The State of Carbon Fiber for Thermal Dissipation in LEDs|
Article - April 7, 2016 By LarsonElectronics.com
The State of Carbon Fiber for Thermal Dissipation in LEDs
Light emitting diodes (LEDs) require efficient heat sinks in order to operate consistently. In an attempt to remedy concerns surrounding the efficiency of such components and to create a solid foundation for high-powered LED variants, manufacturers have been exploring new materials with exceptional thermal dissipating properties.
Specifically, researchers have veered away from metals (copper and aluminum), and have started to focus on non-metals (thermoplastics, carbon fiber and graphite), as well as combinations of metal and non-metal materials.
An example of this breakthrough comes from Korea Electronics Technology Institute. Scientists from the organization released a case study that showed the thermally conductive attributes of carbon nano-fibers (CNFs) in LEDs. The researchers used the material to create a new type of heat sink that is lightweight and inexpensive without compromising performance. The results of the study showed that CNF-mixed epoxy, when applied to LED heat sinks, can improve thermal conductivity by up to 140 percent.
Carbon Fiber Heat Dissipation Properties
Carbon fiber has superior thermal management features. It boasts low thermal resistance- up to 40 percent lower than mainstream aluminum. The material can reach heat resistance thresholds as high as 400 degrees Celsius. This makes it applicable for high-powered LED luminaries in extreme temperature environments. Previously, die-cast aluminum was the heat sink material of choice; but from a manufacturing perspective, the material was difficult and complex to work with, which caused scaling issues for industrial lighting businesses.
Below are the general properties of carbon fiber:
• Corrosion resistance
• Electrical conductivity
• Fire resistance
• Exceptional thermal conductivity
• Low coefficient of thermal expansion
The robust material is also up to 25 percent lighter than aluminum and is equipped with a higher strength-to-weight ratio, compared to conventional metals, giving designers more flexibility to incorporate other components in the fixtures. It is crucial to consider that large and heavy lamps pose serious risks during installation. Furthermore, such negative features contribute to poor wind and vibration resistance. Heavy fixtures are also more difficult to transport in bulk.
Carbon Fiber as a Secondary Component
Carbon fiber is very versatile, and can be combined with other materials to create effective heat dissipating components. Teijin, a Japan-based synthetic fibers technology company, is a pioneer in the application of carbon fiber mixtures in LEDs. The group created a material called Raheama: a thermal-management sheet that is composed of 50-200 micrometer fibers from a graphite fiber stock that measures roughly eight micrometers. It is a carbon fiber heat-conductive filler that conducts high temperatures more efficiently than metals (such as copper or silver).
Raheama contains low thermal coefficient expansion rates- lower than ceramics, making it suitable for applications where stability is needed. The company designed the carbon fiber filler specifically for LEDs. Scientists used the material with polycarbonate sheets to create a heat sink that can disperse heat on the same level as aluminum, without the added weight. It comes in two variants- R-A201 and R-A301. The first option is suitable for components that require high level molding, while the latter contains high heat radiation properties.
Another material that was traditionally used for heat sinks in LEDs was copper. The metal was effective in mitigating heat, but the material was also expensive. It has a coefficient of 16.6 (10-6 m/m K), compared to carbon fiber- which can reach as low as zero. Low coefficient of thermal expansion is important in heat dissipation, because it allows the component to tolerate varying levels of heat without warping or expanding. Recently, manufacturers have combined copper with carbon fiber and/or other graphitic products to increase a heat sink’s tolerance to high temperatures.
By comparison, mixing aluminum and carbon is not recommended, because the combination creates a galvanic couple, which causes rapid corrosion. Because of this, copper is suitable for such pairings. Carbon fiber conductivity is known to present problems in marine environments, due to its ability to facilitate galvanic corrosion in fittings.