At 03:29 PM 1/28/2005, Rick Thompson wrote: >Here's a question for the noise experts: > >I've designed a 4-layer pcb running a 16LF876A at 4MHz to be used in a >VERY noisy environment. Fortunately there's no A/D functionality needed >but there's some timing-critical functions to be upheld (20Hz to 1000Hz >CCP events). Every trick that I could find to make the design immune to >EMI has been included or at least considered. But one consideration that >I don't know enough about is the need for a copper pour. Until now, my >understanding is that a copper pour can be considered as a "poor man's >ground plane" on 1 or 2-layer boards. But if my board already has a >ground plane, am I going to see any benefit by adding a copper pour on any >or every other layer, or am I just wasting my time thinking about it? Place your ground and power planes as the outside layers if you can. Use the inner layers as the signal layers. Us repair and reverse-engineering dudes will hate you but the EMC boys will thank you over and over again. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 20 years of Engineering Innovation (1984 - 2004) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist