When/why (not) to use Tantalum capacitors. Pros, cons, alternatives - Page 1
Forum section: electronics / projects

author: Christe4nM
author_rank: Unknown
timestamp: January 03, 2014, 02:48:05 pm
content: A few weeks ago I worked through the Altium SMPS design course from FEDEVEL academy and that little project left me with an unresolved question. Somehow I got the idea in the past few years that tantalum capacitors are to be avoided, never really knowing why. Yet try to find a 330uF, 6.3V capacitor with ~4mOhm ESR and you’ll find that tantalum is basically the only option. So I wanted to start a discussion about tantalum caps with the main questions being:- When and why to use tantalum capacitors?- Why avoid using tantalum capacitors?- Alternatives to tantalum capacitors with pros and cons.I did some quick research already and here’s summary of what I’ve found so farWhy and when to use tantalum capacitors?Tantalum is used to create small sized capacitors with ‘large’ capacitance. Compared to other materials the oxide layer can be quite thin. So for all applications where pcb space is limited (e.g. mobile phones) they are the to go to type of capacitor when ceramic doesn’t cut it anymore.Also tantalum capacitors can be created with quite small ESR. This is why they are used a lot in (local) switched power supplies as bulk capacitor. Ceramics have even lower ESR, but in power supply regulators that might be too low for loop stability.Why avoid using tantalum capacitors?From what I can find these are the main reasons to avoid tantalum capacitors in your design:Financial:Tantalum capacitors are relatively expensive even when supply and demand are balanced. Not too long ago prices went sky high due to a shortage in raw materials.Reliability:There are numerous reports of tantalum capacitors spontaneously combusting. I haven’t read into this any further, but I take it some forum members can elaborate on this.Moral:Since some of the major tantalum ore (columbite-tantalite / coltan) mines are located in conflict zones (e.g. Democratic Republic of Congo) so one can argue that tantalum is a conflict mineral. I’m not sure though to what extent that still counts today as there are major mines elsewhere in the world too.Tantalum is a heavy metal and as such toxic and not really well for the environment. I did find a paper by AVX that discussed ‘green’ tantalum technology though.Alternatives to tantalum capacitors and pros and cons?Niobium capsApart from being mentioned I haven’t been able to find useful information yet, apart from that there is more Niobium ore available which should make Niobium caps cheaper. On the other hand Coltan is also used for mining Niobium so maybe the conflict argument could apply here too?(Wet) Aluminum Electrolytic caps (Elco)Specific low-ESR Elcos can be used. Larger values, larger ripple current rating, larger voltage ratings are some benefits. I must admit though that I realized that I haven’t seen SMT Elcos a lot outside consumer gear. Did I miss something?Polymer (Solid) Aluminum capsUsed as in- or output bypass caps in SMPSs. Larger values only available in small voltage ratings. I don’t know by how much these must be derated though. Please tune in if you know more about this kind of caps.Monolytic Ceramic capsLarger voltage ratings, smaller derating, and higher ripple current ratings are among its benefits compared to tantalum caps. Since the ESR is much lower a small external resistance may be needed for loop stability in SMPS designs.SourcesHere is some of the info I found. There is a lot to be found, and you'd have sift to get the info you want too. I included the year of publishing when available, since a few years in our industry means lots of changes.AVX. (n.d.). Comparison of Multilayer Ceramic and Tantalum CapacitorsAVX. (n.d.). “Green” Environmentally Friendly Technology For Tantalum And Niobium Oxide CapacitorsDigikey. (n.d.). Tantalum Alternative Solutions by PanasonicEETimes. (2001). Tantalum capacitor options weighedKemet. (2008). Comparison of Ceramic and Tantalum CapacitorsNIC Components. (1999). Alternates to surface mount tantalum electrolytic capacitorsWikipedia. (n.d.) ColtanRelated Threads on the EEVblogTantalum capswhy we tend to not use electrolytics for decoupling to gnd?Output capacitor of a DC/DC converter(edit: URL layout issues )

author: Rerouter
author_rank: Super Contributor
timestamp: January 03, 2014, 02:59:49 pm
content: My opinion on it is there is still a strong stigma from the 1980's - 1990's where endless bits of test gear succumbed to a tantalum shorting out a supply rail or worse, with the last bit of test gear i repaired having over 30 shorted tantalum's, where they used them for decoupling where some values where low enough that ceramic could have been used. (was a current limited switch-mode that would give a negative leading edge if it was driving too big of a load, which likely resulted in blowing one after the other.)in that case, almost all of them where replaced with an electrolytic in parallel with a ceramic, (high speed logic) or plain ceramic on its own, and though i haven't gone and tested the transient response of the board, its happily working.

author: dannyf
author_rank: Super Contributor
timestamp: January 03, 2014, 03:08:46 pm
content: Quote(Earlier liquid / paste-based) tantalum capacitors tend to fail short and regularly. Newer solid state tantalum capacitors don't suffer that particular failure mode and in my view should be used.QuoteLow ESR isn't the only design criteria and in some cases may not be desirable. Great pieces of equipment were produced before tantalum capacitors and can be continued produced without them - you just need to know how to engineer them.

author: calexanian
author_rank: Super Contributor
timestamp: January 03, 2014, 04:20:16 pm
content: Tantalams are great. We have used them in our products for over 30 years and to date have NEVER had a field failure of one without an extreme fault otherwise happening to the unit. Yes, its a left over stigma from the days of old. When people would accidental install them backwards in low impedance circuits they will explode with a small fire ball. They actually make great electric matches. I have also NEVER seen one leak when designed with properly. Ye use about 6 on every single one of our boards and have sold from 1500 to 3000 a year of them for most of the last 30 years. For a matter of cost however we limit our use of them to applications under 35 volts and 10 uF. Above that their attributes are a law of diminishing returns anyways.

author: nctnico
author_rank: Super Contributor
timestamp: January 03, 2014, 05:08:21 pm
content: Tantalums are basically bombs waiting to go off. Oxidizer + fuel. You'd need to control the rate of the current flowing into them or they may ignite. Reverse mounting is also asking for trouble. They will burn right through the board or explode in your face (both happened to me and it was not my fault). Besides that the raw material is found in a place where nature is to be preserved.Nowadays there really is no reason to use tantalum caps.

author: Rufus
author_rank: Super Contributor
timestamp: January 03, 2014, 05:55:00 pm
content: All electrolytic capacitors are have self forming and self repairing dielectric layers.The problem with tantalums is if too much current is allowed to flow through a fault in the dielectric the localised heating can cause more damage not repair. The damage can cause thermal runaway and rapid catastrophic failure.For that reason it is unwise to use tantalums in low impedance circuits which can source a lot of current and wise to substantially underrate their voltage if you must. Some manufacturers recommend adding series resistors to limit current which makes their low ESR rather pointless.

author: SeanB
author_rank: Super Contributor
timestamp: January 03, 2014, 06:48:58 pm
content: Tantalum is really only used where you need ultra small, and the voltage rating is a thing that never ever will be exceeded, and where you never apply a reverse voltage to them, no matter how briefly. You do need to limit power put in them, but if you derate voltage enough they have a very high current capacity.I replaced a 1000uF 16V electrolytic on my PC power supply once with a 10uF 25V wet slug tantalum unit, as I needed a capacitor and this was the only one to hand. Worked well for years afterwards, even though the current in the cap was large. the ripple was lower than what the original capacitor had. This was in a LC output filter on the 5V rail, where the original popped it's top.

author: CSmith
author_rank: Unknown
timestamp: January 03, 2014, 07:47:16 pm
content: The biggest risk with tantalum/nobium capacitors are surges and any reverse polarity at all. These risks can be largely mitigated by generously overrating their voltage. Doubling is a good start. AVX has some good white papers on this stuff.AVXSurge in Solid Tantalum CapacitorsAVXVoltage Derating Rules for Solid Tantalum and Niobium Capacitorsexplores when not quite doubling the voltage rating may not be necessary

author: calexanian
author_rank: Super Contributor
timestamp: January 03, 2014, 08:32:19 pm
content: You still have to design the circuit right. Other than that they are fine.

author: IanJ
author_rank: Unknown
timestamp: January 03, 2014, 08:37:52 pm
content: Quote from: Rerouter on January 03, 2014, 02:59:49 pmJings, that takes me back!.............I can remember that burnt tantalum smell as I type.We used to use them all the time for supply decoupling. It was by far the most common reason for electronics failure.Ian.

author: Niklas
author_rank: Frequent Contributor
timestamp: January 03, 2014, 08:43:19 pm
content: One drawback with tantalum caps is the significant voltage derating at high temperatures. In an automotive application I recently worked with, parts of the potted PCB was a bit over 100 degrees C, resulting in a 70% derating. The 35 V rated capacitor was not good for more than 12 Volts over the complete range of operating temperature.

author: G0HZU
author_rank: Super Contributor
timestamp: January 03, 2014, 11:21:41 pm
content: I'm happy to use them although the inrush and discharge current needs to be managed.The worst tantalum fireball I ever saw was an old school 'blob' type that decided to fail in a big way. It actually detached from the PCB and landed on a work bench and proceeded to eat a decent sized crater into the bench as it crazily fizzed and circled around like a white hot bumble bee that was high on fly spray.

author: calexanian
author_rank: Super Contributor
timestamp: January 04, 2014, 01:37:49 am
content: Once again. You have to design the circuit right. They have no business in power supplies. They are really for RC circuits!

author: G0HZU
author_rank: Super Contributor
timestamp: January 04, 2014, 01:58:23 am
content: I can't remember for sure but the fireball tant was a very early example of a tant cap in a card from an old radar based product. I guess in those days they didn't realise all the risks from these devices. I'd be surprised if a modern tant could expire in quite the same spectacular manner but I know they can get extremely hot and go pop. You also get the classic smell of a dead tant cap filling the lab...I've seen nothing like it since and I've seen plenty of dead tants. Not quite the same as 'Alien' acid blood eating through a bench but it did make quite a decent crater

author: calexanian
author_rank: Super Contributor
timestamp: January 04, 2014, 03:53:09 am
content: I went back and re read the question. So in short, to get esr down you can parallel smaller caps. Electrolytics and add a Mylar cap in there for higher freq stuff. So tantalams as said before have an explosive failure condition, with a side of fire ball. The key is to use them in applications where they will be safe. For power supply filtering they do little. Yes low esr, but you can parallel other caps to the same effect. Also there are high ripple low esr electrolytic caps. Typically orange outer jacket.

author: dannyf
author_rank: Super Contributor
timestamp: January 04, 2014, 02:19:43 pm
content: QuoteLow ESR in some cases can be evil.I do agree with your other point: it is far more important to know what you are doing than to just drop in a low ESR over-spec'd part.

author: Christe4nM
author_rank: Unknown
timestamp: January 04, 2014, 03:38:24 pm
content: OK, so far the consensus considering reliability seems to be that tantalum caps can be used without reliability problems if you take care to design the circuit right.Quote from: nctnico on January 03, 2014, 05:08:21 pmCould you elaborate on that apart from their failure mode?Quote from: SeanB on January 03, 2014, 06:48:58 pmSo basically “you’ll know when you need ‘em” applies here? In other cases use alternatives?Quote from: calexanian on January 04, 2014, 01:37:49 amThis is new to me. The only places where I’ve seen tantalum caps are SMPSs. With RC circuits I immediately think “film caps”, although realizing this is another “I don’t really know why, probably I’ve just been told so once”

author: calexanian
author_rank: Super Contributor
timestamp: January 04, 2014, 05:44:01 pm
content: Classically rc timing circuits were a lot longer I. Duration than today. Delays of up to many seconds were common with 555 timers and tantalum caps were the bees knees for that. Also for delayed rise time there are propably billions of them out there. The mechanism of bang on them is durring over current/voltage heat and gas are generated and they have no vent like an electrolytic so bang is the result and the remains actually are combustible.

author: LukeW
author_rank: Frequent Contributor
timestamp: January 06, 2014, 06:33:30 pm
content: Quote from: Christe4nM on January 03, 2014, 02:48:05 pmI reckon this is not as big a deal as some people think it is.Do you know which country supplies most of the world's tantalum? Hint: A country known for digging stuff up, venomous animals, and eevblog.Personally, I find myself using tantalums less and less today because electrolytics are getting better and better (better reliability and better ESR, and smaller) and SMD multilayer ceramics are getting better and better (higher capacitance and higher capacitance density, at far lower costs than they used to be for the large ones, and lower ESR than Al or Ta.)Another factor to consider for a "where would I choose tantalum" question might be "where would I not choose wet aluminium electrolytics" where large capacitance is needed - for example in high temperature environments, or very low temperature (below freezing) or vacuum environments (eg aerospace) you probably do not want a conventional aluminium electrolytic.

author: calexanian
author_rank: Super Contributor
timestamp: January 06, 2014, 11:49:04 pm
content: That is true. Smd multilayer ceramic will over take tantalum very soon and are far better characterized.

author: Kjelt
author_rank: Super Contributor
timestamp: January 07, 2014, 08:50:14 am
content: How about the reflow "survival" resist, I personally have a lot of bad experience with SMD electrolytics after a reflow process. The small ones are ok but larger ones really need to be glued down which to me indicates a lot of stress from the process. Any one have experience with this?

author: nctnico
author_rank: Super Contributor
timestamp: January 07, 2014, 04:06:38 pm
content: Quote from: Christe4nM on January 04, 2014, 03:38:24 pmCeramics with similar capacities are available and cheap (especially when combined with high frequency SMPS chips).

author: 3roomlab
author_rank: Frequent Contributor
timestamp: October 22, 2015, 11:07:07 am
content: sorry for reopening an old thread. but i think my question is similar related.having no usage experience with tantalums, i thought i try to ask if anyone could enlighten me. i did read up a few articles about pros cons etc, however i am puzzled by what i find in E14.the part i am considering to replace (from a used keithley 2015) is this (see picture). how do you determine its working voltage rating? marking 22uF "10B42" = 10volt, B42 = batch?assuming it is 10v. i had a look at E14, but then i found out that the ESR rating listed are mostly over 0.5ohm and then right down the list this 22u appears and it costs about USD12 a piece. (http://sg.element14.com/avx/trme226k035r0060/cap-tant-22uf-35v-case-e/dp/2353302) do you guys normally buy this?

author: Kjelt
author_rank: Super Contributor
timestamp: October 22, 2015, 11:14:07 am
content: You can find on the same site tantalums of 22uF for $0,10 a piece.If you can't find the voltage you have a few options:- measure the voltage across it- reverse engineer (draw) that part of the circuit- choose the highest voltage possible, one of a kind anyway.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: October 22, 2015, 02:09:37 pm
content: thanks for the tip on AVX. found it inside a AVX catalogue (page 147). E is 25v, the cap is rated for 85oCthe black SMD above it is a inductor - L105 marking**edit based on selection criteria of 25v 22uF++. there is no 10cent tantalum in sight. is that even possible for single qty? (the situation is worse on RS website)

author: Kjelt
author_rank: Super Contributor
timestamp: October 22, 2015, 02:55:43 pm
content: Quote from: 3roomlab on October 22, 2015, 02:09:37 pmIndeed with 25V and single piece it starts around 1$ which is not bad esp. when you find out the shipping costsBut hey not $12 as you originally thought.Be carefull though there are lots of different packages, so check out which is the correct SMD package of the component before ordering.

author: 3roomlab
author_rank: Frequent Contributor
timestamp: October 22, 2015, 05:00:03 pm
content: Quote from: Kjelt on October 22, 2015, 02:55:43 pmi think it is $12 cos i have pre-selected 125oC and low ESRshiet, these things like tiny pieces of gold here.i checked TME.eu ... TME have good prices ( USD 0.3 to 0.6 ). the low ESR are only USD1.7.i wonder what happen to E14

author: KL27x
author_rank: Super Contributor
timestamp: October 22, 2015, 07:03:27 pm
content: When I was researching this subject, years ago, I read something to the effect that MLCCs have lower ESR than tantalum, but only at high frequency. For some reason, tantalum can achieve lower ESR in the kHz range. I thought that was the reason tantalum are still common. I learned some other good reasons from this thread.

author: nfmax
author_rank: Super Contributor
timestamp: October 23, 2015, 01:48:12 pm
content: I've just come across this in the AAIB report of the crash of G-SPAO onto the roof of the Clutha Vaults Bar in Glasgow:QuoteI doesn't seem to have been a material factor, but...

author: rlb245
author_rank: Newbie
timestamp: March 11, 2017, 02:53:53 am
content: I no it an old post but it was a great one for me. This was a great read and vary educational. I'm currently work on several repair projects and one of them just happens to be a TDS540A that was given to me in a box all in parts. I tend to do allot of research on a project before I attempt any repair. I've repaired a couple of these types of scopes with a good success rate (4 for 4) but I've allways use electrolytic capacitor to replace the failed caps. I,m wanting to repair this basket case with tantalums to see if it will work. Thanks for the info

author: Seekonk
author_rank: Super Contributor
timestamp: March 11, 2017, 01:05:18 pm
content: I just found a box of KEMET 10uF 20V little cylindrical tan plastic capacitors for those that don't go back that far. Date is Sep 28 1993. Think these can be trusted to work on items I send out? No need to be super reliable. For home projects I wouldn't care. Hate to throw out a box of 100 tantilums.

author: Smokey
author_rank: Super Contributor
timestamp: July 20, 2022, 06:51:41 pm
content: Bump for the Great Tantalum Debate!Working on a Keithley 2306/2308 Power supply now, with a ton of little yellow land mines all over the place.https://www.eevblog.com/forum/testgear/keithley-2306-dual-battery-simulator-repair-(maybe)/

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2022, 09:19:53 pm
content: I haven't read the thread, so likely there's not much I can add, but here it is anyway.I designed a board in 2008 which needed a 150 uF cap on a 12V rail. Size was very limited, so I picked a solid Tantalum from Kemet in a case code X package. The part worked well, as far as I knew. The trouble is my contract manufacturer was not telling me they were seeing lots of faults with them. When I found out, they couldn't even tell me how many faults.On changing CMs, I found they were seeing cracks in the caps. Then one caught on fire and burned a board. One of the technicians claimed this had to do with moisture processing, but that was BS. When I researched it through the cap manufacturers it is a problem caused by the temperature of the reflow soldering process.The caps develop micro flaws in an insulating layer. When power is applied, the current surges and causes damage, possibly enough to cause the cap to burn. To deal with this problem the current has to be limited on initial application of power. Then the flaw will heal itself.Our test fixture has a resistor in series with the 12V power to the UUT and a jumper which is placed in the circuit after the initial power has been applied.This seems to do the trick. The one problem was picking a value for the resistor. NONE of the information sources provide adequate info on how to size it. I think we ended up with something in the range of 470 ohms to 1k ohms, but I'd have to look it up.Out of 10,000 units, we've never had a failure in the field.

author: uer166
author_rank: Super Contributor
timestamp: July 20, 2022, 09:42:12 pm
content: Quote from: gnuarm on July 20, 2022, 09:19:53 pmIIRC this is one of the limitations of tantalum. E.g. using one at the input of a PCB where power is applied, causing a great current inrush is bound to cause damage and blow it up. But on a current limited buck stage output where no inrush is possible, it is A-ok given appropriate deratings.I've personally used one only once specifically because ofhigh, stable ESR (was in the order of 2Ohms). The LDO I used was a special snowflake and required a specific amount of ESR to be stable. Al-poly caps vary wildly in ESR given temps, and MLCC had way too low of an ESR for that application and too low of a value anyway.

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2022, 09:51:35 pm
content: Quote from: uer166 on July 20, 2022, 09:42:12 pmThat's not correct. Once the capacitor has been "initialized" it is quite reliable. The flaws develop in the soldering step from the high temperatures. They self heal if the current is limited to a level that does not cause damage.QuoteOdd, Tantalum caps typically have a low ESR. Electrolytic caps have high ESR.

author: uer166
author_rank: Super Contributor
timestamp: July 20, 2022, 10:26:03 pm
content: Quote from: gnuarm on July 20, 2022, 09:51:35 pmYou are probably right. I haven't seen much literature about it, but stuff like this:QuoteFromhttps://nepp.nasa.gov/files/24745/2013_n240_teverovsky_estec_derating_paper.pdfmakes me question using a tant in such an application. It seems that if you guarantee a self-healing mechanism and limit dv/dt and inrush, you'll have a more reliable system regardless of the cause of the defect.

author: floobydust
author_rank: Super Contributor
timestamp: July 20, 2022, 11:22:13 pm
content: Tantalums areMODERATE ESRwhich is great for sensitive analog circuits, but terrible and burn up if heated due to high frequency ripple currents if an SMPS is involved.The fact that you have to voltage derate them at least 50% as a norm, is not always known or followed. Any reverse voltage blips and they also fail. Wet tantalums have sulfuric acid electrolyte, gee I wonder what could go wrong there...MLCC's arejust as dangerous- for giving you way low valueright out of the boxand "DC-bias aging" causing later problems.Note auto vendor Continental rallying capacitor manufacturers tostop their bullshitaround Class-II MLCC's. Fake claims on initial capacitance apparently commonplace, then aging happens...Open Letter to AEC-Q200 Committee on MLCC DC BIAS Ageing Capacitance Loss Issuesand thenUpdate 2021/10.Vishay MLCC agingThe 10uF part giving 2.9uFso be careful with MLCC's. Their low ESR adds ringing and resonances that they are not always the best, and self-heating is apparently another concern.

author: gnuarm
author_rank: Super Contributor
timestamp: July 20, 2022, 11:25:09 pm
content: Quote from: uer166 on July 20, 2022, 10:26:03 pmI think I did not make myself clear. The defects happen at the elevated temperatures of soldering. They do not appear after that. Once you "anneal" them with a current limit, they will be fine for many, many hours and not short again. As I said, I have 10,000 boards in the field over the last 14 years, with no returns for this problem. We are shipping another 8,000 boards this year.

author: perdrix
author_rank: Frequent Contributor
timestamp: July 21, 2022, 10:44:37 am
content: Tantalum capacitors are fine so long as you apply the correct guidelines. Lots of space rated circuits use tantalum capacitors - they win on high volumetric efficiency and low ESR.1) Don't run a 6V tantalum cap as a decoupling capacitor on a 5V rail. You need to derate to use at least a 12V or even better a 20V component here. They can and do fail spectacularly if you don't observe this guidance. Much of the bad reputation comes from the time they were initially introduced and the manufacturers believed incorrectly that you could happily use a 5V or 6V cap to decouple a 5V rail. History proved them wrong after a few years.2) Do apply appropriate temperature de-rating. Read the friendly data sheet.3) Pay close attention to ripple/surge current limits.NASA have issue guidelines for the use of Wet Tantalum capacitors:https://nepp.nasa.gov/files/23926/Guidelines%20for%20%20wet%20Ta%20capacitors%20rev.A.pdfThe following makes interesting reading:https://passive-components.eu/tantalum-capacitors-in-space-applications/David

author: Zero999
author_rank: Super Contributor
timestamp: July 21, 2022, 11:24:44 am
content: In all honesty, I've encountered far more bad aluminium, than tantalum capacitors. The difference is, when a tantalum capacitor fails, it burns a hole in the board, whilst an aluminium capacitor just goes bang, leaving a mess.Tantalum capacitors are very reliable, when used properly. They don't dry up and age, like aluminium capacitors do. De-rate them to under2/3of the supply voltage and all will be fine.

author: gnuarm
author_rank: Super Contributor
timestamp: July 21, 2022, 01:27:03 pm
content: Quote from: perdrix on July 21, 2022, 10:44:37 amI've never understood why capacitors have a voltage rating, yet have recommendations to operate at a significant derating voltage. Does anyone understand the purpose of the voltage rating of caps? Why don't they provide the actual operating voltage, rather than some imaginary voltage that has to be adjusted?

author: TimFox
author_rank: Super Contributor
timestamp: July 21, 2022, 01:46:01 pm
content: Quote from: gnuarm on July 21, 2022, 01:27:03 pmBack in the day (say, pre-war), capacitors often had separate maximum and working voltage ratings.

author: srb1954
author_rank: Super Contributor
timestamp: July 21, 2022, 10:01:31 pm
content: Quote from: gnuarm on July 21, 2022, 01:27:03 pmIt all depends on how long a life you want out of your components.The datasheet maximum ratings are determined by the manufacturer or to give an acceptable failure rate over a certain lifetime, which may be relatively short.Typically, a designer will want the product to last a little longer than the manufacturer's specified lifetime and derate components accordingly until the required lifetime is obtained. Some voltage derating on tantalum capacitors can dramatically reduce their failure rate giving a longer useful life of the product. IIRC the failure rate of a solid tantalum capacitor reduces 1000x if it is operated at no more than 1/3 its rated voltage.

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2022, 04:10:36 am
content: Quote from: TimFox on July 21, 2022, 01:46:01 pmAnd what is the purpose of the "maximum" voltage? What does that tell you?

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2022, 04:11:28 am
content: Quote from: srb1954 on July 21, 2022, 10:01:31 pmIs that in the data sheet?

author: srb1954
author_rank: Super Contributor
timestamp: July 22, 2022, 05:28:05 am
content: Quote from: gnuarm on July 22, 2022, 04:11:28 amHere is an extract from a rather old AVX datasheet detailing the reliability improvements obtained from derating tantalum caps.

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2022, 05:34:56 am
content: Quote from: srb1954 on July 22, 2022, 05:28:05 amOk, I get that. But what is the point of having both "maximum and working voltage ratings" then? Having two voltage ratings makes no sense, unless they are both rigorously defined. Normally, the maximum voltage rating is a limit, beyond which damage can occur. You seem to be saying it is just another data point in the voltage/lifetime tradeoff.

author: Zero999
author_rank: Super Contributor
timestamp: July 22, 2022, 08:02:55 am
content: Quote from: gnuarm on July 22, 2022, 05:34:56 amI take the maximum to be the absolute maximum and the working voltage to be just that i.e. the nominal. Structures have the safe working load, which will include a significant de-rating factor and a design load.Regarding tantalum capacitors. Look at the temperature de-rating factors. The resin dipped, solid type must be de-rated by a factor of 0.4 at 85°C. This would explain why de-rating is important. Come to think of it, the tantalum capacitors I've seen which failed were used in hot environments and were probably not de-rated enough.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 22, 2022, 08:46:49 pm
content: FYI, self-healing occurs throughout the cap lifetime, which is why destruction can occur, particularly on high current supplies. IBM did it decades ago (solution: fused types, I believe it was?), and it pops up again and again in various devices. Usually not often, but with such dramatic consequences, they're quite notable among users...Also heard tale that, in some brand of 80s-90s era telecom hardware, they had spooky intermittent failures; eventually, traced to PSU interruption due to tant self-healing. Now, whether those systems should even be that sensitive in the first place (how much does the supply really dip, given the mass of other capacitors on a board?!) might also be a good question, but given there are some cases where you just need precision timing or whatever, and don't have self-clocking data, or support for error detecting/correcting in the protocol, well, that might simply be how it is, and you must have quiet, clean power.Quote from: uer166 on July 20, 2022, 09:42:12 pmY'know they make chip resistors, right?If throwing in a random 0.47R or whatever seems superfluous, I mean, it's still much less cost than the tant it's replacing (including adding the BOM item if none others are needed in the design). Plus you often have similar values around, e.g. for current sense, or if you need a couple other "bulk" / damping capacitors in the circuit.I think about the only place I'd consider tant these days, is, well, timing for one -- that's actually a very good application for them, a long time constant with stable C, and timers have limited current so healing is a non-issue. But for supply purposes, even with individual current limiting (fused? series resistor to make a local supply?), about the best use-case I can think of is for somewhat lower ESL -- and that's still not a big deal, as you can just use wide-body R and C, and a few in parallel if needed, to improve on it further.If you're super strapped for space, maybe you can't afford the resistor at all, but also super compact circuits tend not to have the stray inductance that needs extra ESR to damp it -- a cell phone board say, with inner plane, perhaps over multiple layers at that, and tons of other smaller ceramics strewn about. For which, ceramics are still on the low-ESR side, but it's tolerable enough for most things.----As for comparative ESR, electrolytics are generally mid to high; tant low to high; polymer very low to mid. The important thing to note isa wide range of ESR is available in each family-- there is a lot of overlap -- so shop around to find what specs you need.Tim

author: TimFox
author_rank: Super Contributor
timestamp: July 22, 2022, 09:27:02 pm
content: Quote from: gnuarm on July 22, 2022, 04:10:36 amIf I remember correctly, and these parts were made before I was born, the two voltages were "test" and "working", where (obviously) test > working.

author: coppice
author_rank: Super Contributor
timestamp: July 22, 2022, 10:14:37 pm
content: Quote from: T3sl4co1l on July 22, 2022, 08:46:49 pmMany early digital telephone exchanges built quite a reputation for crashing, before the cause was traced to tantalum decoupling capacitors. Colleagues were involved in some of the analysis. Because the failures were infrequent it took a lot of collaboration to get to the cause. At first, nobody wanted to collaborate, as they assumed the crashes were probably something flaky about their own circuit design, like a timing error. As it became known that most designs were doing similar things people started to work together.Even with a big beefy clean supply a tantalum capacitor developing a whisker short is enough to make the power rail in the immediate surrounding area dip badly for a very short period. If it was near something like a tributary circuit a call might hiccup, and nothing else was noticed. If it was near a core processing element the whole exchange might crash. Try a few microseconds of shorting the power rail somewhere sensitive in any modern computer, and see if it does any better, Philips and others introduced solid aluminium capacitors around this time. The industry moved to those, and the crashes went away.

author: gnuarm
author_rank: Super Contributor
timestamp: July 22, 2022, 11:15:16 pm
content: Quote from: Zero999 on July 22, 2022, 08:02:55 amThe concept of derating is clear. The issue is the definition of the terms, "working" and "maximum". Without a clear definition, they are not useful. The definition could simply be the method used to obtain the resulting numbers.QuoteThose deratings are for power vs. temperature, not voltage.

author: cathykai
author_rank: Newbie
timestamp: July 14, 2025, 01:25:55 am
content: Quote from: LukeW on January 06, 2014, 06:33:30 pmYou're absolutely right to bring this up. Tantalum has historically been classified as a conflict mineral, primarily due to its extraction from columbite-tantalite (coltan) in conflict-affected regions like the Democratic Republic of Congo (DRC). Revenues from these mines have been linked to armed groups, prompting international concern and regulatory responses.However, the situation has evolved in recent years. While DRC and its neighbors still produce tantalum, a significant portion now comes from conflict-free sources in Australia, Brazil, Canada, and Rwanda, among others. Moreover, initiatives like the Dodd-Frank Act (Section 1502) in the U.S. and industry-led programs like the Responsible Minerals Initiative (RMI) have improved traceability and accountability in supply chains.

author: tggzzz
author_rank: Super Contributor
timestamp: July 14, 2025, 10:34:09 am
content: Quote from: calexanian on January 03, 2014, 04:20:16 pmI have. Two milspec axial tants voided their acid over a PCB. Fortunately it was a 2-sided PCB, so repair was trivial. Equipment: Tek 1502, originally designed in 1972; one of the available manuals indicates it was supplied with patriot missile batteries. Capacitors C6341 C6246 Sprague 109D107C7030T2 30V on a 25V rail.Your other point is similar to the "justification" emitted by proponents of fracking, along the lines of "there isn't any water supply contamination when fracking is done correctly". Obviously they would also say that every time there is water contamination, it was because it wasn't done properly - i.e. a self-fulfilling justification.So, whatdoesconstitute "designed with properly"? Tant beads rated 15V on a 13V PSU line clearly isn't "proper" because they regularly detonatePerhaps it would help if you indicate what your organisation defines as the necessary and sufficient conditions for being "properly designed".

author: Siwastaja
author_rank: Super Contributor
timestamp: July 14, 2025, 10:45:23 am
content: Quote from: tggzzz on July 14, 2025, 10:34:09 am(I know this is an old thread but this applies nevertheless:)Interesting thing with tantalum caps not everyone is aware of is a weird manufacturer rating culture, where they refer you toanotherappnote which says that you must derate voltage by 40% (and afterthat, apply any further derating you need for safety margin, margin against your DC bus regulation tolerances, or increased lifetime). In other words, non-derated lifetime is just some tens of hours or so!This is different from every other capacitor type (electrolytics, ceramics, plastic films of different types), which you can use up to the rated voltage no problem (and derating is for yourownpurposes; managing voltage uncertainties or peaks, or just "to be sure"). In other words, tantalum capacitors are nearly the only types of components which areguaranteed to failat the rated operation conditions!I have no idea when or how this specification culture originated; was it originally just poor manufacturing quality or then-unknown characteristics of tantalum caps which surprised even the manufacturers, so that they had to work around by instructing designers to derate, and that stuck? It definitely is difficult to fix the specifications after the fact, as your parts would appear to have worse specs than your competitors (and what you previously had). Instead, we have these pseudo-Volts being used, where 10V actually means 6V, and so on.Anyway, the usual advice which can be confirmed from appnotes is to derate voltage to 60% of rated,andbe careful that peak current specification is never exceeded (inrush!). Derating even more, say to 50% or even 40% of rated, would, AFAIK, allow one to exceed the peak current specification somewhat, but how much I have no idea; I have heard that 60% derating pretty much allows you to ignore the current limit factor but have not seen confirmation to that.

author: Vovk_Z
author_rank: Super Contributor
timestamp: July 15, 2025, 07:43:50 pm
content: Quote from: calexanian on January 04, 2014, 03:53:09 amNo. And no.1) You parallel caps to share a (pulsation) current between them but not to lower ESR (thats can't happen much, because we still can't use superconductve and zero-inductive wires to connect multiple capacitors together).2) Mylar (meant film) cap 99% will have MUCH smaller capacitance and so want help much. The almost only reason to put film in parallel with a large electrolyte is if you don't know what you do and so you just copy some not the brightest dedign. But there are exceptions sometimes in high voltage circuits when a total capacitance is not large (so you really can have the best from two worlds).

author: rsjsouza
author_rank: Super Contributor
timestamp: July 16, 2025, 10:32:08 am
content: For an excellent explanation about capacitors in general and the Tantalum intricacies and the reasons why some need to be derated by 50% and others by 10-20%, check the video below from the Baldengineer guy. The Tantalum subject starts at 22:10

author: Georgy.Moshkin
author_rank: Frequent Contributor
timestamp: July 17, 2025, 05:43:19 am
content: I didn't like tantalums for an awful smell and contamination of surrounding pcb area with a black soot after they burnt. This affects repairability a bit.