Design007 Magazine

PCBD-Jan2017

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16 The PCB Design Magazine • January 2017 by Kelly Dack, CID+, CIT We PCB designers are doing some truly great things with our layout tools. But we must re- member that these tools are so powerful that they will sometimes allow us to design things that can't be manufactured! We must collabo- rate with our fabricator and assembly brethren and embrace the best DFM practices, or face the consequences downstream. Something as seemingly simple as copper- to-edge spacing provides us with plenty of ex- amples of DFM techniques, potentially good and bad. Providing a sufficient amount of copper-to- edge spacing allows for the least costly manu- facturing processes at the PCB fabrication and assembly levels. Extremely tight manufacturing etching and routing tolerances enable the close registration of copper to the cut board edge. On very tight layouts, we see a router profile that is intended to come within .007" of a copper trace. You may have seen closer—and even cases where the copper is designed to extend beyond the the board edge effectively wrapping around the board edge. Granted, sometimes we designers intend for the copper to exist in close proximity to a board edge profile. When close copper-to-edge distance is intended, we ought to always be sure that the copper will end up protected with a coating of resin (if still laminated within the PCB) or plated with a surface finish in order to prevent oxidation or other forms of contamina- tion. While copper print and etch factors are more accurate than ever, and your PCB layout tool will allow you place that copper trace very close to that board edge, stop and wait a min- ute. Think about how this PCB will be fabricat- ed and assembled. If you don't know, set up a meeting with your PCB fabricator and assembler. Ask your manufacturing representatives about their ca- pabilities and processes. Take note, though, with regard to the context of this conversation. If you ask how close you can design copper to the board edge, you will (and should) get an FEATURE TRUE DFM: Taking Control of Your EDA Tool

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