Diode Failure

After about 1000 units all of a sudden two units used by the same customer
have failed.

The diodes are a full short (FMKA140), understanding of a breakdown under
high reverse voltage was that it's non destructive and them the diode will
recover so long as it isn't damaged by heat. There is no sign of heat
damage.

Has anyone ever seen a breakdown like this? Any ideas what would cause it?

Thanks for any help

Ralph

Ralph Mason wrote:

> After about 1000 units all of a sudden two units used by the same customer
> have failed.
>
> The diodes are a full short (FMKA140), understanding of a breakdown under
> high reverse voltage was that it's non destructive and them the diode will
> recover so long as it isn't damaged by heat. There is no sign of heat
> damage.

I can't answer your question. If you are exceeding
the absolute maximun rating of the part, you're asking
for trouble.

On Wed, 10 Dec 2003 12:57:03 +1300, the renowned "Ralph Mason"
<masonralph_at_yahoo_dot_com@thisisnotarealaddress .com> wrote:

>After about 1000 units all of a sudden two units used by the same customer
>have failed.
>
>The diodes are a full short (FMKA140), understanding of a breakdown under
>high reverse voltage was that it's non destructive and them the diode will
>recover so long as it isn't damaged by heat. There is no sign of heat
>damage.
>
>Has anyone ever seen a breakdown like this? Any ideas what would cause it?

Got a schematic?

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Ralph Mason wrote:
>
> After about 1000 units all of a sudden two units used by the same
> customer have failed.
>
> The diodes are a full short (FMKA140), understanding of a
> breakdown under high reverse voltage was that it's non destructive
> and them the diode will recover so long as it isn't damaged by heat.

Where did you ever get such an idea? Your design is faulty.

--
Chuck F () ()
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.net> USE worldnet address!

On Wed, 10 Dec 2003 12:57:03 +1300, the renowned "Ralph Mason"
<masonralph_at_yahoo_dot_com@thisisnotarealaddress .com> wrote:

>After about 1000 units all of a sudden two units used by the same customer
>have failed.
>
>The diodes are a full short (FMKA140), understanding of a breakdown under
>high reverse voltage was that it's non destructive and them the diode will
>recover so long as it isn't damaged by heat. There is no sign of heat
>damage.

You may not be able to see the damage from the outside. A brief very
high current pulse can have enough energy to damage the P-N guard ring
or the junction. That particular part does not have a reverse
avalanche energy rating on the datasheet.

>Has anyone ever seen a breakdown like this? Any ideas what would cause it?

Got a schematic?

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

"CBFalconer" <> wrote in message
news:...
> Ralph Mason wrote:
> >
> > After about 1000 units all of a sudden two units used by the same
> > customer have failed.
> >
> > The diodes are a full short (FMKA140), understanding of a
> > breakdown under high reverse voltage was that it's non destructive
> > and them the diode will recover so long as it isn't damaged by heat.
>
> Where did you ever get such an idea? Your design is faulty.
>
I don't operate them outside the design voltage, I am just trying to think
of any possible reason for the failures.

Ralph

Ralph Mason wrote:
> "CBFalconer" <> wrote in message
> news:...
>
>>Ralph Mason wrote:
>>
>>>After about 1000 units all of a sudden two units used by the same
>>>customer have failed.
>>>
>>>The diodes are a full short (FMKA140), understanding of a
>>>breakdown under high reverse voltage was that it's non destructive
>>>and them the diode will recover so long as it isn't damaged by heat.
>>
>>Where did you ever get such an idea? Your design is faulty.
>>
>
> I don't operate them outside the design voltage, I am just trying to think
> of any possible reason for the failures.

Then I'm confused. If you never exceed the absolute maximum
specs, they should never fail. Your first post implied that
you thought you could get away with exceeding the reverse
voltage specification and get away with it if there were
no heat damage.

Correct me if I'm wrong, but if you apply a high enough
reverse voltage to cause them to breakdown, aren't you
exceeding the abs-max reverse voltage specification?

Time to ask a better question.

"Ralph Mason" <masonralph_at_yahoo_dot_com@thisisnotarealaddress .com> wrote
in message news:jjtBb.24426$...
> After about 1000 units all of a sudden two units used by the same customer
> have failed.
>
> The diodes are a full short (FMKA140), understanding of a breakdown under
> high reverse voltage was that it's non destructive and them the diode will
> recover so long as it isn't damaged by heat.

40V is not a very high voltage rating -- you can easily get
that much when you turn off a coil.

> There is no sign of heat
> damage.
>
> Has anyone ever seen a breakdown like this? Any ideas what would cause
it?

a) defective part
b) incorrect design that failed to account for something
such as in-rush current
c) environmental damage

On Thu, 11 Dec 2003 07:57:12 GMT, the renowned "aurgathor"
<spam-> wrote:

>
>"Ralph Mason" <masonralph_at_yahoo_dot_com@thisisnotarealaddress .com> wrote
>in message news:jjtBb.24426$...
>> After about 1000 units all of a sudden two units used by the same customer
>> have failed.
>>
>> The diodes are a full short (FMKA140), understanding of a breakdown under
>> high reverse voltage was that it's non destructive and them the diode will
>> recover so long as it isn't damaged by heat.
>
>40V is not a very high voltage rating -- you can easily get
>that much when you turn off a coil.
>
>> There is no sign of heat
>> damage.
>>
>> Has anyone ever seen a breakdown like this? Any ideas what would cause
>it?
>
>a) defective part
>b) incorrect design that failed to account for something
> such as in-rush current
>c) environmental damage

d) (possibly included under hazards of c)) something unforseen that
this particular customer is doing to the product. Never underestimate
the creativity of customers in finding design or instruction manual
weaknesses.

Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

"Jim Stewart" <> wrote in message
news:br7kqj$...
> Ralph Mason wrote:
> > "CBFalconer" <> wrote in message
> > news:...
> >
> >>Ralph Mason wrote:
> >>
> >>>After about 1000 units all of a sudden two units used by the same
> >>>customer have failed.
> >>>
> >>>The diodes are a full short (FMKA140), understanding of a
> >>>breakdown under high reverse voltage was that it's non destructive
> >>>and them the diode will recover so long as it isn't damaged by heat.
> >>
> >>Where did you ever get such an idea? Your design is faulty.
> >>
> >
> > I don't operate them outside the design voltage, I am just trying to
think
> > of any possible reason for the failures.
>
> Then I'm confused. If you never exceed the absolute maximum
> specs, they should never fail. Your first post implied that
> you thought you could get away with exceeding the reverse
> voltage specification and get away with it if there were
> no heat damage.
>
> Correct me if I'm wrong, but if you apply a high enough
> reverse voltage to cause them to breakdown, aren't you
> exceeding the abs-max reverse voltage specification?
>
> Time to ask a better question.

Perhaps: Diode broken, why? Is that a good question?

I don't knowingly run the diode in reverse break down or exceed the voltage
spec of the diode. I do know that all of a sudden the diode is failing and
so am trying to figure out why. My understanding leads me to believe that
reverse breakdown is non fatal to a diode.

Ralph