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Thermal interface material
Three types of thermal interface material (TIM) are commonly used in the computer industry:-Thermal pads, graphite pads, also called gap pad, silicone/graphite pad, thermal tape materials.; lots of used for the gap over 0.2mm to 20.0mm of mechanics tolerance.
-Thermal grease, also called thermal grease; apply for CPU, VGA, processors, North/South chipsets on the motherboard.
-Phase-Change material, similar application with thermal grease.
Guidelines for thermal interface materials
-Thermal conductivity of thermal compound - thermal grease, thermal pad, phase change.-Electrical conductivity of material - thermal grease, thermal pad, phase change.
-Long-term stability and reliability of material - thermal grease, thermal pad, phase change.
-Hardness and compressibility of thermal gap pad, silicone pad, graphite pad.
-Ease of application.
Thermal Conductivity of thermal 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 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.
Electrical Conductivity of thermal 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, we do not recommend the use of electrically conductive thermal interface material.
Long-Term stability and reliability of thermal 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, 7days a week).Low-quality compounds and thermal pads (gap pads, silicone pads) may harden or leak out over time, leading to overheating or premature failure of the processor. High-quality compounds and thermal pads provide a stable and reliable thermal interface material through out the lifetime of the processor. Thermal greases with higher viscosities are typically more resistant to pump out effects on lidless processors.
Hardness and compressibility of thermal gap pad, graphite pad
A good compressibility of thermal pad or gap pad means a good ability to absorb the shock like a cushion. It becomes easy to apply a thermal pad for several chips with single heat sink at the same time.We recommend customers to use thermal pads, gap pads to fill the tolerance or gap of each component with heat transfer function inside electronics. The hard and stiff characteristic of thermal pad and graphite pad can be used for heat transfer on X-Y horizontal area. The position of the heat sink can be a suitable place to fit the narrow space or small mechanical design. Some applications used copper foil instead of graphite pad due to EMI issue.
Ease of application
A spreadable thermal grease requires the installer to carefully use the appropriate amount of material. Too much or too little material can cause problems. A fixed size and is therefore easier to apply in a consistent manner.Otherwise, thermal pad with good release paper is another good way applying on the chip or heat sink in mass production line.