[volt-nuts] physical explanation of the tilt effect?

[shalimr9 at gmail.com]

Convection effects inside the package are likely to be position dependent, even if the case itself is kept at a ~constant temperature.

The exact amount of air (or nitrogen) that flows over the chip itself inside the package can redistribute the thermal gradient, however small of an effect that is.

Didier KO4BB


Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: "Dr. Frank Stellmach" <drfrank.stellmach at freenet.de>
Sender: volt-nuts-bounces at febo.com
Date: Sun, 19 Sep 2010 11:52:28 
To: <volt-nuts at febo.com>
Reply-To: Discussion of precise voltage measurement <volt-nuts at febo.com>
Subject: [volt-nuts] physical explanation of the tilt effect?



>I read somewhere that the LTZ1000 chip is mounted in a special way
>to reduce thermal conductivity.  That would sort of indicate some
>kind of edge mount with the chip floating, and that again would
>certainly expose it to gravitational effects.
>
>In that case, it should only have three modes: up, down and sideways,
>where the chip is vertical, but the rotation around the center
>axis should have very little effect.
>
>-- 
>Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
>phk at FreeBSD.ORG  <https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts>          | TCP/IP since RFC 956
>FreeBSD committer       | BSD since 4.3-tahoe
>Never attribute to malice what can adequately be explained by incompetence.


Poul-Henning,

I use an LTZ1000. Its chip is mounted in a standard TO99 package, so your explanation does not fit.

The LTZ1000A is assembled with a thermally insulating die attach (ie epoxy to glue the die to the leadframe).




What all of us is missing is the correct physical explanation, including my assumption, which is derived from the long time constant of the change only.


I.e. if it would be a gravitational effect, please explain how the orientation of gravitational force acts on the circuit, or on the physical package and changes the output that slowly, stable after a minute only, and not instantaneously.

In the case of of an XTAL, one can explain this (known) orientation effect by the Coriolis force, but should act instantaneously. Gyro sensors use this effect for navigation puposes.

For the LTZ, I do not see a similar physical relation at the moment, do you?


A magnetic effect could be the interaction between the vector of the earth magnetic field and the direction of the current flow within the chip, ie the Hall Effect.

But this interaction would be instantaneously also.


A thermal effect could be induced by different heat convection flow from the warm LTZ to the surrounding solder joints.
I isolated the LTZ1000 additionally by a PS cap around it, so i really wonder...

Anyhow, if anybody finds "the missing link" between the drift effect and the physical property, it would be interesting to improve the assembly.


PS: I also have -perhaps - seen a certain drift effect in the same order of magnitude when rotating the 3458A, but as this measurement was too noisy, I cannot tell for sure, neither give any quantitative value.

Frank

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