A heat sink 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, thereby allowing regulation of the device's temperature. In computers, heat sinks are used to cool CPUs, GPUs, and some chipsets and RAM modules. Heat sinks are used with other high-power semiconductor devices such as power transistors and optoelectronics such as lasers and light-emitting diodes (LEDs), where the heat dissipation ability of the component itself is insufficient to moderate its temperature.
Advantages of Heat Sink
Efficient heat dissipation
One of the primary advantages of a heat sink is its ability to efficiently dissipate heat generated by electronic components. Heat sinks are usually made of materials with high thermal conductivity, such as aluminum or copper, which quickly absorb and transfer heat away from the device. This prevents the components from reaching high temperatures that could potentially damage them.
Extended device lifespan
By effectively dissipating heat, heat sinks contribute to extending the lifespan of electronic devices. Excessive heat can cause component failures and reduce the overall reliability of the device. Heat sinks play a crucial role in maintaining optimal operating temperatures, ensuring the longevity of the device and preventing premature failures.
Compact and lightweight design
Heat sinks are designed to be compact and lightweight, making them suitable for various electronic devices with limited space. Their small form factor allows for easy integration into devices without adding significant weight or bulkiness. This advantage is particularly important for portable devices such as laptops and smartphones, where space and weight constraints are critical.
Versatility and compatibility
Heat sinks are versatile and compatible with various electronic devices and components. They can be customized and designed to fit specific devices, ensuring efficient heat dissipation in different applications. This versatility allows heat sinks to be used in a wide range of industries, including automotive, aerospace, telecommunications, and more.
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What Are the Types of Heat Sinks
Passive heat sinks
Passive heat sinks rely on natural convection, meaning the ability of hot air to float causes the airflow generated across the heat sink, and they do not require secondary power or control systems to remove heat. But passive heat sinks are not as effective at removing heat from a system as active heat sinks.
Active heat sinks
Active heat sinks utilize forced air--commonly generated by a fan, blower, or even movement of the entire object--to increase fluid flow across the hot area.
This is like the fan in your personal computer turning on after your computer gets warm. The fan forces air across the heat sink, which allows more unheated air to move across the heat sink surface. This increases the total thermal gradient across the heat sink, allowing more heat to exit.
Hybrid heat sinks
Hybrid heat sinks combine characteristics of both passive and active heat sinks. These configurations are less common, often using control systems to cool the system based on temperature requirements.
When the system operates at cooler levels, the forced air source is inactive, only cooling the system passively. Once the source reaches higher temperatures, the active cooling mechanism engages to increase the cooling capacity of the sink.
The Key Components of a Heat Sink
Base
A heat sink base is typically a flat block or sheet of material with excellent thermal conductivity. The base typically has a consistent cross-sectional thickness, but it can also be designed to have a cross-sectional profile that optimizes heat transfer for the specific geometry of the heat source. The base is typically mounted to the heat source with mounting hardware and thermal paste.
Fins
Fins protruding from the heat sink base are responsible for the transfer of heat to the surrounding fluid. These fins are designed to optimize the surface area that the heat sink presents to the fluid. The larger the surface area, the faster the heat transfer rate.
The fins can either form an integral part of the base or can be attached separately using various techniques, for example, via a compression process. The shape and arrangement of the fins can dramatically improve the heat transfer rate.
Heat Pipes
A heat pipe is designed to transfer heat along its axis. Heat pipes can be incorporated inside standard heat sinks and heat spreaders through press fitting, soldering, and thermally conductive epoxy to improve their heat transfer efficiency. They work by transferring heat via a phase change mechanism that causes fluid to vaporize at the heat source, then travel along the axis of the heat pipe to the point where it cools down and changes back into a liquid via condensation.
Thermal Interface Material
Thermal interface materials, or thermal pastes, are used to significantly improve heat transfer between the heat source and the base of the heat sink by filling any air voids between the heat source and the heat sink. Air is a poor conductor of heat, so filling air gaps with a more thermally conductive material enhances the cooling efficiency of a heat sink. Thermal pastes can be metal, ceramic, or silicone-based, with metal-based thermal paste being the most effective.
Mounting Hardware
Heat sinks can be securely fixed to their target heat sources using a number of different mounting methods. For smaller heat sinks, an adhesive with high thermal conductivity is used to directly stick the heat sink onto a heat source. This method is typically used on smaller PCB components. For larger heat sinks, normal screws can be used, or alternatively, spring-loaded push pins are used to optimize the contact pressure between the heat source and the heat sink.
Methods of Manufacturing Heat Sinks
Skiving: This involves cutting metal into slices. It is a common manufacturing method for producing plate fins for heat sinks. With this method, you can create thinner and closely packed fins.
The heat sinks have some level of surface roughness, thereby increasing the total surface area.
Casting: This involves pouring molten metal into a mold. Thereafter, you allow the molten metal to solidify before removing it from the mold. Pressure die-cast heat sinks have a high level of complexity. They also have good mechanical properties.
Extrusion: It is a swift, efficient and cost-effective method of making heat sinks. It involves forcing hot metal billets, using a steel die. This is the commonest method of making aluminium heat sinks. Extruded aluminium heat sinks are usually anodized before use.
Cold forging: This method is used to manufacture material at a temperature lower than the material's recrystallization temperature.
Given that aluminium has minimal resistance to deformation and high plasticity, this method is suitable for producing aluminium heat sinks.
Cold forging is used to manufacture highly precise heat sinks. You can use it to produce round pin and elliptical pin heat sinks. Also, forged heat sinks have excellent microstructure integrity.
Stamping: This involves punching an aluminium mold that moves under a pneumatic press with some dedicated tools. This method is suitable for large-scale productions. It also produces parts with relatively small dimensions.
How Does a Heat Sink Work
From the definition of sink or heat sink, we can try to understand that this simple transfer of heat from the source to sink happens in four basic steps in any type of sink.
Heat is produced by the source
Any system that generates heat and necessitates its removal to operate properly can serve as the source.
This includes various processes and machines used in Industries, Electronics, Chemical laboratories, Solar panels, and even electrical resistance in conducting devices.
Heat radiates from the origin
Applications that are in direct contact with the heat sink use natural conduction to transfer heat from the source to the heat sink.
This process is immediately impacted by the heat sink material's thermal conductivity.
The most frequent materials used in the construction of sinks are those with high thermal conductivity, like copper and aluminium.
The sink's surface is heated
As heat moves across the thermal gradient from a high temperature to a low-temperature region, it will naturally conduct the heat from the source through the sink.
As a result, sinks frequently become hotter closer to the source and cooler farther away.
Thermal energy leaves the sink
This procedure depends on the temperature gradient of the heat sink and the working fluid, which is typically air or a liquid that isn't electrically conductive.
Thermal convection and thermal diffusion are used by the working fluid as it moves over the warm sink's surface to transfer heat from the surface to the surrounding air.
The Applications of Heat Sinks
Computer Processors
Computer processors (CPUs) produce a large amount of waste heat during operation. They often employ copper heat sinks with an active cooling fan. Cool CPUs can operate more effectively.
LED Lighting
LED lights don't produce heat in the same way an incandescent bulb does. However, the electronics used to make an LED work produce a lot of waste heat that must be transferred away. Small LEDs often use passive heat sinks.
Power Electronics
Power supplies convert AC power to DC power for consumer electronics. This conversion process is inefficient and produces some waste heat that can reduce the life of the power supply unit. Heat sinks on power electronics sometimes employ hybrid cooling and make use of aluminum heat sinks to reduce cost.
Automotive Industry
Apart from the heat sinks used on the control circuitry of vehicles, heat sinks are also used to keep electric motors cool during operation as well as to cool onboard chargers for electric vehicles.
Aerospace Industry
Heat sinks can be found on control circuitry used in aerospace applications. They are also used on spacecraft to transfer heat to the vacuum of space. However, these heat sinks transfer heat purely through radiation as there is no heat transfer fluid in space.
Consumer Electronics
Consumer electronics make extensive use of heat sinks to keep devices cool and operating efficiently. Typical examples include the heat sinks in computers and cell phones.
How to Choose the Right Heat Sink
Fourier's Law of Heat Conduction
At a fundamental level, the idea of a heat sink is quite simple: By attaching a heat sink to a component that is generating a large amount of thermal energy, you are effectively increasing the surface area of that component. That component, which is at a higher temperature, will then transfer heat energy to its lower temperature surroundings.
Heat Sink Design
The most common material used in heat sinks is aluminum. This is because aluminum offers good thermal conductivity properties. Furthermore, the most common type of aluminum heatsink is manufacturing via extrusion -- a process of forcing aluminum to flow through a shaped die. This is typically a low-cost manufacturing process and offers performance qualities suitable for most applications. But it's worth noting that the extrusion method of manufacturing heatsinks does have its limits, particularly when it comes to size. This is mostly due to the fact that there are limits on extrusion width. When large heat sinks are required, say for the turbines at a power plant, they are typically manufactured via bonding (multiple components being built piece by piece and connected together).
Copper Heat Sink
Another popular material for heat sinks is copper. Copper has outstanding thermal conductivity capabilities (around 400 W/m•K for pure copper, which is about twice that of aluminum). It is also corrosion resistant. On the downside, it is much denser than aluminum, and therefore heavier, which makes it a bad choice for applications that are weight sensitive. It is also much more expensive than aluminum.
Heat Sink Thermal Resistance
Choosing a material for your heat sink is largely dependent on one factor -- thermal resistance. Thermal resistance is the ability of heat to flow from your component and into its surroundings. You need to consider the resistance across the entire design. For example, the resistance from the component to its package, the package to the adhesive material, the adhesive material to the heat sink, and the heat sink to the air. When all of these numbers are added up it will give you an overall thermal resistance and help you understand what material you should choose and how big your heat sink should be. You can decrease the thermal resistance in many ways -- changing materials, increasing or changing the design of the fins, using thermal paste designed for heat transfer instead of something like double-sided tape, etc.
Active Heat Sink vs. Passive Heat Sink
Another design consideration is whether you want to use an active or passive heat sink. A passive heat sink simply relies on radiant heat dissipation and any naturally occurring air movement to remove thermal energy. An active heat sink employs an additional component -- such as a fan or a pump -- to actively remove thermal energy and displace it. Unsurprisingly, active heat sinks will be more effective than passive heat sinks with similar physical characteristics.
How to Maintain Heat Sinks so as to Extend Their Service Life
Firstly, it is required to pay attention to the heat sink usage and storage environment. If you are not going to use a heat sink for quite a while, it should be kept securely. When choosing the place for storage, we need to pay attention to any corrosive materials such as acid or alkaline. These materials could cause corrosion to the heat sink to a larger extent and we should avoid this type of exposure as possible.
Secondly, it is required to ensure cleaning up the heat sink. After you have been using a heat sink for quite a while, there might be a large amount of dusts and dirt between the fins. If you don't clean it up in a timely fashion, the dusts piled up and it is inevitable to affect the overall cooling performance of this heat sink. This could be a threat that cannot be ignored for the devices that require cooling. Therefore, it is necessary to carry out comprehensive cleaning up for heat sink on a regular basis.
Moreover, when carrying out relevant anti-corrosion treatments, it is also required to consider a plurality of related issues. For example, if we don't follow the regulated standard to carry out the selection of antifreezes and the surface coating, we might make the heat sink corroded and can no longer be used.
FAQ
Q: What is the purpose of a heat sink?
Q: What is a heat sink in computer science?
Q: Why should you not remove the heat sink?
Q: Is a heat sink used for cooling?
Q: What is better cooling fan or heat sink?
Q: What is the best shape for a heat sink?
Q: What are the criteria for heat sink design?
Q: What is the process of heatsink extrusion?
Q: What is the grease on heat sink?
Q: How to maintain a heat sink?
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