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

Alan Scrimgeour scrimgap at blueyonder.co.uk
Sun Sep 19 12:45:39 UTC 2010

It definitely sounds like a convection effect. It could be internal or 
external to the package, or both. Varying heating/cooling of external solder 
joint may be the cause. Further from the package there is the 
heating/cooling effect of  the surrounding circuitry and the equipment 
enclosure in general. Internally it might change the temperature sensed 
within the package relative to the actual zener temperature. Another 
possibility is due to the very high thermoelectric potential generated with 
silicon as one conductor. The thermoelectric potential for silicon/copper is 
about 400uV/C compared to about 2uV/C for lead/copper. The chip is probably 
electrically connected with aluminium or gold, but the thermoelectric 
potential to silicon will be similar.

Since the package is hermetically sealed it would be possible to distinguish 
internal/external convection effects by
testing the reference board under high vacuum where external convection 
would cease.


----- Original Message ----- 
From: "Dr. Frank Stellmach" <drfrank.stellmach at freenet.de>
To: <volt-nuts at febo.com>
Sent: Sunday, September 19, 2010 10:52 AM
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 
> 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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