In electronics, thermal pads (also called thermally conductive pad or thermal interface pad) are pre-formed rectangles of solid material (often paraffin wax or silicone based) commonly found on the underside of heatsinks to aid the conduction of heat away from the component being cooled (such as a CPU or another chip) and into the heatsink (usually made from aluminium or copper). Thermal pads and thermal compound are used to fill air gaps caused by imperfectly flat or smooth surfaces which should be in thermal contact; they would not be needed between perfectly flat and smooth surfaces. Thermal pads are relatively firm at room temperature, but become soft and are able to fill gaps at higher temperatures.

Five factors affect the choice, use, and performance of the interface material used between the processor and the heatsink：

1. Thermal conductivity of the material

Thermal conductivity is the quantified ability of any material to transfer heat. The thermal conductivity of the interface material has a significant impact on its thermal performance. The higher the thermal conductivity, the more efficient the material is at transferring heat. Materials that have a lower thermal conductivity are less efficient at transferring heat, causing a higher temperature differential to exist across the interface. To overcome this less efficient heat transfer, a better cooling solution (typically, a more costly solution) must be used to achieve the desired heat dissipation.

2. Electrical conductivity of the material

Some metal-based TIM compounds are electrically conductive, whereas ceramic-based compounds are typically not. Manufacturers produce metal-based compounds with low electrical conductivity, but some of these materials are not completely electrically inert. Metal-based thermal compounds are not hazardous to the processor die itself, but other elements on the processor or motherboard can be at risk if they become contaminated by the compound. For this reason, AOK does not recommend the use of electrically conductive thermal interface material.

3. Spreading characteristics of the material

The spreading characteristics of the thermal interface material determine its ability, under the pressure of the mounted heatsink, to spread and fill in or eliminate the air gaps between the processor and the heatsink. Because air is a very poor thermal conductor, the more completely the interface material fills the gaps, the greater the heat transference.

4. Long-term stability and reliability of the material

The long-term stability and reliability of the thermal interface material is its ability to provide a sufficient thermal conductance even after an extended time or extensive use of the computer (for example, servers or personal computers that work 24 hours a day, 7 days a week). Low-quality compounds may harden or leak out over time (the pump-out effect), leading to overheating or premature failure of the processor. High-quality compounds provide a stable and reliable thermal interface material throughout the lifetime of the processor. Thermal greases with higher viscosities are typically more resistant to pump out effects on lidless processors.

5. Ease of application

The thermal silicone pads can be cut arbitrarily, and the protective film is used directly. The tolerance is very small, clean, and saves labor costs.

From the perspective of engineering, the heating pad is matched with the irregular surface of the material from the engineering perspective. It uses high-performance thermal conductivity and eliminates the air gap, thereby improving the overall thermal conversion capacity and making the device working at a lower temperature.

If you would like to learn more about AOK performance thermal materials, please visit our website at www.aok-technologies.com.