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AUGUST 2019 I DESIGN007 MAGAZINE 69 conductive encapsulation products available, largely based on epoxy, silicone, and polyure- thane technologies and with varying levels of viscosity. These thermal management solu- tions are particularly suitable for circuitry ex- posed to the harshest environments and pro- vide high protection whilst enabling even heat distribution to increase the device lifetime. It's All About Thermal Conductivity, or Is It? This is commonly misunderstood, but it's not all about thermal conductivity because thermal conductivity values are measured from bulk material to give a comparison of one product to another; they are not a true reflection of the performance in the final ap - plication. That is related to the thermal resis- tance under the exact conditions of use. Don't be fooled by high thermal conductivity values, which can be misleading due to the many op - tions of testing available. In addition, a high thermal conductivity product may also have a high thermal resistance if it cannot be applied correctly in a thin film at the interface. Any ex - cess material or non-uniform application will result in a variation of heat distribution across the interface, thus leading to inefficient heat transfer. How Do I Achieve the Most Efficient Heat Transfer? As a rule of thumb, apply thin, uniform lay- ers with the minimal amount of product re- quired to remove all air gaps but leave no excess of material. Remember, the heat sink is far mor e conductive than the thermal inter- face material. The job of the interface mate- rial is to remove air so that the heat sink can efficiently transfer heat away from the compo- nent/device. Conclusion When it comes to the choice and applications of thermal management materials, there's a great deal more to discuss, and over the follow - ing months, I hope to provide more useful tips and design advice that will help you in your quest for reliable circuit protection. DESIGN007 Jade Bridges is global technical support manager at Electrolube. To read past columns from Elec- trolube, click here. Also, visit I- to download your free copy of Electrolube's book, The Printed Circuit Assembler's Guide to… Conformal Coatings for Harsh Environments, as well as other educational titles. The voltage of an LED is usually equal to or larger than the bandgap energy per electron charge. A team of re- searchers based at The University of Manchester, Uni- versity of Warsaw, the High Magnetic Field Laboratory in Grenoble and the National Institute for Materials Science in Japan have been able to demonstrate LEDs that turn on at much lower voltages. The idea to stack layers of different materials to make so-called heterostructures goes back to the 1960s, when semiconductor gallium arsenide was researched for mak- ing miniature lasers—which are now widely used. Today, heterostructures are common and are used very broadly in semiconductor industry as a tool to design and control electronic and optical properties in devices. More recently in the era of atomically thin two-dimen- sional (2D) crystals, such as graphene, new types of het- erostructures have emerged, where atomically thin layers are held together by relatively weak van der Waals forces. The new structures nicknamed 'van der Waals hetero- structures' open a huge potential to create numerous de- signer-materials and novel devices by stacking together any number of atomically thin layers. Hundreds of combi- nations become possible otherwise inaccessible in tradi- tional three-dimensional materials, potentially giving ac- cess to new unexplored optoelectronic device functional- ity or unusual material properties. From the fundamental point of view, the observed ef- fects mark an important step towards the realisation of exciton condensation and superfluidity of van der Waals heterostructures. (Source: University of Manchester) Researchers Demonstrate Low Voltage LEDs

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