smd tants vs bead types - Page 1
Forum section: electronics / beginners

author: ME
author_rank: Frequent Contributor
timestamp: May 31, 2025, 04:17:23 pm
content: Are the small yellow/orange smd tantalum caps as bad as the bead type tants for going bad?/sc or exploding?.

author: UnijunctionTransistor
author_rank: Frequent Contributor
timestamp: May 31, 2025, 04:39:21 pm
content: I once read a Kemet white paper, discussing Tantalum cap failures, which mentioned that uneven CTEs could place internal stresses on the SMT caps, which could exacerbate the Tantalum cap weaknesses.But now that Kemet is part of Yageo, the website has been revamped and I can no longer find it.However on one of the datasheetsfor a SMT device, I found the following statement:The KEMET families of surface mount capacitors are compatible with wave (single or dual), convection, IR, or vapor phase reflow techniques.Preheating of these components is recommended to avoid extreme thermal stress.The datasheet also cautions when hand soldering the capacitors.

author: golden_labels
author_rank: Super Contributor
timestamp: May 31, 2025, 05:41:48 pm
content: If a tantalum capacitor fails in an explosive manner, it’s not because the package it was in. It’s because of how it was used.They are very untolerant of voltages exceeding their rated voltage. Those capacitors may also become unstable when operated close to the limits. It’s due to the internal structure, not the package a capacitor is in.Mind that all electrolytic capacitors may fail catastrophically. If we consider possible damage, tantalums aren’t even the worst offenders. How easy it’s to misuse them, combined with the chances of producing high temperature, made them quite infamous. But don’t fall into the trap of making a distinction between tantalum capacitors and other types that straighforward. On the web you can find enough of photos showing aftermath of a large aluminium capacitor exploding, to get a more balanced idea.(1)That said, also consider they’re not more as attractive. In the past a tantalum would offer superior characteristics in a small package, unavailable with other types. Modern solid aluminium caps very often offer the same as their tantalum brothers did in the past. They’re cheaper too and forgive much more abuse.(1)And by “balanced” I mean not only less polarized. I also mean observing that it’s a multidimensional problem. Failures are not created equal and they can’t always be compared directly.

author: jpanhalt
author_rank: Super Contributor
timestamp: May 31, 2025, 06:46:19 pm
content: Quote from: golden_labels on May 31, 2025, 05:41:48 pmI tried to find "SAL" capacitors, and they all came up "obsolete" on DigiKey. Vishay has apparently discontinued them. What's your source?

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2025, 07:15:09 pm
content: this part is sickhttps://www.digikey.com/en/products/detail/kemet/APL90A112LH063/22231807its flat like everyone wants but it also has the wires

author: ME
author_rank: Frequent Contributor
timestamp: May 31, 2025, 07:17:31 pm
content: I was talking about when they are old in test gear,are the cermet ones as likley to say take a rail to ground as the blob tag type?,what goes pop more often?.

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2025, 07:20:32 pm
content: its a stalinist policy alot of people say they are fine lolI think you either prosecute them or don't prosecute themit can have to do with drifted circuit parameters that end up surging them more (i.e. a carbon composition resistor that changed in value and lets more current through then the tantalum wants, drifted power rails, etc)what I do is maybe replace it if its near something that looks like it would be a major bitch to fix like a processor and its also bigI wanna know something else, I wonder about the leads on tantalum capacitors that failed. Did anyone ever do a study to look if the leads were strain relieved for insertion with the right tool? Because you can do it but no one tells you if you should. I think it makes sense. I have seen shorted tantalum once, and it was pressed right into the PCB as far as it would go to maintain a low profile in a tight chassis without forming the leads. Real stiff position. But it just shorted and disable equipment, I found it with DMM, desoldered it and threw it away (no bomb)you can have this:or thisI really wonder if #2 is a good ideathis is what is insidehttps://spectrum.ieee.org/media-library/a-photo-of-a-cutaway-of-a-dipped-tantalum-capacitor.png?id=32840006&width=800&quality=85if you don't form the leads it looks like its putting the capacitor part in a nut crackerhttps://cdnimg.webstaurantstore.com/images/products/large/25222/1861638.jpg

author: David Hess
author_rank: Super Contributor
timestamp: May 31, 2025, 08:23:43 pm
content: Quote from: ME on May 31, 2025, 04:17:23 pmYes, they behave the same.

author: floobydust
author_rank: Super Contributor
timestamp: May 31, 2025, 08:31:15 pm
content: Dipped-bead verses SMT, there is less mechanical (lead, soldering) stress with the through-hole parts. The long leads have some cush and bend I think more than the SMT parts which are sensitive to pad size and spacing, solder fillet etc. and unfortunately there are different footprints out there, which makes it a bit confusing.Unspoken rule-of-thumb is to voltage derate tantalums by 50% for good reliability. About 35x better. Using a 6.3V part at 5V - nope but that's a 0.5-1.1% failure rate, compared to 0.01%-0.03% if derated.sourceThey can also short and burn up if in an SMPS because the ripple current with their moderate ESR heats them up. Power dissipation I did not compare between packages it's 100mW at best. Tantalums are not to be used on SMPS rails without decent bulk caps being there. If the bulk caps (electrolytics) fail and dry out, then I've seen any tantalums on that rail, smoke and burn - but they are not to blame.Before the thread goes into tantalum bashing, they are very well researched for reliability in military, aerospace etc. for decades now. There's a few failure mechanisms - electrical stress, mechanical, heat stress and age.A few picshttps://www.semlab.com/services/electronic-component-failure-analysis/capacitor-failure-analysis/

author: coppercone2
author_rank: Super Contributor
timestamp: May 31, 2025, 08:34:26 pm
content: ANOTHER thing I wanna know is how many of those tantalums that break have not bent leads and then also soldered in place and then folded over to make the board slimmer. Not formed and like fixtured before soldering, but soldered and then just forced over with the thumbI see people do this, its a bad technique IMO to hope the part seal and interconnect is designed to let you FORM the copper into shape USING the part.The bead shape kind of lets you form it because its round on the bottom. If you try it with a cylinder you will get the lead torn out very quickly if you try this trick. But if its round you can kind of do it but its probobly putting a overload stress on the part. Then you crack the interconnect to the capacitor material, make a resistor, it heats up with ripple current and boom. or crack the seal and then contamination.I wonder if tantalums would be having this problem if they were molded into a cylinder shape (that sits flat on its ass) like a radial capacitor instead of a dipped bead shape that encourages bending to 45 degree angle.I don't know how much you can compare it by package alone, because I think the 'important part' is the joint between the capacitor material and the lead. Every combination of materials is gonna be different. Some of them are really good (ductile, tough, etc) and some interfaces are horrible (brittle and weak). You could make the same footprint with different internal 'load' and probobly have vastly different reliability. Something makes me think its more fragile then the usual materials that let you get away with 'lead tricks'.

author: golden_labels
author_rank: Super Contributor
timestamp: May 31, 2025, 09:54:06 pm
content: Quote from: jpanhalt on May 31, 2025, 06:46:19 pmSearch for “polymer capacitors.”Examples: Nichicon PCJ, Panasonic SXV and SVP, Kyocera AVP. Basically all those in metal cans with no vents you see on motherboards for the past 10–15 years. There are also SMD ones in the same rectangular package as tantalums, except usually black instead of yellow/brown.

author: floobydust
author_rank: Super Contributor
timestamp: June 01, 2025, 01:51:49 am
content: Careful that polymer caps have 10-100x the leakage current of tantalums, and 1/100 the ESR.It needs to be taken into consideration, as it can be a wrong move. You don't just hop to a new dielectric, they all have different properties.

author: David Hess
author_rank: Super Contributor
timestamp: June 01, 2025, 01:20:59 pm
content: Surface mount parts have to go through strain caused by heating from soldering. If they go through reforming afterwards, then their failure rate decreases to that of their pre-soldered state.It seems like leaded parts should avoid heating from the soldering process, however they somehow have the same problem.

author: floobydust
author_rank: Super Contributor
timestamp: June 01, 2025, 05:47:49 pm
content: I found it hell to make SMT tantalum capacitor PCB footprints.Despite the EIA case sizes, every manufacturer gives hugely differing pad sizes and spacing.Then, it's different in their app notes. Then it's different in a hi-rel app note. Murder to make a PCB library for these.AVX/Kyocera, Sprague/Vishay, Kemet you all suck for being inconsistent.My worry is about the solder fillet going up the lead, preventing it from bending and stress cracking happening.As if I got time to forecast this. Just another tantalum capacitor frustration.

author: David Hess
author_rank: Super Contributor
timestamp: June 01, 2025, 07:19:01 pm
content: Quote from: floobydust on June 01, 2025, 05:47:49 pmI always make a pad geometry which encompasses the largest dimensions of the manufacturer's recommendations.QuoteWouldn't that depend on the amount of solder applied to the pad rather than the geometry?

author: floobydust
author_rank: Super Contributor
timestamp: June 01, 2025, 07:54:40 pm
content: I find bigger (tant) pads may or may not have bigger spacing. Bigger pads means more paste. This all might be a nothing burger because the leads can bend a little unless the fillet goes up too high. More an issue with MLCC.Pic from NASA paperFootprints all over the place as I recall, I have to find my spreadsheet comparison of 10 different tant footprints. I did scream- you may have heard that across the Atlantic lol.I'll use the 3D model of the part to eyeball the leads and pads fit.But in production, Purchasing buying an alternate part in the same EIA package is a problem when the recommended footprint is quite different. I'll use something in the middle.It's actually really frustrating to simply want a Size B tant cap PCB footprint and quite different ones out there, even within one manufacturer.