[SI-LIST] Re: surface roughness
- From: Cristian Gozzi <cristian.gozzi@xxxxxxxxx>
- To: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
- Date: Sun, 20 Nov 2011 09:31:13 +0100
latest version of Ansoft tools (HFSS v14 and SIwave v6) have implemented
Huray's model, plus the already available Hammerstad model
Regards
Cris
SI & PI Specialist
Technoprobe Spa
2011/11/19 Loyer, Jeff <jeff.loyer@xxxxxxxxx>
> To my mind, there's not a quick answer; there are several issues:
> 1) Does the simulator have any accommodation for surface roughness?
> a. If so, what model do they use?
> i. If it's the Hammerstad model, that's been proven to be
> fundamentally flawed (see the DesignCon 2010 paper, "Impact of Copper
> Surface Texture on Loss, a Model that Works.")
> ii. If it's a more accurate model, you'll need to know some pretty
> sophisticated aspects of your copper roughness.
> b. I believe most models today are rough approximations at best,
> except for some very specific instances where great care has been taken to
> correlate loss to the exact topology of the copper surface
> i. I don't know how you can model surface roughness without a
> sophisticated model of the exact topology - there's going to be a profound
> difference between large, smooth undulating hills, and a surface with lots
> of sharp "fissures"
> ii. Until we understand better the actual copper texture, I don't
> think we can say we have a superbly accurate modeler.
> 2) Copper texture, and the factors that influence it, aren't well
> understood at this time. You can take very smooth copper and turn it into
> a very rough surface by an Oxide Alternative (OA) process
> a. In the PCB world, we're just now beginning the investigation into
> the various aspects of copper texture. I believe there's still a lot more
> that "we don't know we don't know" than we do know.
> b. I haven't seen any papers discussing copper texture in the IC
> world - I'd love to hear about them
> c. On the bright side, if you're talking about IC features, every
> cross-section I've seen has shown those to be extremely smooth, and I
> believe the loss tangents are relatively high. Perhaps the copper texture
> isn't such a huge effect, even up to 50GHz.
> I would guess your best bet is to build some models with the best methods
> available and see if, at their worst, they indicate an enormous effect, or
> one that can be largely ignored. If it's the first, there's a lot of work
> to understand the specifics, if PCB experience is any indication.
>
> I haven't heard of any profound impacts on return loss.
>
> Sources of information that I know of (as well as the DesignCon paper):
> * Paul Huray's book "The Foundations of Signal Integrity"
> * Steve Hall's book "Advanced Signal Integrity for High-Speed
> Digital Designs"
>
> I hope this helps - it will be interesting to hear what folks say about
> copper roughness in IC's.
>
> Jeff Loyer
>
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
> On Behalf Of nagachander.sing@xxxxxxxxxxxxxxxxxxxx
> Sent: Friday, November 18, 2011 11:35 PM
> To: si-list
> Subject: [SI-LIST] surface roughness
>
> Hi all,
> What is the best tool to simulate surface roughness when simulating for
> the differential S-parameters for striplines and microstripline in IC
> packages?
>
> I am interested in simulating till 50GHz.
>
> What kind of effects are you seeing with surface roughness? i mean things
> like does your insertion loss increase? what abt diff return loss?
>
> Any good papers to understand the problems in detail...
>
> Any feedback will be appreciated
>
> Thanks,
> Naga
>
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