[time-nuts] The Smell of Tantalum in the Morning

[paul swed]

My experience is that the plastic ones tend to burn.
The mil grade ones in HP I have never seen fail (As in flame)

On Mon, Feb 8, 2010 at 8:05 PM, Glenn Little WB4UIV <
glennmaillist at bellsouth.net> wrote:

> While in the US Navy, we had to do equipment inspections.
> One quarterly was to examine the capacitors in the power supply of one
> piece of equipment.
> We were to look for leakage (sulfuric acid) from CL65 type wet slug
> tantalum capacitors.
> Shortly after that CL65 type capacitors were disapproved for military use.
> I never saw one that leaked in that equipment, but, have seen a number of
> boards damaged from seal leakage on CL65 capacitors.
> Something to look out for.
> The CL65 capacitors probably have a pure silver case a sulfuric acid as an
> electrolyte.
> The seal is Teflon.
>
> We also had an interesting failure mode for ATC ceramic capacitors.
> This failure mode will only occur in a sealed environment (submarine.
>
> Just an observation.
>
> 73
> Glenn
> WB4UIV
>
>
>
> At 09:46 AM 2/8/2010, you wrote:
>
>> The history of tantalum failures is wide and varied, but
>> there are some common characteristics:
>>
>> 1) The tantalum is in a power supply circuit and receives
>>   a rapid ramp from 0V to operating voltage.
>> 2) The tantalum is spec'd close to its operating voltage,
>>   very close.... 5V on a 6.3V part, 12.5V on a 15V part...
>> 3) The tantalum is dry slug, and is sealed with epoxy.
>> 4) The instrument has been powered down for an extended
>>   period.
>>
>> HP equipment from the 1980's is pretty immune to the problem
>> because they typically use hermetically sealed mil spec
>> tantalum capacitors.  Tektronix equipment from the 1980's
>> is infested with tantalum problems because they used the
>> cheap epoxy dipped parts.
>>
>> Tantalum failures are pretty rare in equipment that is
>> run continuously.  Tantalum has a self healing feature that
>> corrects any small problems while in operating... Large problems
>> result in detonation.
>>
>> Dipped tantalum capacitors of any age are prone to failure.
>> The tendency can be mitigated largely by never allowing a
>> tantalum capacitor to see voltage above 50% of its rating.
>>
>> And finally, powering a tantalum in reverse, will cause instant
>> and irreparable damage.
>>
>> -Chuck Harris
>>
>>
>>
>> Tom Van Baak wrote:
>>
>>> I powered up a 5071A to watch the end of Loran-C today
>>> and was greeted by the special smell that only a mother
>>> board could love.
>>> Does anyone know the history of tantalum capacitor
>>> failures in ten-year old [HP/Agilent] test equipment?
>>> This is not my first. Last one was more like July 4th.
>>> Thanks,
>>> /tvb
>>>
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