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Design007-Jan2021

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46 DESIGN007 MAGAZINE I JANUARY 2021 decisions that are going to affect the manufactured PCB earlier in the design process. And you're bringing fabrication knowledge back to the OEM engineers and designers. Shaughnessy: So it's a matter of designers needing to know more about the fabrication process. Hargin: Right. For instance, I went to a doctor this week, and this is a perfect anal- ogy. I go to this particular specialist every six months or so, and he doesn't remember what we've discussed in the past. He just had a patient leave his office. He got my file folder out, and I can see him thinking right in front of me, looking through my folder. I whip out my laptop and flip it open, and I've got graphs and Excel tables. I've mapped out my history of medications and the resulting symptoms in Excel, and I'm showing it to him. I have better data than he does. I used to hear that engineers are the tough- est consumers in the world to sell to, because they analyze everything. Well, engineers need to do that with stackups and materials. Don't just kick the can down the road and think your fabricators are going to do everything perfectly. And I've had engineers say to me, "Why do I give the same set of requirements to three dif- ferent fabricators, and I even specify the mate- rials, and I get three different stackups back?" In response, I've told them that they need to take more control of the process and leave less margin for the individual fabricators to figure things out separately. Shaughnessy: In their defense, wouldn't the fabricators say that three different fabricators are naturally going to be optimizing for differ- ent processes, chemistry, and sweet spots? Hargin: I think that's a myth, and I don't fault you for saying that at all, Andy. I think that's a common perception. But I think it's a mytho- logical perception that a guy in Shanghai man- ufacturing a board has a different process than one in Guangdong. I know there are differences in chemistry and how they do things, but in the end, you are specifying a board with impedance targets and toler- ances, thickness targets and toler- ances, and they all need to meet those specs. What I'm talking about is at the field solver level: they're coming back with differ- ent results from different tools. Why is that? I think it comes down to operator differences. When you get a stackup back from PCB fabricator A and PCB fabricator B, it's two different people probably running two different field solver tools. So right there you've added two degrees of freedom to the stackup design process. And different fabricators will send stackups back to you in different formats, too. One will send you a PDF, the other will send you an Excel spreadsheet, and if you have a third fab- ricator, they're going to send you a JPEG. The cattle have gotten out of the barn, as it relates to stackups. Who owns the fact that the cattle are out of the barn? It's the OEM design team; it's their hardware, and it's their jobs on the line. So if your cattle are out of the barn, what do you need to do if you're a farmer? I come from farming people way back when in the Midwest. And the first thing you need is a barn. You can't get them back in the barn if you don't have a barn, and to me, the barn is the stackup software. The second thing you need is a fenced area, which is a process to get those roaming cattle back inside the fenced area leading to your barn. Shaughnessy: That's interesting. So, a lot of this confusion could be eliminated if OEMs took ownership of the stackup design process. Hargin: Yes. Don't rely on your fabricators to do all that. They don't talk to each other; you're the only one talking to each one of them as the OEM design team. They don't collaborate; they compete with each other. And so, you've got to own the entire process. Bill Hargin

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