# [SI-LIST] Re: Dust and humidity impact on the signal

• From: "Loyer, Jeff" <jeff.loyer@xxxxxxxxx>
• To: <scott@xxxxxxxxxxxxx>
• Date: Wed, 17 Jan 2007 10:06:03 -0800

```It should be representative dust, with its corresponding Er.  I don't
think sawdust is a representative component, unless you've got your
workshop in the kitchen (not that there's ANYTHING wrong with that,
Scott, if you do - grin). =20

I would propose dog or cat hair as a better material to spread over your
board before TDR'ing it.  If the study is taken to its extremes, the Er
of various breeds could be determined, and characteristic impedance
taken into account when visiting the pound.

I hope the study finds a negligible effect due to dust - every home
computer I've ever worked on has incredible amounts of dust.  Maybe
another reason to recommend stripline.  :-)

Cheers,
Jeff Loyer

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Scott McMorrow
Sent: Wednesday, January 17, 2007 9:39 AM
To: Fabrizio.Zanella@xxxxxxx
Cc: Dorin.Oprea@xxxxxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Dust and humidity impact on the signal

To follow up, accommodation of the impact of humidity on Er and loss=20
tangent should be fairly easy, although I've not tried it.

1) Dry out your target material in an autoclave
2) Weigh it.
3) Place the material in a humidity chamber
4) Weigh it.
5) Compute the percentage water by weight.
6) Compute the average increase in Er and loss tangent by using the=20
ratios of dielectric and absorbed water.

Once you know these, it should be possible to create a lossy dielectric=20
model that is a pretty close match for 2D or 3D solvers.  For extra=20
credit, actual material measurements could be made using one of the many

methods know for Er and TanD extraction, at multiple frequency points,=20
to create a more precise frequency dependent model.  However, I think if

you perform steps 1 to 6 above you'll be closer than you might imagine=20
(assuming that you know your original material properties well.

I wouldn't worry much about dust, except for microstrip.  In that case,=20
I guess one could make some TDR measurements with and without dust and=20
see what happens. (It's not like it's hard to create some good dust ...=20
just get yourself a good circular saw, create some fine dust, and=20
sprinkle it over the trace.

Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1840 Fax

http://www.teraspeed.com

Teraspeed(r) is the registered service mark of
Teraspeed Consulting Group LLC

Fabrizio.Zanella@xxxxxxx wrote:
> Dorin, there's a good paper from DesignCon 2004 which has information
on
> measurements on serial links including the effect of temperature and
> humidity=3D2E
> 'The Impact of Environmental Conditions on Channel Performance', by
Greg
> Sheets, Agere and John D'Ambrosia, Tyco=3D2E  You can take the dk
> information and apply it as a variable in a 3D simulator, and then use
a
> parametric sweep=3D2E
>
> I can send you this paper if you're interested=3D2E
>
> Regards,
>
> Fabrizio Zanella
>
>
> -----Original Message-----
> From: Dorin=3D2EOprea@alcatel-lucent=3D2Ecom
> [mailto:Dorin=3D2EOprea@alcatel-lucent=3D2Ecom]
> Sent: Wednesday, January 17, 2007 10:59 AM
> To: si-list@freelists=3D2Eorg
> Subject: [SI-LIST] Dust and humidity impact on the signal
>
> Hi,
>
> I try to simulate the dust and humidity impact on 10G differential
> signal routed as micro strip on the board=3D2E I know that the dust
> thickness and humidity can vary significantly, but I wonder what would
> be a good approach, for start, to build the corresponding model in a
3D
> simulation tool (suggestions on dk, df)=3D2E
>
> Thanks,
> Dorin
>
>
>
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```