Is the bad reputation of tantalums justified? - Page 1
Forum section: electronics / projects

author: jitter
author_rank: Frequent Contributor
timestamp: September 19, 2015, 06:26:15 am
content: In my work in industrial electronics, I find that the usage of tantalum capacitors is still very common (esp. SMDs), despite having a bad reputation. So I was wondering how justified this reputation actually is.High capacity and low ESR in a relatively small package are of course attractive characteristics when space is limited. And unlike an electrolytic cap, they don't dry out with age.In the past, when switching to the RoHS compliant soldering process, we temporarily saw an increase in tantalum failures. And of course the failure mode of a tantalum cap is quite spectacular, probably strengthening the bad reputation even more.At first we thought that the higher temperature of the leadfree solder process was the culprit. But in all cases an incorrect derating turned out the be the real reason. Look at some tantalum datasheets, and you'll find that the derating can be quite severe. Rule of thumb: use at least twice the rated voltage of the nominal voltage in your circuit. In other words: using a 16 V tantalum on a 12 V rail is asking for problems, use 25 V instead and you're fine.We do see designs appearing that completely avoid the use of tantalums. Tantalium (Ta) is becoming scarce, and so the prices are rising. That higher price seems to be the actual incentive to avoid tantalums, rather than the alleged short life. And of course, nowadays there are alternatives available (e.g. ceramics of high capacities, polymer caps in the same shapes as SMD-tantalums).So how justified is that reputation?

author: EEVblog
author_rank: Unknown
timestamp: September 19, 2015, 06:35:16 am
content: Tantalums are generally not very tolerant of small overvoltage spikes etc.When used within spec they are otherwise very reliable.

author: jitter
author_rank: Frequent Contributor
timestamp: September 19, 2015, 06:51:58 am
content: Might that explain why we saw the most failures during power on? Sometimes as spectecular as shooting a long flame. This destroyed some pcbs, burning right through the FR4 material.

author: John Coloccia
author_rank: Super Contributor
timestamp: September 19, 2015, 06:59:34 am
content: Quote from: jitter on September 19, 2015, 06:51:58 amFlamethrower is the typical failure mode. Power on surges is a common killer. It's really important to follow all the rules when designing with tantalums. It's not like a lot of other devices where you can get away with a little sloppiness. They are quite serious about things like voltage limits, derating, ripple and things like that. It's like charge pumps. When they say that the maximum PS voltage is 13V, or whatever, you'd better be sure it doesn't see 13.0001V because you'll blow it up. Some devices are just like that.

author: Stonent
author_rank: Super Contributor
timestamp: September 19, 2015, 07:02:10 am
content: I guess I've not been lucky enough to see a spectacular failure of a tantalum. I have however heard electrolytics go off like a gun shot in cheap computer power supplies. (Complete with paper fluff all over everything, the blue plastic sleeve on the floor outside the power supply and the metal can laying on some random part of the board.

author: marshallh
author_rank: Unknown
timestamp: September 19, 2015, 07:19:40 am
content: You really do need to follow every single detail with them, I have seen crowbars around tants and series ferrites.Otherwise this happens (and this is a very small one)

author: AndyC_772
author_rank: Super Contributor
timestamp: September 19, 2015, 07:24:01 am
content: I've seen them fail short circuit even in designs where they really aren't subject to over-voltage or other stress conditions. Well-respected brand, close to double the required voltage rating, and still we saw a significant number of failed caps.Ceramics these days are available with such a high capacitance density, I see very little reason to use them any more.

author: Smith
author_rank: Frequent Contributor
timestamp: September 19, 2015, 07:24:20 am
content: They give a nice flash when they go. Had a dozen of boards running at 12V with 10V caps on it for over 20 years (not my build, and they had no 'obvious' voltage rating). I once hot-plugged one of them looking for a failure, and it went kaboomTook me days to replace them all.That was my only bad experience with them in decades, never had any other failing, nor at work, nor at home. I have repaired quite some devices (vintage and new audio, video, laptops etc).

author: Psi
author_rank: Super Contributor
timestamp: September 19, 2015, 07:42:32 am
content: Tantalum on output of Vreg = good (Stable voltage and their ESR is high enough to not cause stability problems like you get with ceramics)Tantalum on input of Vreg = bad (Risk of large input voltage spikes)

author: DutchGert
author_rank: Frequent Contributor
timestamp: September 19, 2015, 09:37:23 am
content: And dont'forget that the tantalum is mined almost exclusively from conflict countries or at leas from places where they do not care a single bit about polution of the environment.For me that is reason enough not to use them.

author: JoeN
author_rank: Frequent Contributor
timestamp: September 19, 2015, 10:07:26 am
content: I put one in backwards in a project once. 100% my fault. It really did go up like fireworks. Here is the charring after I removed it (a 10uF cap).

author: Joule Thief
author_rank: Regular Contributor
timestamp: September 19, 2015, 10:16:54 am
content: In my experience, they are guaranteed to be a contributor to power supply malfunctions in older 400 series Tek scopes.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 19, 2015, 10:33:52 am
content: Quote from: AndyC_772 on September 19, 2015, 07:24:01 amThis has been my experience with tantalum* caps as well. I have never had a problem with quality aluminum electrolytic capacitors and except for really low profile applications there is no job they - along with a ceramic bypass cap in parallel - can't do better and cheaper than a tant (just use a quality elko, and not one of the notorious Wun Hung Lo brands starring on badcaps.net).* - more specifically, the "dry sintered" type, rather than the "wet slug" type used almost exclusively for military/space applications; I have no experience with the latter.

author: Pjotr
author_rank: Frequent Contributor
timestamp: September 19, 2015, 10:46:36 am
content: Tantaliums by themselves are very reliable and long lasting, provided they are properly used. Engineers not understanding and/or neglecting their properties are to be blamed if they fail.Some limitations are limited overvoltage and limited dI/dt. Limited overvoltage is usually not a problem in a well designed circuit. Usually the cause of faillure is a too high dI/dt, especially when used at power rails. That doesn't mean they are no good at power rails, in fact they perform very well there. But you have to take care to stay within their dI/dt limits, especially at power on this is often neglected.

author: IanJ
author_rank: Unknown
timestamp: September 19, 2015, 10:57:56 am
content: Hi,I used them a LOT in the 80's/90's on offshore installations around the world.....let's say 400 pcb's. All of them were across power rails varying from -15v to +24v and across all of those we probably had less than 5 tantalums go bad (short out....bang!)..............for no apparent reason at the time.In the workshop during manufacturing design & test though it was a different story.......assemblers putting them in the wrong way round, the wrong voltage etc etc........we probably had 25 short out.....bang!Never had anything like the same problems with any other passive component.I can still remember the smell even thought it's been many years!Ian.

author: andybarrett1
author_rank: Regular Contributor
timestamp: September 19, 2015, 11:30:47 am
content: My two pennies worth...I repair Industrial ABB circuit boards for my day job,,,,,Rule 1, See a little square Tant cap in a circuit that don't work he be the prime suspect (usually dead short)Why do ABB love those 6.8uf / 35v things....Pain is the arse to source?BRAndy

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 19, 2015, 11:34:22 am
content: Quote from: Pjotr on September 19, 2015, 10:46:36 amOr, really? Then how would you explain the ~0.1% failure rate I observed in tantalum caps coming right off the reel, *before* soldering? Can't really blame *me* for that, can you?Be careful before you call others incompetent.

author: Pjotr
author_rank: Frequent Contributor
timestamp: September 19, 2015, 11:55:11 am
content: Quote from: MagicSmoker on September 19, 2015, 11:34:22 amDo you feel addressed yourself? With such a high failure rate right from your supplier, complain at you supplier then. It is certainly not common. But yeah, modern Chinese stuff........Nevertheless the main failure over time is the neglected dI/dt limit of them. This causes a short with fireworks as a final bonus. It is known for over 40 years, but I have seen many designs that did not take care of.

author: Howardlong
author_rank: Super Contributor
timestamp: September 19, 2015, 12:00:52 pm
content: Quote from: JoeN on September 19, 2015, 10:07:26 amEasy to do. For some reason, on wire ended caps, they place the band on the +ve not the -ve on tantalums, the opposite of standard electrolytics. I learned to make that mistake just the once.With polymer electrolytics and ceramics nowadays, there's less and less reason to need tantalums at all.

author: SeanB
author_rank: Super Contributor
timestamp: September 19, 2015, 12:23:29 pm
content: Quote from: andybarrett1 on September 19, 2015, 11:30:47 amBecause that was a standard value, high enough to be useful, but not a 10uF unit which cost twice the price.I changed many over the years, especially in avionics, mostly the solid slug type which had failed due to them being the cheap ones ( for solid slug that is) with a rubber seal that degraded with time. I used regular aluminium electrolytics as replacements in most cases, just because I could not source the proper ones ( a little sanctions thing), and had a 2 pallet list of everything with the word "cap" in it from stores as a guide to get the stuff out from existing stock. I found a lot of 1000 10uF 10V units in there that had been sitting since the 1970's, and tested 200 before giving up, the only failure was me putting it in backwards and applying 10V with a current limit of 10A. then I used them as small howitzers, especially the ones I removed which still had some capacitance and thus some electolyte. They do go through thin board at short range though you needed the 28VDC bus rail with the 50A breaker to get the full effect.The dry ones will go crispy, especially the orange or blue ones, the older coloured band units were a lot more reliable, probably because those have not been made for 40 years so all the early failures would have gone bang by now. The orange would burn through the board, the blue ones would just burn.I wonder how those ceramic caps will behave with time, I am very suspicious of them, as they are both thin, exposed to contaminants ( no real seal on the active layer) and they have had reliability issues. Ask anybody who used those first gen ceramic decoupling caps in glass tubes, or the yellow dipped cases, and how many caught fire on 5V rails in computers. I have seen them lit up like a lamp on the board, as the power supply was not quite capable of blowing them out, and had the overcurrent limit drop the voltage to around 3V with no foldback.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 19, 2015, 01:03:03 pm
content: Quote from: Pjotr on September 19, 2015, 11:55:11 amYou made the blanket statement bolded/underlined above and so I was deemed incompetent by you via implication.That said, the capacitors which were DOA on the reel were made by AVX, so not a "no-name" Chinese supplier (although I am sure they were made in China, just like every other electronic component these days), however, identical value/package capacitors from Kemet and Cornell-Dubilier also failed in circuit.Quote from: Pjotr on September 19, 2015, 11:55:11 amYes, the dI/dt limit for tantalum caps - as well as failures due to ripple and surge currents, and overvoltage - are reasonably well known, especially among those who design or service switch-mode converters and limiting surge current into or out of the capacitors is easy enough to do. I am saying that even when I have addressed all of the aforementioned restrictions I still had tantalum caps fail prematurely in-circuit (as well as straight off the reel).

author: jitter
author_rank: Frequent Contributor
timestamp: September 19, 2015, 01:42:28 pm
content: Quote from: MagicSmoker on September 19, 2015, 01:03:03 pmOr so we think.Some examples:Look at ON-Semi devices with a lot code that starts with R. That's for Roznov in the Czech Republic.The other day I was looking at a reel of IM03GR relays from TE/Axicom: made in Portugal. Same brand, different type: Czech Republic.OP627AP's: Thailand. The list could be continued with: Malaysia, Philippines, Israel (e.g. Vishay/Kemet), Korea etc.

author: G0HZU
author_rank: Super Contributor
timestamp: September 19, 2015, 10:34:51 pm
content: QuoteThat's my experience too. I've designed large boards with lots of SMD tants on. i.e. dozens and dozens of them per PCB and we made many, many thousands of these boards with no reliability issues at all. I've been using tants in all my designs for over 25 years and if I thought there was an issue with them then I'd stop using them and so would the company I work for. So I speak for over 100 engineers across maybe 30 years of designing high end comms products. The bottom line is that tants are high performance components with excellent reliability over time and temperature etc provided they are used correctlyI've seen what happens if an engineer uses them incorrectly. Usually the failure rate becomes quite high with many tants failing during initial development or during initial acceptance testing. In a bad design they can fail spectacularly the first time the unit is switched on.

author: sarepairman2
author_rank: Frequent Contributor
timestamp: September 20, 2015, 12:57:06 am
content: i always thought tantalums is something you put on the pampered isolated front end that uses a bunch of linear regulators.i wonder if alot of failures are due to spikes on power on...perhaps i should start adding littleRC filters to the en pin on regulators.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 20, 2015, 11:48:51 am
content: Quote from: G0HZU on September 19, 2015, 10:34:51 pmOkay, so how do you use them correctly, or was the purpose of your post - like Pjotr's earlier - merely to tell us how awesome you are?

author: AndyC_772
author_rank: Super Contributor
timestamp: September 20, 2015, 01:22:27 pm
content: I read 'inexperienced' rather than 'awesome'. I thought tantalum caps were perfectly reliable too, right up until the point I came across a design in which they simply weren't.

author: KJDS
author_rank: Super Contributor
timestamp: September 20, 2015, 01:27:09 pm
content: I shipped about 1000 units out that all tested fine. They were integrated by the customer and had a few days of testing there. 35V devices on an 8V rail. Unfortunately they were in backwards, and because they were so heavily derated took a couple of weeks to fail, by then they were spread over about 300 sites across Europe. Oops.Mostly they're fine, but it's common to open up an old instrument and find one that's changed colour on a board with dozens on. Easy enough to spot so they're an easy repair. Never known one die spectacularly unless abused.

author: DimitriP
author_rank: Super Contributor
timestamp: September 20, 2015, 01:46:35 pm
content: What I find interesting is on Digikey's web site in the parametric search for capacitors, Tantalum capacitors have selection for reliability and another for failure rate .Looking at a list of 10uF 50V prices range from $3.75 to $50.68 for qty 1 !

author: G0HZU
author_rank: Super Contributor
timestamp: September 20, 2015, 09:36:49 pm
content: Quote from: MagicSmoker on September 20, 2015, 11:48:51 amThe purpose of my post was merely to provide a real world example where engineers like myself have been successfully designing with tants for decades and we still use them in our designs today. We would stop using them in new designs if we thought the technical risk was too great.QuoteIf you are in doubt I would recommend reading the datasheet carefully and/or speaking to reps from the manufacturer to discuss specific design requirements. eg to see if tants are suitable for a particular circuit design.

author: tom66
author_rank: Super Contributor
timestamp: September 20, 2015, 10:18:00 pm
content: Little reason to use them now.- Ceramics have high capacitance figures.- Polymer electrolytics for where ceramics lack.- Ordinary electrolytics when treated well last a long time.- Modern LDOs are perfectly stable with zero ESR, as are many switching regs (and ceramics can offer better transient response with near zero ESR**)- No need to worry about voltage rating for ceramics as they will be perfectly tolerant of overvoltage. Only concern is capacitance rolloff.** D-CAP2 and other such hysteretic switchers excepted: due to how the internal ripple reference is generated lower output ESR causes worse transient response. ask me how I know.I'm sure for some applications e.g. high temperature ultra high reliability they may still be desired but in the electronics I work on, I haven't seen a tantalum used for 10 years.

author: Pjotr
author_rank: Frequent Contributor
timestamp: September 21, 2015, 08:53:58 am
content: 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.

author: coppice
author_rank: Super Contributor
timestamp: September 21, 2015, 09:15:29 am
content: Quote from: MagicSmoker on September 19, 2015, 11:34:22 amHow long had those been in storage before coming off the reel? 0.1% sounds a high failure rate for freshly made parts. For parts that have been in storage for a while, whiskers shorting the plates might account for 0.1% failures.

author: mrpackethead
author_rank: Super Contributor
timestamp: September 21, 2015, 10:03:53 am
content: I dont' like using tantalums because So much tantalum is mined by children under very dangerous circumstances.

author: wraper
author_rank: Unknown
timestamp: September 21, 2015, 10:05:54 am
content: Quote from: coppice on September 21, 2015, 09:15:29 amOr ordered from some shady supplier, so might be counterfeits as well.

author: coppice
author_rank: Super Contributor
timestamp: September 21, 2015, 10:12:19 am
content: Quote from: mrpackethead on September 21, 2015, 10:03:53 amWill their lives somehow be improved by trashing the market value of the commodity which appears to be their best choice for an income right now?

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 21, 2015, 11:25:31 am
content: Quote from: AndyC_772 on September 20, 2015, 01:22:27 pmYes, I'm beginning to suspect the same thing - that those who have not had any problems with tantalums have simply not come anywhere close to any of their datasheet limits. Don't get me wrong - I always use components at less than datasheet-claimed specifications, but at some point derating goes from "prudent" to "absurd". I mean, if I have to derate working voltage, ripple current and temperature on tantalum caps by >50% to keep them from blowing up (and worry about the rate of change of current and voltage, to boot) then why the hell should I select them in the first place? I can suffer the same voltage/temperature restrictions with a high-K MLCC (though with entirely different consequences) and still don't have to worry about too much ripple current (within reason, of course)!

author: AndyC_772
author_rank: Super Contributor
timestamp: September 21, 2015, 11:31:21 am
content: The design in question was, IIRC, using a "35V" capacitor on a 20V rail.I wonder whether any cap manufacturer has ever been successfully sued over their misleading ratings? The idea that a design engineer should have to implicitly know and understand that the data sheet specs are garbage, doesn't sit well with me at all. The manufacturer is in a much better position to know what voltage a component will really withstand, over time, temperature and a large population of parts. Not me.

author: John Coloccia
author_rank: Super Contributor
timestamp: September 21, 2015, 12:03:38 pm
content: Read the datasheet.

author: wraper
author_rank: Unknown
timestamp: September 21, 2015, 12:08:32 pm
content: Quote from: MagicSmoker on September 21, 2015, 11:25:31 amThat exactly what manufacturers suggest depending on the conditions.http://www.kemet.com/Lists/filestore/Derating%20Guidelings%20for%20Tantalum%202011%20(3).pdfhttp://web.arrownac.com/sites/default/files/pdfs/voltage%20derating%20rules%20.pdfhttp://www.kemet.com/Lists/TechnicalArticles/Attachments/164/2004%20CARTS-Europe%20-%20Derating%20Differences.pdfQuoteQuote

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 21, 2015, 01:14:20 pm
content: Quote from: wraper on September 21, 2015, 10:05:54 amIf by shady supplier you mean DigiKey, well, guess I'm guilty.Quote from: wraper on September 21, 2015, 12:08:32 pmRight... so I guess you didn't pick up that I was basically saying that once you do all the necessary derating to ensure a tantalum cap can survive such a stressful application as, say, board-level supply bypassingthat tantalum is no longer even remotely competitive with al. electrolytic and/or MLCC types?

author: wraper
author_rank: Unknown
timestamp: September 21, 2015, 01:32:39 pm
content: Quote from: MagicSmoker on September 21, 2015, 01:14:20 pmWell, if you use MLCC of comparable capacitance without significant voltage derating, you'll find that there is not so much of the rated capacitance left. MLCC capacitors are prone to become shorted too. So, your reasoning about being completely not competitive is quiet questionable. Also if you need some thin boards, electrolytic capacitors are not any good and have own downsides.

author: AndyC_772
author_rank: Super Contributor
timestamp: September 21, 2015, 02:01:51 pm
content: Here's quite a good presentation comparing different capacitor types for use in power applications:http://www.kemet.com/Lists/TechnicalArticles/Attachments/5/Avnet2012PowerForum_CapacitorsSelection.pdf

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 21, 2015, 08:39:14 pm
content: Quote from: wraper on September 21, 2015, 01:32:39 pmThis really only applies to Y5V and Z5U dielectrics, which can lose as much as 60% of their capacitance when 100% of rated DC voltage is applied; the capacitance of X7R (and similar dielectrics) only declines by about 10% under the same operating conditions.Now one problem with Y5V and Z5U MLCC capacitors that you didn't point out is their distressingly high piezoelectric effect but that, again, mainly applies to the highest-k Y and Z dielectrics, is much less of a problem with the X series dielectrics, and even less so with NP0/C0G types.Quote from: wraper on September 21, 2015, 01:32:39 pmOne common cause for an MLCC to fail short is flexure, especially if lead-free solder is used (something I thankfully don't need to use). Aside from using leaded solder, there are usually "soft-termination" versions of MLCCs which are much more tolerant of flexure, and there are even safety-rated versions that are guaranteed to open like a fuse if they fail short for any reason. Conversely, the only choice you have with tantalum failure modes is whether it just blackens the board from overheating or it also turns into a little flamethrower.Now, all that said, I mainly design stuff for industrial and transportation applications, so a very hostile operating environment with plenty of temperature swings, vibration and impact shock, etc., yet I have never had a single MLCC fail on me and by now I've probably used about a million of them.Quote from: wraper on September 21, 2015, 01:32:39 pmQuestion my reasoning all you like; matters not to me.Quote from: wraper on September 21, 2015, 01:32:39 pmWell, I'll grant you that one advantage for tantalum: they do come in much lower height packages for an equivalent CV rating. They do tend to take up a lot more board area, however, to achieve a usable confluence of C, V and Irms.

author: ez24
author_rank: Super Contributor
timestamp: September 21, 2015, 10:03:48 pm
content: Quote from: AndyC_772 on September 21, 2015, 02:01:51 pmAdded this tohttps://www.eevblog.com/forum/beginners/electronics-primers-course-material-and-books/thanks

author: splin
author_rank: Frequent Contributor
timestamp: September 22, 2015, 12:17:45 am
content: Quote from: MagicSmoker on September 21, 2015, 08:39:14 pmX5R & 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.pdfYou can reduce the problem by choosing larger parts with larger case sizes or paralleling lower capacity parts with the same size but it doesn't come for free - the larger parts are more expensive.Worse, the loss of capacitance increases with time so it might lose another 5 to 15% over the course of a few years at room temperature and considerably worse at higher temperatures. The ageing rate is also dependant on the DC bias voltage. Interestingly Y5V is so bad that Kemet state:QuoteSome information on ageing can be found here:https://books.google.co.uk/books?id=tdx7lS4fO9wC&pg=PA418&lpg=PA418&dq=x7r+ageing+dc+bias&source=bl&ots=OZm-1hMU3W&sig=GbPCbe62Hq4GUsKuZpcpkFaHBGs&hl=en&sa=X&redir_esc=y#v=onepage&q=x7r%20ageing%20dc%20bias&f=false

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 22, 2015, 12:31:15 pm
content: Quote from: splin on September 22, 2015, 12:17:45 amWell, 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).

author: wraper
author_rank: Unknown
timestamp: September 22, 2015, 01:17:56 pm
content: Quote from: MagicSmoker on September 22, 2015, 12:31:15 pmCapacitors from all vendors experience this behavior. You usually can find data in the datasheet for particular part number, or using calcucators from manufacturers where you can select particular series but this DC bias stuff usuallyis even less obvious than derating requirements from tantalum capacitors. Murata has this data in their datasheets toohttp://psearch.en.murata.com/capacitor/product/GRM21BR61A106KE19%23.pdfFor this particular X5R, 10 uF, 10V, 0805 capacitor, only 25% of the rated capacitance is left at the rated voltage.If you consider the capacitance dropping more than by half being insignificant, my condolences to your customers. Yet again, I wrote:QuoteBecause you were arguing:QuoteI guess they are supposed to compete in similar usage scenario?

author: wraper
author_rank: Unknown
timestamp: September 22, 2015, 01:28:46 pm
content: Or this Murata X5R 10uF, 25V, 1206 caphttp://psearch.en.murata.com/capacitor/product/GRM31CR61E106KA12%23.pdfAt 10V, only half of the capacitance left, at 25V only about 18%

author: derGoldstein
author_rank: Regular Contributor
timestamp: September 22, 2015, 01:47:54 pm
content: 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. I don't think I've ever seen them fail to ignite black powder, and sometimes they're hot enough to ignite candy rockets with no additional chemicals (though you'd probably want to sprinkle a tiny amount of magnesium powder to increase the temperature of the ignition).Their advantage over heating wire (nichrome) is that you can hook them up using extremely thin wire-wrapping wire, much thinner than you'd usually need to use, so they're great for pencil-scale rockets and tiny remote-activation circuits.After you use them in that way for a while, you get used to *always* do a reverse bias test every time you start using a new model of tantalum capacitor. And I would never use an older dipped tantalum capacitor in any circuit, no matter how cheap I manage to get them. They're a huge fire hazard.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 22, 2015, 02:27:04 pm
content: Quote from: wraper on September 22, 2015, 01:17:56 pmFirstly, 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?Secondly, there is usually no penalty to specifying a much higher voltage rating for the MLCC than is necessary. For bypassing I mainly use 50V rated X7R caps in values of 1uF and 100nF, depending on how much current the particular IC uses and how much dI/dt might be expected. Even for a 15V rail this results in precious little reduction in capacitance from DC biassThirdly, 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.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.

author: wraper
author_rank: Unknown
timestamp: September 22, 2015, 02:57:47 pm
content: Quote from: MagicSmoker on September 22, 2015, 02:27:04 pmThis 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.QuoteIf looking on something like 33 or 47 uF with the same capacitance, tantalum caps could be even cheaper.

author: Pjotr
author_rank: Frequent Contributor
timestamp: September 22, 2015, 03:25:09 pm
content: Quote from: MagicSmoker on September 22, 2015, 02:27:04 pmAt least it made this thread lively and encouraged many to come up with the right docs to answer OP question.

author: jitter
author_rank: Frequent Contributor
timestamp: September 22, 2015, 04:12:18 pm
content: Quote from: Pjotr on September 22, 2015, 03:25:09 pmIndeed. 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.

author: Bud
author_rank: Super Contributor
timestamp: September 22, 2015, 05:05:56 pm
content: Quote from: MagicSmoker on September 22, 2015, 02:27:04 pmYes 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.

author: jitter
author_rank: Frequent Contributor
timestamp: September 22, 2015, 07:05:20 pm
content: 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 needsome(>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 threadmight be the reason why.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 22, 2015, 10:18:07 pm
content: Quote from: Pjotr on September 21, 2015, 08:53:58 amAnd 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.

author: Someone
author_rank: Super Contributor
timestamp: September 23, 2015, 12:47:49 am
content: 10uF X5R capacitance and leakage vs DC voltage plots here:https://www.eevblog.com/forum/projects/mlcc-discharge-curves/msg735041/#msg735041

author: retrolefty
author_rank: Super Contributor
timestamp: September 23, 2015, 12:53:23 am
content: 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.

author: Niklas
author_rank: Frequent Contributor
timestamp: September 23, 2015, 05:54:26 am
content: Quote from: MagicSmoker on September 22, 2015, 12:31:15 pmIt 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.

author: Zero999
author_rank: Super Contributor
timestamp: September 23, 2015, 09:18:03 am
content: Quote from: derGoldstein on September 22, 2015, 01:47:54 pmInterestingly 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.Quote from: retrolefty on September 23, 2015, 12:53:23 amI 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.