Thermal paste is another crucial component in the thermal management of electronics. It is also called heat sink compound, thermal compound, or thermal grease. When used with a heat-producing component, thermal pastes prevent the formation of air pockets that can render heat transfer (to the heat sink) ineffective, and enhances thermal conductivity ultimately making the PCB more rugged.
Thermal pastes are generally of two types
- Silicone-based
- Silicone-free
Silicone-based chemical formulations find extensive use in electronic applications, owing to their augmenting characteristics. Silicone possesses attributes that render it suitable for demanding operational environments, including resilience against vibration, chemicals, and wide temperature ranges. These formulations are typically composed of silicone polymers, like silicone oils or greases, blended with fillers to enhance thermal conductivity. It is a non-conductive material that has good thermal conductivity and can withstand high temperatures. It is easy to apply and remove, making it ideal for use in applications that require frequent maintenance or replacement.
Silicone-free formulations are devoid of silicone compounds, relying instead on non-silicone polymers like acrylics, polyimides, metals, or ceramics. Due to the absence of silicone, they demonstrate reduced outgassing tendencies, reducing the potential for contamination or deterioration of neighboring components.
Types of Silicone-Free
Metal-based thermal grease: Metal-based thermal grease is a type of thermal grease that contains metal particles, such as copper, silver, or aluminum. These particles improve the thermal conductivity of the grease, making it more effective at transferring heat away from electronic components.
Ceramic-based thermal grease: Ceramic-based thermal grease is a type of thermal grease that contains ceramic particles, such as boron nitride or aluminum oxide. These particles provide high thermal conductivity and excellent thermal stability, making it ideal for high-temperature applications. Ceramic-based thermal grease is typically more expensive than other types of thermal grease but can provide superior performance in extreme environments.
Carbon-based thermal grease: Carbon-based thermal grease is a type of thermal grease that contains carbon particles. These particles provide good thermal conductivity and are less expensive than metal or ceramic-based thermal grease. Carbon-based thermal grease can be used in a variety of applications but may not be as effective as other types of thermal grease in high-temperature environments.
Phase-change thermal grease: Phase-change thermal grease is a type of thermal grease that changes from a solid to a liquid state when it reaches a certain temperature. This allows it to conform to the surface of electronic components and provide excellent thermal conductivity. Phase-change thermal grease is typically more expensive than other types of thermal grease and can be difficult to apply and remove.
Graphene-based thermal grease: Graphene-based thermal grease is a relatively new type of thermal grease that contains graphene particles. Graphene has excellent thermal conductivity and can provide superior heat dissipation compared to other types of thermal grease. Graphene-based thermal grease is typically more expensive than other types of thermal grease and may require specialized equipment for application.
Tech Tip: Some thermal materials utilize a conductive powder, sometimes insulated, which allows them to absorb or attenuate stray electromagnetic emissions. This provides protection similar to a faraday cage, which can be especially helpful on integrated circuits.
Conclusion
The case study discusses effects of thermal aging on silicone-based and silicone-free thermal fillers. The results depict that post thermal aging at 125°C, the silicone-free material undergoes a hardening process, whereas the silicone-based material retains its viscoelastic properties. This suggests that the silicone-based material holds potential for prolonged use in high-temperature applications.
While silicone-based material exhibits superior mechanical and thermal attributes in high-temperature settings, the dielectric properties of silicone-free material reveal lower conductivity. This makes it a more suitable choice for applications requiring greater electrical insulation.
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References - Chemtronics: ruggedizing electronics best practices for bullet-proof devices
Chemtronics: Repairing & Avoiding Electronic Faults with Thermal Paste