[SI-LIST] Temperature effects on backplanes?
- From: "Bond, David" <David.Bond@xxxxxxx>
- To: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx>
- Date: Fri, 18 May 2012 13:13:19 +0000
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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