This article will show you the reason for aluminum heatsink is becoming the main choice for engineers. Firstly, thermal conductivity is the most important performance in the choice of heat sink material, and different materials have different thermal conductivity. The heatsink materials can be diamond, silver, copper, aluminum, steel, etc. You can see their thermal conductivity accordingly as follows:
Thermal conductivity = k = W /(m k)
Obviously, the diamond has excellent thermal conductivity. Diamond does not conduct electricity and electrons cannot move freely, so its thermal conductivity basically comes from the propagation of carbon atom vibrations (that is, phonons). Due to the small mass of carbon atoms and the strong carbon-carbon bond, the propagation of vibration in the diamond is very smooth. Because of this, the thermal conductivity of diamond is very excellent, almost the highest, and almost 5 times that of silver.
Diamond not only has ultra-high thermal conductivity but also it’s excellent mechanical, optical, acoustic, electrical, and chemical properties, which makes it significantly superior to other materials in terms of heat dissipation of high-power optoelectronic devices. Of course, the cost of the diamond is extremely expensive, which makes it not the preferred material for ordinary heatsink products.
The metal with the best heat dissipation is silver, but it is very soft, which is not conducive to manufacturing high-density devices such as heat sinks. As a precious metal, gold is not a suitable heatsink material because of its expensive cost. The lowest cost material is iron, but its thermal conductivity is only one-third of that of aluminum, which is not the mainstream heatsink material. But it is mostly used for radiators for homes because of good corrosion resistance.
These factors have led to the current use of copper or aluminum as mainstream heatsink materials.
Copper has better thermal conductivity than aluminum. However, when considering thermal conductivity, the cost is another factor that cannot be ignored. The thermal conductivity of copper is twice that of aluminum, but its density is three times that of aluminum. This means that the weight of a heat sink that provides similar heat flow in copper will increase by about 50%. Actually, many copper heat sinks are overweight beyond design limits on weight. When calculating the cost per ton (copper is currently about 3.5 times the cost of aluminum), and you will find that the cost of copper will be much higher than that of aluminum solutions for the same heat sink design.
Aluminum, especially 6xxx-series aluminum alloy, can be simply extruded into various shapes, including complex heat sinks. Although copper can also be extruded, such as rods, it is very difficult to extrude into the shape of a heat sink, and the cost is also very expensive.
These factors make aluminum extrusions best in most heat sinks.
The thermal conductivity of pure aluminum is 237 W/m•K, but pure aluminum is relatively soft in mechanical properties, so alloy aluminum is usually used as the heatsink material. When alloyed with other elements (mainly manganese, silicon, magnesium, copper, and iron), the thermal conductivity changes. The alloy is selected based on its mechanical properties (including corrosion resistance, tensile strength, and hardness) for special applications. Aluminum alloys with different alloy compositions have different thermal conductivity. 6060, 6061, and 6063 have excellent extrusion properties, so they are the most common aluminum heatsink materials. Their heat dissipation rates are as follows:
6061 160 W / m•K
6063 201 W / m•K
6063 209 W / m•K
The extruded aluminum heatsink is in a leading position in most industrial applications due to its low price and lightweight. Because the thermal conductivity is only half of the copper, some engineers embed a copper plate on the base of the aluminum alloy heatsink to increase the thermal conductivity, which is a good idea.