A heat spreader helps transfer heat from a thermal source to a heat transfer medium, such as a heat sink or finned radiator. It is used when the medium cannot absorb enough heat on its own. The spreader must be a good thermal conductor with a calculated surface profile for maximum exposure and circulation.
A heat spreader is a device that aids in the dissipation of heat from a thermal source into a heat transfer medium. This is a rather complex way of saying that a heat exchanger helps keep appliances or equipment cool, or in some cases warm, by getting the heat from where it’s being generated to where it needs to be. This is usually required when the heat transfer medium, or the place where the heat has to go, is unable to absorb the required amount of heat by itself. Good examples of this theory include copper bases on stainless steel cookware or finned heat sinks on high current electronic components. The copper base helps the steel pan absorb and hold heat, and the heat sink helps the microprocessor dissipate heat.
Heat transfer, or rather adequate heat transfer, is not always as simple a concept as it might seem. Getting enough heat from or to one medium or material in another depends on a number of technical factors which can, at times, confuse the issue completely. The main problem in this regard is the difference in the heat flux density of different materials. Simply put, this means that some materials require a much larger area of exposure than others to absorb the same amount of heat. Heat sinks commonly mounted on electronic components or the fins on an oil heater or radiator are examples of how heat spreader theory works to get around this problem.
For example, the surface of a high-gain transistor generates far more heat than the air in contact with it can absorb in a given period of time. To get around this phenomenon, a heat sink or heat sink is attached to the transistor. It is typically a heavy copper or aluminum base with a large number of fins protruding from its surface. This achieves a large increase in the volume of air exposed to the heat source which negates the heat flux density differential between the transistor and the air. In this way, the overhead diffuser becomes the mechanism of the primary heat exchanger which helps the secondary exchanger, the air, effectively absorb the generated heat energy.
Obviously the use of the heat spreader is limited to applications where the secondary heat transfer medium is unable to overcome the heat flux density differences between it and the heat source material. Heat diffusing materials should be good thermal conductors and the surface profile should be calculated carefully enough to offer maximum exposure and circulation. Even the union between the heat source and the diffuser must be a thermal transition as efficient as possible. To this end, heat conducting pastes are often applied to the surfaces before the heat spreader is attached.
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