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PCBD-July2014

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July 2014 • The PCB Design Magazine 45 design for manufacturing two traces can increase the creepage distance. Leakage from one trace to the other along the laminate surface would have to travel around the air gap. Alternatively, a vertical barrier of in- sulating material could be placed in the space, which would increase both the creepage and clearance distances. Keep in mind the spacing on assembled boards when you consider creepage and clear- ance requirements for layout. The distance be- tween an uninsulated edge of a charged com- ponent and the edge of an adjacent component could be too small to meet a clearance require- ment, even though the creepage distance be- tween their traces is sufficient. Moreover, there may be some operations needed during assem- bly to meet clearance requirements, for exam- ple, applying potting compound to isolate the leads on the package of a power semiconductor from a nearby component. If your project does not require compliance with a particular safety standard, you can rely on the latest version of IPC-2221, the gener- ic standard for PCB design, for clearance and creepage guidance. In any case, consultation with your PCB fabricator and assembler regard- ing suitable materials and design alternatives will help you achieve a safe product that meets your performance objectives at the lowest pos- sible cost. Our quick trip through the basics of lay- ing out boards that involve hazardous voltage amounts to just a first step, simply an opportu- nity to point to out some helpful and hopefully familiar guideposts as you start your journey. Consider this presentation my personal opinion only and certainly not legal advice. PCBDESIgN Amit Bahl directs sales and marketing at sierra Circuits, a PCB manufacturer in sunnyvale, California. he can be reached by clicking here. CONSIDERINg CREEPAgE AND CLEARANCE continues realtimewith.com CliCk To View Video Interview Clyde F. Coombs Jr., editor of the venerable Printed Circuit handbook, discusses the up- coming 7 th edition, and what readers can expect. he ex- plains how the book's content has evolved over the years, and why some readers are not "board guys" in the classic sense. Printed Circuit Handbook, 7th Ed., Coming Soon by Real Time with... IPC APEX EXPO

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