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26 DESIGN007 MAGAZINE I NOVEMBER 2020 Feature Interview by the I-Connect007 Editorial Team Andy Shaughnessy, Happy Holden, and Dan Feinberg recently met with James Hofer, general manager of Accurate Circuit Engi- neering, to discuss via design techniques and via reliability from the fabricator's view- point. As Hofer explained, even with open lines of communication between the designer and the board shop, there are plenty of vari- ables to contend with regarding proper via design, especially when working with PTFE materials. Andy Shaughnessy: James, start by telling us some of the problems that you see with fail- ures in vias and microvias. James Hofer: I face a couple of challenges. Designers tend to want to do HDI designs with laser-drilled vias with aspect ratios of 1.5:1 or 1.8:1, or they want to do laser-drilled vias through multiple layers without remov- ing pads. I don't yet have a reliable copper-fill process that gives me as flat a surface fill as I want. As you know, most of our product is PTFE. Stacking laser vias on PTFE and copper- filled vias presents a couple of challenges. I see more and more customers want a PTFE dielectric, and they want to put a 4- or a 6-mil via in it. That presents issues both in the drill- ing of the via and with the plating of the via. I see a lot of that, so I find myself trying to redo designs after the fact with most customers. Shaughnessy: They're trying to use HDI when they don't necessarily need it. Hofer: And when they don't necessarily under- stand some of the give and take that goes with it. They don't want to abide by some basic principles and rules that we manufacturers have to live by. Happy Holden: Why would they get into HDI but not do any basic investigation on how to optimize drills or design with it? Hofer: I agree. That's exactly what we face. Holden: Or they read about it or heard about it, and they're going to use it, even though they don't know anything about it. HDI Design, Landless Vias, VeCS, and More

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