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'Thermal grease' (also called 'thermal compound', 'heat paste', 'thermal paste', or 'heat sink compound') is a substance that increases thermal conductivity between the surfaces of two or more objects. In electronics, it is often used to aid a component's thermal dissipation via a heat sink.

Contents

Basic types

Purpose

Properties

Applying and removing

See also

References

External links

Basic types

Today, thermal grease is produced by many companies. There are many types of thermal grease:
# Zinc Oxide-based thermal grease has generally good thermal conductivity, is usually suspended in a silicon compound. A variant is a wax based adhesive that is factory applied to heat sinks. AMD recommends against the latter for newer, high wattage CPU's.
# Ceramic-based thermal grease contains ceramic particles suspended in other thermally conductive ingredients. It conducts heat better than most zinc oxide greases, but poorer than metal greases.
# Metal-based thermal grease contains metal particles (usually silver) and other conductive ingredients. It has a better thermal conductivity (and is more expensive) than zinc oxide based grease. It is also more electrically conductive, however, which can cause problems if it contacts the pins of an integrated circuit. Some thermal pastes are made of liquid metal alloys of gallium.

Purpose

Thermal grease's primary purpose in electronics is to mediate small surface imperfections between an integrated circuit (also known as a chip) and a heat sink. When applied in ''appropriate quantities'', it fills the tiny pits and grooves — particularly on today's central processing units (CPUs)— thereby increasing the amount of surface-to-surface contact with the CPU by eliminating air pockets. Without thermal grease aiding the heat sink, CPU power dissipation overheating can occur and will generate logic errors as the heat raises electrical resistance on the multi-nanometer wide circuits.^[1]

Properties

The thermal grease's most important property is its thermal conductivity, measured in watts per metre-kelvin (W/(m·K)). Typical thermal conductivity for silicone and zinc oxide thermal compounds is 0.7 to 0.9 W/(m·K). (In comparison, the thermal conductivity of copper is 401 W/(m·K) and of aluminum 237.) Silver thermal compounds may have the conductivity of 2 to 3 W/(m·K) or more. The compound must also be smooth so that it is easy to apply in a very thin layer.
In compounds containing suspended particles, the properties of the fluid may well be the most important. As seen by the thermal conductivity measures above, the conductivity is closer to that of the fluid components rather than the ceramic or metal components. Other properties of fluid components that are important for thermal grease might be:
# How well it fills the gaps and conforms to the component's uneven surfaces and the heat sink
# How well it adheres to those surfaces
# How well it maintains its consistency over the required temperature range
# How well it resists drying out or flaking over time
# How well it insulates electrically
# Whether it degrades with oxidation or breaks down over time

Applying and removing

The grease is applied on both surfaces with a small plate or credit card. Even silver compounds do not conduct electricity well, so several minor drops on the chip pins usually do not damage the device.
Because thermal grease's thermal conductivity is so poor in comparison to the metals they couple, it is important to use no more than is necessary to exclude any air gaps. Excess grease separating the metal surfaces further will only degrade conductivity.
The preferred way to remove typical thermal grease from a component or heat sink is by using isopropyl alcohol.

See also

★ Computer cooling

★ Arctic Silver

★ Thermal pads

★ Thermal adhesive

References

1. Intel - Nanotechnology

External links

★ The Heatsink Guide: Thermal Compound by Tillmann Steinbrecher

★ Thermal Transfer Compound Comparison by Daniel Rutter