Issue link: https://iconnect007.uberflip.com/i/1500943
60 DESIGN007 MAGAZINE I JUNE 2023 b e t w e e n 12- and 16-mils diam- eter larger than the component pin at maximum material condi- tion (MMC). MMC is the condition where the hole is drilled at the low end of the tolerance range, and the pin measures at the high end of the tolerance range. Pin loca- tions should be placed at nominal location, or the basic dimension shown on the datasheet. 3. Let the datasheet tell the real story ird-party CAD libraries can contain millions of different parts, so discrep- ancies are inevitable. When the datasheet and the library part don't match, address the delta before submitting the design. Always check any library part for accuracy before using it the first time. e datasheet for a part usually tells the real story—a long story, but one worth read- ing. Some datasheets can run up to 200 pages, but only a few lines provide the information needed to make the crucial decisions about sizing. It's important to read and comprehend the key parts of datasheets so problems in CAD don't lead to the wrong sizing and spacing on the PCB. 4. Pay attention to pinouts when using alternate vendor parts Even if pin size and through-hole size are a confirmed match, and even if solder joints appear sound, a part can still not work as expected. Similar parts with the same foot- print might look like they should act identi- cally, but they won't always have the same pinout. Each transistor has a gate, drain, and source, but different manufacturers can vary in what goes where. For example, a Motorola part can differ from a Texas Instruments part. When it comes to generic s, there i s e ven more potential for variance. e same ba s ic comp onent will come in multiple p a c k a g e s . S o m e times the variations are tossed into the back of a datasheet as an afterthought, but these can be critical. Similarly named pack- ages can even come in different widths. 5. Be aware of mechanical fit It's not just the footprint and through-holes that are important; physical size of a compo- nent can keep parts from fitting into designated spaces. MMC body size should be the rule, so pay close attention to the tolerance range. As parts get larger or are sourced from multi- ple vendors, footprint size may need to expand considerably to accommodate all of the dimen- sion and tolerance variables. When combining multiple part body dimensions, always take the largest dimension or it may become more possible for parts to end up smashed together on the board. Maintaining awareness of these key areas will help ensure parts-related manufacturabil- ity issues are avoided. DESIGN007 Matt Stevenson is vice president at Sunstone Circuits. To read past columns, click here. Matt is also the author of the popular book, The Printed Circuit Designer's Guide to... Designing for Reality.