Thermal pad and paste are two commonly used thermal interface materials, they are often compared when applied to heat sinks. This article will deeply analyze the two materials, and introduce the differences between thermal pad and paste, helping you make a proper decision.
What Is Thermal Pad
The thermal pad is a solid material to be used for filling air gaps, and it is composed of silicone, graphite, or other fillers. It has uniform thickness and flexible sizes, you can customize any shapes or thickness according to your requirement. The types of thermal pads include metal-based, silicone-based, graphite and so on.
What Is Thermal Paste
Not like thermal pads, the thermal paste has no fixed shape. It consists of base material and thermally conductive fillers, and finally appearing as a viscous liquid. Thermal pastes are used to fill in the gaps between electric components and heat sinks to exclude air, and enhance the efficiency of transferring heats.
Differences Between Thermal Pad And Paste
Coverage
Areas covered by the materials are an important difference between thermal pad and paste. Thermal paste has good fluidity that can fill in minute irregularities, but the thickness is difficult to achieve uniformly. It is also easy to leak, and needs professional operation.
The coverage of thermal pads is 100%. It can be cut for any size or shape to meet different requirements of components. The thermal pad has a simple installing process and no leak issue, the thickness can be also customized according to your need.
Thermal Conductivity
The thermal conductivity of thermal pads is typically in the medium level, which is lower than thermal paste. But it is enough for most medium-to-high power electronic equipment. The thermal pad is too hard to cover some tiny gaps, and it may even make the gap become more and more larger if the pressure is insufficient.
While thermal paste generally possesses higher thermal conductivity, it can form a thin and tight layer between chips and heat sinks. For tiny and irregular air gaps, thermal paste can fill them completely due to its excellent liquidity. This feature makes it have high efficiency to transfer heat, and decrease thermal resistance.
Durability
Thermal pad has a stable structure and buffering capacity, it can maintain good performance even in shocking environments. In the harsh conditions, the thermal pad will not dry out, it can endure high temperatures of about -40 – 200 ℃. But with the time going, it may soften.
Pump-out often occurs after a long time using thermal paste, it refers to the appearance that paste is extruded from the surface because of the heat cycle. Additionally, part of thermal paste may dry out to impact heat dissipation performance, and decrease the service life. You should reapplication regularly to keep the normal performances.
Use Method
The thermal pad is easy to apply and does not need cure time, just pre-cutting and installing certain equipment. It can achieve standardized operation through automatic placement equipment, and the process is very clean. Once the thermal pad is fixed to components with certain pressure, it is not easily deviated.
It has strict technical requirements to apply the thermal paste for the operator, application amount, uniformity, thickness of thermal paste should be strictly controlled. If the operation is incorrect, it may lead to unstable thermal conductivity or leakage, which will damage other components. While you can try to use the automatic applying equipment to improve the usage efficiency of thermal paste.
Safety
All of the thermal pad has an insulation function, it can prevent short circuits issues and is more safe to use in electronic devices. If the thermal paste is insulated depending on the materials that compose it, not all thermal paste possess insulation properties. Non-conductive raw materials such as ceramics can give the thermal paste a performance to block electrical conduction. But if there is metal material, thermal paste may have a risk of short circuit, and it is not easily used in the electric industry.
Cost
Although the thermal pad price is higher, it is easy to install and can be reused more than once. This means it does not need too much manual intervention or maintenance, offering a long service time.
Unit cost of thermal paste is usually lower than thermal pad, it is economical in the initial stages. However, the production process of thermal paste is more complex, and it requires more maintenance for long term using. If there exist failures caused by improper application, it will need re-work or repair, increasing your overall cost.
Application
Thermal pads are more suitable for the applications with complex structure, high stability, and difficult maintenance, such as automotive electronic control unit, RAM, IGBT power module, memory chip, custom applications, etc. These equipment usually operate in outdoor or harsh environments, require soft and compressible material to fill in gaps and absorb mechanical stress.
For high power density and excellent heat dissipation requirement products, thermal paste is more suitable, including CPUs, power supplies, AI computing card, GPU accelerator and so on. These products mostly work in a controlled environment, and can be maintained regularly. They can be cleaned or replaced in time when issues occur. Common industries that use thermal paste include high performance computing(HPC), medical devices, and consumer electrics.
Select Between Thermal Pad And Thermal Paste
When to Use Thermal Pad
If the products need to work stably in a harsh environment and are not suitable to maintain frequently, thermal pads can meet the requirement. It can avoid issues such as pump-out, dry-cracked, and make the material keep a stable condition. When you meet the following situations, choosing the thermal pad:
1. Products in the environment with temperature cycle, wet change or strong shake;
2. There is a big structural tolerance between chips and modules, need high thickness to fill;
3. Mass production that need automated and standardized processes;
4. High difficulty or cost of maintenance, requiring long service life.
These situations need a thermal pad because it is stable and easy to install. It combines thermal conductivity with electrical insulation properties, and is suitable for mass production. The cost of long term use is lower.
When to Use Thermal Paste
If the products demand extreme heat dissipation performance, and have a target for controlling the thermal resistance, then thermal paste may be the best choice. The following are some typical application scenarios to use the thermal paste for your reference:
1. The chip has high power and local temperature is easy to increase;
2. There are many tiny and irregular gaps need to be filled;
3. Products work environment can be controlled, without temperature shock or violent shake.
4. Devices have a regular maintenance plan, re-applying paste when they age or pump out.
The ultra-thin interface of thermal paste can significantly reduce heat resistance. And liquid properties make the thermal paste fill any tiny gaps. If your project is sensitive to cost, it may be a good choice.
Conclusion
The thermal pad and paste differ in many ways, choosing a proper thermal interface material can not only improve the performance and stability of equipment, but also decrease total cost of ownership. If you are troubled with selection, feel free to contact us for a professional thermal material solution.
FAQs
1. How to choose suitable thermal interface materials?
When you want to choose a suitable thermal interface material, the heat conductivity, applications, performances, use methods of the material are core factors to consider. You should determine the requirements of your devices. Knowing if the device needs high thermal conductivity or stability, if the maintenance is convenient, if air gaps have special shape, etc. And then choosing a suitable one.
2. How to avoid “floating” or air gap issues with thermal pad?
“Floating” and air gap issues are caused by the improper install. It needs to control the thickness and pressure ratio properly in the design process, and install a support tool to maintain the uniform pressure. This method can help thermal pads achieve complete cover, and increase the efficiency of thermal conductivity.
3. How to determine if the thermal paste fails?
The typical signals of thermal paste failure include abnormal high temperature of the device, overheating, and frequent downclock of the system. When you open the equipment to check, if the thermal paste is significantly dry, crack or pump out, it means the thermal paste fails. Cleaning and replacing new material is a good solution.
