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10 The PCB Design Magazine • November 2016 Andy Shaughnessy is managing editor of The PCB Design Magazine. He has been covering PCB design for 17 years. He can be reached by clicking here. Other bits of interesting info from our via survey: • About 85% of respondents said they use blind and/or buried vias • 83% use thermal vias • Only one respondent uses landless vias; many said their fabricator couldn't manufacture them if they asked • Dog bone and via-in-pad were the most popular methods to breakout vias for BGAs • Many readers have never used or even heard of landless vias or back-drilling vias We asked what you wanted to know, and as usual, you were not shy. In a typical cry for help, one respondent asked for an "inexpensive method to increase packing density before re- sorting to microvias and/or blind and buried vias." Another asked, "What is the difference between tented and capped vias?" Still another wondered, "How do we form vias that are con- ducive to plating?" As you can see, vias are subject to all sorts of challenges—electrical, chemical, and mechani- cal—all of which can lead to increased cost and lower manufacturing yields. Much of this confu- sion seems to be caused by a lack of information about fabricators' via capabilities. To paraphrase an answer given by several respondents, "What is the smallest via that can be reliably manufac- tured in North America, and elsewhere?" All of which brings us to our November is- sue on vias. This month, we have a cover story by David Wolf, vice president of technical mar- keting for Conductor Analysis Technologies. Wolf takes us through the company's analysis program and highlights some of the trends and problems areas he sees in via structures. He also details his work with IPC on the Process Capa- bility and Relative Reliability (PCQR 2 ) assess- ment. Mark Thompson of Prototron Circuits ex- plains some of the typical via missteps and mis- cues that he sees in from his viewpoint in the CAM department, including when to use meth- ods such as via stitching, via-in-pad, epoxy fill. He also provides a primer on calling out toler- ances for vias. Martyn Gaudion of Polar Instruments dis- cusses the link between vias, modelling and sig- nal integrity, with a look at what a transmission line signal "sees" as it enters a badly designed single-ended via. We also have an interview with Sun- stone Circuits' David Warren, who discusses the company's shift into the RF and micro- wave market, and how Sunstone plans to gain market share in this competitive arena. It's hard to believe that it's November, partly be- cause it's still 75° every day here in Atlanta. But DesignCon and IPC APEX EXPO are just around the corner. I'll see you next month. PCBDESIGN THE HOLE TRUTH Researchers report in the journal Angewandte Chemie that a highly concentrated electrolyte so- lution may make the sodium–oxygen battery more stable, and therefore more practicable. Sodium–oxygen cells surprisingly do not produce sodium peroxide, instead making mainly sodium superoxide (NaO2), which can be almost reversibly converted back to the elements during charging. By using Raman spectroscopy of NaTFSI/DMSO electrolyte solutions in conjunction with computa- tional simulations, the scientists were able to explain why this is so. The researchers built a small battery with this sys- tem. It demonstrated good electrochemical prop- erties and underwent 150 charge/discharge cycles without any notable loss of efficiency. In contrast, cells with a dilute electrolyte solution could only last for 6 cycles. Salty Batteries

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