is a thermal interface material that is widely applied in high-heat-generating cores such as computer central processors (CPUs) and graphics processing units (GPUs) and their heat sink bases.
Key Properties of Thermal Paste
The thermal paste has the following properties:
| Property | Practical Impact |
| Thermal Conductivity (W/m·K) | Higher values mean faster heat transfer. |
| Thermal Impedance (°C·cm²/W) | Lower is better. |
| Electrical Conductivity (S/m) | Usually, non-conductive pastes are safe because conductive pastes can cause short circuits if they spill. |
| Viscosity (Pa·s) | High-viscosity pastes are less prone to leakage but are difficult to apply evenly. Low-viscosity pastes are easier to apply but may overflow. |
| Specific Gravity / Density (g/cm³) | Affects material handling, dispensing behavior, and weight. |
| Operating Temperature Range (°C) | Temperature range within which the thermal paste can maintain stable performance. |
| Lifespan (Years / Hours) | High-durability pastes can usually last 3 – 5+ years. |
Why is Thermal Paste Necessary?
Thermal paste is vital for electronic components because it can fill microscopic surface irregularities and prevent the processor from getting damaged due to overheating.
When the surfaces of two metals are pressed together, the microscopic irregularities will cause a large number of tiny air pockets. If you do not apply thermal paste, the air will cause heat to accumulate rapidly on the chip or component surface and fail to transfer to the heat sink.
As a fluid medium, the thermal paste will flow and fill all the microscopic irregularities. This displaces air from the interface, making thermal conduction smooth.
Moreover, in consumer electronics, modern central processing units (CPUs) and graphics processing units (GPUs) generate a significant amount of heat during operation. Without the thermal paste for CPU, chip temperature can soar above 100°C, causing computer lag, frame drops, or even automatic power-off.
In industrial and automotive electronics, the absence of thermal paste can cause the junction temperature to exceed limits. This can lead to thermal runaway, directly resulting in physical burnout of components or widespread light degradation in high-power inverters (IGBTs) or high-brightness LED cores.
How Does Thermal Paste Work?
The operation principle can be divided into four steps:
- The thermal paste is forcibly pushed into these microscopic grooves between two metals, and it expels trapped insulating air outwards.
- Thermally conductive fillers create heat-transfer pathways through the interface, while the paste fills surface irregularities and reduces the amount of air.
- The pressure applied by the heat sink causes the thermal paste to reach the minimum bond line thickness, so the thermal resistance is very low.
- Chip temperature will fluctuate, causing thermal expansion and contraction of the metal. High-quality thermal paste can maintain stability during this dynamic process and maintain good thermal conduction.
What are the Different Types of Thermal Paste?
Thermal paste is mainly made of base liquids (such as silicone oil and polymers) and thermally conductive fillers. According to different fillers, the thermal paste is divided into several types.
Ceramic-based Thermal Paste
The fillers of the ceramic-based thermal paste are zinc oxide or aluminum oxide powder. It is cost-effective and has good insulation. Even if spilled onto the motherboard, it won’t cause short circuits. Therefore, it is ideal for general users.
Carbon-based Thermal Paste
The carbon-based thermal paste uses carbon-based fillers such as graphite, graphene, or carbon nanotubes. It is also non-conductive and offers superior heat dissipation.
Metal-based Thermal Paste
The metal-based thermal paste contains micron-sized silver or aluminum particles. In comparison, it has higher thermal conductivity, but some may have slight electrical conductivity. Therefore, you need to be careful when you use it.
Liquid Metal
This type is made from special metals (such as gallium-indium alloy). It has superior thermal conductivity, but it is highly conductive and corrosive. So it should generally not be used with aluminum heat sinks. That makes it only suitable for enthusiasts.
How to Apply Thermal Paste?
To properly apply thermal paste, you can follow these 4 steps.
Step 1. Remove the Old Residues
Remove the power supply and the heat sink. Use high-purity alcohol and non-woven fabric to wipe clean the dried old paste until you are sure that there is no grease, residue, or fiber left on the metal surface.
Step 2. Choose Dispensing Patterns
You need to select a suitable pressing method according to the size and shape of the heating chip. Here we introduce 4 methods:
| Pea-sized Dot | Create a circular dot (3-4 millimeters) in diameter in the center of your chip. | The simplest method with almost no bubbles. |
| Cross Pattern | Draw two intersecting thin lines from the four corners of the chip towards the center. | Can ensure that the thermal paste spreads more evenly to the four edges of the chip. |
| Line Method | Draw a thin line vertically in the center of the chip. | Suitable for Rectangular chips and most laptop GPU cores. |
| Manual Spread | Use the included scraper to manually spread the thermal paste into a thin, transparent film. | Suitable for high-viscosity silicone grease or the core of the graphics card. |
Step 3. Install the Heat Sink
Position the heat sink directly over the chip and lower it vertically onto the interface. Align it with your chip, and tighten the fixing screws in an X-shaped sequence in turn.
Step 4. Cleaning and Inspection
Finally, inspect if there is any leakage. You can use a cotton swab dipped in alcohol to wipe if thermal paste spills out, but ensure that there is no spillage if you use liquid metal.
Tips for Applying Thermal Pastes
- Take care that you have removed the plastic protective film (if there is) before applying thermal paste.
- Never apply new thermal paste if the old one has not been cleaned, because residual thermal paste can create an inconsistent interface and increase thermal resistance.
- Do not apply too much thermal paste. Otherwise, it may become a thermal resistance layer.
- Once the thermal paste is applied, you cannot move your heat sink because that can introduce air into the paste, causing bubbles.
What are Thermal Paste Applications?
Uses for thermal paste include almost all semiconductor and electronic power components that need to dissipate heat through metal heat sinks.
- Consumer Electronics
Thermal paste is widely used to manage heat dissipation for high-performance computing chips, including CPUs, GPUs, delidding, and home game consoles.
- Servers
Multi-core Xeon or EPYC processors need thermal paste to deal with the large amount of heat generated when working.
- Telecom Systems
The RF modules and power amplifiers operate in a harsh environment, so thermal paste is always used to conduct heat to the heat dissipation plates on the cabinet.
- Power Electronics
Thermal paste must be applied between power transistors and diodes and the heat sink.
Solid-state relays (SSRs) generate a significant amount of heat during high-frequency switching operations, so they also need thermal paste to dissipate heat.
- Automotive and EV Industry
Thermal management is very important for automobile security. For example, according to different requirements, you can use thermal interface materials such as thermal pads, gap fillers, gels, and thermal pastes between battery modules and cooling plates.
- LED
The light chips of LEDs will convert the vast majority of electrical energy into heat. Therefore, the back of the light chip substrate should usually be fully covered with thermal paste.
Comparison of Thermal Paste with Other Materials
Thermal paste is often compared with other materials, such as thermal pads, thermal gel, silicone pads, etc. You may feel confused about their differences and do not know how to choose the suitable one for your industry. From the following comparison charts, you can get more details.
Thermal Pad vs Thermal Paste
| Feature | Thermal Pad | Thermal Paste |
| Form | Pre-formed solid pad | Viscous paste or grease |
| Gap Filling | Better for larger or uneven gaps | Best for microscopic surface gaps |
| Thickness | Predefined | Application-dependent |
| Surface Conformity | Good | Excellent for fine surface irregularities |
| Thermal Performance | Depends on pad material and thickness | Often offers low interface resistance with proper application |
| Assembly / Handling | Easy to install; the thickness is predetermined. | Requires controlled dispensing and thickness management. |
| Typical Applications | Power modules, VRMs, memory, battery systems | CPUs, GPUs, power components, heat sinks |
From the comparison of thermal pads and paste, thermal pads are more suitable for controlling larger gaps, while thermal paste is better for filling the tiny gaps.
● Can I Put Thermal Paste on Thermal Pads?
Usually, it is not advisable to apply thermal paste on thermal pads. That may change the interface thickness and affect mechanical compressibility and thermal performance.
Thermal Gel vs Thermal Paste
| Feature | Thermal Gel | Thermal Paste |
| Form | Soft, gel-like material | Thicker paste or grease |
| Gap Filling | Better suited to larger or uneven gaps | Best for very thin, microscopic gaps |
| Application | Easy to dispense and conform to complex surfaces | Requires controlled application and thickness |
| Thermal Performance | Depends on formulation and gap thickness | Generally effective for low-thickness interfaces |
| Mechanical Flexibility | High | Moderate |
| Typical Applications | Complex components, power electronics, automotive electronics | CPUs, power devices, heat sinks, electronic assemblies |
From the comparison between thermal gel and paste, you can find that the thermal gel is more suitable for managing interfaces with larger gaps, uneven surfaces, or greater mechanical movement. Thermal paste is preferred for thin, closely mating surfaces.
Silicone Pad vs Thermal Paste
Comparing silicone pads with thermal paste, the former is better for controlling thickness, easier assembly, or larger interface gaps, while the latter is better suited to thin interfaces.
| Feature | Silicone Pad | Thermal Paste |
| Form | Pre-formed solid pad | Viscous paste or grease |
| Gap Filling | Suitable for larger or uneven gaps | Best for thin, microscopic gaps |
| Thickness | Predefined | Application-dependent |
| Application | Easy to place and assemble | Requires controlled dispensing or application |
| Mechanical Stability | Good | Depends on formulation and application |
| Typical Applications | Power modules, batteries, VRMs, industrial electronics | CPUs, power components, heat sinks, electronic assemblies |
How to Choose the Best Thermal Paste?
When choosing thermal paste, there are five core factors you must take into consideration.
- Conductivity and Impedance
Usually, the higher the thermal conductivity coefficient, the faster the theoretical heat conduction. However, the actual effect is more largely influenced by its thermal impedance. The mainstream carbon-based thermal paste (4-9 W/m·K) is usually sufficient. For extreme overclocking, you can choose 13 W/m·K ones or liquid metal.
- Electrical Conductivity
Liquid metal has strong performance, but it is highly conductive and prone to short-circuiting if it spills. In comparison, non-conductive ceramic-based or carbon-based thermal paste is safer.
- Viscosity
For equipment with high heat density, a high-viscosity and high pump-out resistance is necessary, or the silicone grease may be squeezed out of the core.
- Curing Period
Choosing advanced modern silicone-based thermal paste without a curing period can largely save your time.
- Longevity
High-quality thermal paste can remain undried for 3 to 5 years or even longer.
How to Choose Thermal Paste for Different Applications?
For Laptops
Laptops have low clamping force heat sinks, high heat density chips, and intense instantaneous temperature fluctuations. Therefore, when choosing thermal paste for laptops, you need to select thermal paste with high viscosity and resistance to pump-out to avoid the pump-out effect.
For Industrial Applications
To choose thermal paste for industrial applications, you must pay attention to stability throughout the entire life cycle, high-volume automated production efficiency, extreme environment tolerance, and fail-safe security.
- Physical Feature
Different materials determine your production-line technique. For thin gaps, industrial-grade thermal grease is the preferred choice. For irregular large gaps, liquid gap fillers are better.
- Degradation Resistance
Industrial thermal paste must have high viscosity, low pump-out, and dual-component thermal conductivity. And the moisture-proof, corrosion-resistant, and weather-resistant properties are also important in industrial applications.
- Electrical Insulation
For high-voltage power electronic equipment, the thermal paste must be non-conductive and must not contain conductive metal particles.
- Silicone-Free Requirements
Some industries have silicone-free requirements, such as high-precision optical instruments, aerospace, automotive painting workshops, etc. You have to choose silicone-free thermal paste.
- Thermal Conductivity
Conventional thermal load design in industrial design usually requires a thermal conductivity of 3-5 W/m·K or above. High-density PCBs or high-power lasers may need a value of 8 W/m·K or higher.
- Thermal Resistance
The thermal resistance under clamping force and specified thickness is vital.
FAQ
Is Thermal Paste Toxic?
The toxicity of thermal paste depends on its specific components.
Some thermal pastes made of silicone oil and some non-conductive fillers such as zinc oxide, aluminum oxide, or carbon particles are non-toxic.
Liquid metal is corrosive and poses a risk to humans, so you must follow the manufacturer’s safety instructions and SDS when applying it.
Anyhow, you should always check the manufacturer’s SDS and safety instructions before handling or disposing of the material.
How to Replace Thermal Pads with Thermal Paste?
On most occasions, we do not recommend that you use thermal paste to replace thermal pads, because it cannot reliably maintain a specified interface thickness. If you have to find an alternative solution, using thermal putty can be more suitable.
When Should I Replace the Thermal Paste?
Usually, the thermal paste will gradually dry out, harden, and lose its effectiveness after 2 to 3 years. Therefore, it is recommended that you replace it when its thermal performance deteriorates, the material dries out or pumps out, or maintenance procedures specify replacement.
Is It Worth Upgrading the Stock Thermal Paste?
This depends on your hardware and current usage status. For the following conditions, it may be worthwhile to change or upgrade thermal paste.
If your electrical equipment has been used for more than two years, the original thermal paste may dry out, crack, and become cement-like, so it can be changed. Some devices have high chip density, such as gaming laptops or mini PCs. Their original thermal paste may have a pump-out effect, so you can consider upgrading it. Some original thermal paste for high-power LEDs has low thermal conductivity. You can check if it needs to be replaced.
Can I Mix Different Types of Thermal Pastes?
No. Different thermal pastes are formulated with different base carriers and different particle formulations. Their chemical components may undergo incompatible reactions, leading to rapid layering, solidification, caking, or premature drying of the silicone paste.
You must not mix liquid metal with any other standard thermal paste. Otherwise, the liquid metal will be pushed to the edge of the chip, and the heat dissipation performance will be destroyed.
Can Thermal Paste be Reused?
No. The thermal paste that has been applied to the chip and pressed down cannot definitely be reused. Once you remove the heat sink, you must clean it and reapply the paste.
Can Thermal Pastes Improve Gaming Performance?
Thermal Paste cannot directly affect the computer’s theoretical computing power. However, it can improve your game’s performance to some extent. For some devices that generate too much heat when operating, a high-quality thermal paste can increase FPS and eliminate lag.
Can I Remove Thermal Pastes with Regular Cleaning Solutions?
Usually, we do not recommend using regular cleaning solutions as a substitute for 90% or 99% isopropyl alcohol (IPA). Moreover, never use water or soapy water, glass cleaner, nail polish remover, or premium spirits.
Is It Normal for Thermal Pastes to Have a Curing Period?
Yes. Some traditional thermal pastes require a curing period that lasts for hundreds of hours. Some modern carbon-based or ceramic-based thermal pastes have suspended base carriers. Their curing period is almost zero.
Final Thoughts
Thermal paste plays a vital role in realizing efficient heat conduction, stable operation, and long-term electronic reliability. If you are considering getting new thermal paste, Gallop Innotek can offer various types to meet your thermal conductivities, thermal resistances, temperatures, and application requirements. Contact us, and our professional team can help you determine the material that is most suitable for your application.
