[SI-LIST] Re: PEC in 3D field solver?
- From: Istvan Novak <istvan.novak@xxxxxxx>
- To: Inmyung <imsong91@xxxxxxxxx>
- Date: Thu, 14 Apr 2011 08:53:42 -0400
It is true that when you actually use the package with die and board
connected at its top and bottom, the power and ground nets will be
connected through some impedances. However, these connections happen at
the pins/bumps/pads on the top/bottom horizontal planes. If you put PEC
boundaries flush to the top/bottom layers of the package and leave the
side walls open (magnetic wall), this may brute force the silicon/board
short at all frequencies, but then there is not much where you can
connect your ports to analyze the structure. If you force the
power/ground continuation by putting electric walls vertically around
the package so that it shorts the power ground planes around the package
edges, this will change the modal resonance pattern of the power/ground
cavities from open to shorted boundary conditions and this will shift
all resonance frequencies. So eventually it depends on the purpose of
the simulation. Whether you want to analyze only signal-trace behavior
in the package, or want to analyze only the power structure, or the
interaction of power cavities to signal traces, the choice of suitable
tool and setup need to be different.
Also, as Steve pointed out, it is very likely that you can not run the
full package in HFSS. A typical workaround is to truncate the package
around the feature you are interested in, this however also shifts modal
resonances, misses some and creates new artificial resonances. You can
see details about it in the paper: Jason Miller et al., "Examining the
Impact of Power Structures on EM Model Accuracy" You can get it from
http://www.electrical-integrity.com/
Regards,
Istvan Novak
Oracle
On 4/14/2011 3:45 AM, Inmyung wrote:
> Hi everyone,
>
> Some engineer try to analyze the package by using 3D full wave field
> solver such as HFSS.
> But as you know, the power and ground nets was disconnected generally.
> So they put the PEC metal to short the disconnected ground nets.
> Is it a right method?
> Is there any other methodology to simulate package?
>
>
> How about Hybrid tools?
> They do not use PEC but pin grouping.
> I guess pin grouping means equi-potential so that is similar with PEC right?
>
> Thanks,
> Delta
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