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Andy Shaughnessy, Happy Holden, and Dan Feinberg recently met with James Hofer, general manager of Accurate Circuit Engineering, to discuss via design techniques and via reliability from the fabricator’s viewpoint. As Hofer explained, even with open lines of communication between the designer and the board shop, there are plenty of variables 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 failures 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 removing 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 drilling 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 understand 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.
Hofer: That sums it up right there. The majority read something about it. Perhaps they read the first couple of paragraphs of one of Happy’s articles and think, “Great, I can do this,” and then off they go. It is far more appropriate to discuss with the manufacturer before you implement the technology.
Holden: The HDI Handbook is free. It goes into reliability and plating and metallization, materials, aspect ratio, and cycle integrity.
Dan Feinberg: Why wouldn’t they read it and use some of those recommendations? That’s a good investment.
Holden: Or just type HDI into Google or Yahoo.
Shaughnessy: Don’t designers communicate with you beforehand? I know they say they’re going to talk to their fabricator, but do they really?
Hofer: No. We face that problem pretty much on a daily basis.
To read this entire interview, which appeared in the November 2020 issue of Design007 Magazine, click here.