You're pretty much guaranteed to see tantalum capacitors in use in any height/space constrained device. They come in thicknesses from 1.2mm to ~6mm, while "cans" start at ~8mm for the smallest capacitances. There are some high capacitance ceramic parts, but they come with their own baggage.

Niobium capacitors are the new tantalum alternatives. They have lower capacities, but also don't go up in flames when stressed. Keep in mind that standard tant's may be "stressed" if the voltage isn't derated by 100%! (A tantalum on a 12V line wants to be rated at 25V, etc.)

There are also "organic polymer" versions of aluminum and tantalum capacitors which offer much lower impedance and better reliability for a higher price - although the only applications which really benefit are high density power supplies.

Thing is: I don't think tantalums are really recommend for use in the audio signal path:
http://pdfserv.maxim-ic.com/en/an/AN3171.pdf
If they're for bypassing the power supply, that's all well and good, but they typically aren't used anywhere you want an "ideal" capacitor....

 

I've found that with sufficient voltage derating (someone mentioned 100%) but I've used as low as 50% _AND_ derating in the ripple current spec, they can be very reliable.

If the physical space is available, I would not risk using a tantalum.

Also to be proper, a tantalum capacitor is an electrolytic. The electrolyte is tantalum. A clear way to distinguish is "Aluminum electrolytic" versus "tantalum electrolytic."

 

Interesting. I have 2 tantalums in my whole collection, both 16v 10uf . I bought them for some mic's that reccomended them. I then read about unreliability both here and on Rod Elliot's site and have never actually installed them. I currently have one across an ADC's power supply (currently on breadboard). I am hoping to not need it on the "real" version which has a 100uf low impedence electrolytic (suitable for SMPS type) nearby. I also read the tantalum comes from a Gorilla habitat and that it is damaging that habitat by us taking it?

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It also depends on whether you're talking about the SMT or TH blob style packages, I've heard that some of the older TH designs can have reliablility issues.

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Actually I use a Lot of them this way. No Problems.

** Maybe there using Poor Quality one.

But on the other hand, I bought 7,500, 1uf @ 35 volt rating at a Surplus place for less than 1 cent each.
Never had one fail yet and I'm down to my last 2,500 piece roll.

Definately One of my Better Buys.

As to Voltage ratings Verses the Supply voltages, Most often my caps are rated at Double the Supply. I can't say if this makes a difference, But Possibly it does.

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I Really Don't belive that statement.

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Gorillas are breaking in the plant at night, doing bad things to the caps and leaving?? Not sure I believe it either..

 

Nigel, you keep stateing that tantalum's are very unreliable or have been in the past, what are the failure mode's they're known for, and specifically why do they fail? The link Gramo posted seems to praise tanlums in pretty much every deparment, except price? chemelec doesn't recommend them for use in 'brute force' filtering, but I have some from a bulk cap pack I got and was thinking about using them as motor filter caps eventually.

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They are both good to a degree, and both are necessary for some circuits.

Tantalum are capable of storing much more energy than an electrolytic - But they discharge about twice as fast; hence there use in high frequency designs. Also Tantalum's have a 'infinite' life span. They are the superior product, and you pay for what you get, its just too bad that Tantalum is one of the most rarest materials.

You would not use a Tantalum in a high current circuit such as a DC motor power supply - an electrolytic would be more suited. Electrolytic have a much slower charge/discharge time, hence a lower value Tantalum can replace a higher value Electrolytic. Electrolytic’s also have a rather short life span.

Not sure if it’s an issue with Nigel, but many people don’t realize Tantalum's are polarized components as well, and incorrect use will make them very unreliable.

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Actually true. Tantalum caps are made from coltan ore, found primarily in the politically unstable Congo. It has helped fuel a bloody war. Most of the ore on the market has probably been smuggled out of the Congo and sold in neighboring countries. The mining operations may adversely affect the threaten Eastern Lowland Gorilla population.

http://en.wikipedia.org/wiki/Coltan

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They always fail S/C, usually as supply decouplers on PCB's fed from regulated supplies - but I suspect that's probably just because that where they tended to be used?.

As to why they fail?, I've no idea - as far as I remember they were usually 25V rating on 12V regulated lines? - I've always assumed it's because they are crap!

I don't know if people here remember the valve days?, but a common capacitor manufacturer was Wima (non-electrolytics) - and those were also extremely unreliable. To the extent that if you ever saw them used in a piece of equipment for repair, the first thing you did was replace them all - and that would cure 90%+ of the faults. Tantalums aren't quite that bad, but if you see any on a board the first thing you do is check them all to see if they are S/C - this finds the majority of faults (or did, back when they were used!).

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Were Wima caps as bad as Hunts?

 

On regulated lines the failure rate increases because of the low output impedance of IC regulators. In those applications the operating voltage should be much less than the rated one.

 

This was pre-IC regulators - but in any case that doesn't make much sense?.

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Some app notes suggest that the operating voltage should be 30% of the rated one, when tantalum caps are used with regulated power supplies. If the output voltage is 12 V or more, 36 V rated tantalum caps are expensive. And aluminum electrolytic technology has improved... they fearure low ESR as well and higher voltages.

An interesting reference: http://www.hitachi-aic.com/english/p...infotumtal.pdf