[SI-LIST] Re: Reset problem with power supply

Hal, yes the halogens are from cleaning solvents.  It is a very well 
known issue.  Typically you don't find a whole lot of cleaning 
information on individual data sheets.  Major manufacturers like NCC/UCC 
offer a lot of process and reliability information. 

In my limited exposure to military, AFAIK Al electrolytics are avoided 
in favor of tantalums.

The temperature derating for Al electrolytic caps is the Arrhenius 
equation.  Life doubles for every 10C below the rated temp.

Best Regards,


Steve

Hal Murray wrote:
> weirsi@xxxxxxxxxx said:
>   
>> Electrolytic caps come along with some engineering requirements.  The
>> first is long term product life:  electrolytics have a typical shelf
>> life of 5-10 years for cheap to very high quality.  This is a function
>>  primarily of the seals.  However it is not that unusual to find a box
>>  with large body computer grade electrolytics going for more than 20
>> years.  The big issues: are  initial conditioning, adequate
>> temperature,  voltage derating, and absolutely : NO EXPOSURE TO
>> HALOGENS.  A 10 year  life is readily attainable, and with a lot of
>> derating 20 years can be  had in large body parts.  Miniatures are
>> really constrained to about 10  years no matter what is done.
>> Consumer products contain only miniatures  these days, and are so
>> fiercely price sensitive that no one pays for the  kind of derating
>> needed to see long service lives.  As a result, the  electrolytics
>> rank #1 to #2 for failure rates in consumer electronics  ahead or
>> behind of the power semiconductors.
>>     
>
> Thanks.
>
> I assume the halogens mostly come from cleaning.  Has that been solved by the 
> save-the-ozone efforts?  Do assembly houses know about that?  Is it in the 
> data sheets?
>
> I don't remember hearing it before, but I could easily have not paid 
> attention.  I just scanned one handy data sheet.  I didn't see anything about 
> cleaning.  It's probably buried off in an app note or such.
>
> I did see that they are only rated for 2000 hours.  I hadn't paid much 
> attention to that before.  That's under 3 months at 24/7.  Ouch.  Thanks for 
> the heads up.  I'll have to find the temperature re-rating specs.  Sigh.
>
>
> What do military or other high reliability folks do?
>
> I expect a lot of military gear is still in service after 10 years.  (B-52s 
> are still flying.)  Does the electronics turn over fast enough to avoid this 
> problem?
>
>
>
>
>   


-- 
Steve Weir
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