Issue link: https://iconnect007.uberflip.com/i/1174596
OCTOBER 2019 I DESIGN007 MAGAZINE 15 sign and fabricate it beforehand. So, I wonder about printed electronics with conductive sil- ver and the dielectrics that printed electronics have. If you come up with a working proto- type, does that mean anything if you're going into medium- or high-volume production and have to switch to laminate? Hartley: No, it doesn't mean a thing because all of the parasitics change. Everything changes. Creeden: There's a theoretical simulation that is valuable to understand the target of how you want to lay it out, which is good. Hartley: Right, but do most people today know to do that without that simulation? Creeden: Yes and no because each chip that you're driving has different properties, and then the environment in which you plan to drive it in has variables. The goal is to send it through a theoretical construct, but then you must follow it up with looking at actuals. When you plug them into many of the analysis tools that are out there, there are often missing links, and tools are becoming better at finding those. For example, people will say, "I have a plane here." But I ask, "What is that plane? Because if you're going to tell me it's a power plane, I have issues." They don't understand it. A lot of times, it's from a coplanar waveguide to transition into a launchpad. All of those lit- tle parasitics add up. Hartley: Exactly. And sometimes, it's a split ground plane, which screws everything up. Creeden: I hate dual asymmetrical stripline because you can come up with an impedance coupon that looks great, but then the design- er will not follow that construct of the cou- pon; instead, they will make it broadside cou- pled. The parasitics and crosstalk are off the charts. Hartley: That's one of the things I try to teach people in my classes; if you're going to use dual asymmetric stripline, first, you have to route them in alternate directions—X and Y— in the two layers. Creeden: Good luck with that. Hartley: I understand that it's very challeng- ing, especially for high-density boards. But you also want to use copper pours on all of the lay- ers and the area around the signal so that each