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PCBD-Nov2016

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28 The PCB Design Magazine • November 2016 .004" hole, you will need to look at laser drill- ing. The laser-drilled hole uses the pad and cap- ture pad to register so these very fine laser holes typically have excellent registration, an obvious benefit for very dense parts. Stacked vias are, as the name suggests, layer formations of very thin substrates with vias di- rectly on top of each another. They typically are only used when board real estate is at a premi- um. Clearly the via is an ever-changing multi- functional structure. I have barely scratched the surface of the various uses of vias. Note from a Fab standpoint on a Common Drawing Note A common drawing note involves adding teardrops to all via terminations. A teardrop is added where the trace intersects the pad, in an effort to mitigate any misregistration of the via at the trace/pad intersect area. The problem is that vias are typically not on any specific grid and are sometimes placed very close to other metal features, making "tear- dropping" difficult and sometimes not possible without creating further gap issues. I have enjoyed discussing the various uses of vias this month, and I hope you all learned a few useful tricks that will help you the next time you face a via problem. I will write another column on vias in the not-too-distant future. As always, I appreciate your time. If you have any questions or comments, feel free to contact me. PCBDESIGN Mark Thompson is in CAM support at Prototron Circuits. Figure 3: Stitching vias in a ground strap. Figure 4: Vias stitched on either side of an impedance-controlled structure may provide better signal integrity and EMC. Engineers at the University of Cali- fornia San Diego have fabricated the first semiconductor-free, optically- controlled microelectronic device. A team of researchers in the Applied Electromagnetics Group led by elec- trical engineering professor Dan Sievenpiper at UC San Diego sought to remove roadblocks to conductivity by replacing semicon- ductors with free electrons in space. However, liberating electrons from materials is challenging. "Next we need to understand how far these devices can be scaled and the limits of their performance," Siev- enpiper said. The team is also explor- ing other applications for this technol- ogy besides electronics, such as photochemistry, photocatalysis, enabling new kinds of photovoltaic devices or environmental applica tions. Semiconductor-free Microelectronics Are Now Possible, Thanks to Metamaterials HEY, THEY'RE JUST VIAS—OR ARE THEY?

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