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January 2015 • The PCB Design Magazine 35 that in a fabrication environment, these will start on no more than quarter-ounce copper foils. I harken back to previous columns about the general rule of thumb for etch compensa- tions based on starting copper weights. For every half ounce of copper, we do a half mil of compensation, so that when all is said and done after etch the trace is as the customer de- sires. For true .003"/.003", if we attempted to start with .5 oz., 1 oz., or 2 oz. copper, we would NOT be able to impose an etch compensation and still be able to process the resulting space. This is one you will want to talk with your fab- ricator about. I also see many more alternative surface finishes being used this coming year. For the past five years, the surface finish of choice has been electroless nickel immersion gold (ENIG). I see more of that, but I also see more electro- less nickel electroless palladium immersion gold (ENEPIG) being used for telecommunica- tions devices, tablets, cell phones, etc. Lastly, I foresee more interaction with the board houses. As the design complexity grows there are more challenges for fabricators. And I imagine we'll have many more new custom- ers with new design engineers who are not dis- suaded by the speed bumps of the past. I see this as an opportunity for the U.S. fabricators to help educate the customer about how we oper- ate and what we can do for future board fabri- cation. Not all solutions require a new process or new technology. Many times it is simply a mat- ter of understanding your customers' desires so that you become a part of their team and vol- unteer solutions. Many times it is as easy as material and sur- face finish selection based on their applications; other times it may require process changes. Ei- ther way, the extra few moments you spend un- derstanding your customers' needs will pay off in time and money. As always, thanks for your time. I appreci- ate any feedback. Please feel free to contact me. PCBDESIgN WHAT WILL 2015 BRINg? continues the bare (board) truth Mark Thompson is in engi- neering support at Prototron Circuits. his column, The Bare (Board) Truth, appears bimonthly in The PCB Design Magazine. To read past columns, or to contact Thompson, click here, or phone 425-823-7000, ext. 239. In the race to design a universal quantum computer, a special kind of diamond defect called a nitrogen vacancy (nv) center could play a big role. now a team of researchers has taken a major step forward in effectively enhancing the fluores- cent light emission of diamond nitrogen vacancy centers—a key step to using the atom-sized de- fects in future quantum computers. The tech- nique hinges on the very precise positioning of nv centers within a structure called a photonic cavity that can boost the light signal from the defect. Photonic cavities best enhance the signal of nv centers located in a "hot spot" where the cavities' resonant fields are strongest, but making sure an atom-sized defect's location matches up with this spot is extremely tricky. The team took an important first step toward this goal by controlling the depth of the diamond defects using a technique called delta doping. The technique confines the possible location of nv centers to a layer approximately 6 nanome - ters thick sandwiched inside a diamond mem- brane approximately 200 nanometers thick. The researchers then etched holes into the membrane to create the photonic cavities. The team believes they can further enhance the emission by also controlling the position of the defects in the horizontal plane and are current - ly working on possible ways to achieve full 3-D control. Diamond Defect May Lead to a Qubit Computer

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