Tantalum Cap Replacement by Tantalum Polymer - Page 1
Forum section: electronics / projects

author: gnuarm
author_rank: Super Contributor
timestamp: October 23, 2022, 08:17:24 am
content: I've used a 150 uF, 20 V tantalum cap on the original board simply because I could not get this value on the board without a huge footprint. I'm doing a respin after 14 years and I've looked again and found Tantalum Polymer caps. They have a larger footprint, but they are not tall like aluminum electrolytic caps.The tantalum caps have issues with various failure modes. It appears the tantalum polymer caps do not have this problem. But the manufacturer says they are, "process sensitive". I assume they are referring to the temperature profile used in soldering.Anyone have experience with these parts?Here's one.https://www.vishay.com/docs/40216/t52.pdf

author: jmelson
author_rank: Super Contributor
timestamp: October 23, 2022, 03:22:11 pm
content: You should look at Aluminum polymer caps, too. I've been using them on one board for some years.Jon

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 23, 2022, 08:55:28 pm
content: Whether aluminum or tantalum, polymer capacitors have low ESR. Electrolytic capacitors have moderate to high ESR. Thus, they are not a drop-in replacement for each other. If you put a polymer in that location, you may experience power supply ringing or oscillation. Or you may not! It depends on what the rest of the power distribution network looks like. There are other considerations here, but that's the main one.Tantalum electrolytic capacitors these days are safe if applied correctly. (They were much less safe prior to around 2000.) That means with an appropriate voltage derating, temperature-voltage derating, and provisions to limit surge inrush. As I understand it, it's mainly surge that blows them up; voltage and temperature weaken them to make it easier for the surge to have its way. But that might be wrong. In general I have no compunctions using tantalums inside a design, but hesistate to expose them to the outside world (on connectors or whatever), where I include other boards in the system in "the outside world".We'd need more information to give you a firm recommendation, but as it stands I would probably not make this swap.

author: twospoons
author_rank: Frequent Contributor
timestamp: October 23, 2022, 09:02:13 pm
content: We had Vishay rep in the office a couple of weeks back telling us all about how these new polymer tantalums fix all the problems the old ones had. Maybe its true. We remain skeptical, and unwilling to invest time and money to find out.

author: David Hess
author_rank: Super Contributor
timestamp: October 24, 2022, 03:32:13 pm
content: Quote from: twospoons on October 23, 2022, 09:02:13 pmPolymer tantalum capacitors do not suffer from the self healing thermal runaway problem that solid tantalum capacitors do. They have much lower ESR which may or may not be a problem in specific circuits, and more limited lifetime because of gradual deterioration of the conductive polymer electrolyte.

author: JohanH
author_rank: Frequent Contributor
timestamp: October 24, 2022, 03:59:52 pm
content: I don't have practical experience, but I did some data sheet reading for an application that required low leakage caps. My conclusion was that in this particular application (a few hundred microfarad), lowest leakage had some low leakage Nichicon aluminium electrolytic capacitors. Regular solid tantalum came next. (Ceramics could possibly work, but that would have to be measured; they don't specify leakage in the same way. At lower capacitance, NP0 and film wins, of course). The polymer caps I looked at had typically 10x more leakage than that. Other than the leakage, most features of the polymers looked way better than aluminium and tantalum. I did read something about that latest generation of polymers supposedly have even lower leakage than typical electrolytics, but I didn't do any more research, so didn't see any data that backed it up.

author: gnuarm
author_rank: Super Contributor
timestamp: October 25, 2022, 04:00:11 am
content: Quote from: twospoons on October 23, 2022, 09:02:13 pm"Old ones" meaning old Tantalum Polymer caps or old Tantalum caps?

author: gnuarm
author_rank: Super Contributor
timestamp: October 25, 2022, 04:10:09 am
content: Quote from: David Hess on October 24, 2022, 03:32:13 pmI did not see that reported. What is the nature of the deterioration? Is it to the ESR, the capacitance value? Something else? Or do they just fail with a clear bathtub curve at some hours?

author: gnuarm
author_rank: Super Contributor
timestamp: October 25, 2022, 05:25:38 am
content: Quote from: JohanH on October 24, 2022, 03:59:52 pmI don't have a leakage spec to meet. I'm looking for 150 uF @ 25V (12V circuit) in as small a package as I can get. The 7343 tantalum was rather tall for the app, 4.3 mm. The Tantalum Polymer caps seem to be shorter, with a larger footprint (7361 with various heights) which might not be an issue this time. I've found nothing else that suits these size requirements.QuoteI'm really just looking for a part that is available and won't burn up my board.I remember many moons ago when ceramic chip caps were young, a computer I worked on had multiple supplies with kW ratings (the size of boot boxes) in parallel. One of the caps on a memory board shorted and burned a hole in the board. It caused a lot of excitement on the test floor. LOL Someone said flames were shooting out of the machine. I'm sorry I wasn't there to see it.We've had to replace a lot of these Tantalum caps, but only one caused damage to a board and that was still usable. We shipped it! Still, I'd like to prevent the entire issue and be done with it, if I can. So that's why I'm looking to move away from the solid tantalum caps.

author: David Hess
author_rank: Super Contributor
timestamp: October 25, 2022, 05:05:47 pm
content: Quote from: gnuarm on October 25, 2022, 04:10:09 amThe way I understand it, the solid conductive organic polymer electrolyte degrades with exposure to humidity and high temperature. I think that will result in a gradual increase in ESR and loss of capacitance.

author: gnuarm
author_rank: Super Contributor
timestamp: October 25, 2022, 10:15:01 pm
content: Quote from: David Hess on October 25, 2022, 05:05:47 pmAnything concrete on that? Any mention of what constitutes "high temperature"? This system is fan cooled and these modules are not particularly high power, so temps should be pretty moderate, for some definition of "moderate".I don't think the ESR would be much of an issue since the currents are not terribly high. The frequencies of interest are audio, so that is what drives the capacitance. I might be more interested in the capacitance loss. I didn't see anything about this in the data sheet.

author: David Hess
author_rank: Super Contributor
timestamp: October 25, 2022, 11:50:53 pm
content: Quote from: gnuarm on October 25, 2022, 10:15:01 pmI never found anything specific about it that was not behind a paywall,like this.Questions 24 and 25 onpage 8 heredescribe what I suggested, but without any numbers.

author: gnuarm
author_rank: Super Contributor
timestamp: October 26, 2022, 01:38:43 am
content: Quote from: David Hess on October 25, 2022, 11:50:53 pmGreat reference! Question 23 on page 7 gives derating charts that show huge gain in reliability with voltage derating, 500 fold at 50% derating. Another 10 fold by keeping the temperature at 40 °C or better. I think that will work well.

author: David Hess
author_rank: Super Contributor
timestamp: October 26, 2022, 12:52:42 pm
content: Quote from: gnuarm on October 26, 2022, 01:38:43 amThe AVX technical paper is new since I last searched on this subject. Last I knew, polymer tantalum capacitors had no voltage derating so that is good to know. Of course solid tantalum capacitors originally has no voltage derating.

author: exmadscientist
author_rank: Frequent Contributor
timestamp: October 26, 2022, 06:32:47 pm
content: OP: If you are blowing tantalum capacitors, that probably means you have a circuit design problem. It would be best to understand that problem before just swapping a part and declaring it fixed. If you're more open to sharing things privately than publicly, you can send me a PM.Quote from: David Hess on October 26, 2022, 12:52:42 pmNew to me as well. I notice the TCJ data sheet has some reliability guidelines now that I don't think were there before. I have some AVX catalogs from past years I could compare against, but it seems a moot point.

author: gnuarm
author_rank: Super Contributor
timestamp: October 26, 2022, 09:43:38 pm
content: Quote from: exmadscientist on October 26, 2022, 06:32:47 pmI'm not shy about this. The problem was one of the nature of solid tantalum caps, as documented by multiple sources, including all the manufacturers I found. These parts have an intrinsic problem of having flaws in the dielectric layers which cause shorts. In the manufacturing process they are tested with a current limited supply that allows the flaw to heal itself.On being run through the reflow oven in the board manufacturing process, more flaws develop. When powering up the boards, the supply current must be limited until these new flaws can self-heal. I was not aware of this originally and manufacturing was not telling me about the high defect rate. It was only after I changed contract manufacturers that I was told about the problem, did my research and came up with a solution, that required the testers to manually remove and reinstall a jumper which inserts a limiting resistor in the power supply to the cap.The problem now is, I believe the test operators are not doing the job properly and omit these steps in the procedure. I need to add them to the computer test program prompts.QuoteWe have plans to redesign these boards as well as the test fixtures. I was thinking of adding software control over the current limit of this supply, but I would prefer to just get rid of the problem, and be done with it.The only real issue is that the old part seems to be readily available, while the new parts are in stock in smaller numbers and a higher price, $2 vs. $1. It's also a larger part. I'm not really concerned about any of this. I just want to make sure I'm actually solving a problem and not just trading one for another.I do see that the solid Tantalum caps are available with slightly higher voltages now. But I've not found info that says this will make much difference in the problem I see. Logically, I don't see the voltage rating having any impact on this self healing issue.

author: David Hess
author_rank: Super Contributor
timestamp: October 27, 2022, 01:37:21 am
content: Quote from: gnuarm on October 26, 2022, 09:43:38 pmI suspect you watched the same video that I did. It left me wondering why leaded solid tantalum parts which do not go through reflow have the same problem, or seem to.QuoteI thought polymer tantalum capacitors were suppose to completely solve that problem.QuoteAs far as I can tell, hermetic leaded solid tantalum parts do not suffer from the stress induced problems of epoxy dipped or molded parts, which I think should be expected because of their construction, and for this reason they are available with higher voltage ratings. I think this further confirms that stress inducted failures are the problem with epoxy dipped or molded parts.

author: gnuarm
author_rank: Super Contributor
timestamp: October 27, 2022, 02:39:33 am
content: Quote from: David Hess on October 27, 2022, 01:37:21 amNo video. I read a number of articles and papers from the cap vendors. One article in a trade journal, was a "I learned from this" where a guy added a resistor to the test fixture, like I've done. One of the test floor guys is using a PSU with a current limit, but I'm not clear on where he puts the setting.QuoteThey should, but the polymer caps are something I just started exploring, however, I've been thinking about the test fixtures for a few weeks now. That's why I say I prefer to change out the part and not need the special circuit. However... because of supply issues, I will probably design the test fixture to support either.QuoteI just checked on these parts, which I think Digikey is listing as "Hermetically Sealed". 150 uF, 30V is $50 a pop! I guess you weren't suggesting that I use these, you were just making a point of construction differences.

author: David Hess
author_rank: Super Contributor
timestamp: October 28, 2022, 11:42:03 pm
content: Quote from: gnuarm on October 27, 2022, 02:39:33 amHere is the video where I first came across a detailed description of the problem:https://youtu.be/ZAbOHFYRFGgQuoteI just brought them up as an example of a solid tantalum capacitor which does not suffer from the stress related cracking because of its construction, and is also rated at higher voltages. They were quite common in higher end test instruments in the 60s and 70s.

author: gnuarm
author_rank: Super Contributor
timestamp: October 29, 2022, 02:58:11 am
content: I watched the video. it was pretty much what I had heard. They make the tantalum caps work out of manufacturing, then we break them again with the reflow. So we need to fix them again when we first apply power. He didn't really talk about the fixing part so much, actually. I expect I'll go with a tan poly part if they are available enough. There are more than one part I could use, but they are only in stock in the low thousands and are $2 and up. The T491 solid tant part I'm using now has 35,000 available at a buck.But it was a good talk and I learned (or relearned) a couple of things about ceramic caps. There was a point or two about X5R that he skipped, but that's ok (like is an X5R and X7R with the same specs in the same package, basically the same?). I use them pretty much everywhere on this board because of their density. A few set the frequency response. Rather than worry about getting exact values of capacitance for those circuits, I push the corner frequencies out and test to -1.5dB rather than -3dB. I wouldn't mind using more poles on the high frequency side (delta-sigma ADC/DACs), but the board has been in production for 14 years this way and there's no real reason to change. I might try to get X7R parts if I can find them in the same package.I'd really like to find some alternative opamps, but I keep looking and not finding anything that will drive the output current. We manage to push a 7.5V sine wave into a 50 ohm load with the LM8272. Most parts crap out a bit below that, or are designed for driving DSL lines and are pricey and larger packages. The LM8272 can be hard to get at times. I wonder how the Asian suppliers get them when onshore distributors are quoting 52 week lead time and up.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 29, 2022, 01:25:34 pm
content: Quote from: gnuarm on October 26, 2022, 09:43:38 pmI think this is where you went wrong. IMHO, tantalum capsalwaysrequire current-limited supply, not just once after manufacture and then for the second time after reflow. I never use them on the input, but at the output of current-limited linear regulators, for example. Input is fine of course if you can prove absence of hotplug transient, or enough series resistance to limit the current.Consider tantalum capacitors parts which always require voltage, temperatureand currentlimits, and you should be fine.

author: Stray Electron
author_rank: Super Contributor
timestamp: October 29, 2022, 04:21:29 pm
content: How much current limiting do they need? Is there any king of R-C time constant or other parameter that we can use in the design to keep them within safe operating limits?

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 29, 2022, 05:01:13 pm
content: Quote from: Stray Electron on October 29, 2022, 04:21:29 pmA limit within one they can't start a fire? So that's signal circuits and power circuits after a regulator IC with a built-in current limit.

author: gnuarm
author_rank: Super Contributor
timestamp: October 30, 2022, 05:47:04 am
content: Quote from: Siwastaja on October 29, 2022, 01:25:34 pmI've never seen any evidence of that and the Kemet guy in the video explicitly says this is not an issue other than due to "damage" caused by reflow.QuoteVoltage and temperature are easy. I've seen no one claim there is a need to limit current other than first power on after reflow. Did you watch the video? It's a pretty good one, not long winded at all. The guy works hard to only present essential info with support and not drag out anything. Nice. I think it's worth a few minutes of your time.

author: HalFoster
author_rank: Frequent Contributor
timestamp: October 31, 2022, 10:07:30 am
content: Quote from: Vovk_Z on October 29, 2022, 05:01:13 pmIn lower power supplies (1A or so limited) I use them wherever I like as needed. On anything larger I am more cautious - a smaller value further away from the PS input gives a small amount of trace resistance and inductance to ease the dI/dT somewhat. All in all, modern Al electrolytics have specs that are good enough to use them where once a tant was an attractive option. And of course polymers top both, for lower voltage applications at least. I do, however, use a lot of dipped tants on personal projects because I have 10-20K of them in storage (bought out a closing mil surplus electronics shop) just have to remember to derate them appropriately.Hal

author: Siwastaja
author_rank: Super Contributor
timestamp: October 31, 2022, 02:01:11 pm
content: Quote from: gnuarm on October 30, 2022, 05:47:04 amI have seen and heard that countless and countless times. First result of 30 seconds in Google gives this NASA paper:https://nepp.nasa.gov/files/24745/2013_n240_teverovsky_estec_derating_paper.pdf"When the power is turning-on, high inrush currents through the capacitor can cause so-called surge current failure"Or this Stack Exchange site:https://electronics.stackexchange.com/questions/388781/maximum-allowable-ripple-current-and-surge-current-for-tantalum-capacitor"I've never seen an actual spec for the surge current that tantalum capacitors can withstand.It's usuallyjust phrased as "tants can't withstand surge current," full stop"Or this EEVblog forum result:https://www.eevblog.com/forum/projects/tantalum-inrush-current/"I've always heardthat when you use Tantalum caps, you need to be careful with inrush current to keep from damaging them."Emphasis mine - I have always heard that too, so I find it odd you have never heard about it before.I agree it's hard to find actual numbers, or evidence of current limiting being actually necessary. But given the facts that:1) need of current limiting is widely accepted and discussed (even if not proven),2) you have an actual problem with blowing up tants, which people who follow said current limiting practice do not have,maybe it would be best to be on the safe side and stop ignoring this advice despite it being poorly documented in official data such as datasheets and appnotes.

author: gnuarm
author_rank: Super Contributor
timestamp: October 31, 2022, 02:37:08 pm
content: Quote from: Siwastaja on October 31, 2022, 02:01:11 pmYou don't seem to understrand the problem. This NASA paper specifically refers to, "first turn-on failures". So this citation agrees with me.I would also point out that the paper is ten years old and says these failures, have "not been understood completely". We now understand them better.QuoteSo you are citing Jalalipop as a reference? When I said "no one", clearly I meant no one with any authoritative background. I don't think Jalalipop qualifies.I find one of the hardest parts of electrical engineering is often to weed my way through the folklore and mythology and simple poor understanding of issues, to find the truth. Often it requires multiple attempts to address and understand the problem, rather than rushing (pun intended) to a quick fix. This is one of those times.QuoteMy comment is taken out of context. EVERY CAPACITOR has inrush current limits. But this is not the issue being discussed. We are discussing a particular failure mechanism specific to solid tantalum capacitors which has to do with minute flaws in the dielectric layer and self healing if the current is limited when initially powered up after reflow. Once that first power on is completed, the capacitor fixes itself by isolating the short and from then on, will live a rich full life without further attention.QuoteActually, one of the problems I've had all along with this problem is that people confuse it with inrush current damage as well as the voltage derating which is about the over all lifespan of the capacitors. They are generally rated for 1,000 or 2,000 hours at a given temperature and voltage. If you derate the temperature you can get a 10:1 improvement in life expectancy, and if you derate the voltage to 50% of rated voltage, you get a 500:1 improvement in life expectancy. But this has nothing to do with the problem being discussed, the initial failure from reflow temperatures inducing flaws in the capacitor.So, are we clear now? My design has no problem with current surge ratings of the capacitors. Once they pass test and are shipped, we have no returns for tantalum capacitor failures. The problem is the solid tantalum proclivity to self destruct on the first application of power after reflow.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 31, 2022, 02:46:19 pm
content: Quote from: gnuarm on October 31, 2022, 02:37:08 pmFollowed by "areoftenattributed". What does "often" mean? Then comes a long list of other possible mechanisms.QuoteOnly if you cherry pick parts of the paper, ignoring complete words and parts of it.I understand you perfectly well. You have consciously decided to ignore this common advice (and lie about you never having heard about it), and you have decided you will do whatever in your power, including cherry-picking, to lie to yourself and others in the process. Your process is perfect, you don't make mistakes, you know it better - you don't have any problem so you don't need help. Yet for some reason you are posting and asking for help with capacitors blowing up.This is all fine to me - you are the one who faces the consequences. Good luck.

author: HalFoster
author_rank: Frequent Contributor
timestamp: October 31, 2022, 03:54:57 pm
content: More information on the topic:https://www.technonet.co.kr/data/bbsData/tantal1.pdfhttps://www.avx.com/docs/techinfo/VoltageDeratingRulesforSolidTantalumandNiobiumCapacitors.pdfAlso in MIL-PRF-55365 - I can't easily find an free online copy (I purchased my copy), but it goes into some detail.Hal

author: David Hess
author_rank: Super Contributor
timestamp: October 31, 2022, 04:54:22 pm
content: The problem extends to more than "first turn-on failures". Solid tantalum capacitors which have been in service for years or even decades can suddenly fail, and voltage derating to 2/3 or 1/2 practically eliminates these failures. The NASA paper I studied suggested that these were caused by "field crystallization" of defects in the dielectric layer of *high voltage* parts, but all of the failures I have seen were in low voltage parts operated with little or no voltage derating. Because I only find these failures in epoxy packaged parts and not metal can parts, I suspect strain applied to the tantalum pellet through the epoxy encapsulation causes further damage which would normally self heal but inadequate voltage derating instead causes thermal runaway. The strain comes from the epoxy responding to temperature and humidity changes.One sure way to increase the failure rate is to apply an unlimited surge current, like at the unregulated input of a voltage regulator.Voltage derating is suppose to reduce the failure rate by providing a thicker dielectric layer so that self healing can occur without thermal runaway. Polymer tantalum parts are suppose to self heal without any mechanism for thermal runaway.

author: gnuarm
author_rank: Super Contributor
timestamp: November 01, 2022, 05:50:58 am
content: Quote from: Siwastaja on October 31, 2022, 02:46:19 pmI've already explained, quite clearly, how three different effects are often confused and conflated, this issue being discussed from reflow temperatures, current surge and derating to extend life span.You can choose to ignore these if you want. Or you can watch the bleeding video about it and learn something.

author: gnuarm
author_rank: Super Contributor
timestamp: November 01, 2022, 06:01:25 am
content: Quote from: David Hess on October 31, 2022, 04:54:22 pmSorry, i don't follow your logic. How are you equating these clearly different issues to be different manifestations of the same problem?I bet you didn't watch the video either. The speaker in that video clearly states theinitialpower on failure problem, is not a life span problem. Once it is fixed by the appropriate start up on the first power application, it is not seen again. That does not mean the part will never fail fromall causes.QuoteDo you really think the people making these parts would not figure out this is happening and work to understand it?QuotePolymer tantalum parts do not have the oxygen generation which is the element that results in thermal run away.How does voltage derating impact the dielectric layer??? You mean you will be using a part with a thicker dielectric? Even if that is so, I'm not following your reasoning. The healing happens when the conductive layer above the dielectric layer is chemically changed to an insulator, isolating the short in the dielectric layer. No? I don't see how this is related to the thickness of the dielectric layer. Your rational would result in all higher voltage parts being less subject to the problem rather than having to do with the applied voltage.

author: David Hess
author_rank: Super Contributor
timestamp: November 01, 2022, 07:16:32 am
content: Quote from: gnuarm on November 01, 2022, 06:01:25 amIt is the same problem involving thermal runaway during self healing of a flaw caused by strain in the tantalum pellet. In one case the strain is the result of heating during assembly, and in the other the strain is from thermal expansion and changes in humidity over time.QuoteThen why did it take them 60 years to advertise the problem?QuoteWith more volume and mass, self healing can complete before thermal runaway occurs. Voltage derated parts are more likely to complete self healing without failure initially and later. In some cases the failure rate in tests was zero.

author: gnuarm
author_rank: Super Contributor
timestamp: November 01, 2022, 03:47:23 pm
content: Quote from: David Hess on November 01, 2022, 07:16:32 amThese are wear issues. You want to say it is the same problem even though the causes are different. They may have similar components, but they are not the same issue.QuoteYou are missing the fact that this would be related to the size of the part only, not the voltage rating vs. operation, i.e. derating factor. You are saying this yourself, "With more volume and mass". Don't listen to me, listen to yourself.