Electronic devices are being improved as the technology is escalating to different levels. Ensuring high speed and making the devices more compact is the idea for upcoming years, and yes, that could be challenging. For this purpose, thermal management becomes important to the functionality of electronic devices. The vital step is to ensure that heat is radiated through an integrated circuit and heat spreader to a heat sink. This could be done if the net thermal resistance of the thermal interface is reduced.
These silicon-based materials that are highly conductive are used to displace air at uneven places for the cooling effect. Thermal interface materials are considered to be best for transferring heat where there is a wide gap range, and because of their improved performance, they are used for high-end applications. These thermal interface materials are available in many forms, such as elastomer pads and phase change materials that capture the thermal advantage performance of grease and assembly of the solid pad. Let us study these materials in detail-
Greases-Thermal Compound
Greases are silicone or hydrocarbon oils with various fillers, and their primary goal is to eliminate microscopic air pockets. They are the oldest class of materials and are considered messy because they are not easy to work with due to their high viscosity. Working with grease, manufacturers try to achieve full coverage with an appropriately thin gap.
The components require mechanical clamping and a pressure of about 300 kPa to enable optimal thermal performance. Traditional grease has high interface resistance as compared to the new ones when they are heated during the usage; the viscosity drops that wet the contact surfaces further by improving the performance by reducing the interfacial resistance. Due to this reason, they are used widely in consumer products. New formulations are being developed for enhancing the microprocessor packaging by using two thermal interface materials for interfacing its latest products with heat sink, and they are produced using greases.
Elastomeric Pads- Extension of Grease
They are polymerized silicone rubbers in the form of easy-to-handle solids. To improve handling, most elastomeric pads assimilate fiberglass carrier and contains inorganic fillers just like the greases. They are simple to assemble, but the trade-off is that they require high pressures to achieve an adequate interface. With elastomers, applications are limited to those with modest thermal requirements.
Thermal Tapes- for Heat Sink
They were developed for a heat sink as they eliminate the need for external clamps; thereby, reducing the overall hardware requirement. Thermal tapes are filled with pressure-sensitive adhesives coated on support matrix-like fiberglass mat or aluminum foil. The reason for using is that they adhere to surfaces by slight pressure when applied. The resistance for thermal pads depends on surface quality, and the adhesive property is considered to be second. Otherwise, they have limited compliance and are sometimes not suitable for BGA packages with concave top surfaces.
Phase Change Materials-
They combine the performance of grease with the convenience of elastomer pads. Phase change materials are waxes that melts at a temperature range from 50 degrees to 80 degrees. Mostly, they are low-temperature thermoplastic adhesives that are conductors of heat both above and below melting points. When phase change materials are used above the melting point, they are used with a clamp as they need mechanical support. With pads and tapes, they can be obtained in various configurations and loaded with fillers to enhance thermal conductivity.
