[SI-LIST] Re: Inductance of PWR&GND plane and other signal line

plus lee wrote:

> Hi, all experts,
> Sorry my poor English.
> The below inductance data was 4 metal layers BGA 
> simulated by Paksi-E package software.
>             m1       m2        m3        m4         wire       ball
> GND   0.093   0.0043  0.0005   0.0031    0.084    0.235
> PWR  0.094   0.0001  0.0017   0.0036    0.114    0.268
> S1      1.42     0.0038  0.0077   0.3563    1.919    4.056
> S2      1.67     0.0024  0.0062   0.0782    2.176    4.271
> 
> Why m1, wire, & ball inductance of S1,S2(signal line)
> is larger than GND&PWR plane?
> 
> Is this the series circuit or other reason?
> 
> I could understand m2 and m3 is minor because of large plane, but how
> about m1 and m4?
> 
>  
>
 Without knowing exactly how you had your extraction setup defined in 
PakSI it is difficult to evaluate your results.

While I agree that at first glance it is counter-intuitive as to why the 
partial inductances contributed by the BGA balls and the bond wires are 
so much greater for the signal lines than for the power planes, without 
knowing how your problem was defined makes it  most difficult to provide 
an exact reason.
Are you sure you have your sources, sinks, and floating nodes correct? 
Are the stackup dimensions correct for all the layers? Have you done a 
2-port or multi-port extraction? Take a look at the current distribution 
that the extractor has calculated. Does it appear that the currents are 
flowing where you would expect them to flow?

Extractors usually provide quite accurate answers to problems, however 
quite often the answer given isn't the answer to the problem you really 
wanted to solve, but to the problem you defined. PakSI is pretty good 
about simplifying the problem setup as compared to some other well known 
3D extractors, but it is still possible to go wrong.

-Ray Anderson

Senior Signal Integrity Staff Engineer
Advanced Packaging R&D
Xilinx Inc.

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