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From: legg <legg@nospam.magma.ca>
Newsgroups: sci.electronics.design
Subject: Re: Ambient temperature control
Date: Wed, 03 Jul 2024 09:03:12 -0400
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On Tue, 02 Jul 2024 09:19:45 -0700, john larkin
<jlarkin_highland_tech> wrote:

>On Tue, 02 Jul 2024 10:24:58 -0400, legg <legg@nospam.magma.ca> wrote:
>
>>On Mon, 01 Jul 2024 07:46:52 -0700, john larkin
>><jlarkin_highland_tech> wrote:
>>
>>>On Mon, 01 Jul 2024 10:34:46 -0400, legg <legg@nospam.magma.ca> wrote:
>>>
>>>>On Sun, 30 Jun 2024 18:14:32 -0700, Don Y
>>>><blockedofcourse@foo.invalid> wrote:
>>>>
>>>>>Assuming you can keep a device in its "normal operating (temperature)
>>>>>range", how advantageous is it (think MTBF) to drive that ambient
>>>>>down?  And, is there a sweet spot (as there is a cost to lowering the
>>>>>temperature)?
>>>>>
>>>>If all you're thinking of is MTBF, adding the complexity of an active 
>>>>cooling element is a big step in the wrong direction for the system.
>>>>
>>>>Reducing the thermal impedance of the source, to ambient is the 
>>>>usual way to go, when addressing a specific aging factor.
>>>>
>>>>https://ve3ute.ca/2000a.html
>>>>
>>>>If you're thinking of performance, It's cheaper and more reliable 
>>>>to concentrate on reducing the temperature of the point source, not 
>>>>the rest of the planet.
>>>>
>>>>RL
>>>
>>>Tubes? The cathodes fail eventually. Reduce filament voltage and
>>>suffer the reduced gain. Better yet, don't use tubes.
>>>
>>>But for most parts that dissipate power, the big win is to have some
>>>air flow. A fan can reduce the theta of your parts by 2:1.
>>>
>>>Nowadays, parts are very good, with failure rates in the ballpark of
>>>one failure per billion hours, the Bellcore and MIL217 FITS numbers. 
>>
>>This was an example of a demonstrated and documented failure mode 
>>in a specific component (glass electrolysis) that is/was largely 
>>ignored by the general user.
>>
>>If you know what the specific aging mechanism is that you're 
>>trying to address, your methods of improving mtbf will be more 
>>effective.
>>
>>RL
>
>Given non-junk products from you-know-where, most electronics failures
>are not from classic parts failure. Few real products, in the field,
>get close to the standard-calculated-method MTBF rates. They die from
>bad design, bad packaging and soldering, or external effects like ESD.
>
>Sometimes one of our customers will ask for a calculated MTBF, so we
>dutifully crank one out. We both know that the number is prfetty much
>fantasy.
>
A standard calculation can be rubbish - often it will to be 
deliberately fudged to get an acceptable result - ignoring 
actual temp, stress or mtbf measurements in favor of guestimates 
or assumptions. 

'You can't handle the truth !'

An external esd event is predictable and the strike count can 
be addressed for a specified environment, by built-in design, 
by opperator precaution or by environmental proscription.

RL