What is a Heat Sink?
Traditionally is one of the most efficient methods to cool down an appliance is to put an air cooling fan on top and letting them start working, based on the shape of the device however, this might not be the most practical of options. In addition, it won’t be suitable for devices that can quickly heat up or single component regions whose heating is concentrated in a particular region.
The term “heat sink” refers to a passive exchanger that absorbs heat from an area through conduction and then disperses it into the surrounding atmosphere. In the field of electronics, a heat sink is usually a solid block of aluminum or copper with multiple fins which increase the surface area available to transfer heat. In the constant need to squeeze more processing power in smaller sizes innovations in heat sink design are more crucial than ever in the past.
Heat Sink Materials
The most affordable, durable and widely used, copper and aluminum remain the most common “gold standard” for heat sinks. Innovation in this area is greater to do with metal alloys and the way you make use their strengths as well as weaknesses materials as opposed to exotic materials (although we’ll talk about these a bit later).
Copper The thermal conductivity for pure copper is around 386 W/mK with the density of 8.96 grams per cubic centimeter, and a price of about 6000 USD per metric ton in August 2018.
Aluminum Conductivity: The thermal conductivity of pure aluminum has been measured at 204 W/mK with the density of 8.96 g/cm3, with an estimated price of 2300 USD per metric tonne in August 2018.
While copper is more efficient in thermal conductivity, aluminum offers the weight and cost advantage. Deciding which material to select is a matter of balancing with the particular requirements of the project. In this field, innovation often involves finding the balance between the best and worst of both materials. For instance using copper as a baseplate in order to transfer heat away from a computer into a lighter, cheaper aluminium heat sink. It’s important to remember that heat transfer from aluminum/copper to air is comparable, because the thermal conductivity of air is the main bottleneck. The advantages of heat transfer of copper over aluminum isn’t so great as one might think from their thermal conductivities this is the reason aluminum is the most sought-after metal for heat-sinks.
Conductivity of thermal energy is just one element to design a high-quality heat sink. The ability to squeeze out performance gains from heat sinks on the latest chips used in tablets and smartphones requires a new approach to the layout and geometry of fins. The principle concept to be grasped is fin efficiency, the ratio of fin efficiency in terms of heat transfer to rate of heat transfer for the optimal fin (one that is Tfin + Tbase).
The greater the efficiency of the fin more efficient the fins are, the better convection of heat to the atmosphere around it. Optimizing the geometry of fins can help maximize the flow of air throughout the heat source. There are two basic fin designs:
Pin Fin: Creating pins in a forest from flat bases is a well-known method to increase the surface area. They perform best when air flows in a radial direction along the pins.
Straight Fins are also referred to as heat sinks with plate fins straight fins span through the entire length of flat base, maximizing surface area. They perform most efficiently when air is flowing parallel towards your heat sink.
There are many ways to improve airflow and cooling
Active cooling: New and cutting-edge GPUs like the GeForce GTX 1180 from Nvidia make use of a combination of fans as well as heat pipes and vapor chambers to control temperatures.
Cross-cutting flat fins by taking straight fins and dividing it into short sections may increase the efficiency of heat transfer on the fin’s surface but however it reduces the areas of surface exposed to air stream and creating an increase in pressure; most effective when used to respond to erratic airflow.
Augmented (curved) fins By adding curvature to the trailing and leading side of the straight fin may remove “dead” air molecules away from the fin’s surface and improve the flow.
To determine the proper fin geometry you’ll have to utilize your preferred CFD software to understand the fluid dynamics within the sphere of your device.
It’s not obvious that the method by which the heat sink is made can affect the thermal performance.
Extruded: The most cost-effective choice high-tech, automated extruded heat sinks are usually aluminum and allow the maker to fabricate the fins and base in one piece.
Bonded Fin The base and the fin are constructed separately and need to be joined. Although heat exchange between bases and bonds take some damage, the construction of each permits for more complex geometries, which can result in significant increases in surface area, which will more than make up for the drawbacks.
Zipper: The most economical alternative for high-density heat sinks. The fins have been made out of metal, then formed into shape using interlocking grooves prior to attaching to the base.
Fins that fold are created by bent copper and aluminum sheets prior to bonding to the base. Fins made of this material can be smaller than standard extruded or connected fins, and can offer greater surface area and densities.
The fins as well as the base are made out of a single piece metal by cutting the top of a metal belt and folding it over the base. Skived heat sources can be constructed with thin fins and high-density geometries, while benefitting in the conductivity and thermal efficiency of an even sheet of steel (no resistance to bonds).
The advancement in technology has made skived and folded processes more feasible, and are gradually and are gradually removing older techniques like extrusion. The increasing demand for higher thermal conductivities and surface area is likely to continue in this direction.
The Future of Heat Sinks
In the case of heat sinks, researchers have come up with interesting materials over the years which could change the game. As I mentioned in the past, I’ve listed a few of the most exotic substances that could be the next frontier in the design of heat sinks:
Carbon Nanotubes (CNT) have impressive thermal and electrical characteristics (thermal conductivity of between 3000-6000 W/mK) It’s no wonder that scientists are trying out experiments using CNT thermal sinks as well as copper CNT composites. Unfortunately, it’ll be a while before they’re commercially available.
The diamond heat sinks have in the works. Metal-diamond composites have a lower energy density (6-12 ppm/K) with excellent thermal conductivity (300-650 W/mK).
Graphene is another of the carbon-based metamaterials that have captured the imaginations of scientists.
HOPG (highly ordered graphite hydrolytic) is an anisotropic mineral that has a thermal conductivity of around (2000 W/mK).
The most popular way to improve material for heat sources is to start with classic aluminum or copper and then dope the matrix of metal with a very high thermal conductivity metamaterial (often carbon). It’s hard to say what kind of material will rule this future generation of heat-sinks but one thing will always be certain: the most effective thermal management systems employ an integrated approach that combines heat sinks with cooling methods like heat pipes, heat spreaders or vapor chambers.