Thermal paste
Thermal paste (also called thermal compound, thermal grease, thermal interface material (TIM), thermal gel, heat paste, heat sink compound, heat sink paste or CPU grease) is a
As opposed to thermal adhesive, thermal paste does not add mechanical strength to the bond between heat source and heat sink. It has to be coupled with a fastener such as screws to hold the heat sink in place and to apply pressure, spreading and thinning the thermal paste.
Composition
Thermal paste consists of a
Silver thermal compounds may have a conductivity of 3 to 8 W/(m·K) or more, and consist of
The most effective (and most expensive) pastes consist almost entirely of liquid metal, usually a variation of the alloy galinstan, and have thermal conductivities in excess of 13 W/(m·K). These are difficult to apply evenly and have the greatest risk of causing malfunction due to spillage. These pastes contain gallium, which is highly corrosive to aluminium and cannot be used on aluminium heat sinks.
Uses
Thermal paste is used to improve the heat coupling between different components. A common application is to drain away waste heat generated by electrical resistance in semiconductor devices including power
Factory PCs and laptops (though seldom tablets or smartphones) typically incorporate thermal paste between the top of the CPU case and a heat sink for cooling. Thermal paste is sometimes also used between the CPU die and its integrated heat spreader, though solder is sometimes used instead.
When a CPU heat spreader is coupled to the die via thermal paste, performance enthusiasts such as overclockers are able to, in a process known as "delidding",[3] pry the heat spreader, or CPU "lid", from the die. This allows them to replace the thermal paste, which is usually of low-quality, with a thermal paste having greater thermal conductivity. Generally, liquid metal thermal pastes are used in such instances.
Challenges
The consistency of thermal paste makes it susceptible to failure mechanisms distinct from some other thermal interface materials. A common one is pump-out, which is the loss of thermal paste from between the die and the heat sink due to their differing rates of thermal expansion and contraction. Over a large number of power cycles, thermal paste gets pumped out from between the die and the heat sink and eventually causes degradation of thermal performance.[4]
Another issue with some compounds is the separation of the polymer and filler matrix components occurs under high temperatures. The loss of polymeric material can result in poor wettability, leading to increased thermal resistance.[4]
Health hazards
Zinc oxide emits toxic fumes that must not be inhaled and a particulate respirator is necessary for any use. The chemical is also highly toxic to aquatic organisms and may cause long-term negative effects to aquatic environments.[5]
See also
- Computer cooling
- Hot-melt adhesive
- Phase-change material
- Thermally conductive pad
- List of thermal conductivities
References
- ^ Werner Haller; et al. (2007), "Adhesives", Ullmann's Encyclopedia of Industrial Chemistry (7th ed.), Wiley, pp. 58–59.
- ..
- ^ "What is delidding? - ekwb.com". ekwb.com. 2016-08-25. Retrieved 2018-10-18.
- ^ a b Viswanath, Ram; Wakharkar, Vijay; Watwe, Abhay; Lebonheur, Vassou (2000). "Thermal Performance Challenges from Silicon to Systems" (PDF). Intel Technology Journal. Archived from the original (PDF) on 8 August 2017. Retrieved 8 March 2020.
- ^ "ICSC 0208 - ZINC OXIDE". www.ilo.org. ILO.
External links
- Media related to Thermal grease at Wikimedia Commons