Managing the thermal load generated by your design is key to driving performance -- so where do you start?
Everyone who has worked with or built designs with electronic components knows that, generally speaking, heat is the enemy of performance. When it comes to electronics, excessive heat can prevent a component from operating at optimal levels or, even worse, cause permanent damage to the component and its surrounding parts that can lead to failure.
One of the tried-and-true methods for managing and neutralizing the heat generated from modern components is the use of heat sinks -- the multi-finned, (usually) aluminum heat exchangers that help to dissipate thermal energy more effectively. In this article, we’re going to be taking a dive into the world of heat sinks and look at some of the design factors, materials, and applications driving modern heat sink design.
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 (typically, air -- though in some instances it can be water or a special oil). This concept is governed by a simple formula, known as Fourier’s Law of Heat Conduction that is written thusly:
In this formula, qk is the rate at which heat is transferred and is proportional to the product of the temperature gradient and the cross-sectional area through which heat is transferred. Simply put -- the greater the temperature difference between the object (in our application, the heat generating component) and its ambient surroundings (the air or other material around the heat sink) and the larger the heat sink, the faster the heat will be neutralized.
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.
Finally, there is the physical design of the heat sink itself. The number of options for the fins is seemingly limitless, with pin, straight, and flared fins common choices that can be configured in endless patterns and arrays. The performance of these fins depends on many factors, and while it is commonly thought that increased surface area leads to increased performance, that is not always the case and can depend on many additional factors such as overall thermal resistance and the way in which the air or liquid flows through the fins.
LED Heat Sinks
To date, the most common applications for heat sinks have been in the management of heat generated from CPUs. Open any computer and you will likely see a number of heat sinks, fans, and other devices or systems designed to help keep the computer running efficiently and at near-optimal temperatures. Even the popular Raspberry Pi performs better when a heat sink is used. But as higher-performance electronics enter the market, additional heat sink applications are emerging.
One of the areas in which heat sinks are seeing widespread use is in modern lighting solutions. LEDs have been around for many years, but advancements in LED solutions have significantly changed the amount of thermal energy these components generate. Where LEDs were once used mostly for indicator lights and low-power applications, today LEDs are used for everything from home lighting to automotive headlamps and even stadium lights -- huge installations that generate massive amounts of thermal energy.
Like other electronic components, heat is bad news for LEDs. In fact, excessive heat can damage them, leading to lower light output, changes in color, and a large decrease in life expectancy. To combat these problems, LED design engineers are using heat sinks to better transfer thermal energy and keep LEDs performing at optimal levels.
Another growth sector for heat sinks is being fueled by the Internet of Things, Machine Learning, and Artificial Intelligence. These growing segments of tech have fueled a massive increase in the generation of data, as well as the corresponding analysis of those data points. Big data, as it’s often referred to as, requires powerful processors to dissect the information and robust GPUs to visualize the vast quantities of information being recorded. These powerful systems generate a great deal of heat which, in turn, needs to be managed -- and heat sinks are the answer.
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When it comes to building your design, choosing a heat sink that will meet your required thermal needs is extremely important to the overall performance and lifespan of your system. Arrow offers a large selection of heat sinks and other thermal management solutions that will keep your design working how it should.
