Emi

[Rod Ladwig]

Hi Tom

Radiated emmssions for high frequency PCBs. What are the recommendations for controlling these? On planes like power planes using muliple slipt/mixed planes, how does this affect the EMI? Can you recommend any books? Or have you got any guide lines on this subject?

Thanks

Rod Ladwig
Unique Designs

[Tom]

See this thread in the IPC Advanced Certification section:

http://www.pcbstandards.com/forums/showthread.php?s=&postid=3750#post3750

[Tom]

Rod Ladwig
Radiated emissions for high frequency PCBs. What are the recommendations for controlling these? On planes like power planes using multiple spilt/mixed planes, how does this affect the EMI?
I wanted to address this single question regarding multiple split/mixed planes. Every signal in your PCB design requires a return path to its origin. Signals require a plane to perform this function. If the plane is broken up by multiple splits or if you route traces on the plane layers, this interferes with the signal return path. When the return path is broken, this causes EMI (Electro-magnetic Interference).

Also, vias with oversized plane clearances (anti-pads) where the traces cross over these plane clearances will cause EMI problems. The same as a row of vias with overlapping plane anti-pads with traces running in-between the vias. Especially high speed traces that leave or enter a fine pitch BGA processor chip. High Speed Traces & Overlapping plane anti-pads will have a negative effect on the performance of the circuitry.

One of the solutions that we are experimenting with is "No signal routing on the Outer Layers". Use the Outer Layers for via fanout and mixed power plane floods. You can split up an outer layer with multiple voltages and I would suggest that a solid ground plane be placed on the layers next to the outer layers. On a 10 layer board that would be layers 2 & 9.

[Tom Frayda]

Rod-

Have a look here for a description of 3 good books relating to the subject:

http://www.hottconsultants.com/mini_library.html

HTH


+Tom