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10 The PCB Design Magazine • March 2015 feature In many cases, the term DRC, which stands for design rule checking, is also used inter- changeably with DFM and creates further confu- sion. That's understandable, because DRC issues detected in manufacturing can indeed have a di- rect impact on the manufacturability of a PCB. However, DRC is markedly different from DFF and DFA. Think of DRC as a hard pass/fail detec- tion of a problem in a PCB. Either a problem ex- ists or it doesn't. In engineering, DRC is used to ensure that PCB layout connectivity accurately reflects the connectivity defined in a board's as- sociated schematic diagram. But connectivity is only one aspect of DRC. The "R" stands for rules. The rules are used largely to define the minimum spacing allowed between various PCB objects for the entire PCB or for individual layers, nets or areas on the PCB. In engineering, the spacing may have direct impact on circuit performance. In manufacturing, spacing may play a pivotal role in the ability to fabricate or assemble a PCB. DFM, DRC, DFF, DFA, DFwhat? These are all terms used daily in the PCB design world re- garding manufacturing analysis, and they are often used interchangeably. But what exactly is DFM and why is it such an important, but often ignored aspect of the PCB design process? Let's start by clarifying some terms. DFM is short for "design for manufacturability." It is the process of arranging a PCB layout topology to mitigate problems that could be encountered during the PCB fabrication and assembly pro- cesses required to manufacture an electronic system. Addressing fabrication issues is what's known as design for fabrication (DFF), and ad- dressing assembly issues during design is known as design for assembly (DFA). The two together mostly make up DFM analysis—mostly. by Rick Almeida DownsTReAM TeCHnologies Understanding DFM and Its Role in PCB Layout

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