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68 DESIGN007 MAGAZINE I OCTOBER 2019 moval of the contaminant. Ultimately, leaving contaminants on a PCB before encapsulation could lead to shorting and will result in the premature failure of the unit. 5. What Are the Consequences of Taking in Too Much Air When the Resin Is Being Mixed? Taking in too much air during mixing can cause a whole world of pain; this is a very com- mon problem. The incorporation of air into the resin is to be avoided at all costs, as exces- sive air can lead to a lower-density material being created. In the case of mixing machines that dispense by volume, this means that there is insufficient resin being applied once the air has been released during the pouring and ini- tial curing time of the resin. If the air is trapped in the final cured resin, this can lead to pre- mature failure of the resin due to voids being created, which are weak spots, particularly for thermal and physical shock. The actual resin thickness applied will be lower than it appears, resulting in potentially lower performance and premature unit failure. If the cured resin containing entrapped air is subjected to pressure or vacuum, the resin could rupture, exposing the PCB and compo- nents to the atmosphere. If the void created by the trapped air is directly next to a com- ponent or copper tracks, it acts as a concen- tration point for static charges to built-up. In certain applications, this can reach an energy level that is powerful enough to punch its way through the resin layers to ground itself and cause a short circuit. I can't emphasise enough how important it is to give very careful atten- tion to the prevention of air entrapment. Future Columns When it comes to discussing the choices, applications, and protective properties regard- ing resins, there's a great deal more to cov- er. In my future columns on resin systems, I hope to provide some useful tips and design advice that will help you achieve the highest level of circuit protection whilst guiding you through the pitfalls and pain points that are best avoided to prevent shorting and prema - ture unit failure. DESIGN007 Alistair Little is global business/ technical director—resins—at Electrolube. To read past columns from Electrolube, click here. Also, visit to download your copy of Electrol- ube's book, The Printed Circuit Assembler's Guide to… Conformal Coatings for Harsh Environments, as well as other free, educational titles. Scientists from the Max-Born Institute for Nonlinear Optics and Short Pulse Spectroscopy (MBI) have demon- strated for the first time how to tell apart topological materials from their trivial counterparts within a millionth of a billionth of a second by probing it with ultra- fast laser light. Although the topology of the system is deeply linked to the be- havior of electrons in it, the im- print of topological properties on electron dynamics at the time scale of a millionth of a billionth of a second has not been discovered up to now. This pro- cess lasts merely an infinitesimal part of a second but is enough for an electron to "feel" the fine difference between the energy structures of trivial and topological insulators and "en- code" this information into the emitted light. The theoretical proof of this ef- fect could bring forward the im- plementation of topological mate- rials in optically-controlled elec- tronics. (Source: Max-Born Institute (MBI)) Spying on Topology

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