[SI-LIST] Re: effects of stitching vias last attempt- without attachment
- From: Tesla <emcesd@xxxxxxx>
- To: bradb@xxxxxxxxxxx
- Date: Thu, 29 Nov 2012 09:46:19 +0800 (CST)
Hi, Brad
Thank you for the experience share.
"you should make your air box larger (e.g. 1 inch) in the lateral direction to
totally suspend your substrate/planes"
if the sbustrate is totally suspended, plane resonance will be observed.
Is it true that "infinite" planes imply DC equal in MOM simulator?
Thanks.
Tesla
At 2012-11-29 04:24:43,"Bradley Brim" <bradb@xxxxxxxxxxx> wrote:
>Hi Matthew,
>
>You software vendor's local tech support engineer can help you understand some
>of the details of what you are really simulating inside the EM solver you are
>using. For example, in 3D FEM solvers a radiation boundary condition behaves
>like a sheet resistor of 377/sqrt(Er) ohms/square on you lateral edge of the
>substrate between the planes. Therefore, the planes really are connected even
>without stitching vias. To force no connection between the planes other than
>bulk/sheet capacitance you should make your air box larger (e.g. 1 inch) in
>the lateral direction to totally suspend your substrate/planes. Your feedline
>distance will affect the results, since it controls both the plane capacitance
>and the point at which the port launches equal current into the top/bottom
>local planes for the feedline port.
>
>In general, you will want to be very careful with such simulations and
>understand very well the solver you are using. If you examine the same designs
>with a planar Method of Moments solver (sometimes called 2.5D) you will get
>completely different answers if you mesh the power planes versus if you mesh
>the antipads in the ground planes through which the vias pass. When you mesh
>the planes the results are what you would measure with unconnected planes when
>you fabricate a small multi-layer board. When you mesh the antipads it can run
>faster because the unknowns are only the equivalent magnetic currents in the
>antipads rather than the many more electric currents flowing in all the
>planes. However, the planes are then "infinite" and have an infinite
>capacitance; implying they are at equal DC potential. Such antipad-meshed MoM
>simulations will show DC continuity of a single-ended via regardless of how
>many [otherwise unconnected] planes you pass through vertically.
>
>Cheers,
> -Brad Brim
> Cadence
>
>-----Original Message-----
>From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
>Behalf Of Matthew Severini
>Sent: Wednesday, November 28, 2012 11:00 AM
>To: scott@xxxxxxxxxxxxx
>Cc: si-list@xxxxxxxxxxxxx
>Subject: [SI-LIST] Re: effects of stitching vias last attempt- without
>attachment
>
>Scott,
>
>Thanks for your rapid response. I am using HFSS as a modeler. I have about
>1/4 inch of stripline on either side of the via to ensure that the signal
>does not have any port induced higher order modes when it hits the via.
>( this means my board ends up being a 1/2" square). Then I have an air box
>that is about a 1/2" cube with the board centered in the z- dimension, and
>a radiation boundary on the surfaces of the air box. (in the x/y plane this
>box is exactly the same size as the board) I think this means that any
>energy that gets to the edges of the ground plane is radiated out, but any
>energy trying to radiate in the z-direction sees the real world
>air/dielectric boundary. I wanted to use a radiation boundary on the edges
>of the board because the size of the board I used is arbitrary, and I don't
>think that I want the plane resonances caused by this size to affect my
>results. I am using a wave port and a terminal soulution. I did a modal
>solution to ensure that the ports were properly sized, and did not have any
>resonances.
>
>Thanks again,
>
>Matthew Severini
>
>Research & Development Engineering
>Endicott Interconnect Technologies, Inc.
>Phone: (607) 755-8119
>
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