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NNTP-Posting-Date: Tue, 02 Jul 2024 16:19:44 +0000
From: john larkin <jlarkin_highland_tech>
Newsgroups: sci.electronics.design
Subject: Re: Ambient temperature control
Date: Tue, 02 Jul 2024 09:19:45 -0700
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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.