A heat sink works by increasing the transfer rate of heat from the hot solid medium to a less hot or cool fluid medium. The heat sink achieves this with the use of pins or fins to increase the surface area and sometimes with the aid of a fan to increase the flow rate. The rate at which heat is dissipated is determined by the heat sink size, type, material, and location.
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Different devices need heat sinks to remove heat from areas that need to stay cool. Heat sinks will absorb and disperse heat from devices to prevent overheating. If an electrical component is not thermally managed then the internal resistance can increase while also leading to degradation of the materials, which in turn affect the performance and reliability.
There are six heat sink types that can be part of an active or passive system. They are commonly made of either aluminum or copper. The active systems use a fan to induce extra airflow over an area to improve cooling. The passive system relies on increasing the surface area of the component to allow more heat to be dissipated. Listed below are the types of heat sinks:
Bonded heat sinks are manufactured by using a conductive epoxy to adhere fins to a base. They can be made of either copper or aluminum or a mixture of both aluminum and copper. Bonded heat sinks are used for applications that require a high fin density. They have a much higher fin density than extruded heat sinks. This increased fin density is best used in an active system with forced airflow. The size of the bonded heat sink is virtually unlimited, and so they are generally used for applications that require very large heat sinks.
Skived heat sinks feature a series of tightly packed fins on a base that has been manufactured in one piece of metal which results in minimal thermal resistance. They are used in applications with high airflow and minimal space. This is the most cost-effective and reliable way of producing heat sinks. Skived heat sinks are made out of copper or aluminum. The maximum width of a skived heat sink is approximately 400 mm with a height of 200 mm. However, the length of the heat sink is only bound by the length of the copper bar that is used. Skived heat sinks have a dissipation capacity of around 1.5&#;2 times that of a bonded or soldered heat sink.
Extruded heat sinks are the cheapest to manufacture as the process involves extruding one long piece of metal continuously in a cross-section that forms fins and a base together. These heat sinks are used for high-powered semiconductor devices, and in medium to high airflow applications. While copper heat sinks can be extruded, most extruded heat sinks are aluminum. Extruded heat sinks are available up to a width of 400 mm and height of 60 mm. Since they are extruded, the length is unlimited.
Forged heat sinks are manufactured using compressive force to shape the metal. Forged heat sinks are usually made out of copper as it is more malleable which means it requires less heat to forge. They use either fins or pins to disperse heat. Forged heat sinks have low thermal resistance as there is no medium between the fins/pins and the base. They have a length and width of around 500 mm and a height in the 70 mm range.
A stamped heat sink is produced by stamping the fins out of sheet metal. The stamped metal fins are then held together using one or more zipper fins which are perpendicular to the normal fins and interlock to keep the distance. Stamped heat sinks are low performing, and so are used in low-power applications. The set of fins is usually soldered to the base. The size and geometry of the fins can be adjusted by using a different stamp.
CNC machined heat sinks are best used for one-time production requirements as they are not cost-effective to repeat and there are no extra tooling requirements for a one-off heat sink. Machined heat sinks are therefore used in bespoke, one-off applications. Copper is hard to machine, so machined heat sinks are mostly aluminum. The size of the heat sink will be limited by the capacity of the CNC machine used.
The main benefits of using heat sinks for different applications are:
The biggest challenge is that the performance of one heat sink type will vary depending on the environment in which it is used. Factors that will affect the choice of the heat sink are:
The best way to overcome these challenges is to use thermal-modeling software to predict which heat sink may be right, and then test it in real-world applications.
The main factors affecting heat sink performance are heat sink material, type, and location. If the material used has a high thermal resistance, it will not be an effective heat sink. So choosing a low-resistance material is key. However, the design can also increase thermal resistance if it uses a bonded or soldered joint between the base and the fins. The location and orientation of the heat sink will also affect its performance. Heat sinks should channel airflow parallel to the fins to maximize the surface area between the air and the heat sink.
The number of free electrons in a material will directly affect its ability to dissipate heat. The more free electrons, the better the heat will disperse, and the reason the two most used heat sink materials are metals. For more information, see our guide on What is Aluminum Alloy?
As the temperature of a device increases, its efficiency and reliability will decrease. This is because as the temperature increases so does the resistance. Therefore, to increase reliability and efficiency, heat sinks are used to moderate the heating effect.
Yes, a bigger heat sink can result in better thermal management. However, this will only be true if the right heat sink is selected for the application. Often, heat sinks are constrained by the other components around them, so a bigger heat sink is not always possible. In addition, a more efficient design of heat sinks may have better thermal management than one that is simply bigger.
Yes, heat sinks do need thermal paste to transfer heat from the component to the heat sink effectively. If thermal paste, or thermal paste substitute, is not used, the thermal resistance between the heat sink and the component is increased. This will negatively affect the heat sink performance.
No, heat spreaders do not work on the same principle as heat sinks. Heat sinks are used to transfer heat away from the component into a fluid medium, usually air but sometimes water or oil. Heat spreaders move the heat from the component to a large conductive body which has a similar effect but is not the same. Heat spreaders can be used in sealed units whereas heat sinks often use fans to move airflow over the heat sink. For more information, see our guide on What is a Heat Spreader?
This article presented heat sinks, explained what they are, how they work, and showed six things to consider when choosing one for your application. To learn more about choosing heat sinks, contact a Xometry representative.
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Diodes, transistors, and integrated circuits generate considerable amounts of heat during operation. Extreme heat can damage or significantly affect the performance of semiconductor devices, and therefore, supplemental cooling is necessary to maintain the temperature within the limits specified by a manufacturer. Whereas some electronic components can dissipate heat on their own, most optoelectronic devices &#; like lasers and power transistors such as MOSFETs and IGBTs &#; cannot sufficiently dissipate heat without a heat management solution. How to dissipate heat in this case? This is where a well-thought-out heat sink design can make a big difference.
How To Dissipate Heat
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What are Heat Sinks Used For?Heat sinks are used in electronic devices and assemblies to provide supplemental cooling that is required to prevent overheating of components. These elements are designed and optimized to ensure that electronic devices operate within the temperature ranges provided by manufacturers.
Despite the significant manufacturing cost reduction of electronic boards and enclosures for devices, it is still a daunting and time-consuming task to analyze the thermal performance of a new design. Download this case study to learn how to dissipate heat, and the thermal performance of a printed circuit board was investigated using thermal analysis in a web browser.
Heat sinks are designed using thermal conductive materials &#; like copper and aluminum &#; and they work by dissipating heat through liquid cooling, natural convection, forced convection, or radiation. Thermal management needs vary from one application to another. Therefore, it is essential to look beyond the heat sink when designing a thermal solution for a particular application. Some of the important factors that should be considered include heat sink level requirements, component level requirements, system-level requirements, and chassis-level requirements.
Heat Sink Design
Key Considerations in Heat Sink Design CAD model of a heat sinkA heat sink transfers the thermal energy generated by an electronic assembly or component into a cooling medium. The heat is transferred from a higher temperature region (electronic component) to a lower temperature region (fluid medium) by conduction, convection, radiation, or by a combination of these heat transfer methods.
The performance of this passive heat exchanger is determined by many factors including the velocity of the coolant fluid, the thermal conductivity of the material, the thermal interface material, and the attachment method. For a specific application, the parameters of a heat sink can be precisely determined through modeling and analysis. To illustrate the key factors affecting the heat sink design performance, we used one of the public projects from the SimScale library &#; electronics cooling using conjugate heat transfer.
Conjugate heat transfer analysis of a heat sink ran in a web browser with SimScaleIn this project, the heat flow in a heat sink design was simulated. To use it as a template, just create a free Community account here and then copy the project.
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Thermal resistance refers to the sum of resistances to heat flow between the die and the coolant fluid. These heat flow resistances include the resistance between the die and the component casing, the resistance between the casing and the heat sink (thermal interface resistance), and the resistance between the heat sink and the fluid in motion. Thermal resistance does not factor non-uniform heat distribution and it is unsuitable for modeling systems that are not in thermal equilibrium.
Although the thermal resistance value is an approximation, it enables the modeling and analysis of the thermal characteristics of semiconductor devices and heat sinks. Analyses of different heat sink designs are used to determine heat sink geometries and parameters that enable maximum heat dissipation. Complex modeling of thermal characteristics can be achieved by meshing heat sinks using 3D thermal resistances. The image below illustrates the mesh of an electronics enclosure design created in a web browser with the SimScale cloud-based simulation platform.
Mesh of an electronics enclosure created with SimScaleThe hex-dominant parametric (only CFD) mesh was used to generate the mesh for the 4 volumes (3 solids and 1 fluid). This is used to create refinements and maintain the volumes as different regions to later define interfaces.
Heat sinks are designed using materials that have high thermal conductivity such as aluminum alloys and copper. Copper offers excellent thermal conductivity, antimicrobial resistance, biofouling resistance, corrosion resistance, and heat absorption. Its properties make it an excellent material for heat sinks but it is more expensive and denser than aluminum.
Diamond offers a high thermal conductivity that makes it a suitable material for thermal applications. Its lattice vibrations account for its outstanding thermal conductivity. Composite materials such as AlSiC, Dymalloy, and copper-tungsten pseudo-alloy are also commonly used in thermal applications.
The flow of the coolant medium is greatly impacted by the arrangement of fins on a heat sink. Optimizing the configuration helps to reduce fluid flow resistance thus allowing more air to go through a heat sink. Its performance is also determined by the shape and design of its fins. Optimizing the shape and size of the fins helps to maximize the heat transfer density. Through modeling, the performance of different fin shapes and configurations can be evaluated.
Heat sink fins receive heat from an electronic device and dissipate it into the surrounding coolant fluid. The heat transferred by a fin to the coolant medium decreases as the distance from the base of the heat sink increases. Using a material that has a higher thermal conductivity and decreasing the aspect ratio of the fins help to boost the fins&#; overall efficiency. The following image is part of the results of a simulation investigating the temperature characteristics of a heat sink design.
Temperature streamlines: heat sink design simulation carried out in a web browser with SimScaleSurface defects, roughness, and gaps increase thermal contact resistance thereby reducing the effectiveness of a thermal solution. These defects increase the heat flow resistance by reducing the thermal contact area between an electronic component and its heat sink, and therefore the heat sink efficiency. Thermal resistance is reduced by increasing the interface pressure and decreasing the surface roughness. In most cases, there are limits to these resistance reduction methods. To overcome these limits, thermal interface materials are used. The electrical resistivity of a material, contact pressure, and size of the surface gaps should be considered when selecting a thermal interface material for a given thermal application.
The thermal performance of a heat sink can be enhanced by selecting an appropriate method of attaching a heat sink to an electronic device or component. The selection process should factor in both the thermal and mechanical requirements of the thermal management solution. Common heat sink attachment methods include standoff spacers, flat spring clips, epoxy, and thermal tape.
Heat Sink Efficiency
Design ConclusionsHeat sinks are essential parts of most electronic assemblies, power electronic devices, and optoelectronic components. These passive heat exchangers dissipate heat generated by electronic devices to ensure that they are operating within the limits specified by manufacturers. Some of the key factors that should be considered in heat sink design include thermal resistance, material, fin configuration, fin size and shape, fin efficiency, heat sink attachment method, and thermal interface material. Geometries and parameters that provide maximum heat dissipation are obtained by analyzing different heat sink models.
Download this free case study to learn how QRC Technologies used thermal simulation with the SimScale cloud-based CAE platform to optimize their design, improve heat sink efficiency, and prevent thermal damage to electronics. Alternatively, watch the recording of a webinar on &#;Thermal Simulation for Better Electronics Enclosure Design&#;. All you need to do is fill out this short form and it will play automatically.
If you&#;d like to read more about how to design a heat sink electronics cooling, this article might be of interest to you: Thermal Design for Electronics with Cloud-Based Engineering Simulation.
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