HEATSINKS - BASICS AND APPLICATIONS

INTRODUCTION:

What is a heatsink?

A heat sink is basically a passive heat exchanger that transfers heat from a heating component. It consists of a metallic part that can be attached to a component generating heat, with the goal of dissipating the heat to a surrounding fluid in order to regulate the temperature and prevent the overheating of that component. It achieves this by driving the heat away through its enlarged surface and fins, to the surrounding cooler fluid flowing through it.

In most applications, the component is an electronic device like a CPU, GPU, Chipsets, Ram module, Microprocessor, Microcontroller, etc. and the surrounding fluid is air. Transfer of heat to the heatsink is done by conduction. Usually, a Thermal Interface Material or TIM is used to aid the transfer of the heat from the component to the heat sink as it has the lowest thermal resistance.

How does a heat sink function?

The temperature regulation of the component is executed in the following processes:

Step 1: The electronic component generates heat. The heat then flows to the surface of the component.

Step 2: The heat from the surface which is in contact with the heat sink travels to the Thermal Interface Material then to the heat sink.

Step 3: The heat, by conduction, naturally flows up to the heat sink fins and is then cooled by the surrounding fluid, usually air.

This is why the heat sink, when observed, will be hottest towards the source end, and cooler at the upper extremes towards the fins.

What are the types of heat sinks?

Heat sinks are categorized into various types depending upon the types of airflow, materials used, and fin efficiency. Heat sinks are usually used in two configurations: Active and Passive.

Active Heat Sinks make use of forced air to increase fluid flow across the hot area. The air is forced most commonly by a fan or a blower. The fan or blower forces the air throughout the heat sink, constantly cooling the heat sink and thus increasing the cooling capability of the heatsink. Examples of active heat sinks can be found in PC components like the CPU cooler, GPU cooler, etc.

Passive Heat Sinks depend on the natural convection of heat. The hot air naturally rises to the top due to the buoyancy of air. Passive heat sinks are less effective than active heat sinks at driving heat away from the component but have the advantage of not needing any external power for the fan or blower. Examples of passive heat sinks can be seen for chipsets, microprocessors, microcontrollers, etc.

According to the types of materials used heat sinks are categorized into three types

Aluminium Alloys

Aluminum is commonly used in heat sinks because it is relatively cheap and a comparatively softer material that possesses ease to form it into different shapes. Aluminum alloys have one of the higher thermal conductivity values up to 229 W/m•K which is effective in Heat transfer from source to the surroundings.

Copper Heat sinks

Copper, as compared to Aluminium is much pricey but also has a higher thermal conductivity of around 400 W/m•K for pure copper. Despite the high price where there is a requirement for higher thermal transfer copper just might be the best choice.

Aluminum copper Hybrid

Al-Cu mix is used when the Thermal requirements are high but the cost is not affordable. Lower cost is achieved by using copper as a base plate material to transfer heat away from the source and is attached to an aluminum fin stack to provide a larger surface area for Heat transfer. This is the most common use case for heat transfer in Electronic systems as there is a balance between performance and cost-effectiveness.

According to the types of Manufacturing Techniques:

  • CNC Machined heat sinks - These can be used when the requirement is of High thermal conductivity or requires intricate design options. This is a costly option whilst having a relatively slow throughput rate.
  • Forged and Die Cast heat sinks- These processes have low unit cost for high volume production. Die-cast heat sinks are good for applications where natural convention and slightly thicker heat sinks may be used. Both the Processes have good thermal performance whilst also offering good design flexibility. The only limitations in a forged heat sink are the airflow management and design.
  • Zipper Fin Heat sinks- These heat sinks have the ability for thin and densely packed fins. The cost of manufacturing is also reasonable considering the low weight and integration of these with two-phase devices.
  • Skived Fin heat sink- Skived fin heat sink have low tooling cost, a high fin aspect ratio & thin fins, which can easily become bent and thus hamper the thermal performance. They can be used in medium to high-performance applications.

  • Bonded Fin heat sink- Bonded heat sinks can be used when the requirement is of a fairly large heat sink or of different materials such as a different material for the base plate and for the fin stack. The bonding is done by using thermal epoxy or by brazing. The drawback of Bonded Fin heat sink is that the manufacturing process is not automated.
  • Stamped heat sink- These heat sinks are made by stamping out a piece of metal in a press. Because of being low in performance, they are used in low-power They are less expensive than other heat sinks.

Applications of above heat sink types

Forged:

  • Cooling solutions for electric vehicle controllers.
  • Battery pack cooling solution.
  • Motor housing cooling.
  • Inverter cooling.
  • IT telecommunication cooling.

Skived fin:

Computers and electronic components.

Telecommunication equipment.

Bonded:

  • Uninterruptible power supplies (UPS)
  • Variable speed motor controls
  • Welding units
  • Power rectification equipment
  • Laser power supplies
  • Traction drives

Stamped:

Stamped fin heat sinks provide a solution to a variety of application requirements. The combination of copper, aluminum when designing stamped fin heat sinks is uncommonly responsive to the cooling requirements of increased performance circuitry, such as overclocked computers. Other uses for a stamped fin heat sink include applications that have forced convection currents, chips with high power (usually over a hundred watts), and small, difficult-to-fit space requirements.

Here we conclude that heat sinks are an important part of the electronic system for them to function properly while regulating their temperatures under extreme workloads.

This blog has been submitted by VCET Robotics Club, VCET Vasai under the Robocraze Club Outreach Program.

Author: Udesh Kushte, Aryan Sawant, Suyash Dandekar and Shubham Irkar

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