Issue link: https://iconnect007.uberflip.com/i/1284035
SEPTEMBER 2020 I SMT007 MAGAZINE 69 you may not even know about it; they just went ahead and hand-placed something for you and didn't tell you. Something didn't quite fit, or it was really tricky, and they had to go hand-rework things. You may not know if you aren't specifically trying to ask, "Was there any issue with panelization? What could be better? What was different?" That's another really big gotcha in fab notes, call out to score those tabs. By default, shops do not score them; for production, that is com- mon, but in prototype, it is needed. I don't know how many places still use wave solder, but that's another important issue for where you're placing your surface mount components so that things can properly fit on the pallets to go through wave solder properly. There's a cer- tain clearance you have to have. Johnson: Like so many functional roles, there used to be a job for this, and the job has gone away. Now, the people doing the job don't have the history, tribal knowledge, or intuition to get it done properly and effectively. Is that a fair statement? Warren: I would say so. I was lucky enough when I started that I was young and a couple of designers where I worked took me under their wings and taught me the ins and outs. Not everybody has that. It really is up to a designer to make sure that they're paying attention to what's going on and asking the right ques- tions and learning from mistakes for one thing. That's how you're going to get that knowledge, but a lot of it's been lost because those jobs just don't exist anymore for most companies. Johnson: In this case, it's still important for them to pay attention to it and how it's going to fit into the mechanical enclosure. Kolar: It's really an awful thing to find a fun- damental mistake once you get to assembly because you've spent so much time and money on the physical boards, you may have used parts that are irreplaceable. It's really awful to find out that information that late in the game. Everything that can be done to proactively look for potential errors and potential issues up front is critical because you're pretty much putting the project on hold and starting over at that point, depending on what issue it is. Warren: I had a love/hate relationship with our manufacturing engineers in the jobs I worked with, but they saved me I don't know how many times from looking like a complete idiot by catching things that we just didn't notice. As I said, you learn from that process. I learned a lot from manufacturing engineers. Kolar: And ask as much as possible of the cus- tomer. "What is this going to go inside of? What does this mate to? Depending on the tool, can I get a 3D model that I can put into the tool, overlay it, and see if there are any clearance issues? Can I get a DXF of the enclo- sure? Can I find out what it is mating into?" The tools these days are sophisticated enough to do multi-board checks. Andy Shaughnessy: What advice would you give to designers as far as things they could do to make things easier at the assembly level? From what I understand, most designers don't really think much about assembly until they get up into the million parts. Kolar: One is making sure that they have a good assembly diagram that has all of the polarities and PIN1s called out. Especially once you get to production, most production boards don't have silkscreen, so it is really critical the assem- bly diagram is good. For ones that have it, cleaning up their silkscreen. We get a number of customer boards that have silk overlapping parts, and we have to tell the vendors to trim it off in fab because the customer's designer just didn't even bother to pay attention to it. All those things make the assembler's life a lot harder. They do use that silkscreen during the QA process. Then, think about, "How big is this board? How densely are you placing things to make rework possible, especially if it's an earlier generation of a board? Are you adding test points? Are you making some recommen- dations that make it easier to test?"