Issue link: https://iconnect007.uberflip.com/i/1467185
MAY 2022 I DESIGN007 MAGAZINE 15 component manufacturers, or you're doing SI/ PI analysis, and iterating much more into DFM. At that scale, no, you're not. But for an average board, it's oen, "Here are my controlled imped- ances. I'm going to do my best to calculate them in Polar. I'm going to put this together and send it off, and the fab shop will tweak as needed." Matties: As Cory was describing, he's adding extra safeguards in the design to make sure it gets through. As you're pointing out, there are downsides to this approach. Why is it so difficult to get that communication up front? Grunwald: It depends on the company structure and the way they work. We work directly with fab shops a lot. But in previous companies I've worked at, the design was basically handed over to purchasing, and purchasing found whoever can supply that board the cheapest. Not knowing who it ends up with was a big deal. ere wasn't any talking with a board shop at the beginning because who knows where it would end up. Happy Holden: e danger is that suppliers may be quoting a lower price because they think they can meet the design rules, but then they discover the process wasn't so robust. ey have yield loss, which they conceal rather than talk about it. Eventually they've got to come back with this big price increase. Now you're stuck because of schedule. If you had gone with supplier B or C, that wasn't the lowest price, but they may have had more capability. When you're pushing close to the edge, a fab- ricator doesn't necessarily have the time and money to have 99% confidence that the pro- cess is robust enough to build it. And if they do, they're going to quote higher. Matties: Cory, how do you alter your process when you are designing in a vacuum? Grunwald: It depends on the end-product we're trying to develop. For a general type of board without a lot of high speed or a simpler design, you can go with bigger traces and spaces, and with bigger vias. But when you go into smaller and higher-speed designs, you just make assumptions and are willing to change the design at the DFM stage, if needed. Matties: ose assumptions can be costly. Kolar: It can be frustrating. Sometimes, we'll release the design and if we haven't been involved in the DFM and fab process, the customer may come back and say, "What the heck? is isn't buildable. Why did you design a non-buildable board? e vendor is saying, we can only do X, Y, and Z." But we never had those requirements in the first place, so it can end up with a situation where it makes us look bad. We're also hav- ing to read the Magic 8-ball. We may not real- ize that they decided to change and go with a much less-expensive vendor that can't sup- port what we thought they could, or they've changed vendors halfway through the process, and we weren't told. Grunwald: In the end, the communication will happen anyway. It's just a matter of whether it Cory Grunwald