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78 DESIGN007 MAGAZINE I SEPTEMBER 2020 time, would you please make sure to regenerate the drill drawing." One of the things that we added in our fab notes that have uniformly saved us at least 24 hours every time is that we call out overhang- ing parts in assembly. If you haven't told the fab vendor in advance that you have overhanging parts, how are they supposed to know? They send you back a panel to review, and then you say, "Wait, I need X millimeters of clearance in each of these different areas." People don't think about assembly when they do fab notes. They think the parts should be in assembly, but they're fundamental to the panel. That's one example of something that massively improved our throughput. It's so simple. Shaughnessy: What would you say are some of the most common problems that you see in fab notes that just never seem to go away? Kolar: Some of the biggest problems are not updating drill tables, not having the dimen- sions match the Gerbers, or having every pos- sible impedance in the world in the table, even if not used. Another problem is having multi- ple boilerplate notes that don't apply and may contradict. Some companies have boilerplate fab notes that are like, "If it's a production build, do this, or for an ENIG finish, do this, and for OSP do this." Another problem we see often is not calling out important things, such as, "Don't add thieving in this area with all the copper cleared out." Dan Warren: I want to touch on the impedance. It's pretty common that you'll get a layer stack back from your fab shop up front, so you tell them, "I want 90-ohm pairs, 80-ohm pairs, and 50- and 45-ohm single-ended." They'll come back, and every layer will have that calculated. Some people put all of that in the fab draw- ing, even though that 90-ohm pair may only be on two layers. If it's called out on any of the others, most fab shops will stop and question you: "We can't find this on any other layer. Is it supposed to be there?" You just lost a day. Don't put anything on the drawing that's not in the database. And I know it's tedious, but I go through every one and match my impedance on my layers and make sure that table's up to date. There's nothing extra in there. I'm not saying I don't miss one once in a while, but I make an effort to ensure there isn't extra data in there. We've gotten people out of the habit of just copying the layer stack from the fab shop. Kolar: That's a common one, in addition to not calling out intentional shorts. Warren: We had quite a few questions on some of these common areas before our current process. Once we added to our processes and made it part of our notes and it became a part of our stock drawing example, we don't get many calls on that anymore. But as far as the stuff not getting updated, anything that has to be updated manually is usually the stuff that doesn't get updated and causes a problem, even if it's just something simple. One of my pet peeves is why have a note with the drawing number in it, the drawing number is already on the drawing, and then you added another note over here with a call-out, and you have to update all three? Kolar: We treat design as a first-order engineer- ing effort. We care about the quality of what we put out. We want the boards to look nice, not just work. We want the product to be con- sistent and look nice. That's something we also really indoctrinate in our folks, and we've had to indoctrinate in the new folks. "No, it's not just throwing slop together and getting it over the wall. It does matter how it looks. There's a reason why, and you'll learn when you get to more complicated designs." Warren: As Jen said, we try to let everybody know how important it is. I've had to flat-out tell a designer, "If you keep producing this, you're not going to be around here much longer." And Jennifer Kolar

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