6 Things to Consider on How To Choose the Right Heat Sink for My Application?
Heat sinks are devices used in a large number of electronic applications to manage the heating of electrical components. A heat sink can be active or passive and works mainly on the principle of increasing the fluid flow over a component by increasing its surface area for cooling. Different devices need different heat sinks based on cost, location, and cooling requirements. The thermal resistance of a heat sink material will directly impact the effectiveness of the chosen heat sink. Listed below are the six things to consider when choosing heat sinks:
The thermal requirements are the amount of heat energy dissipated per unit of time. They must first be established to set up the criteria for choosing a heat sink. If the proper thermal requirements are not established, then it will not be possible to choose the appropriate heat sink for the application. By identifying the thermal requirements, the heat sink can optimize component performance.
Heat sinks can be separated into either active or passive types. Active heat sinks increase fluid flow over the heat sink. Passive heat sinks rely on the heating effect to circulate air. It is necessary to choose the appropriate heat sink type because each type will perform differently depending on the environment. By choosing the right heat sink, maintenance, and costs can be minimized and performance optimized.
The thermal resistance of the heat sink is a measure of how well a heat sink conducts and dissipates heat. The surface area, size, and material of the heat sink all affect its thermal effectiveness. The formula for calculating the thermal resistance of a flat plate heat sink is:
Resistance =(Thickness of the plate)/(The material conductivity * The surface area of the plate)
By correctly calculating the thermal resistance of the heat sink, the most effective solution can be chosen.
The airflow available is the amount of air that flows over a heat sink in a given period. For passive systems, this is the established airflow, and for an active system, it is the airflow created by the fan. The airflow needs to be determined to identify how effective the thermal management system will be. High airflow is indicative of an efficient heat sink. A passive heat sink will not benefit from the addition of a fan because the design shape will not allow for increased airflow. It may also be better to use established airflows as the addition of fans will create noise and the end-user will usually want the device to be as quiet as possible.
The bigger the heat sink, the more heat it will be able to dissipate. However, the size of the heat sink will be limited by the space it must fit in and the contact area between the heat sink and the component it is cooling. In addition, just because a heat sink is larger does not mean it is more effective. Other variables such as material conductivity, airflow, and thermal resistance of the design are also factors.
The thermal interface material is the substance that sits between the heat sink and the component it is cooling. The interface is used to effectively transfer heat from the component to the heat sink. The interface may be referred to as:
- Thermal grease
- Heat sink compound
- Thermal compound
- Gap filler
- Thermal paste
Without the right choice of a compound, the thermal resistance will increase possibly to the point at which the heat sink is no longer useful.
A heat sink is a device used to decrease the thermal resistance of a component to keep it cool. It could be as simple as a metal plate on a printed circuit board to increase thermal conductivity. Heat sinks are more commonly finned metal devices attached to a fan to maximize airflow and aid the cooling of a component. For more information, see our guide on What is a Heat Sink?
Figure 1 below is an example of a heat sink:
Heat sink on a computer motherboard.
Image Credit: Shutterstock.com/IhorL
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.
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:
- Increased device efficiency.
- Increased device performance.
- Increased device life span.
- Prevent overheating.
- Keep components within the temperature range they are designed to operate in.
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:
- How the airflow interacts with the design.
- How the heat from surrounding components affects the heat sink.
- The space restrictions of the location.
- The budget for a heat sink.
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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