Issue link: https://iconnect007.uberflip.com/i/1276973
14 DESIGN007 MAGAZINE I AUGUST 2020 Shaughnessy: Kelly, on your side, you've been dealing with a lot of these manufactur- ing notes. Tell us about your engagement with manufacturing notes and some of the issues that you've seen. Kelly Dack: It's a pleasure to speak with Dana. I think it's good to clarify that notes are meant to specify or define what a designer wants in a bare PCB. As we go through a list of notes, we need to be able to communicate and define and specify the bare board in order to end up with what we want. For instance, a board outline can be manu- factured in several dif- ferent ways. We don't necessarily need a manufacturing note to tell the board shop that the edges of the board shall be routed unless it really matters in the rest of the design or that the board edges shall be V-scored. We do better by defining the board outline and tolerance, let- ting that stand as the specification, and allow- ing the manufacturer to deliver the specifica- tion. Korf: I agree. As I tell people, "Tell me what you want, not how you want me to do it. I won't tell you how to design the board, and you don't tell me how to build a board." The most common problem I see in notes is that, a lot of times, the designer cut and paste from other boards, and they may not make sense. Or you have new designers who aren't familiar with the specs. My favorite one is, "This board shall meet IPC Class 3 requirements," yet the annular ring doesn't. You have to go back and say, "Your board doesn't meet Class 3, and I can't get there with this design. What do you want me to do?" You hear back, "Well, make it Class 2." Dack: I can totally relate. Working for an EMS, I see a myriad of notes that just don't make sense. Sometimes, we can tell that they've been cut and pasted, and the designer has no clue about what they are inflicting on the bare board manufacturer. I just had a scenario where a board requirement came in. The mate- rial was FR-4, and there were not too many notes. Our job as an EMS provider is to get this board quoted at several board shops with which we have relationships. We're going to get numbers based on what the bare board shop says they can do. Believe me, their job is to win the quote, and they're not going to do it by quoting the highest-rate materials or the highest Tg materials. They're going to presume that they can use the lowest-rated materials. We had a board that was quoted at 130 Tg material, but it needed to be changed to 170 Tg because of all the different thermal excursions that it would be going through in assembly. A high-temp material would have been a better choice, but because it wasn't specified, we ended up wasting a lot of people's time. Actually, the designer, through his lack of specification skills, ended up wasting a lot of people's time. Korf: Back when high-end boards were U.S.-cen- tric or European-centric, the fabricator wasn't as cost-sensitive. The fabricator would pick a material beyond maybe what the designer wanted because we knew better. It would prob- ably last better or perform better. Then when we started shifting to Asia, they did exactly what you said. You said FR-4, they quoted standard Tg FR-4, and they always came in cheaper. We had to kind of retrain everyone to say, "Give them what they say, because that's the world now. Don't give them more than they're will- ing to pay for." We had a great example in China a couple of years ago. A company came in and just said FR-4, so we put in a halogen-free mid-Tg mate- rial, and we built the prototypes in a couple of cycles. It went just fine. We got it quoted. Correction quotes went out, and everyone was happy. Then, the final drawing came in, and it said, "We want high-Tg FR-4." "But that's not what you said on the prior two revisions." Everyone freaked out. "It's the fabricator's fault." Kelly Dack