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November 2017 • The PCB Design Magazine 21 paste on the trace itself. Of course, as speeds get higher you probably don't want to put the paste on there. Probing just the trace is certainly an option, although sometimes probing the trace will deform the trace, so now you're introduc- ing another aspect of altering the circuit. Las Marias: Vince, from an EMS provider stand- point, what do you think our readers should consider when it comes to HDI assembly? Burns: Honestly, I think one of the best com- ments I've heard today was just more commu- nication and better communication up front. So for the design and the fab end of it, the readers should consider contacting not just the OEMs but some EMS manufacturing facilities and ask them up front what their capabilities are. If we go smaller and smaller, what do we need to do as an industry to be able to manufacture things at that level? This also goes to the component manufacturers because now we're also looking at components that have to be mounted on these boards. We need the designers and the fab guys to understand the conditions that these boards are going to go through when they get to our end and a lot of it is heat. We're concerned about the number of heat cycles we can run a board through, and how we can keep from damaging things as we go through the heat cycles. From the material aspect, we need to make sure that the materials are robust enough to withstand the things that we're going to put them through at our end. Matties: All right then. Thank you, everybody. This was great. Burns: Yeah, that was good. Bird: Thanks. Torres: Thanks, I appreciate it. PCBDESIGN THE HDI ROUNDTABLE EXPERTS DISCUSSION In a new study funded by the Academy of Fin- land, Aalto University researchers Alex Westström and Teemu Ojanen propose a method to go be- yond special relativity and simulate Einstein's the- ory of general relativity in inhomogeneous Weyl semimetals. The theory of Weyl metamaterials combines ideas from solid-state physics, particle physics and cosmology and points a way to fabri- cate metallic designer materials where charge car- riers move like particles in curved space-time. "The systems we introduced offer a route to make the charge carriers move as if they were liv- ing in a curved geometry, providing a tabletop laboratory for simulating curved-space quantum physics and certain cosmological phenomena," Alex Westström explains. Weyl semimetals are an example of recently dis- covered quantum materials that have received a lot of attention. Charge carriers in these materials behave as if they were massless particles moving at the speed of light. "We discovered that Weyl metamaterials may serve as a platform for exotic electronic devices such as the 3D electron lens, where the trajectories of charge carriers are focused much like beams of light in an optical lens," Teemu Ojanen says. The theory of Weyl metamaterials also paves the way for fundamentally new elec- tronics applications, for instance, the devel- opment of electronic invisibility devices. New Quantum Materials Offer Novel Route to 3D Electronic Devices

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