In the previous blog we began a series of informative blogs about thermal management and cooling systems for electronics. The first was Heat Pipes, a fairly common cooling source for many electronics. This week takes a look at the most common cooling source, known as a Heat Sink. Microprocessors and semiconductors are common examples requiring a heat sink, but they can be found in other applications such as refrigeration and A/C systems and more recently in integrated circuits such as digital signal processors and graphics processing units.
Basic Workings of a Heat Sink
A heat sink is more of a passive device than a heat pipe in that it cools mainly by dissipating the heat into the air. There are two basic types of heat sinks. The first is known as an active heat sink that will utilize power and are common to incorporate some sort of a fan type device to handle the cooling duties. A passive heat sink has no mechanical components to fail which makes them more reliable and are of the radiator type that dissipate heat through convection. They do, however, require a steady flow of air circulating through its fins to operate to their full capacity.They use a metal object to draw the heat from a heat source by increasing the surface area in contact with the air around it, and often times utilize a thin thermal interface material to mediate the contact at the heat source. The thermal interface material accomplishes this by evening out the surface below the heat sink and filling in any gaps that will allow air to penetrate. Air is not a good thermal conductor and by removing the gaps, the heat sink can work to its full capacity. Thermal conductor materials often used are aluminum and copper because they have a high thermal conductivity, however when looking at cost effectiveness, aluminum would be the better choice due to its lightweight makeup and the fact that copper is a more expensive material.
Engineering Improvements in thermal management
Just like any other product, heat sinks must advance as the technology around it advances. Licensed mechanical engineers with the ability to utilize computation fluid dynamics (CFD) software can run analysis on CAD models to create the most effective properties of thermal management for a given device. With computers continuing to require more power they require higher and higher levels of cooling. One of the biggest challenges is finding lighter and more conductive materials to make heat sinks as efficient as possible as well as keeping costs down. Companies have recently tried bonding copper and aluminum together, combining the lightweight properties of aluminum and the high thermal conductivity of copper. In theory this would work very well, but copper and aluminum are not easily bonded and in inexpensive heat sinks it can do more harm than good. In 2008 an engineering firm named Applied Nanotech™ designed an isotropic material named CarbAl that had a thermal conductivity of 350 W/mK (watts per meter * Kelvin) which is higher than both copper and aluminum, and weighs about the same as aluminum. The make-up of this material allows for a quicker removal of heat than that of other passive thermal management materials.
By working to develop different types of materials and designs of heat sinks, mechanical engineers working in the fields of electronics cooling hope to keep up with the demand for smaller, more powerful and more cost effective computers and electronic devices. One such company that is working on new designs for metal core circuit boards is SinkPAD(TM). The high thermal conductivity of the metal board allows for high power to remain cooler. You can read our previous blog regarding the metal core circuit boards for more information.