We’ve all heard about the perils of counterfeit chips, and more than a few of us have probably been bitten by those scruple-free types who run random chips through a laser marker and foist them off as something they’re not. Honestly, we’ve never understood the business model here — it seems like the counterfeiters spend almost as much time and effort faking chips as they would just getting the real ones. But we digress.
Unfortunately, integrated circuits aren’t the only parts that can be profitably faked, as [Amateur Hardware Repair] shows us with this look at questionable tantalum capacitors. In the market for some tantalums for a repair project, the offerings at AliExpress proved too tempting to resist, despite being advertised alongside 1,000 gram gold bars for $121 each. Wisely, he also ordered samples from more reputable dealers like LCSC, DigiKey, and Mouser, although not at the same improbably low unit price.
It was pretty much clear where this would be going just from the shipping. While the parts houses all shipped their tantalums in Mylar bags with humidity indicators, with all but LCSC including a desiccant pack, the AliExpress package came carefully enrobed in — plastic cling wrap? The Ali tantalums were also physically different from the other parts: they were considerably smaller, the leads seemed a little chowdered up, and the package markings were quite messy and somewhat illegible. But the proof is in the testing, and while all the more expensive parts tested fine in terms of capacitance and equivalent series resistance, the caps of unknown provenance had ESRs in the 30 milliohm range, three to five times what the reputable caps measured.
None of this is to say that there aren’t some screaming deals on marketplaces like AliExpress, Amazon, and eBay, of course. It’s not even necessarily proof that these parts were in fact counterfeit, it could be that they were just surplus parts that hadn’t been stored under controlled conditions. But you get what you pay for, and as noted in the comments below the video, a lot of what you’re paying for at the parts houses is lot tracebility.
I once had a cheap Arduino Mega board with a tantalum input capacitor. I plugged in a heavy duty DC power supply. The inrush current made the capacitor explode with a loud pop. A fireball flew out and landed on my keyboard. It melted into a key. I blew out the flame. It left a small crater. If that landed in my eye instead I would have serious eye damage. That day I swore off tantalum.
Tantalum capacitor have a lower maximum current than their short circuit current, so it is asking for trouble.
Electrolytic capacitors do not produce fire, just confetti.
These days there are good quality solid state electrolytic and good multi-layer ceramics.
I have a pair of glasses with a mark right in the middle of one of the lenses where an exploding tantalum caps hit
Also tantalum is a conflict mineral, so it’s better to avoid them altogether unless you know your application can’t possibly use any of the alternatives.
Tantalums are nasty when they go because of the epoxy encapsulation, it shatters like a fragmentation grenade and throws very sharp bits of shrapnel with some force.
One of my colleagues had a scar on his thumb from a Tantalum in a Compaq Portable PC power supply, the cap exploded between his fingers when he was demonstrating how the squealing noise changed whenhe squeezed it.
But electrolytics are also pretty dangerous, there were a good number of dents and even a few embedded capacitor cans in the ceiling above my repair bench from televisions,monitors and power supplies that had decided to die in interesting ways, they could easily have cost me an eye if I’d not had a good pair of safety goggles.
MLCCs can catch and do fire if you mistreat them mechanically or electrically but they don’t explode…
A number of years ago, we designed in a few Sprague 1000uF/6.3V low ESR tantalum caps (big orange blobs) on a board. They performed really, relly well, but on a few rare occations they would spontaneously self-combust quite violently without warning. Burning deep holes into the table or floor whereever they ended up after desoldering themselves from the charred PCB.
It could be due to surges as you described – we never fully understood it. It only happened when we worked with the boards in the lab not in the field (further indicating it could be related to surges hooking the boards up to lab power supplies).
I never really liked working with tantalum caps ever since…
Maybe it is irrelevant, but was said capacitor installed with polarity reversed?
There probably wasn’t enough “evidence” to determine that.
No. The DC power supply had a low ESR output capacitor. It the barrel jack connector could spark when plugged into a board with a low ESR input capacitor. It wasn’t a polarity issue.
remember doing pc repair on an old machine and so i put it on the bench, took the side panel off. after some initial dust bunny removal i flipped the switch. a cap on one of the vrms exploded and projected a fireball across the room. not sure if it was tantalum or not (dont know anything else that would project a fireball), but it was kind of cool.
Meh. I still have a 5mm scar on my hand from when my soldering iron slipped almost 50 years ago.
I lived to tell the tale.
I hear you. A few years ago i actually went through my partkeepr and weeded out all the old tant parts and scrapped them. Nasty little things.
Still if it gets the job done then not a problem, 2 ali one is still cheaper then 1 US one :D
The ESR is far too high on the fakes though. That said, you can solve that by putting them in parallel.
The Aliexpress looks like they are sanded and repainted.
I don’t mind getting scavenged parts (like (E)EPROMS or old 5V RAM) but please leave the old markings one and advertized them as scavenged.
Very much so, 30 milliohms isn’t unreasonable for a tantalum so they may not be out of spec for the original part but they definitely aren’t the part advertised.
The most amusing Ali purchase I made was for some “AMD” 16 bit EPROMs, they all arrived with the same part number and a cople of different date codes but the chip dies are of course visible through the quartz window and there were 4 very obviously different dies.
Also, because they were ceramic packages the sanding and remarking process hadn’t worked well at all and the original manufacturer markings were still very visible under the AMD branding and part number, ISTR they were Intel, ST, Fujitsu and Toshiba.
All the chips worked, my EPROM programmer ID’d the parts and they all programmed perfectly.
” But you get what you pay for, ”
… only if you are lucky. The saying should be, “You seldom get more than you pay for, but you frequently get less.”
pretty much this. people make fortunes selling products that dont work and we the consumer constantly let them get away with it.
of course when i buy parts its for some project that im still working on and by the time i get a prototype together on the bench the buyer protections have expired. its not always practical to test everything that comes in the mail, especially given my limited test equipment.
Also, lets not forget the middle men, Amazon, Ali, etc. are all making money from the sale of products that don’t work (and other scams) and have little incentive to stop it. Often these middle men have complicit policies that make it hard to do anything other than leave a bad review – because if you can’t get a refund the middle men get to keep their money.
My experience with leaving reviews on Banggood, is if you say anything good, such as the the packaging was good, it doesn’t matter if your review of the product is 1 star, they will list it as 5 stars because of the package.
Don’t tantalum caps fail short? Super dangerous imo for electronics. I’ve killed a Macintosh se/30 by using tantalum caps as replacements 10 years ago, then recently one failed and took out the adjacent IC rendering the audio completely useless and unfixable except for replacement with a spare special apple only OF from another donee board. Hasn’t been made in 30+ years.
Heads up to those who think tantalums are the end all be all best thing ever.
Shorting is one failure mode and on application of voltage, the inrush current can heat the electrolyte to vaporize and explode. Decades ago we used wet slug through hole Ta caps by bypassing due to their small size. Ended up doing a screening procedure to weed out potential failures down the road. Screening was to apply voltage and remove it, repeat X times. If the cap lasted it was unlikely to form the dendrites that short it out. It reminded me of that Bugs Bunny cartoon where he’s testing the big shells by hammering them. If it didn’t explode, it got a “dud” label.
“Provenance, what are you using a fancy French word like that for?
Call it a car hole like everybody else!”
-Moe (paraphrased)
What’s really exciting is when your regular manual insertion line personnel call out sick, and the replacement folks aren’t told the little orange blobs have a polarity marking.
Let’s just say that overnight “Burn In” took on a whole new meaning on the production floor.
The solid tantalum capacitors with their manganese dioxide are chemically similar to aluminum and iron oxide respectively. You may recognize the latter pair as thermite. When a tantalum capacitor fails with sufficient energy, it does indeed undergo a thermite reaction with the attendant heat. Thus some of the events listed by others above.
A military customer of a vendor of high-end airborne camera systems had a unit fail due to loss of image quality. Examination revealed the windows and optics had a nearly opaque coating. Disassembly revealed that the 18 tantalum capacitors used to buffer power to the motion control motors had one of their number fail in thermite mode. Which caused those adjacent to it to do so, and on until all 18 had blown, providing that coating and also burning through the circuit board as well. I got to replace the former engineer’s design with ceramic capacitors and they never had another failure.
Tantalums are good if designed in properly, but there are quite a few requirements for that to happen!
Excellent report and your sense of humor is appreciated too!
Personally I have focused myself on JFET’s and OPAMPS from Ebay. The general conclusion must be to never ever buy these from Chinese sellers. There is no guarantee that you get what you order, and even if you think you got a device that is either a jfet or opamp, you have no guarantee that it works as intended. Worst were the cases where the J310 turned out to be a NPN-BJT, or when a TL071 performed worse than a 741 (or TL072 worse than LM358). I received refurbished IC’s sold as new, but seemingly working properly. And some looking perfectly new that did not work at all.
I received J310’s that had both their Vgs and Id suspiciously lower than a reference device. I received BF245C’s where one lot worked in a VFO, while the other lot was not working at all. And also here the specs differed significantly from reference devices.
Without any exception I got a refund after filing a complaint (which I only did when the device was demonstratably flawed), but that is not the point. I sent in a formal complaint to Ebay, but never got a reply. Every now and then I order some semiconductors, but only for the sake of testing them. Should I be lucky enough to receive authentic parts for Ebay prices, I celebrate that as winning a modest jackpot. In all other cases I get a refund, and Ebay hopefully yet another reason to one day implement a three strikes out system.
I specifically buy those 2TB thumb drives to get a free 32-128MB one. (After refund).