Why are hermetically sealed tantalum capacitors so expensive? - Page 1
Forum section: electronics / beginners

author: XOIIO
author_rank: Super Contributor
timestamp: April 19, 2014, 12:24:44 pm
content: I have heard on several videos from a couple different people that these capacitors are ridiculously expensive, even being as much as 30 bucks each, and they aren't even that large, I am wondering why they are so expensive, and what applications they are used in that would make that cost worthwhile.

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2014, 12:47:53 pm
content: Cost of the metal inside, the need to make a sintered slug individually for each unit and attach a solid Tantalum wire to it, then sinter in a vacuum and then oxidise the unit carefully to get the required thin oxide layer. then the slection to the right value per unit, assembly in a housing then soldering the housing closed, along with then testing and checking each unit.Yes, that all adds cost as opposed to taking a long reel of foil, etching it in a continuous bath, cleaning then slitting and tabbing, winding with a paper layer in electrolyte, and then sticking in a can then closing with a bung, almost all of which can be done automatically on a line.

author: ecat
author_rank: Frequent Contributor
timestamp: April 19, 2014, 01:25:20 pm
content: They sounded interesting so I did a quick search...that's what these silver caps are, marked 150D fyi.Me thinks this cheap power supply I bought is a tad over engineered.Left and right close-up of the controller board

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2014, 01:39:39 pm
content: I take it it was not new when you bought it. The big advantage that the glass seal Tantalum capacitors have over any other is that the operational life and storage life is indefinite, and they will meet the specs even after 50 years of storage providing they have not been outside the storage envelope. They also are space rated, and are flying on the Voyager and Pioneer spacecraft, which are still operational after decades in space. i tested a batch of 500 after they had been in storage for around 20 years, and reformed the first batch of 100 for 3 hours, then tested every one. second batch I did not, and tested the remainder only as spot checks, as there were no failures and no difference in the spread of capacitance and ESR between the reformed and unreformed units. All were in tolerance. I did test a couple for explosive value, you need to apply 20V in reverse with a 5A current limit, when the unit under test will get warm, get hot, split the outer PTFE sleeve then pop out the slug when it reaches solder melting point. I only did that once on a board by accident.The cheaper ones use a rubber seal, and these do degrade with time and fail as high ESR. Those when far gone do not even pop when tried in reverse, and the tantalum leadout on the positive end will not solder, and as well is very hard to cut, it will leave a nick in any edge cutter unless it has hardened steel ground blades meant to cut spring steel or guitar strings.

author: XOIIO
author_rank: Super Contributor
timestamp: April 19, 2014, 01:49:34 pm
content: Ah, cool, so they would be ideal for critical equipment that would be running for a very long time then, that's neat.

author: Marco
author_rank: Super Contributor
timestamp: April 19, 2014, 01:59:05 pm
content: How do solid electrolyte elcos compare?

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2014, 02:12:12 pm
content: Not enough real lifetime data, and they still have rubber seals so will degrade. Glass frit seals do not degrade easily unless the unit corrodes through.

author: ecat
author_rank: Frequent Contributor
timestamp: April 19, 2014, 02:12:49 pm
content: Sound like something between the duck's guts and the dog's bollocks.The psu was ebay of course. It's big, heavy and cost £20 iircfree documentation is non-existent, but for parts alone I'd recommend it to anyone at twice that price. The blue edge connector shown in my previous post is for an external controller, this I do have documentation for so fancy controls and lcd displays are a possibility.Apologies for the digression.

author: Marco
author_rank: Super Contributor
timestamp: April 19, 2014, 02:29:53 pm
content: Quote from: SeanB on April 19, 2014, 02:12:12 pmWhy can't they just close them up with epoxy, like some smaller solid tantalums? If cured epoxy starts to deteriorate you probably have bigger problems ...

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2014, 02:49:17 pm
content: Epoxy does not chemically bond to the underlying metal, and will still fracture with time. Glass seals though are both chemically inert and are chemically bonded with the support. As well it will not lend itself to fast assembly and will make the price quite high. I do have some regular electrolytics made in the 1970's that were epoxy filled over the rubber axial seal, and while they do last longer they do eventually dry out and die, and only have a regular -20 to+70 C temperature range.

author: ecat
author_rank: Frequent Contributor
timestamp: April 19, 2014, 02:52:55 pm
content: Quote from: Marco on April 19, 2014, 02:29:53 pmI'm sure deterioration is a factor but it is also about permeability, over the course of decades as SeanB was saying.Here's a handy two page summary on permeability:http://link.springer.com/article/10.1007%2Fs005420000056#page-1Click 'Look Inside'

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2014, 06:46:28 pm
content: I'm not sure those are tantalum on your board, I want to say regular electrolytics were packaged that way too. That said, those TO-39 canned op-amps were never particularly cheap, so you can rest assured they were going for reliability in that build.I happen to have a small baggie of M39003 dry slug tantalums. These are the same formulation as any other: lots of black stuff inside. They're awfully heavy for 50V 10uF. As such, they are -- well, I should expect -- as sensitive to failure as otherwise, with the exception that, because there's so much metallic mass inside, it should take much more to kick off. They're expensive, but not wet-slug expensive.Wet slug tants are, I believe, M39007 or thereabouts. These are the ones with gel sulfuric acid electrolyte (I'm not kidding) and 200C (or something high) temp ratings. And >$100 price tags.Tim

author: SeanB
author_rank: Super Contributor
timestamp: April 19, 2014, 06:54:46 pm
content: Regular electrolytics yes, but the wet slug CTS13 units are next to the 10 turn pots in the top image, and near the middle of the second.

author: Marco
author_rank: Super Contributor
timestamp: April 19, 2014, 07:06:57 pm
content: Quote from: SeanB on April 19, 2014, 02:49:17 pmSounds reasonable, but since reality isn't always reasonable I decided to double check ... yeah,it does.ecat, those first 2 pages will fail to give you their final conclusion : "These permeation rates can be compared to those with laser welded packages" (also some caveats about long time stability still needing testing, but copy/pasting only gives gibberish and I'm not manually copying it).

author: SeanB
author_rank: Super Contributor
timestamp: April 20, 2014, 12:24:21 pm
content: Note the curing conditions are a 170C cure for 30 minutes. Not exactly a method you want to use on a water based fill, and definitely not something you want to expose many plastic materials to either. The common low temperature epoxies will have worse adhesion, and in a fill where you have both a caustic liquid, and where you are placing the fill over a wetted part a solder preform with a short period of heating to do a localised reflow will work better.I agree epoxies can make a good seal on dry well prepared surfaces, and probably can get leakage rates as low or lower than a laser welded or soldered seal, but doing so in a wet environment with surface contamination on all the surfaces will not be reliable or even high yield.

author: amyk
author_rank: Super Contributor
timestamp: April 20, 2014, 01:44:47 pm
content: Quote from: XOIIO on April 19, 2014, 12:24:44 pm$30 is not that expensive...http://www.mouser.com/Vishay/Tantalum-Capacitors-Wet/HE3-Series/_/N-1z0zls5Z75hr5Z1yzsq8j

author: SeanB
author_rank: Super Contributor
timestamp: April 20, 2014, 05:37:40 pm
content: Quote from: amyk on April 20, 2014, 01:44:47 pmNo wonder we could not get those I ordered, with that lead time. Was looking in a box today and found one, died from poor seals, hermetic outer case but inside they used regular axial rubber bung units soldered to a PCB and connected to the terminals. 3000uF 35V in a rectangular soldered can. Thankfully the 5V regulator it was in worked well with 5V of ripple on the input, and the output had a 5600uF 16V unit, and probably most of the work was done by the 100uF capacitors on the various boards as these were also pretty poor. No way to change them as nothing would fit there without the 100 pages of mods, and I was only part way through......

author: XOIIO
author_rank: Super Contributor
timestamp: April 20, 2014, 08:04:27 pm
content: Holy crap over $1000 for two of them? Damn

author: amyk
author_rank: Super Contributor
timestamp: April 21, 2014, 04:27:58 am
content: Quote from: XOIIO on April 20, 2014, 08:04:27 pmThat's the priceeach, if you order two of them.

author: LukeW
author_rank: Frequent Contributor
timestamp: April 21, 2014, 05:24:31 am
content: These are the so-called wet tantalum caps, where the tantalum slug is bathed in a sulfuric acid electrolyte inside the can, right?The can material is either pure silver or tantalum itself. Tricky construction techniques are needed to fabricate these thing, especially for high milspec reliability.They offer high capacitance density in a small package, high reliability, long life, high temperature tolerance and vibration/shock tolerance and low ESR, making them attractive for applications such as space, military, avionics and specialist industrial applications such as down-hole oil logging instruments operating at relatively high temperatures in demanding environments.http://www.vishay.com/docs/40021/wtintro.pdf

author: XOIIO
author_rank: Super Contributor
timestamp: April 21, 2014, 09:00:38 am
content: Quote from: amyk on April 21, 2014, 04:27:58 am

author: lapm
author_rank: Frequent Contributor
timestamp: April 21, 2014, 10:46:27 am
content: 1000$ is cheap is device sit at bottom of ocean or in orbit where you just cant have EE open it, fixit if component goes bad...Im glad i dont need to work on that sort of reliability levels. I have friend who works on space stuff... All type of things they need to taken in count when designing stuff for space environment.. Aging of components and materials used, effect of heat, etc....