Issue link: https://iconnect007.uberflip.com/i/1284035
68 SMT007 MAGAZINE I SEPTEMBER 2020 that into the board and put in exactly what they've specified. That's what all their auto- mated testing will be reliant on. Once you get to a production level, you see that coordina- tion and that very careful specification. Warren: A five-cent difference in cost when you're building a million versus 200 makes a big difference. Johnson: What are some of the "no-nos" that assemblers are going to point out to you right away? We already talked about overlapping parts. Kolar: The other thing that's really hard on them is a very different density of parts right next to each other. If you have lots of tiny pas- sives, and then tall shadowing parts next to them, that's an issue. Not only does it make rework almost impossible, but you can't heat the different coppers at the level they need to properly solder. You're either going to get a cold joint on one or have part sliding issues on the other. One is really paying attention to the density of parts as they're near each other and closeness. We do a lot of boards that are below IPC recommended spacing requirements. When you're getting to consumer devices, we have to do that. Again, it's about working with the assembler to see what they're comfortable with. Warren: One of the things I always come back to is "just because you can doesn't mean you should." Anyone associated with lay- outs knows that most land patterns have IPC- defined or customer-defined courtyards, but just because you have no DRC errors doesn't mean the two parts should be butted up to where the courtyards are touching. A lot of times, your surface-mount courtyards are set up for cramming in surface mount parts, not against a large through-hole part. I don't know of anyone who has these anymore, but we used to have manufacturing engineers. They would go through the boards and make sure that before it went into being fabricated and assembled, the components were placed prop- erly, and that we didn't have any gotchas or stuff like that. That's fallen mainly on the EEs now and the designers. It's a learn-as-you-go process, unfortunately. There's a whole section in IPC about large components, valleys, and shadowing. If you followed that guideline and have a really small product, you might not be able to make that product, so you have to infringe on it. There's where it's really important to include the assembler to get DFA feedback, as Jen said. For me, it's a luxury because we have proj- ect managers who handle most of that for me. I just tell them we need DFA, and here's the board. They'll do it, and I'll get a report back. For most places, they don't have that luxury, so designers need to be more proactive, push that with their own internal or external cus- tomers, and remember to do it. You have got to be assertive enough to be able to make sure that these get done. Kolar: Then, it's working with the assemblers. Again, we do a lot of work that ultimately goes to production. In the prototype builds, assem- blers, especially prototype assemblers, will just make it work. If there's a panelization issue, Dan Warren