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

How does copper weight affect impedance control?  I understand the concept
of trapezoid trace cross section and it would be more pronounced with higher
weight copper but that should not affect impedance accuracy if properly
accounted for - should it?
Thank you
Aleks

On Sun, Jul 27, 2008 at 3:31 PM, steve weir <weirsi@xxxxxxxxxx> wrote:

> 1/2 oz Cu is more amenable to manufacturing thin traces required for
> impedance control with signal to plane dielectric 5mils or less.
>
> Unless you have a lot of links that are 6Gbps or faster, most of your
> energy is closer to 1GHz than 10GHz.
>
> Steve.
>
> V S wrote:
> > 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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