[SI-LIST] Re: Information regarding Stackup Design.

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.


      
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