Thermal interfacial materials (TIMs) are thermally conductive materials, which are applied to increase Thermal contact conductance

Thermal contact conductance

In physics, thermal contact conductance is the study of heat conduction between solid bodies in thermal contact. The thermal contact conductance coefficient, h_c, is a property indicating the thermal conductivity, or ability to conduct heat, between two bodies in contact...

 across jointed solid surfaces, such as between microprocessor

Microprocessor

A microprocessor incorporates the functions of a computer's central processing unit on a single integrated circuit, or at most a few integrated circuits. It is a multipurpose, programmable device that accepts digital data as input, processes it according to instructions stored in its memory, and...

s and heatsinks, in order to increase thermal transfer efficiency. These gaps are normally filled with air which is a very poor conductor

Thermal conductivity

In physics, thermal conductivity, k, is the property of a material's ability to conduct heat. It appears primarily in Fourier's Law for heat conduction....

.

They take many forms. The most common is the white-colored paste or thermal grease

Thermal grease

Thermal grease is a viscous fluid substance, originally with properties akin to grease, which increases the thermal conductivity of a thermal interface by filling...

, typically silicone oil

Silicone oil

A silicone oil is any polymerized siloxanes with organic side chains. They are formed of alternating silicon-oxygen atoms or siloxane, rather than carbon atoms . Other species attach to the tetravalent silicon atoms, not to the divalent oxygen atoms which are fully committed to forming the...

 filled with aluminum oxide, zinc oxide

Zinc oxide

Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. The powder is widely used as an additive into numerous materials and products including plastics, ceramics, glass, cement, rubber , lubricants, paints, ointments, adhesives, sealants,...

, or boron nitride

Boron nitride

Boron nitride is a chemical compound with chemical formula BN, consisting of equal numbers of boron and nitrogen atoms. BN is isoelectronic to a similarly structured carbon lattice and thus exists in various crystalline forms...

. Some brands of thermal interfaces use micronized or pulverized silver.

Another type of TIM are the phase-change materials

Phase Change Material

A phase-change material is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy...

. These are solid at room temperature but liquefy and behave like grease

Grease (lubricant)

The term grease is used to describe semisolid lubricants. Although the word grease is also used to describe rendered fat of animals, in the context of lubrication, grease typically applies to a material consisting of a soap emulsified with mineral or vegetable oil...

 at operating temperature

Operating temperature

An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the...

s. They are easy to handle and are not messy.