How to cool Power-Hungry Electronics properly

Everything around us is controlled by some form of electronics. With higher complexity, computing power has to increase. Therefore, the heat output increases, so it has to be cooled. That is the job of a heat sink, which works by heat conduction.

Heat conduction is a fundamental process of heat transfer where thermal energy is transported from a higher-temperature region to a lower-temperature region within a material. In solids, this process is primarily due to the transport of phonons, which are quantized modes of vibration occurring in a rigid crystal lattice. Both phonons and free electrons contribute to heat conduction in metals, with free electrons typically playing a more significant role.

When a temperature gradient is established, these phonons or free electrons move from the hot end to the cold end, carrying thermal energy. Fourier’s Law describes the rate of heat transfer by conduction, which states that the rate of heat transfer is proportional to the negative gradient in the temperature and the area at right angles to that gradient through which the heat flows.

What are the most common ways to produce heat sinks?

• Heat sinks are typically made of thermally conductive materials, most commonly aluminium. Several methods are used to manufacture heat sinks, including skiving, milling, extrusion, and casting.
  
  
• Skiving: This process involves slicing a solid aluminium block into thin layers and bending them to form the fins. The entire heat sink is made of a single piece of metal, eliminating the need for joining pieces of metal.
  
  
• Milling: This is a machining process in which a rotating cutting tool removes material from a workpiece. Milling can create complex shapes and features in a heat sink.
  
  
• Extrusion: This is the most cost-effective process for producing heat sinks with plate fins. In this process, aluminium is pushed through a die of the desired cross-section under high pressure.
  
  
• Casting: HPDC allows for functional integration of mounting and touchpoints on the electronics. It also allows for complex or angled fin shapes.
  
  

Are the heat sinks all the same?

While a material’s inherent thermal conductivity does not change, manufacturing can introduce defects, such as dislocations, that can affect heat flow. These processes can potentially alter the heat sink’s effective thermal conductivity.

Dislocations are defects in the material’s crystal structure that can affect heat flow. They can scatter phonons, the primary heat carriers in a solid. This scattering can reduce the mean free path of phonons, thereby reducing the thermal conductivity.

Whereas the skiving, milling, and extrusion heat sinks can work with pure aluminium to ensure the highest heat conductivity, HPDC is typically limited to high silicon alloys (AlSi7 or higher) to ensure castability.

However, with Rheocasting, castability is not defined by the silicon content. Therefore, you can use AlSi2 and reach a heat conductivity of up to 198 W/mK. That is close to pure aluminium, which has 225 W/mK and is done with a 100% secondary alloy. You’re also fully flexible in the geometry. Whether you want to cast a 5G antenna, a server heat sink, or a water-cooled PSU box, Rheocasting has you covered!

We have written an in-depth case study on thermal management, “How to make the most efficient Heat Sinks”. Download it and also check out the Rheocasting Strategy Development service.