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32 The PCB Design Magazine • September 2017 to take new designs to market. DFM has evolved to become an integral part of new product in- troductions (NPI). Today's NPI software spans design and manufacturing to accelerate the opti- mization of a PCB for manufacturing. It looks at the entire design-to-manufacturing release pro- cess and deliverables, then streamlines them. Engineers at best-practice companies use NPI software to help identify ways to optimize their design during the initial release process, with a holistic view of their bareboard fabrica- tors' and assembly suppliers' capabilities. It's not simply a matter of catching mistakes these days. It's about understanding the various chal- lenges and limitations involved in the chosen manufacturing processes and then empowering the product owner to make the trade-off deci- sions that best serve their objectives. NPI software must employ expert system logic to automate DFM analysis. Quality DFM analysis is based on a combination of PCB tech- nology classifications and manufacturing con- straints. PCB classification can be determined automatically through intelligent design data. For example, the copper weight of each layer is important in the fabrication DFM analysis because the etch compensation applied and, thus, resultant etch-back are going to be differ- ent based on the copper weight used, varying between inner and outer layers (Figure 2). A 3-mil spacing on an inner layer made of 0.5 oz. copper may be acceptable, whereas the outer layer on the same board may need 4-mil spacing based on the use of 1 oz. copper. Fur- thermore, a PCB constructed with sequential lamination is going to use different DFM rules than a conventional, single-lamination PCB. Having the DFM software assign those attri- butes automatically saves engineering time and effort. DFM systems that use algorithms based on CAD feature shapes can perform analysis in a matter of minutes compared to systems based on vector data, which can take hours to run, and who has hours to wait for DFM analysis these days? IT'S NOT YOUR FATHER'S DFM ANYMORE Figure 2: An intelligent DFM application will automatically derive the appropriate rules to be used for analysis based on the attributes in the design data.