FreeLists / si-list / [SI-LIST] Re: Conductivity for FR4

["Joachim Mueller" <jmueller@xxxxxxxxxx>]

The problem with conductivity is that it scales with frequency. Your
2.5Gbit signal has frequency components from zero to 1/(PI *rise time). In
Ansoft SI2D (I am assuming this is the field solver you are using)  the
problem is, that you can not define functions with frequency dependent
variables. I ended up to define conductivity and permittivity of FR4 as
constant variables and swept the value of them in 31 individual setups vs.
frequency.  This will provide you with 31 simulation runs, each at a
specific frequency, using the correct conductivity and permittivity. The
results of this can than be extracted and converted into a tabular W
Element for Hspice.

It would be much easier if Ansoft would allow the definition of loss
tangent rather than conductivity for dielectrics. Also the definition of
frequency dependent variables (like conductivity) would simplify the effort
a lot.

cheers

Joachim

-- - --
Joachim Mueller
EMC/SI-Engineer, W.L.Gore & Associates

Nordring 1
91785 Pleinfeld
Germany
Phone: +49 9144 6016368
Email: joachim_mueller@xxxxxxxxxx



                                                                                
                            
                    Alfredo.Moncayo@in                                          
                            
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                    si-list-bounce@fre       Subject:     [SI-LIST] Re: 
Conductivity for FR4                
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                    06.11.01 23:43                                              
                            
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                    Alfredo.Moncayo                                             
                            
                                                                                
                            
                                                                                
                            






That has worked well for me.  I haven't methodically gone through
and determined the effect of the frequency term in the end result,
but so far have achieved very good correlation when using 3x the
base rate of the signal that would be used on the interconnect.

Alfredo



> -----Original Message-----
> From: Khalid Ansari [mailto:khalida@xxxxxxxxxxx]
> Sent: Tuesday, November 06, 2001 10:44 AM
> To: si-list@xxxxxxxxxxxxx
> Subject: [SI-LIST] Conductivity for FR4
>
>
>
> Hi all,
>
> I am using a 2D field solver to extract the RLGC parameters for a
> stripline differential pair.  When defining FR4 it asks me for the
> conductivity of the material.  I looked up the loss tangent for FR4,
> which is .02 (around 2.5 Gbps).  Can I use the formula:
> Loss tangent = conductivity/(2*pi*f*EoEr) and get the appropriate
> conductivity value for the field solver, or do I need to worry about
> something else.
>
> Thanks,
> Khalid
>
> ------------------------------------------------------------------
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