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28 DESIGN007 MAGAZINE I NOVEMBER 2020 Hofer: That sums it up right there. The majority read something about it. Per- haps they read the first cou- ple 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 dis- cuss with the manufacturer before you implement the technology. Holden: The HDI Handbook is free. It goes into reliabil- ity and plating and metal- lization, 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. Feinberg: What do you consider to be the most reliable process for electroplating copper vias? Is it still a thin coating of electroless copper followed by an electrolytic? Is it a thick coating of electroless, as one company was trying to push a couple of decades ago? Hofer: Generally, the most-used process is a thin-to-medium deposition of electroless, and then into barrel plating the vias and copper plating them. Copper-filled through-vias are making an emergence, especially in mixed materials or PTFE or hybrid materials, the most tried and true method is still to plate the via, fill it with a non-conductive fill, and plate over the top. In HDI design, where we stack the vias, we're looking to offset that stack so that they're not dead center on top of each other. Holden: We have a lot more material choices today than we did way back then, but fewer laminate makers are making the materials. Hofer: I agree. They have really consolidated. Shaughnessy: Tell us about landless vias. Last year, you were doing a lot of landless vias. How did you get into that, and what are the benefits? Hofer: The main benefit is savings on real estate, and we got into that with exactly the same kind of situation we face now, where somebody wanted to stack microvias but didn't really know what they were doing. We found a way not to have to stack them, and that's with landless vias. It's a take on copper- filled vias. You make the land into the void of the drilled hole. Again, it's involving button plating and still the same copper electroless and electroplate, and then button plate to fill the hole with copper. At that point, you have a landless via. If I were asked about the biggest changes in the last 20 years, it's the fact that everything has to be smaller, more reliable, and cost less. Those are the big industry changes, and the industry has adapted. One of those things was stacking microvias and going to landless vias. That's how rigid-flex started to come in, so we could connect things without having to do a ribbon bonding, and that's where we're at today. Holden: The other big change from long ago was that technology used to be driven by the military, and today, the most advanced tech- nology is the consumer segment. James Hofer is the general manager of Accurate Circuit Engineering.

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