A heat spreader transfers energy as

heat In thermodynamics, heat is defined as the form of energy crossing the boundary of a thermodynamic system by virtue of a temperature difference across the boundary. A thermodynamic system does not ''contain'' heat. Nevertheless, the term is al ...

from a hotter source to a colder

heat sink A heat sink (also commonly spelled heatsink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, th ...

heat exchanger A heat exchanger is a system used to transfer heat between a source and a working fluid. Heat exchangers are used in both cooling and heating processes. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contac ...

. There are two thermodynamic types, passive and active. The most common sort of passive heat spreader is a plate or block of material having high

thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...

, such as

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

, aluminum, or diamond. An active heat spreader speeds up heat transfer with expenditure of energy as work supplied by an external source. A

heat pipe A heat pipe is a heat-transfer device that employs phase transition to transfer heat between two solid interfaces. At the hot interface of a heat pipe, a volatile liquid in contact with a thermally conductive solid surface turns into a vapor ...

uses fluids inside a sealed case. The fluids circulate either passively, by spontaneous convection, triggered when a threshold temperature difference occurs; or actively, because of an impeller driven by an external source of work. Without sealed circulation, energy can be carried by transfer of fluid matter, for example externally supplied colder air, driven by an external source of work, from a hotter body to another external body, though this is not exactly heat transfer as defined in physics. Exemplifying increase of

entropy Entropy is a scientific concept, as well as a measurable physical property, that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynam ...

according to the second law of thermodynamics, a passive heat spreader disperses or "spreads out" heat, so that the heat exchanger(s) may be more fully utilized. This has the potential to increase the heat capacity of the total assembly, but the additional thermal junctions limit total thermal capacity. The high conduction properties of the spreader will make it more effective to function as an

air The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing f ...

, as opposed to the original (presumably smaller) source. The low heat conduction of air in

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

is matched by the higher surface area of the spreader, and heat is transferred more effectively. A heat spreader is generally used when the heat source tends to have a high heat- flux density, (high heat flow per unit area), and for whatever reason, heat can not be conducted away effectively by the heat exchanger. For instance, this may be because it is air-cooled, giving it a lower heat transfer coefficient than if it were liquid-cooled. A high enough heat exchanger transfer coefficient is sufficient to avoid the need for a heat spreader. The use of a heat spreader is an important part of an economically optimal design for transferring heat from high to low heat flux media. Examples include: * A copper-clad bottom on a

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

stainless steel Stainless steel is an alloy of iron that is resistant to rusting and corrosion. It contains at least 11% chromium and may contain elements such as carbon, other nonmetals and metals to obtain other desired properties. Stainless steel's corros ...

stove-top cooking container * Air-cooling

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

s such as a

microprocessor A microprocessor is a computer processor where the data processing logic and control is included on a single integrated circuit, or a small number of integrated circuits. The microprocessor contains the arithmetic, logic, and control circu ...

* Air-cooling a

photovoltaic cell A solar cell, or photovoltaic cell, is an electronic device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physics, physical and Chemical substance, chemical phenomenon.concentrated photovoltaics Concentrator photovoltaics (CPV) (also known as concentration photovoltaics) is a photovoltaic technology that generates electricity from sunlight. Unlike conventional photovoltaic systems, it uses lenses or curved mirrors to focus sunlight on ...

system Diamond has a very high thermal conductivity.

Synthetic diamond Lab-grown diamond (LGD; also called laboratory-grown, laboratory-created, man-made, artisan-created, artificial, synthetic, or cultured diamond) is diamond that is produced in a controlled technological process (in contrast to naturally formed ...

is used as submounts for high-power integrated circuits and laser diodes. Composite materials can be used, such as the

metal matrix composite In materials science, a metal matrix composite (MMC) is a composite material with fibers or particles dispersed in a metallic matrix, such as copper, aluminum, or steel. The secondary phase is typically a ceramic (such as alumina or silicon carb ...

s (MMCs)

copper–tungsten Copper–tungsten (tungsten–copper, CuW, or WCu) is a mixture of copper and tungsten. As copper and tungsten are not mutually soluble, the material is composed of distinct particles of one metal dispersed in a matrix of the other one. The micro ...

AlSiC AlSiC, pronounced "alsick", is a metal matrix composite consisting of aluminium matrix with silicon carbide particles. It has high thermal conductivity (180–200 W/m K), and its thermal expansion can be adjusted to match other materials, e.g. silic ...

(

silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal sin ...

in aluminium matrix),

Dymalloy Dymalloy is a metal matrix composite consisting of 20% copper and 80% silver alloy matrix with type I diamond. It has very high thermal conductivity of 420 W/(m·K), and its thermal expansion can be adjusted to match other materials, e.g. sili ...

(diamond in copper-silver alloy matrix), and

E-Material E-Material, also called E Material, is a metal matrix composite consisting of beryllium matrix with beryllium oxide particles. It has high thermal conductivity (210-230 W/m K), and its thermal expansion can be adjusted to match other materials, e.g. ...

(

beryllium oxide Beryllium oxide (BeO), also known as beryllia, is an inorganic compound with the formula BeO. This colourless solid is a notable electrical insulator with a higher thermal conductivity than any other non-metal except diamond, and exceeds that of m ...

beryllium Beryllium is a chemical element with the symbol Be and atomic number 4. It is a steel-gray, strong, lightweight and brittle alkaline earth metal. It is a divalent element that occurs naturally only in combination with other elements to form mi ...

matrix). Such materials are often used as substrates for chips, as their thermal expansion coefficient can be matched to ceramics and semiconductors.

Research

In May 2022, researchers at the

University of Illinois at Urbana-Champaign The University of Illinois Urbana-Champaign (U of I, Illinois, University of Illinois, or UIUC) is a public land-grant research university in Illinois in the twin cities of Champaign and Urbana. It is the flagship institution of the Univ ...

and

University of California, Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public land-grant research university in Berkeley, California. Established in 1868 as the University of California, it is the state's first land-grant u ...

recently devised a new solution that could cool modern electronics more efficiently than other existing strategies. Their proposed method is based on the use of heat spreaders consisting of an electrical insulating layer of poly (2-chloro-p-xylylene) (

Parylene Parylene is the common name of a polymer whose backbone consists of ''para''- benzenediyl rings –– connected by 1,2-ethanediyl bridges –––. It can be obtained by polymerization of ''para''-xylylene . The name is also used for se ...

C) and a coating of copper. This solution would also require less expensive materials.

References

{{Reflist Computer hardware cooling Heat transfer Residential heating appliances

Research

See also

References