Issue link: https://iconnect007.uberflip.com/i/1525004
AUGUST 2024 I DESIGN007 MAGAZINE 13 Design Mishaps As designers, it's our job to make sure the PCB functions correctly and meets the required specifications. We spend most of our time in design making sure the board meets our internal or customer specifications, but the fabrication and assembly specifications are just as important when trying to avoid increases in cost. Poor footprint design can oen lead to added costs in manual rework, additional sten- cil orders, and poor yield. One of the most common footprint errors is missing solder mask openings. Missing openings are typi- cally discovered aer a stencil has already been ordered, and results in the assembler needing to scrape solder mask off pads and reorder sten- cils to salvage the build. is kind of rework is not always possible, and if the assembler can't make it work, another set of corrected PCBs will need to be ordered. A favorite error of mine, and of many assem- bly shops, is when two designs are panelized together, and they share designators. ere are many beneficial use cases to panelize boards together, such as multiple boards that will always be used in a set and share a stackup, but make sure to either do the designs in the same schematic and database or verify that you don't share designators between the designs. A sim- ple way to do this is to use a matching prefix number on your designators for each design. Design A uses C1XX, R1XX, and U1XX, while Design B uses C2XX, R2XX, and U2XX. Also be aware that if too many different boards are together in one array, you can end up with a mismatch of component density across the panel, which can cause warpage during assem- bly. Combining designs on one panel is oen a cost savings attempt that can create more headaches and time cost down the road. A general area that I can't stress enough in design is the KISS factor: Keep It Simple, Stu- pid. If you don't need trace width and spacing under 6/6 mils, don't use it. If you don't need microvias, don't use them. If you don't need blind or buried vias, don't use them. If you don't need via-in-pad, don't use it. If you don't need a really tight via/pad aspect ratio, don't use it. If you don't need your components as absolutely as close together as possible, don't do it. Even if you design to Class 3, but your prototype build only needs to be to Class 2, make sure to let the fabricator know. Your fab- ricator may specify that they can build boards at a 3-mil trace and space, but this doesn't mean they can do it at 100% yield, and the added cost of those failed boards gets passed on to you and your customer. Newer designers tend to use more com- plicated via structures, smaller features, and tighter spacing to make routing a design easier. Not only does this drive up cost in manufactur- ing, but it also adds time, and risks yield and In this mishap case we have a size profile of a board that was intended to insert into another connector. The customer didn't specify a stackup or an overall thickness, so a standard one was chosen by the fab vendor that was too thick. We had to scrap and rebuild.