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36 The PCB Design Magazine • November 2017 This example assumes dimensions and di- electric constants of standard FR-4 materials. More dramatic increases in plane capacitance can be achieved using dedicated C-ply materi- als, which can have thicknesses well below 1 mil and dielectric constants greater than 10. Summary There are several benefits to implement- ing HDI technology, including routability and electrical performance. One aspect of electrical performance, power integrity, is influenced sig- nificantly using HDI technology. Whether it be the reduction in plane perforation, or the re- duction in mounting inductance of capacitors, or the increase in embedded capacitance of the board, an HDI board can have superior power integrity when compared to a traditional board design. PCBDESIGN THE IMPACT OF HDI ON PCB POWER DISTRIBUTION References 1. "Power Integrity Effects of HDI," by Pat Carrier and Happy Holden. Craig Armenti is a PCB marketing engineer for the Board Systems Division of Mentor, a Siemens business. Armenti has more than 25 years of experience in the EDA industry. He has held marketing and application engineering positions with several major telecommunication and software companies. Scientists at The University of Manchester have fabricated highly miniaturised pressure sensors us- ing graphene membranes which can detect min- ute changes in pressure with high sensitivity, over a wide range of operating pressures. Writing in Nanoscale, Dr. Aravind Vijayaragha- van and recently graduated PhD student Dr. Chris- tian Berger have shown that it is possible to make an atomically thin membrane of graphene float just nanometers above the surface of a silicon chip. When pressure moves this membrane closer to the surface of the chip, the resulting change in capacitance is measured to read out the pressure change. By fabricating thousands of such floating membranes next to each other, a device can be made of exceptionally high sensitivity to pressure changes. Dr. Vijayaraghavan said, "Despite its amaz- ing strength, a single atomic layer thin graphene membrane is impossible to grow and handle with- out causing cracks and pin-holes, which would lead to the failure of the device. "In order to overcome this, we use this graphene membrane in conjunction with a very thin polymer support layer, which allows us to produce thousands of floating graphene membranes closely packed into a small area, resulting in this highest performance pressure sensor." Dr. Vijayaraghavan and Dr. Berger have established a spinout company, Atomic Me- chanics, with a view of commercialising this technology. Dr. Berger, and fellow PhD stu- dent Daniel Melendrez-Armada, were also recently awarded the Eli and Britt Harari Gra- phene Enterprise award for their touch inter- face concept based on this pressure-sensor technology. Graphene Performs Under Pressure