Issue link: https://iconnect007.uberflip.com/i/1520701
30 DESIGN007 MAGAZINE I MAY 2024 To me, producibility and constraint management are like a belt and suspenders. ity expert, and say, "is is what I want to do. We need 12 layers; we're going to do micro- vias, we're not going to stack them, and we need to meet these specific electrical require- ments." He understands all that. He'll size the vias for me, knowing which drill will be used. You don't want to specify a drill in your design that's between sizes. He has the intelligence, education, and experience to know because he was selling boards in the industry for 15 years. I would say that the companies who aren't sure about stackup are just throwing it out there because someone told them it looks good. Ask the board house, "Do you have someone in- house who can do this?" If not, they're not a good board house. Dack: The biggest point you make is to have it done up front. In the scenario I mentioned, the stackup is done three months after the boards have been ordered. e stackup is the spine of the design. Without it, you can't go anywhere. I could design the board for six weeks, and then have to change it all. All my clearances just go out the window. e boss will say, "What do I pay you for? Why are you making this so hard? I don't have six more months to get this done." I recently had a design with over 400,000 vias. It took me 14 months, and it was an intense design. We had to redo it several times because we had to add new vias and layers and change our scope and everything. It took us forever. But when we were done, it got fabricated and assembled. ey sent it to test and, aer five months of testing, there was not one problem. at tells you a lot about the board house: With that many holes to match, just imagine how many drill bits they went through for one board. Shaughnessy: What would you recommend if a designer is trying to avoid overconstraining or underconstraining his design? Front-load your design process with people who are experts at what they're doing. I'm in a big company. We don't have just power integ- rity and signal integrity guys; we also have people who are experts with the materials. ey know what the material is capable of with respect to SI and PI, especially the SI. ey are experts at choosing the materials, so we con- sult them first. I'll ask, "Do I have to use Rog- ers? Do I have to use exotic materials?" Again, at most board fab houses, they have somebody there, and if they don't know, they'll tell you who to talk to. Talk to the materials experts and the board shop. I would leave it to the experts and not leave it to a board designer. But yes, there are people using FR-4 for high-speed designs today, while other people will never do that, and they'll rely on Rogers. Shaughnessy: So, the designers shouldn't be selecting material anyway? I'm not trying to be mean, but most design- ers don't know materials. I'll leave it to the guys who know what they're doing, and I'll try to learn from them. As far as I'm concerned about constraints, we've also made it part of our pro- ducibility to put in all the constraint manage- ment of our design up front, so we don't have any issues later on. To me, producibility and constraint manage- ment are like a belt and suspenders. Once you set up those two initially and know what you're doing, you just get it done. A lot of designs are iterative, especially RF. But chances are, you won't have to change things around a lot because you've done those two things. If you get those two things done at the front end, your chances of being highly successful are far better than not doing it at all. Shaughnessy: Thanks for speaking with us. Any time. DESIGN007