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66 SMT007 MAGAZINE I SEPTEMBER 2020 apart very well. There wasn't a void in the panel where an overhanging part was or, in some cases, they couldn't even install the part because there wasn't a cut-out in the outline where an over- hanging part was, especially like a mid-mount connector that encompasses both sides of the board. Those really come back and get you. As part of our process improvements, we've documented in our fab drawings that it's required to have that information in the draw- ing, so when they go to create the panel data, those items are taken care of, and consider- ation is given to overhanging parts and proper pullbacks with the routing channel from those parts. Regarding other issues for panelization, I'm going to defer to Jen because I don't see too much once I pass that data on. Then, I can get a finished panel back. Kolar: Fab vendors don't think about assembly requirements. We have instilled in our design- ers that overhanging part input needs to be in the fab drawing because the fabrication shops are never ever going to look at the assembly diagram. Overhanging parts is one concern, and another is where you have break-off tabs. For example, if you have parts really close to the edge of the board and they're fairly frag- ile parts, or they might be really fine pitch, if you have the breakaway tabs right by those, you risk those connections when the tabs get broken away after assembly. Sometimes, we'll also want to look at calling out whether there can be breakaway tabs or not, or whether it should be V-scoring or mouse bite if we can't really afford any vibration from the breakaway at all. The same is true about calling out where mouse bites are so that they can be filed down. Depending on where it goes into a final enclo- sure, there may not be an option for any resi- due left whatsoever. Those are common issues I've seen. Another thing to consider with the panelization is the thickness of the board and how stable it is. You could get away with a full working panel, like an 18 by 24 panel, and end up with a large array that processes fine in fab depending on the technology. However, if it's a really thin design, that could be really varying and really flexible as it goes through assembly. That can cause a lot of risks. The bigger the board going through assembly, typically, the more varia- tion there is in the density of part sizes. As that's going through reflow, the more difficulty they're going to have getting that reflow pro- file correct so that it will properly solder the entire board. There are a lot of structural things. You need to be thinking about whether fixturing is required; some connectors and overhang- ing parts are really heavy. They have to be fixtured, and you want to think about where might that fixture go, and how might you con- nect it to the board even with the array or out of the array? Where do you need to have cut- outs in there? Even if there are cut-outs, the weight of the board and how the connectors mate might keep it from being flat; this also impacts fix- turing. There are a lot of things to think about where I would encourage people to talk to their assembler to gain requirements if they're doing something with particularly heavy con- nectors and edge mount connectors. When we came up with the requirements that we use in our fab notes, that was one of the things Jennifer Kolar

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