All electronic devices and circuitry generate excess heat and thus require thermal management to improve reliability and prevent premature failure. The amount of heat output is equal to the power input, if there are no other energy interactions. There are several techniques for cooling including various styles of heat sinks, thermoelectric coolers, forced air systems and fans, heat pipes, and others. In cases of extreme low environmental temperatures, it may actually be necessary to heat the electronic components to achieve satisfactory operation.
Overview
Thermal resistance of devices This is usually quoted as the thermal resistance from junction to case of the semiconductor device. The units are °C/W. For example, a heatsink rated at 10 °C/W will get 10 °C hotter than the surrounding air when it dissipates 1 Watt of heat. Thus, a heatsink with a low °C/W value is more efficient than a heatsink with a high °C/W value. Given two semiconductor devices in the same package, a lower junction to ambient resistance (RθJ-C) indicates a more efficient device. However, when comparing two devices with different die-free package thermal resistances (Ex. DirectFET MT vs wirebond 5x6mm PQFN), their junction to ambient or junction to case resistance values may not correlate directly to their comparative efficiencies. Different semiconductor packages may have different die orientations, different copper(or other metal) mass surrounding the die, different die attach mechanics, and different molding thickness, all of which could yield significantly different junction to case or junction to ambient resistance values, and could thus obscure overall efficiency numbers.
Thermal time constants A heatsink's thermal mass can be considered as a capacitor (storing heat instead of charge) and the thermal resistance as an electrical resistance (giving a measure of how fast stored heat can be dissipated). Together, these two components form a thermal RC circuit with an associated time constant given by the product of R and C. This quantity can be used to calculate the dynamic heat dissipation capability of a device, in an analogous way to the electrical case.
Thermal interface material
A thermal interface material or mastic (a.k.a. TIM) is used to fill the gaps between thermal transfer surfaces, such as between microprocessors and heatsinks, in order to increase thermal transfer efficiency. It has a higher thermal conductivity value in Z-direction than xy-direction.
Applications
Personal computers Due to technological developments and public interest, the retail heat sink market rose high. In the early 2000s, CPUs were produced that emitted more and more heat than earlier, escalating requirements for quality cooling systems. Overclocking has always meant greater cooling needs, and the inherently hotter chips meant more concerns for the enthusiast. Efficient heat sinks are vital to overclocked computer systems because the higher a microprocessor's cooling rate, the faster the computer can operate without instability; generally, faster operation leads to higher performance. Many companies now compete to offer the best heat sink for PC overclocking enthusiasts.
Soldering Temporary heat sinks were sometimes used while soldering circuit boards, preventing excessive heat from damaging sensitive nearby electronics. In the simplest case, this means partially gripping a component using a heavy metal crocodile clip or similar clamp. Modern semiconductor devices, which are designed to be assembled by reflow soldering, can usually tolerate soldering temperatures without damage. On the other hand, electrical components such as magnetic reed switches can malfunction if exposed to higher powered soldering irons, so this practice is still very much in use.
Batteries In the battery used for electric vehicles, Nominal battery performance is usually specified for working temperatures somewhere in the +20 °C to +30 °C range; however, the actual performance can deviate substantially from this if the battery is operated at higher or, in particular, lower temperatures, so some electric cars have heating and cooling for their batteries.
Methodologies
Heat sinks
Heat sinks are widely used in electronics and have become essential to modern microelectronics. In common use, it is a metal object brought into contact with an electronic component's hot surface—though in most cases, a thin thermal interface material mediates between the two surfaces. Microprocessors and power handling semiconductors are examples of electronics that need a heat sink to reduce their temperature through increased thermal mass and heat dissipation (primarily by conduction and convection and to a lesser extent by radiation). Heat sinks have become almost essential to modern integrated circuits like microprocessors, DSPs, GPUs, and more. A heat sink usually consists of a metal structure with one or more flat surfaces to ensure good thermal contact with the components to be cooled, and an array of comb or fin like protrusions to increase the surface contact with the air, and thus the rate of heat dissipation. A heat sink is sometimes used in conjunction with a fan to increase the rate of airflow over the heat sink. This maintains a larger temperature gradient by replacing warmed air faster than convection would. This is known as a forced air system.
Cold plate Placing a conductive thick metal plate, referred to as a cold plate, as a heat transfer interface between a heat source and a cold flowing fluid (or any other heat sink) may improve the cooling performance. In such arrangement, the heat source is cooled under the thick plate instead of being cooled in direct contact with the cooling fluid. It is shown that the thick plate can significantly improve the heat transfer between the heat source and the cooling fluid by way of conducting the heat current in an optimal manner. The two most attractive advantages of this method are that no additional pumping power and no extra heat transfer surface area, that is quite different from fins (extended surfaces).
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