Aluminum Heat Sinks – The Invisible Saviors!

An aluminium heat sink

It is commonly noticed that if you use your laptop or computer for longer hours or run applications which require a lot of graphics processing, the system starts lagging. Play video games long enough and chances are your computer will unexpectedly throw a tantrum. It might even trigger an unexpected shutdown. The reason why it happens like this is because the processors responsible for working inside your ‘closed’ device get hotter as the time passes. If the load is not decreased or the hot components don’t get cooled down soon enough, they may burn out and damage the device. Therefore, every electronic device, like some mechanical devices (cars), has a ‘heat sink’ where the immediate exchange of heat takes place to cool off these parts to increase their performance and longevity.  

The cooling mechanism. Courtesy: Wikipedia

A heat sink is thus, usually a device which is required to cool off parts of a machine which generates a lot of heat under continuous performance. There are two heat sink types: active and passive. Active heat sinks consume power and are usually a fan type cooling device. Commonly, passive heat sinks are made of an aluminum-finned radiator that dissipates heat through convection (remember the “hot air goes up, cold air comes down?). Passive heat sinks to work when there is a steady air-flow moving across their fins. These heat sinks are 100% reliable, as they have no mechanical components.

Different types

A heat sink is usually made out of copper and/or aluminium. Alloys of these metals are also used to increase the performance and sturdiness. In principle, a heat sink is designed to maximize its surface area in contact with the cooling medium surrounding it, for example - the air. Copper is used because it has many desirable properties for thermally efficient and durable heat exchangers. It is an excellent conductor of heat. This means that copper's high thermal conductivity allows heat to pass through it quickly.

Aluminium alloys are the most commonly used materials and have significant advantages over copper. Alloy 1050A has one of the higher thermal conductivity values but is mechanically soft. Although copper has around twice the thermal conductivity of aluminium and more corrosion resistant, copper is three times as dense as aluminium and even more expensive. Aluminium heat sinks can be extruded, but the less ductile copper cannot. Aluminium alloys 6060, 6061 and 6063 are also commonly used.

Aluminum has a thermal conductivity of 235 Watts per Kelvin per meter (W/m/K). (The higher the thermal conductivity number of a metal, the more heat that metal can conduct.) Aluminum is also inexpensive to produce and is lightweight. When a heat sink is attached, its weight puts a certain level of stress on the motherboard of the device. This is undesirable. In 2008, Applied Nanotech announced that the future of heat sinks is a material called CarbAl. It is made up of 20% aluminum and 80% of two different carbon-derived materials with excellent thermal conductivity. Essentially, CarbAl is more conductive than copper and weighs the same as aluminum, making it the best of both worlds.

Pin Type

The applications in the mobile phones, computers, and other semiconductor devices demand reliable and heavy duty heat sinks. It is thus imperative to choose a right sink for appropriate uses according to their ‘thermal resistance’. Thermal resistance is defined as temperature rise per unit of power and is expressed in units of degrees Celsius per watt (°C/W). The most common types of sinks are pin sinks. In a pin fin heat sink, the pins extend from its base. These can be cylindrical, elliptical or square. Another type of heat sink fin arrangement is the straight fin. These run the entire length of the heat sink. In general, the more surface area a heat sink has, the better it works. However, this is not always true. The concept of a pin fin heat sink is to try to pack as much surface area into a given volume as possible. They work well in any orientation.