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May 2017 • The PCB Design Magazine 51 of processing are important, conformal coat- ings will always be the preferred choice, particu- larly as the thin cured film of a modern, well formulated coating can provide a high level of protection in any case. At this point, I can't re- sist coming back to the new two-part confor- mal coatings that I mentioned earlier, as they have rather muddied the waters as far as mak- ing that choice between potting and coating is concerned. Two-part conformal coatings can be applied relatively thickly without risk of crack- ing, giving a sharp edge coverage that performs somewhere between where a conventional con- formal coating fails and potting is required. A two-part conformal coating's environmental protection capability is also rather impressive. For example, in environmental chamber tri- als simulating highly condensing conditions, while a urethane resin potted assembly gave the highest overall values in terms of circuit pro- tection—and showed the least change during condensing events—the very large difference in thickness between it and a two-part conformal coating didn't show a large increase in perfor- mance. Indeed, the two-part coating achieved much the same results as the potting compound at one tenth the thickness. Despite these advances in conformal coating chemistries, potting and encapsulation resins will always offer the highest level of protection for PCBs, whether used to protect against me- chanical shock and vibration, thermal cycling, chemical attack or the presence of high voltages where maximum dielectric strength is needed to avoid damaging discharges and leakage cur- rents. The trade-offs are added weight, loss of rework capability, longer processing times and high cure temperatures. If you do experience problems choosing between these methods of circuit protection, remember, there are experts out there to help. And it is always worthwhile taking the trouble to test alternative methods of protection, pref- erably at the prototype stage before you make your final choice; the experts are ready to help you with this task as well. PCBDESIGN Alistair Little is technical director of Electrolube's Resins Division. TO ENCAPSULATE OR COAT: THAT IS THE QUESTION Researchers of Karlsruhe Institute of Technology (KIT) and their European partners plan to develop an innovative sulfur-based storage system for so- lar power. The pre-development work under the PEGASUS project will be funded by the EU with about EUR 4.7 million. The long-term goal of PEGASUS is the devel- opment and demonstration of an innovative solar power tower facility. A solar absorber is combined with a thermochemical solar power storage sys- tem based on elementary sulfur and sulfuric acid. The partial project executed by KIT focuses on the technical implementation of combustion. It is planned to develop a lab-scale sulfur burner for stable combustion in the range from 10 to 50 kilo- watts at high power densities under atmospheric conditions and temperatures higher than 1400°C. Elementary sulfur is produced by the dispro- portionation of sulfur dioxide, i.e., conversion of sulfur dioxide into sulfur and sulfuric acid. The fo- cused sunlight of the solar power plant supplies the process heat with the energy and temperature required to close the sulfur cycle and to convert sulfuric acid back into sulfur dioxide in the pres- ence of suited catalysts. Use of the stored energy in a burner makes these power plants capable of providing base-load power. In the long term, system costs will be lower than estimated for photovoltaic systems. Using Sulfur to Store Solar Energy

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