Taming the Heat: Overcoming Thermal Challenges in Compact Electronics

Thermal management in electronics is vital for keeping devices safe and operational, but this gets challenging with small devices. As hot electronic components come closer together, heat has a harder time getting out. Electronics cooling solutions with small form factors are thus essential to get right in electronic product design.

All electric and electronic devices generate some amount of heat as they operate. This is due to the inherent resistance of circuit components, which is necessary for controlling performance and preventing short circuits, but generates heat as a result.

Resistance impedes the flow of electrons by making them collide with the material they’re travelling through. They thus lose kinetic energy, which converts to heat dissipated to the surrounding materials. Sometimes this heat is desired, as with electric heaters, but it usually needs to be removed promptly.

Heat damages electronics through:

• Broken connections: Since materials expand as they rise in temperature, overheated solder joints can expand and crack. This leads to devices performing poorly or shutting down
• Loss of battery life: If the lithium-ion batteries of our devices get too hot (above 45°C), they can lose their charge and even their rechargeability. Higher temperatures accelerate their internal chemical reactions that produce charge, which stresses the battery and can even make it leak
• Reduced performance: High-performance tasks like streaming videos generate significant heat, especially in screens. Insufficient electronic cooling can cause the device to automatically reduce processing to allow for cooling, which degrades video output
• Fire: Most drastically, overheated components can ignite, leading to serious health and safety concerns

Small electronic devices pack multiple high-performance electronic components tightly together, leaving little room for cooling airflow. This means that all generated heat can easily spread around the entire device. This makes electronics cooling solutions vital for keeping these devices safe while maintaining the high performance we expect.

A heat sink collects a device’s built-up heat and disperses it to a surrounding medium. That medium is usually air, but cooling liquids can also be used.

Heat sinks feature a central conductor that’s connected to a device’s semiconductors. It absorbs heat and further conducts it to protruding fins or pins, which collectively have a large surface area for dissipating heat.

When selecting a heat sink for your application, consider the following types and factors:

• Passive heat sinks: Their fins rely on natural surrounding air/liquid flow for heat dissipation, but that typically requires larger sizes to maximise surface area. Examples include the fins protruding from electric motors
• Active heat sinks: Devices with active heat sinks have some method, typically a fan, of forcing air/liquid flow over the fins. That increases the cooling rate possible for a given surface area and allows small form factors. Laptop and desktop computers commonly use active heat sinks (with fans)

Fin materials are usually either copper or aluminium. Copper has the best thermal conductivity, but that comes with increased cost and weight. Aluminium has decent conductivity and is lighter and less expensive. It can also be formed into thin sheets for maximising surface area.

Heat sinks can feature either fins (long, wide shapes) or pins (thin, cylindrical shapes). Pins have more surface area but are more expensive to manufacture. They’re less common for consumer devices.

Overall, consider how much cooling your device needs and what you can spend on a heat sink. Achieving more cooling within a small space requires more elaborate fin shapes and more expensive manufacturing.

When a heat sink attaches to a device’s semiconductors, the mating surfaces appear flat but are actually a rough, jagged interface at the microscopic level. All the tiny pockets between these rough surfaces are filled with air, which has a much lower thermal conductivity than these otherwise directly contacting metal parts. To maximise heat transfer to the heat sink, something more conductive needs to fill those gaps.

Thermal interface materials (TIMs), also known as thermal gap pads, fill that need. They’re sandwiched between the heat sink and the semiconductor to form an efficient conductive bridge. TIMs are an essential finishing touch for electronic cooling and can also absorb physical shocks.

TIMs come in forms such as greases, gels, tapes, pads, and adhesives. To select the best one for your application, you’ll generally compare ease of application with thermal conductivity performance.

Greases and gels can fill very thin interfaces, but are messy to work with and require curing time and clamping. Any clamping force requires more features and hardware, meaning more complexity and cost. Adhesives and tapes are easy to apply and don’t require clamping. Thermal pads can have adhesive sides for quick application and can be easily cut to fit the shape you need.

Also, consider whether you need materials that can withstand humidity or airborne chemicals, and whether materials like vapourised silicone can damage the device. With the range of TIMs available, there’s likely to be one that can help with your electronic cooling.

Compact fans have small form factors for fitting inside personal computers, yet they can achieve significant cooling despite their size. They expel air from an enclosed system, forcing cooling convection airflow along heat sink fins and other components.

Compact cooling fans vary in their impeller and housing shapes:

• Axial fans: These draw in and expel air in the same direction (the same axis). They have good performance with minimal power consumption
• Centrifugal fans (blowers): These expel air at 90° to its entry direction. They’re a good choice in tight spaces, such as laptops. They can require more power, though
• Diagonal fans: These expel air at a diagonal angle to its entry direction, making an axial cone outflow. They can achieve a greater pressure increase than axial fans, with less noise, although they can draw the most power of these types. They’re good for cooling cabinets with multiple tightly packed components

When selecting a fan, consider your system’s heat load, ambient temperature, acceptable noise, fan power draw, expected vibrations, and back pressure (the pressure the fan needs to push air against).

The fan’s flow rate (Q, m³/min.) may be its most important factor, so you’ll need to calculate what rate can keep the system within an acceptable temperature rise (ΔT, °C) given the generated heat (H, watts):

Q = H / (20 x ΔT)

Finally, regularly clean the dust these fans accumulate to ensure they stay safe and effective.

These electronics cooling solutions all need free-flowing airflow to be effective. Here are some airflow design tips to consider:

• Start with the fact that hot air naturally rises. Place cooling fan exit points near the top of the device and air entry vents near the bottom. Similarly, the components that run the hottest will become even hotter near the device’s top. This is useful for desktop computer design, but less so for laptops
• With the space you have available, prioritise breathing room around the hottest components. Components that run cooler during operation can be packed more tightly together
• Place heat sinks and hot components in the airflow’s main entry-to-exit path, where it’ll be moving the fastest. Parts that require less cooling can go in more stagnant zones
• Align heat sink fins lengthwise with the airflow direction to ensure air picks up heat without obstruction
• Consider placing baffles to concentrate airflow on hot spots, but test this to ensure it’s effective
• Ensure airflow isn’t obstructed at the entry and exit points. If components block these crucial zones, this will diminish the air’s flow rate and cooling capacity

Our everyday electronic devices continue to shrink and become more powerful, so they evidently have electronic cooling figured out. Here are some examples of successful thermal management in electronics in small sizes.

Laptops, given their size, pack a tremendous amount of high-performance electronics into a small size while staying fairly cool. Their electronics cooling solutions include:

• Copper ‘heat pipes’ direct heat in paths around the laptop to heat sinks and cooling airflow
• Laptop heat sinks use very thin fins to maximise cooling surface area
• Centrifugal fans or slim, high-speed axial fans are good for achieving cooling airflow in flat shapes
• TIMs are used to bridge components and ensure efficient heat conduction

Miniature water chillers use water as the active heat transfer fluid rather than air (a form of air conditioning). They have a compressor, condenser, and pump that circulate water in small tubes within the electronic device to manage its heat. These chillers are more elaborate and better suited for industrial devices with precise temperature control needs, such as semiconductor lithography tools or fibre laser cutters.

We’ve looked at the breadth of innovations available for thermal management in electronics. Along with heat sinks and TIMs, we offer compact axial fans for all your electronic cooling needs.