[sdiy] Tantalum manufacturing / assembly failures OT?

Tim Ressel timr at circuitabbey.com
Thu Nov 15 19:41:04 CET 2018


HP I mean Agilent I mean Keysight Once did a project to increase the 
reliability of their products. After studying the repair records of 
their plant all over the world the number one failure was capacitors. 
They figured out that derating caps voltages made a huge difference in 
reliability. The rule after that was 100% derating on cap working 
voltages, that is to say a cap on a 12 volt line needs to be a 25 volt 
cap. Using a 16 volt cap is a no-no.

That being said, cheap bastards using uber cost saving cheap caps can 
also be a factor...

--timmers

On 11/14/2018 1:16 PM, Ullrich Peter wrote:
> Hi Ritchie!
>
> We had some failures with Tantalum capacitors but not that much.
>
> The Austrian Kemet Sales Manager once gave us a presentation about derating you should take care of.
> I found this presentation online - you can have a look at it here at Digikey:
> https://www.digikey.com/en/ptm/k/kemet/derating-guidelines-for-surface-mount-tantalum-capacitors/tutorial
>
> Ciao
> Peter
>
> ________________________________________
> From: Synth-diy <synth-diy-bounces at synth-diy.org> on behalf of Richie Burnett <rburnett at richieburnett.co.uk>
> Sent: Wednesday, November 14, 2018 18:46
> To: SDIY List
> Subject: [sdiy] Tantalum manufacturing / assembly failures OT?
>
> Since we're discussing Tantalum capacitors, has anyone else who manufactures
> things in reasonable quantities, (either hobby, SDIY or in their day job,)
> had problems with SMD Tantalum capacitors failing short or partially shorted
> due to excessing heat during reflow?
>
> I've had a bunch of boards made by a well known UK PCB fab and population
> company, and several off them had 100uF/25V Panasonic SMD Tantalums fail
> short-circuit within about 10 seconds of powering up the board.
>
> Just to rule out a design issue, the two capacitors that were failing only
> saw 15VDC from a well regulated power supply, and charge slowly through a
> resistor so there is no significant inrush current or AC ripple current
> either.  And they weren't installed with incorrect polarity!  The two
> devices that failed on each board are right next to a D2PAK SMD power device
> that is clearly discoloured from excessive temperature during assembly, so I
> can only suspect that the use of a hot-air pencil during assembly is the
> culprit!
>
> I haven't used SMD tants that extensively in electronics, so would be
> interested to hear others experiences, either on list or via PM.
>
> -Richie,
>
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-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com




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