Burn in of Tantalum caps

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We are seeing around 1 in 100 Tantalum caps fail shorted when initially pow
ered up on the test fixture.  There was a discussion here about such failur
es being an initial short from fabrication or created when reflowed on the  
board.  An article was linked which discussed a real world app where they p
owered up the board with a voltage ramp and enough series resistance to pre
vent the cap from creating a hard short and failing.  But no information on
 how slow is "slow" and how much resistance is needed to prevent damage whi
le clearing the short.  

On the test fixture we can add a resistance to be bypassed with a jumper.  
We can't control the ramp up time of that voltage rail other than adding mo
re capacitance to slow it down.  I suppose that is an option if we know a t
arget ramp rate.  I've asked the manufacturer of the regulator (CUI V7812-1
000) what the ramp rate is and how it varies with capacitance.  We'll see i
f they respond.  

Any suggestions on improving this problem?  It's not a big deal, but we did
 have one cap that failed catastrophically and actually burned the board, b
ut not beyond repair.  

  Rick C.

  - Get 6 months of free supercharging
  - Tesla referral code - https://ts.la/richard11209

Re: Burn in of Tantalum caps
snipped-for-privacy@gmail.com wrote:
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Could it be the polarity is reversed relative to the marking and the  
orientation in the reel?




Re: Burn in of Tantalum caps
On Fri, 11 Jan 2019 01:19:39 -0500, "Tom Del Rosso"

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Tantalum caps are bombs-by-the-reel. The tantalum pellet is the fuel
and the MnO2 is the oxidizer. It's prudent to not detonate them.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Burn in of Tantalum caps
John Larkin wrote:
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Yeah, I've read that they blow up if reversed.  But what if the voltage  
is low and derated?




Re: Burn in of Tantalum caps
On Friday, January 11, 2019 at 12:19:15 PM UTC-5, Tom Del Rosso wrote:
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When you read how they come up with the various derating factors it turns o
ut the real issue is surge current.  So rather than derate the voltage whic
h really doesn't solve the problem necessarily, the surge current should be
 calculated and accounted for.  

Applying a derating factor to the voltage as a way to account for surge cur
rent is lazy engineering.  

  Rick C.

  -+ Get 6 months of free supercharging
  -+ Tesla referral code - https://ts.la/richard11209

Re: Burn in of Tantalum caps
On Fri, 11 Jan 2019 12:16:40 -0500, "Tom Del Rosso"

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Bypassing a power rail, voltage derating by 3:1 seems safe, but we
never use them on a big input power rail... usually on a regulator
output. I prefer aluminum polymer caps, but some voltage regulators
like the ESR of tantalum caps.

We don't deliberately reverse bias tantalums; I'm not sure what's safe
there. I've tested some aluminum polymers for bipolar use, and
selected some that seem reliable at serious reverse voltage.



--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Burn in of Tantalum caps
On Fri, 11 Jan 2019 09:45:40 -0800, John Larkin wrote:


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1 V is enough to do it.  Supposedly, even an old voltmeter on the Ohms  
range could do it.

Jon

Re: Burn in of Tantalum caps
On Fri, 11 Jan 2019 07:31:45 -0800, John Larkin wrote:

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Yup, I don't use them for that reason.  I use Oxi-Caps (AVX Niobium  
Oxide) instead.  Some cost a bit more, some are less than equivalent  
Tantalum parts, but I've used thousands, all reflowed, and never had one  
fail, unless a first article had some put in backwards.  (That did happen  
once.)

Jon

Re: Burn in of Tantalum caps
On Monday, January 14, 2019 at 3:12:46 PM UTC-5, Jon Elson wrote:
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I can't seem to find a magic bullet replacement in this case.  Niobium Oxide caps don't seem to be available in the voltage range.  The highest I can find are rated for 10 volts.  

How are Tantalum Polymer caps?  


  Rick C.

  ++ Get 6 months of free supercharging
  ++ Tesla referral code - https://ts.la/richard11209

Re: Burn in of Tantalum caps
On Thu, 10 Jan 2019 20:28:11 -0800 (PST), snipped-for-privacy@gmail.com
wrote:

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 dV/dt  

https://www.avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdf


Regards,

Boris Mohar

Got Knock? - see:
Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca

void _-void-_ in the obvious place

  

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Re: Burn in of Tantalum caps
On Fri, 11 Jan 2019 02:16:14 -0500, Boris Mohar

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Fig 4 is interesting, especially for "one or more current surges."

Fig 8 is crazy. Add all that stuff to every cap?

Their math is pretty flakey.




--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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Re: Burn in of Tantalum caps
On 1/11/19 3:23 PM, John Larkin wrote:
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Specially using a single JFET for a high-current totem pole. ;)

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Or just limit them to the outputs of linear regulators and stuff like  
that.  It's the supply input that has the issue.  (Our stuff has to be  
able to handle being connected to two car batteries in series, because  
people actually do that.)

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Burn in of Tantalum caps
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Put together an automotive box last month, it can pretty much handle any  
input voltage, continuously, until the MOV goes up in smoke.

Fairly easy to do stuff like that when your box uses only a watt or two,  
though!

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
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Re: Burn in of Tantalum caps
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We normally use 24V wall warts anyway--it's the inrush torture test that's the issue.  

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Yup. Not hard, just necessary.  

Cheers

Phil Hobbs

Re: Burn in of Tantalum caps
On Sun, 13 Jan 2019 00:17:17 -0800 (PST), snipped-for-privacy@gmail.com wrote:

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Users will plug in the wart and then connect the 24 volt end. Zap!


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Burn in of Tantalum caps
On Sunday, January 13, 2019 at 10:58:37 AM UTC-5, John Larkin wrote:
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Right it's hot plugging that can cause issues.  
I made a circuit power by a 48V wall wart.  When unplugging it sparked  
enough to leave a scar, got ugly after a while.  

George H.  
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Re: Burn in of Tantalum caps
On Friday, January 11, 2019 at 2:03:36 AM UTC-5, Boris Mohar wrote:
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powered up on the test fixture.  There was a discussion here about such fai
lures being an initial short from fabrication or created when reflowed on t
he board.  An article was linked which discussed a real world app where the
y powered up the board with a voltage ramp and enough series resistance to  
prevent the cap from creating a hard short and failing.  But no information
 on how slow is "slow" and how much resistance is needed to prevent damage  
while clearing the short.  
Quoted text here. Click to load it
.  We can't control the ramp up time of that voltage rail other than adding
 more capacitance to slow it down.  I suppose that is an option if we know  
a target ramp rate.  I've asked the manufacturer of the regulator (CUI V781
2-1000) what the ramp rate is and how it varies with capacitance.  We'll se
e if they respond.  
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did have one cap that failed catastrophically and actually burned the board
, but not beyond repair.  
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NiobiumCapacitors.pdf

Author of that article is an idiotic moron from hell. Who in hell would thi
nk the voltage rating of the capacitor could possible affect peak current s
urge. So either that fool is an idiot or something is being lost in transla
tion.

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.ca


Re: Burn in of Tantalum caps
On 1/12/19 11:57 AM, snipped-for-privacy@gmail.com wrote:
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Take a look at Eq. 2 and the surrounding discussion.  Their resistance  
appears to be constant for any given series.

Cheers

Phil Hobbs

--  
Dr Philip C D Hobbs
Principal Consultant
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Re: Burn in of Tantalum caps
On Sat, 12 Jan 2019 08:57:05 -0800 (PST),
snipped-for-privacy@gmail.com wrote:

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But voltage derating does make tantalums reliable.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Burn in of Tantalum caps
What rating and test voltage, out of curiosity?

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
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