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Design007-Dec2023

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DECEMBER 2023 I DESIGN007 MAGAZINE 13 be done from a board outline standpoint. Now, how do we process that and incorporate DFM? ere are other fabrication consider- ations such as excising, because every board, regardless of its shape, has to be nested inside a manufacturing panel for the bare board manufacturer. How do we break an unconvention- ally shaped board out of a panel? Moyer: e other big one from a manufacturing point, espe- cially with these smaller and smaller boards, is stackup. Too many engineers and design- ers now are just leaving a generic note saying, "Make my board out of FR-4," and not consid- ering how fragile this stuff is, the Tg you need, the laminate thicknesses you want, and so on. Back in the day, boards were 62- or 93-mils thick with four layers, and they were built like a Mack truck. But now we're trying to make Fitbit trackers and you have 20 layers of board in something that's 30-mils thick. It's as thin as paper, flexible, and fragile. ere are definitely manufacturing challenges there. We have to remember one other thing too. Nowadays, the boards are getting so small, with some of these oddball jumpers (like in the wearables market), that you have to assem- ble them in a pallet array. It means that now die-cutting a bare board out of a panel could change. How do you manage to die cut so it goes around all these components soldered onto the board and not damage them? Dack: Have you ever rolled out cookies at Christmas? It's like a cookie cutter. You have the sheet of cookie dough and stamp the cut- ter through. But on an assembled board, you have all the components on there. If I have a big LCD module on my board and I bring a big steel die cutter down, I now have a mechanical interference, and potential damage to my com- ponents. Moyer: Typically, good board designers will design the break- off rail or the panel ahead of time in the capital before it ever goes to the fabricator or the assem- bler. Sometimes if it's still just a small board, you can put a note in that says, "I want this in a 4"x4" assembly pallet array in the panel. e fabricator will stamp out the array for the assembler and then have the appropriate break-off or removal material that the assembler can remove the individual boards from. It's a designer's job to know where their stuff is going. I tell all my students that if your com- pany is sending the board to an assembly com- pany and letting them subcontract the fabrica- tion, they should say, "at's fine. I still want to know which specific fab company you're using, and I want to know what the panel looks like." Dack: Kris, I love your fortitude, and I totally agree that's what we should do. However, the feedback is not working for you because nobody knows where their boards will be built. I deal with designers, and it's a hot-but- ton around here. I'm dealing with 20 designs a week, and you would think that the PCB designer didn't know much about anything. Moyer: I'm changing that with my classes (laughs). Dack: Telling designers that they must have information about where their designs will be manufactured is a noble concept. But I think we've established from speaking with PCB designers, for the time being, that they usually have no clue. Nobody's telling them, because it's a dynamic situation based on quoting, that your boards can go to India based on one set of pricing, and then suddenly they're in Asia for another set—just because they want to save five cents on a board. Again, it's back to this volume thing. Kelly Dack

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