Is the bad reputation of tantalums justified?

[wraper]

Firstly, X7R MLCC capacitors are mainly used for bypass/decoupling, and I really can't think of a case where a bypass capacitor won't do its job even if its capacitance has dropped by 50%. I mean, do you seriously think that, say, a uC is going to start glitching or an op-amp start oscillating because a 1uF cap bypassing the supply rail is really only 0.5uF?

This is not exactly the region where they mostly compete but where some bulk capacitance is needed. It's not too wise to decouple IC's with 1uF tantalum capacitors.

Thirdly, if you want to claim that any given tantalum is equivalent to a MLCC then lets not forget about case size and cost. I have not exhaustively searched DigiKey et al., but a cursory search shows that, e.g., a tantalum 6.8uF/10V/0805 capacitor will cost 2x as much as the equivalent X7R MLCC.

If looking on something like 33 or 47 uF with the same capacitance, tantalum caps could be even cheaper.

[Pjotr]

But hey, if you want to use tantalum and I don't then what's the big deal? Frankly, I am sorry I ever commented to this thread and will definitely think twice about relaying my experience here in the future. I really have spent way more time here on this than is warranted. Good day.

At least it made this thread lively and  encouraged many to come up with the right docs to answer OP question.

[jitter]

But hey, if you want to use tantalum and I don't then what's the big deal? Frankly, I am sorry I ever commented to this thread and will definitely think twice about relaying my experience here in the future. I really have spent way more time here on this than is warranted. Good day.

At least it made this thread lively and  encouraged many to come up with the right docs to answer OP question.

Indeed. Thanks for all the replies.

Although it may look like the manufacturers are selling (e.g.) 25 V tantalums as 50 V and then telling you to not go above 25 V to be safe, that's not the case.
Take the time to read one of the linked documents and it becomes clear why that is. I also know now why we saw a temporary increase in failures when we went leadfree, the solder process is an important factor in tantalum reliability. This went back to normal as soon as the insufficiently derated tantalums were corrected in the designs.

Infant failure rate of tantalums is higher than that of electrolytic caps, but as the lifetime progresses the failure rate of electyrolytics gets progressively worse while tantalums stay pretty stable. Long term, tantalums beat electrolytics. So I tend to agree why those that use tantalums the right way say that they're relaible. It is also my own experience in industrial electronics in which tantalum capacitors are still very common.

All types of capacitor have their place. It is likely, though, that new designs avoid the use of tantalums, but as I wrote before, that may be more of a result of rising prices of tantalum capacitors and the availability of (now cheaper) alternatives rather than bad reliability.

[Bud]

I really can't think of a case where a bypass capacitor won't do its job even if its capacitance has dropped by 50%. I mean, do you seriously think that, say, a uC is going to start glitching or an op-amp start oscillating because a 1uF cap bypassing the supply rail is really only 0.5uF?

Yes generic LDO voltage regulator may start oscillating if the capacitance drops below specification.

The other (not) use case would be in circuits that employ reference, calibration, etc, where the balance may be disturbed by changing level of noise/spurs, etc, because capacitance of the bypass caps changed with voltage or temperature. 

[jitter]

I would expect that the LDO has some "large" capacitance (say 1-10 uF) close to its output to mitigate this problem, maybe some more scattered around the board, and then ceramics close to the ICs.
Although putting ceramics parallel to tantalums might introduce stability problems in older generation LDOs that need quite a bit of ESR to remain stable (source), not  just a minimum capacity.
I would expect more modern LDOs to be designed with a very low ESR in mind, but they still need some (>15 mOhms)

This is what the ubiquitous LM337 will do if the ESR of the capacity on the output is below the minimum requirement (minimum capacity requirement fulfilled):


The oscillations would not occur when a mere 0.15 Ohms was put in series with the output pin.
Edit: if this waveform looks familiar, this thread might be the reason why.

[mikeselectricstuff]

Agree with that Tom. But high value ceramics have also their peculiarities to take care of. Their value fades over time so you have to count that in for their lifetime. And they are prone to mechanical stress, especially the >= 1808 sizes can have issues with that and thermal cycling of the boards. More rugged ones with a polymer strain relief barrier are also more expensive.

And they can "sing" due to piezoelectric effect if subject to high ripple.
Aluminium polymer caps are pretty close the the "perfect" cap - insanely low ESR. Pity they're so expensive.

[Someone]

10uF X5R capacitance and leakage vs DC voltage plots here:
https://www.eevblog.com/forum/projects/mlcc-discharge-curves/msg735041/#msg735041

[retrolefty]

There is no escaping it, capacitors of all kinds, are the most emotional component used in electronic. Resistors get no respect in comparison. So many cap myths, strong personal opinions and anecdotes. I always liked the blues ones. 


 Ever see the prices the audioFools pay for capacitors? Amazingly they mostly only op for upgrading caps in the signal path as they 'know' power rail caps have nothing to do with the output signal. 

[Niklas]

....
X5R & X7R can also have terrible voltage coefficients - there are plenty of graphs showing 70% loss at rated voltage and more than 50% of their capacitance at 50% rated voltage. It depends on the film thickness - the smaller the part is physically for a given rated capacitance the worse - for examples see page 5 of:

http://www.yageo.com/exep/pages/download/literatures/High%20Capacitance%20MLCCs_2012.pdf
...

Well, I stand corrected. I don't use Yageo parts, nor do I have the pressing need to cram 10uF into a 0603 package, but all that said it does appear that there is quite a wide range of DC bias characteristics vs. package size and capacitance value for the X7R dielectric from one of my preferred suppliers, Murata (another supplier, Kemet, doesn't even bother to quantify this behavior for their commercial and automotive parts, only military).

It might not be in the datasheet from Murata, but have a look at their website and search for their SimSurfer application. It will give you several charts, for instance capacitance-frequency, impedance-frequency, capacitance-DC bias. A bit slow to load, but quite handy.

[Zero999]

Slightly off-topic -- I've worked with rockets and fireworks hobbyists on all sorts of ignition circuits, and a very cheap and reliable way to ignite a charge is using a 90's era dipped tantalum capacitor. The ones I've used are 10uF, 10v ones.
When you hook them up in reverse and pump around 100 milliamps at 50V into them they blow up instantly and very impressively for their size.

Interestingly I tried a similar thing when I was an apprentice. I was hoping for an explosion but I was disappointed. It drew a large current, the capacitor melted and started to glow cherry read. I suppose it could be used as a thermal detonator but not a squib.

Ever see the prices the audioFools pay for capacitors? Amazingly they mostly only op for upgrading caps in the signal path as they 'know' power rail caps have nothing to do with the output signal. 

I regularly use tantalum capacitors and have found them to be very reliable. I am aware of the violent failure modes but aluminium capacitors can also explode, spewing their guts everywhere. Tantalum capacitors have the advantage of being completely solid, with no electrolyte to dry up. Their capacitance is stable over time, doesn't change with the applied voltage, the ESR doesn't increase with age and they're more mechanically robust than ceramics.

In my most recent project I'm using tantalum capacitors for AC coupling an audio signal. They work quite well and there's no measurable distortion. Because they're either in series with resistors or on the output of an op-amp, the current will be limited and they're run at under half their rated voltage, so I'm pretty confident they won't blow up.