I have used Power Islands in the signal layers to reduce the number of layers. These power islands can usually not be the IO plane and can be successfully used for processor core and other places where it goes to few isolated pins and not to the whole board. The traces should be short and wide. For impedance, I usually let the PCB vendor send me the details of the Er assumptions at frequencies involved. I have however not worked at 10 GHz. http://referencedesigner.com Gurus, I would like to get your valuable feedback on the following: 1) Advantages/Disadvantages about using 1/2 Oz Cu for signal routing on the inner layers. One issue that I can think of is the potential increase in DC IR drop if I plan to use the signal layers for carving out a power island. Are there any other issues that I need to be aware of before going down this path? 2) I have seen substrate vendors specifying two different Er/Df values for two different frequencies (1GHz, 10GHz). What is the current industry practice about which Er value to use when coming up with the trace geometries to meet impedance requirements? I was planning to use the Er value at high frequency since the edge rates for my scenario are fast. Any suggestions from the group are welcome. Thanks, Ravi. ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List technical documents are available at: http://www.si-list.net List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu