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June 2017 • SMT Magazine 45 Intermetallics, however, cannot be addres- sed in either of the same ways. Temperature therefore is an extremely critical parameter to control during long-term storage. Intermetallic growth rate is strongly temperature-dependent and doubles for each 10°C temperature incre- ase. This aging process can be slowed by appro- priate cooling. However, the risk of whisker for- mation of tin alloys increases with decreasing temperature. Studies and practice have shown that a storage temperature of 12°C is optimal to best mitigate both risks, while maintaining a storage humidity of <5% to arrest oxidation and preserve solderability. SMT References 1. Joelle Arnold, Cheryl Tulkoff, Greg Cas- well, DFR Solutions, "Solderability after Long- Term Storage." Rich Heimsch is a director at Protean Inbound and for Super Dry-Totech EU in the Americas. To read past columns, or to contact Heimsch, click here. LONG-TERM STORAGE OF ELECTRONIC COMPONENTS AND COMPOSITIONS Research from the University of Manchester has thrown new light on the use of miniaturized 'heat engines' that could one day help power nanoscale machines like quantum computers. Dr. Ahsan Nazir, a senior lecturer and EPSRC Fellow based at Manchester's Photon Science Institute and School of Physics and Astronomy, wanted to see how heat engines performed at the quantum level. Heat engines at this scale could help power the miniaturized nanoscale machines of the future, such as components of quantum computers. Dr. Nazir's research, published in the journal Physical Review E, showed that heat engines were inclined to lose performance at the quantum scale due to the way such devices exchange energy with external heat reservoirs – and more investi- gation would be needed to remedy this challenge. "Recently, much interest has focused on quan- tum realizations of engines to determine whether thermodynamic laws apply also to quantum sys- tems. In most cases, these engines are simplified using the assumption that the interaction between the working system and the thermal reservoirs is vanishingly small. At the classical macroscop- ic scale this assumption is typically valid – but we recognized this may not be the case as the system size decreases to the quantum scale," explained Dr. Nazir. "Consensus on how to approach ther- modynamics in this so-called strong coupling re- gime has not yet been reached. So, we proposed a formalism suited to the study of a quantum heat engine in the regime of non-vanishing interaction strength and apply it to the case of a four stroke Otto cycle. "This approach permitted us to conduct a complete thermodynamic analysis of the ener- gy exchanges around the cycle for all coupling strengths. We find that the engine's performance diminishes as the interaction strength becomes more appreciable, and thus non-vanishing sys- tem-reservoir interaction strengths constitute an important consideration in the operation of quan- tum mechanical heat engines." Miniaturized 'Heat Engines' Could Power Nanoscale Machines of the Future

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