[SI-LIST] Re: Temperature effects on backplanes?
- From: steve weir <weirsi@xxxxxxxxxx>
- To: si-list@xxxxxxxxxxxxx
- Date: Fri, 18 May 2012 06:27:26 -0700
I suspect moisture absorption issues changed you tangent loss. What was
the humidity for these tests?
Steve
On 5/18/2012 6:13 AM, Bond, David wrote:
> Overt the last few years, I've been asked to support a mechanism whereby the
> transmitter's and receiver's equalization on a 10Gps link can be re-optimized
> while operating in mission mode. The claim is that temperature swings can
> wreak havoc on the channel characteristics. I've resisted this because I had
> no data to support it.
> Recently, though, I received S-parameter models for two channels on a back
> plane each extracted a 3 widely spaced temperatures: -25C, +25C and +75C. I
> have very few details on the channel, but expect that it is FR4. To my
> surprise, there is a large change in the channel's behavior.
>
> The Return Loss doesn't change much.
>
> The Insertion loss degrades badly above 5G, develops some very deep and
> narrow nulls around 10G.
>
> What's weird is the pulse and step response. The -25C and +25C pulse delays
> vary a small amount: maybe a 25% increase in delay between the two
> temperatures. However, the difference between 25C and 75C is>300%. (!) for
> both the short and long channels. The attenuation and ISI both increase with
> temperature.
>
> Is this an expected characteristic of FR4? Can anyone explain the non-linear
> increase in delay at the high temperature?
>
> Thanks in advance,
> David Bond
>
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