Classic Bead Tantalum Capacitor Failure

[mediatechnology]

Some years ago I bought a used Tektronix 'scope plugin on ebay.
Almost immediately after I powered it the +5V supply crowbar'd from a dead short.
I could tell by smell and the burnt look which cap in the new plugin it was.

Today, about 10 years later, I realized I should have changed the two in the bipolar supplies.



The one cap shorted after about 5 minutes of use after being powered down for years.
A bead of hot molten tantalum flowed out of the fissure.

I replaced both caps with Aluminum electrolytics so I wouldn't have to do this again.
This is what classic bead tantalum capacitor failure - when used in bypass applications - looks like.

[JR.]

+1

I would hope tantalum is more robust these days, but modern low esr aluminum is cheaper and safer.

JR

[KMN]

Tantalums are pretty well against my religion...

I got tired of trying to figure out how to keep them happy in high current ripple applications.

Though I hear the tantalum polymers are quite a bit more tolerant high ripple current...the little beasts are way to rich for my blood.

Then there is the possibility of the Tantalum mines deciding to hold the world for ransom...again

I thought that ceramic was the future until...

have you noticed how difficult it is to source some types of MLCC's lately? I am seeing over 1 year lead time on specialized ceramics now...prices are going up due to supply and demand.

It's getting ugly out there...What in the world are we supposed to use for decoupling caps now? Films? My products all just grew by 50% in size.

[mediatechnology]

I had an unfused Tantalum burn a 1" charred hole about 30 years ago in a PCM3324 card.
It was unrepairable.
I'm glad Sony decided to replace it for free.

Aren't most modern SMT Tantalums fused?
The one in the Sony was a Kemet and wasn't fused.

[KMN]

If the fuses stop the explosions, it might convince me to consider straying from the flock. Hard to deal with, expensive parts that fail safe are better than not shipping due to long lead part sourcing problems.

I've also experienced the cratering. Often the collateral damage seeming much more dramatic than the energy involved in the circuit could apparently account for.

I seem to recall , my memory escapes where at the moment, some or all using magnesium in the manufacture of the leads. That might explain the craters.

[JR.]

Adding an internal fuse in series with a low impedance capacitor seems to partially defeat the benefit of low impedance, while it will calm fears about spectacular meltdowns.

I am probably repeating myself but not in this thread (yet). The only time in recent history that I intentionally used a tantalum capacitor was back in the -80s in a kit CX decoder (vinyl playback NR), to mimic more precisely the DA of a tantalum cap used in the encoder compression side chain time constant circuit.

This was arguably grossly over engineered but I was inclined to do things like that.

JR

[AnalogJoe]

Old thread, but I also had the same problem with a Tektronix pulse generator, the tantalum bypass caps kept blowing up, I replaced them with Panasonic aluminum electrolytics and problem solved. I dont know why would anyone use Tantalum in audio equipment, I cringed when I saw a pair of 47uF Tantalums back to back in a NP configuration straight on the output of the Line input differential amp on each channel of my MCI console, they had to go. Everytime I see the distortion curves of tantalum caps I go

[JR.]

Old thread, but I also had the same problem with a Tektronix pulse generator, the tantalum bypass caps kept blowing up, I replaced them with Panasonic aluminum electrolytics and problem solved. I dont know why would anyone use Tantalum in audio equipment, I cringed when I saw a pair of 47uF Tantalums back to back in a NP configuration straight on the output of the Line input differential amp on each channel of my MCI console, they had to go. Everytime I see the distortion curves of tantalum caps I go

Tantalum caps used to be premium caps back in the day (for compact size for one thing, low z another).

These days a low impedance aluminum (developed for switching PS apps) would be a sensible replacement.

BUT I already said that in 2018.

JR

[terkio]

These days a low impedance aluminum (developed for switching PS apps) would be a sensible replacement.

I like to hear this.
Tantalum was said to be unique with some best unbeatable characteristics. A bad point since Ta ore is mostly under control of African maffias and chinese grab on such high tech elements.
For effective low ESR; Can I forget about Tantalum caps, thanks to now days aluminum electrolytics ?

[JR.]

These days a low impedance aluminum (developed for switching PS apps) would be a sensible replacement.

I like to hear this.
Tantalum was said to be unique with some best unbeatable characteristics. A bad point since Ta ore is mostly under control of African maffias and chinese grab on such high tech elements.
For effective low ESR; Can I forget about Tantalum caps, thanks to now days aluminum electrolytics ?

IMO yes, but not just any aluminum, these are special designed for use in switching power supplies. As with any capacitor purchase look at the data sheet and what your needs are.

JR

PS: Tantalum mining has long been dirty (in more ways that one). US passed laws years ago about component manufacturers being forced to document and certify sources of the raw material they use (like tant). I recall several large capacitor companies having trouble with this, apparently lots of shady middle men that everybody tolerated for years.