Electronics Cooling – A Review through Methods and Components
An explanation of electronics cooling methods and types of electronics cooling equipment
Greater processing capacity, especially in consumer electronics, has rapidly evolved thermal management technologies. Liquid cooling technology, for instance, was previously limited to high-capacity computing hardware, but that is not currently the case. Recently, some smartphones have incorporated such thermal management technologies. Several surveys have also indicated that the smartphone and tablet material market has seen considerable growth in the past decade. This market is now expected to rely mostly on advanced materials for cooling solutions rather than secondary heat sinks. Along with such market trends, chip-cooling solutions have also evolved over the past few years to accommodate the increase in heat flux in electronic devices. Furthermore, manufacturers are trying to develop advanced cooling solutions based on multi-phase heat transfer technologies by developing advanced solutions such as nanotechnology and smart materials. These facts prove that heat dissipation, namely cooling, is the key player within the electronics industry.
Why is Electronics Cooling Essential?
This “key player” is essential because of various factors.
Generally, an electronic device consists of many different kinds of components. Out of these, each electronic component has a thermal limit, which is its maximum operating temperature. If this is reached, the component will burn out. Consequently, failure to properly manage such heat in electronic components and microprocessors can lead to the destruction of the circuit board and, finally, a system malfunction of the entire device. Therefore, to keep the circuit operating stably so that the device’s lifespan can be extended, the device must be equipped with a measure to remove heat generated by the device.
How can we remove heat? What kind of methods and components can be used for cooling electronics? Placing a focus on this point, this entry describes cooling methods and components.
Electronics Cooling Methods
Cooling methods are classified according to the mechanism or medium used to transfer the heat during the cooling process. The following shows and describes each representative cooling method.
We cannot say that air is an outstanding thermal conductor which only has a thermal conductivity of 0.026 W/mK. But there still exist advantages, including its universal availability, ability to insulate, and non-corrosive nature. Broadly speaking, air cooling can be divided into natural air cooling and forced air cooling.
In natural air cooling, the air rises as it is heated because of its decrease in density. This airflow is referred to as laminar flow, which provides a natural means of removing heat generated by power electronics components. On the other hand, forced air cooling uses air fans to increase the air velocity to generate turbulent airflow rather than laminar flow, effectively increasing heat dissipation to the surrounding atmosphere.
Forced air cooling has been a standard heat management solution for PCs by literally removing heat from internal components.
Gas cooling removes heat by using gas sealed within the device. Gases used for this cooling method include hydrogen gas, dried air, and SF6 gas. Since an internal gas-cooling unit is necessary, this cooling system is generally used for larger systems.
Phase transition cooling
Phase transition cooling uses evaporation and condensation of a two-phase working fluid or coolant to transport large quantities of heat with a very small difference in temperature between the hot and cold interface. In this cooling method, the cooling fluid evaporates at the location of the heat source. The vapor carries the heat to a condenser, where the fluid is then condensed back to its liquid form. Examples of application of this method include pool boiling, heat pipes, spray cooling, and so forth.
Liquid cooling is highly effective in removing excess heat utilizing the convection or circulation of a liquid, which generally involves water or a mixture of water and glycol as the heat transferring medium. A typical application of this method includes computing and HVAC, incorporating cold plates, heat exchangers, and pump systems to circulate cold fluid past a heat source. When it comes to computing and electronics, liquid cooling involves technology that makes use of a special water block to conduct heat away from the processor as well as the chipset. This method can also be used in combination with other traditional cooling methods such as those that use air.
Electronics Cooling Components
Searching for ways to remove heat and keep a device cool effectively, manufacturers and their engineers have developed a wide variety of electronics cooling components. The following takes you into the world of various electronics cooling components.
Heat sinks (heat pipes)
Heat sinks (heat pipes) are one of the most common thermal management technology forms. Their main applications include industrial facilities, such as power plants and solar thermal water systems. At the same time, they are also actively used in the microprocessor cooling area. In computers, which are their typical application, heat sinks are used to cool CPUs, GPUs, chipsets, and RAM modules.
A heat sink is a component that increases the heat flow away from a heat source. The heat removal process by using a heat sink follows the following four stages: (1) The source generates heat. (2) Heat transfers away from the source. (3) Heat is distributed through the heat sink. (4) Heat dissipates from the heat sink.
Heat sinks can often pull away heat more effectively from the CPU. The larger the contact area to the air becomes, the more effectively it can remove heat. A heat sink usually has a simple structure, ensuring a lower possibility for causing the system to malfunction. It also produces no sound or noise. The temperature does not drop lower than the ambient temperature, so the cooling process does not cause condensation.
An example of a combination of heat pipes and heat sinks
Plate heat exchangers
Plate heat exchangers offer a highly efficient mechanism for heat transfer, while taking on various forms including brazed and gasketed types. Their applications include water heaters, waste heat recovery, heat pump isolation, and thermal storage systems.
A plate heat exchanger uses metal plates to transfer heat between two fluids. It usually has a specialized design well suited to transferring heat between medium- and low-pressure fluids. Welded, semi-welded and brazed heat exchangers are used where a more compact product is required. The plates used in a plate and frame heat exchanger are obtained by one-piece pressing of metal plates. Stainless steel is a commonly used metal for the plates because of its ability to withstand high temperatures, its strength, and its corrosion resistance.
Plate heat exchangers can often be configured in a more compact design allowing for easy maintenance and cleaning. They are also designed to facilitate easy installation and removal of plates to expand or reduce its heat transfer capacity. These advantages add value to them as ideal thermal management solutions for small district heating, beverage cooling, food and pharmaceutical production, and low-duty oil cooling applications.
A radiator is another type of heat exchanger, used for various applications including cars, buildings, and electronics. A typical application we can cite is engine cooling, but in electronics, radiators are also used for cooling CPUs for computers.
As a heat exchanger, a radiator transfers thermal energy from one medium to another for the purpose of cooling and heating. It consists of a large amount of cooling surface exposed to large amounts of air so that it spreads through the water to cool it efficiently. To increase the surface area available for heat exchange with the surroundings, a radiator has multiple fins, in contact with the tube carrying liquid pumped through the radiator. Air, or other exterior fluid, in contact with the fins carries off heat. Dirt or damage to the fins could cause ineffective heat transfer.
Benefits of cooling radiators include more efficient heat removal effect than air cooling. Use of cooling radiators will not just prolong your hardware’s lifespan, but it also ensures they are being cooled efficiently at all times.
Thermal paste is a thermally conductive chemical compound commonly used as an interface between heat sinks and heat sources. Thermal paste is used to improve the heat coupling between different components. A common application is to drain away waste heat generated by electrical resistance in semiconductor devices, including power transistors, CPUs, GPUs, and LED COB.
In a computer, the heat sink presses tightly against the CPU. The surface of the CPU and the heat sink’s contact plate is covered in tiny grooves and gaps. If not properly sealed up, these gaps allow air to come in between the processor and the heat sink, reducing the heat transfer efficiency. This is where thermal paste can be a good fit. Thermal paste is a good heat conductor, but also it can get into those small gaps and grooves on the surfaces of the hardware. This creates an air-tight seal and increases the rate of heat transfer.
Applying thermal paste can contribute to improving the entire performance with its ability to be easily spread. Although thermal paste is not a must to boot up a computer, it is very useful for keeping temperatures down. It also contributes significantly to prolonging the computer’s lifespan.
A Peltier device, employing the Peltier effect as a thermoelectric cooler, is a thermoelectric element that functions to transfer heat thanks to the Peltier effect. Peltier devices are ideally suited for high density, high power medical and industrial applications, refrigeration, and sealed environments where forced air cooling is not an option.
The Peltier effect is the key element for a Peltier device. The device has two sides, and when a DC electric current flows through the device, it brings heat from one side to the other, so that one side gets cooler while the other gets hotter. The heat transferred to the hot side is dissipated with a heat sink attached so that it remains at ambient temperature, while the cool side goes below room temperature.
A significant advantage of Peltier devices is that they have no moving parts, producing no mechanical wear. Reduced instances of failure due to fatigue and fracture from mechanical vibration and stress increases the system’s lifespan. This also lowers the maintenance requirements.
Thermal conductive sheets
Thermal conductive sheets are also referred to as heat dissipation sheets. Many thermal conductive sheets are made of silicon or acrylic resin. The sheet-like structure is quite flexible and excellent for adhesiveness. Therefore, they are widely used for heat dissipation of IC chips and batteries installed in small home appliances and electronic devices, in combination with other heat transfer components such as heat sinks.
IC chips and batteries produce excessive heat when a device is operated, so that heat dissipation components are also installed. The surface of a heat dissipation component attached to the heat source looks seemingly flat, but it has fine gaps and grooves that allow the air to come in. Installing a thermal conductive sheet between them enables the heat to propagate through the thermal conductive sheet, improving the heat dissipation effect more efficiently.
Use of thermal conductive sheets with high thermal conductivity can eliminate the bottleneck of heat release, efficiently releasing heat and reducing the temperature of a heat source. This results in the further benefit of increasing the device and system lifespan.
A Vapor Chamber is a two-phase device used to spread heat from a heat source to a heat sink. Vapor Chambers are used when genuine two-dimensional heat spreading is required, when a single microprocessor or multiple processers in a single plane should be cooled, and when high heat flux is applied. With its design flexibility, Vapor Chambers are now frequently used in applications ranging from hard drive disk cooling, PC cooling, graphic card cooling, server cooling, high heat flux chips (IGBT and MOSFET), LED, and in consumer products, particularly mobile devices such as smartphones and tablets.
A Vapor Chamber has a metal enclosure that is vacuum sealed, an internal wick structure installed inside, and a working fluid that moves within the system thanks to capillary action. In detail, the heat source makes direct contact with a portion of the Vapor Chamber and a finned heat sink attached to the top. Some of the working fluid vaporizes and flows to cooler areas. Heat absorption causes the vapor to condense and return to liquid which is reabsorbed by the wick structure and distributed to the heat source.
One of the greatest benefits of using Vapor Chambers is derived from its design flexibility which can make the entire chamber unit be thinned to 0.25 – 0.2 mm thickness. The flat shape of a Vapor Chamber also means they can make better surface contact with IC chips to create a more direct heat transfer path. They are also less affected by orientation, unlike a traditional heat pipe where the direction of gravity can affect its cooling efficiency. Therefore, these features offer significant benefits in shaping and manufacturing smaller portable devices. Their capacity to cool multiple components also provides effective and efficient heat management.
DNP’s Vapor Chambers
Vapor Chambers powered by DNP are highly conductive, thin, and light, but flexible in order to fit complicated platforms with curved planes and multiple levels. Because of such fantastic flexibility, DNP’s Vapor Chambers are expected to be widely used for a variety of applications as a major shift toward 5G electronic devices is occurring in the industry. They are also an excellent solution for heat management for miniaturized electronic devices with increased inner components. DNP’s Vapor Chambers can demonstrate their real strength in various electronic devices, including 5G smartphones, thin laptops, and tablets. They are also the excellent heat dissipation solution for wearables, such as VR, AR, and MR terminals, along with drones, and electronic vehicles. DNP’s high-definition patterning technology underlies the manufacturing of such attractive Vapor Chambers. By making full use of its knowledge covering a wider range of industries and ever-extending networks, DNP will seek and pursue unique heat management solutions that only DNP can develop. （Information as at Feburary,2022）