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Faulty name-brand ceramic capacitors - common?
Posted by
Corporate666
on 13 Oct, 2017 19:24
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I have experienced a 500% increase in failures in the field over the last few months for one specific product. I've gotten some of the units back and it was just this week I was able to go through all the failed units, do a thorough post-mortem and tabulate the results.
It turns out a capacitor on the power input was failing as a dead short, causing the traces on the board leading to that cap to ultimately massively overheat and go up in smoke.
The capacitors are CL21A226MOCLRNC from Samsung. I went through our stack of boards that failed post-assembly testing and were awaiting rework, and found that most of the failures there are also due to this same capacitor. I then went through the drop-bin on the pick and place machine (where it drops parts it could not place for whatever reason), and pulled out all of the aforementioned caps and tested them... about 5% were bad - just a dead short. I looked under a microscope and there's nothing unusual to see, no cracks or problems with the solder points or anything else.
But the fact that I saw so many failed parts in the PnP reject bin tells me that it wasn't the reflow process, nor the testing process, nor the use in the field that was causing the issues... it was bad parts right off the reel.
I was wondering if anyone has seen anything like this before? Digikey has ~200,000 of these caps in stock, so it seems to be a pretty common usage part, and I am very surprised that a major manufacturer would be shipping parts with this problem. But maybe I have just been lucky in the past?
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#1 Reply
Posted by
georges80
on 13 Oct, 2017 20:28
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It's an MLCC - so likely internally shorted and likely due to an assembly issue or PCB layout issue (i.e. micro cracks leading to internal short).
I'd find it hard to believe they are faulty right out of the chute... I'd pull a bunch of parts straight off the reel and measure/test before any pnp machine etc has gotten to them.
IF you find them faulty on the reel then I would contact Digikey to figure out what is going on.
cheers,
george.
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#2 Reply
Posted by
GreggD
on 13 Oct, 2017 20:36
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Could someone be bending the pcb and causing micro cracks ?
Is there a heavy component on the pcb so that if the pcb is picked up by one end the heavy part flexes the board.
This is quite common and causes a dead or near dead short.
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#3 Reply
Posted by
Leo Bodnar
on 13 Oct, 2017 21:01
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I have just ordered a few hundred from DK. Maybe I get lucky too - will let you know.
I get ceramic caps failing shortcircuit now and then but they are usually already assembled and nowhere close to even 1%.
Leo
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#4 Reply
Posted by
wraper
on 13 Oct, 2017 21:26
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In my experience MLCCs fail because of mechanical stress. PCB may have 10s of the same ceramic capacitors on the single power rail, and it's always same single cap failing somewhere nearby to the mounting hole or board edge. Larger sizes are more susceptible.
You won't see something like this unless cut capacitor in half.
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#5 Reply
Posted by
wraper
on 13 Oct, 2017 21:31
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But the fact that I saw so many failed parts in the PnP reject bin tells me that it wasn't the reflow process, nor the testing process, nor the use in the field that was causing the issues... it was bad parts right off the reel.
I rather suspect PnP machine was smashing them while picking up or something like this. Are there multiple such capacitors on the PCB and only particular destinator failing?
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#6 Reply
Posted by
Leo Bodnar
on 13 Oct, 2017 22:03
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I have seen capacitors with visible cracks and chips right off the [undamaged] tape when I have been assembling prototypes manually.
They were 1206 with high C / high V value for that package so not a cheapo 0.1uF runarounds. Can't remember exact brand but definitely well branded - TDK, Murata or Kemet.
Anyone who worked in manufacturing will know that weird things do happen and when they do happen there are usually a lot of them.
Leo
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Well, a plot twist... not all of the failed boards were PnP placed. The board doesn't have too many parts on it, so if the PnP is already set up for another job and we just need a run of 20 boards or such, we will hand-place them.
Due to our manufacturing process, I know which boards were hand placed and which were PnP placed, and a proportional quantity of the boards with failed caps were hand placed. I also went through the tub of components that they use when hand placing boards and tested a bunch and found several that were failed with a dead short also.
Nothing in the PCB or assembly process has changed - and based on the batch numbers and estimating how many parts are taken off the reel for hand assembly, not only were all the bad parts from a single reel, but it looks like it was just part of the reel that was bad. In other words, it appears that maybe just a couple of meters of that reel had a ton of bad parts and the rest were fine.
I wonder if something could have happened during reeling or during storage/transit to cause this? Like the reel got squished by something or someone dropped something on it in the shop?
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#8 Reply
Posted by
Leo Bodnar
on 13 Oct, 2017 22:12
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I wonder if something could have happened during reeling or during storage/transit to cause this? Like the reel got squished by something or someone dropped something on it in the shop?
Do you use DK re-reeling service or buy full reels?
Leo
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#9 Reply
Posted by
TimNJ
on 13 Oct, 2017 22:20
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Ceramic caps, especially those with class 2 dielectrics (X7R), are prone to endcap separation due to mechanical stress. Caps placed near the edge of a board or near heavy components are more likely to fail. Also, an incorrect soldering temperature profile, or even worse, hand soldering, can cause the endcaps and ceramic chip to expand at different rates and crack. NP0/C0G caps don't experience these problems as much.
You might want to take a look at MLCCs with "flexible terminations" like FT-CAP from Kemet:
http://www.kemet.com/Lists/ApplicationBriefs/Attachments/58/Flexible%20Termination%20Technology%20(FT-CAP).pdfThese caps have a layer of a epoxy (of some sort) that make them more resilient to mechanical stress.
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#10 Reply
Posted by
Leo Bodnar
on 13 Oct, 2017 22:24
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I know this is internet but could we please concentrate on the fact that a lot of failed caps have never been on the PCB in their entire life?
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#11 Reply
Posted by
rx8pilot
on 13 Oct, 2017 22:25
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Following this thread.....
Sent from my SM-G892A using Tapatalk
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#12 Reply
Posted by
thm_w
on 14 Oct, 2017 00:10
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5% is incredibly high, did you contact Samsung with the production date to see if they can provide any insight?
I have just ordered a few hundred from DK. Maybe I get lucky too - will let you know.
I get ceramic caps failing shortcircuit now and then but they are usually already assembled and nowhere close to even 1%.
Yes, same experience here, a few ceramics failed after production (<0.1%), and a handful failed returned from the field (<0.2%). Its always the same ones in the power section, so maybe they are stressed or due to their larger size (1210 10uF 25V X7R Murata).
In the field case they could have been abused (overvoltage, roughly handled in shipping, etc.), so cannot say for sure if they were actually defective.
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#13 Reply
Posted by
wraper
on 14 Oct, 2017 08:24
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Yes, same experience here, a few ceramics failed after production (<0.1%), and a handful failed returned from the field (<0.2%). Its always the same ones in the power section, so maybe they are stressed or due to their larger size (1210 10uF 25V X7R Murata).
It's not "OR" situation. Larger sizes are more susceptible to mechanical stress. I would look into how caps are mechanically located and how these boards are depanelized. You could, say, rotate them by 90
o and this could fix the issue.
In the field case they could have been abused (overvoltage, roughly handled in shipping, etc.), so cannot say for sure if they were actually defective.
If there is mechanical stress at production, they may fail short later. Overvoltage unlikely to be the issue, MLCC easily survive 10x of the rated voltage.
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#14 Reply
Posted by
Psi
on 14 Oct, 2017 10:43
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I've seen some 10uF Yageo 0603 caps fail semi-shorted recently. But being cheap Yaego caps it didn't surprise me that much.
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#15 Reply
Posted by
SeanB
on 14 Oct, 2017 11:18
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Position dependant on the reel only, so my guess is that the reel was dropped at some point on edge on a hard surface. Check the reel itself for edge damage, and you will find a flat spot where it deformed. Likely the reel tape inside was not tightly wrapped, and the loose turns had enough shock from hitting each other to crack the capacitors as they impacted inside the reel tubs and crack them.
Take the reel, and sacrifice a few meters of capacitors, peeling the tape off after attaching the reel to a hard flat surface, and look inside the plastic tubs to see the indents the capacitors would have left there on impact. Use a microscope to see, and take a photo of dented versus undented, and have a word with the supplier and the shipper, for both dropping shock sensitive items and for not packing properly in a box with adequate shock dampening material.
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I wonder if something could have happened during reeling or during storage/transit to cause this? Like the reel got squished by something or someone dropped something on it in the shop?
Do you use DK re-reeling service or buy full reels?
Leo
Bought as a full reel, new in package.
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5% is incredibly high, did you contact Samsung with the production date to see if they can provide any insight?
I haven't, but I will probably do that this week. I don't imagine much of a result... especially since the reel has since been used up and the only parts I have are the failed ones, those in the hand-placement tub, and the miplaced parts catcher from the PnP. At best they will ask for some of the parts back for analysis and maybe will send me some replacements. We'll see.
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#18 Reply
Posted by
T3sl4co1l
on 15 Oct, 2017 09:01
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FWIW, 1210 is large, but even the conservative IPC doesn't worry about them: in fact, they recommend 1210 as the largest reliable size.
In any case, forget about soldering defects, parts were bad off the reel. Can't people read?
Second the suggestion of calling Samsung and notifying their quality dept somehow. Or if not them directly, then the supplier -- for that matter, I suppose you might ask if you can get a refund/credit or replacement for the bum parts. Then if they decide to notify the mfg, it's up to them (and they probably have better contacts than you, anyway?).
Tim
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#19 Reply
Posted by
Leo Bodnar
on 16 Oct, 2017 08:35
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Bought as a full reel, new in package.
Corporate666, I have just received DK order.
There is good news and bad news.
Good news is there are no shorts.
Bad news is capacitance is about half of what you'd expect. They are all in the 13-14µF range.
Leo
https://www.digikey.co.uk/products/en?keywords=1276-6780-1-ND1276-6780-1-ND .07430 7.43 T CAP CER 22UF 16V X5R 0805
HTSUS: 8532.24.0020 ECCN: EAR99
LEAD: LEAD FREE ROHS: ROHS
Mercury: Cert on File.
For more information contact RoHS@DigiKey.com
COUNTRY/ORIGIN:CHINA
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#20 Reply
Posted by
jbb
on 16 Oct, 2017 08:58
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Half the expected value is odd, unless it's due to DC bias. Do you know what voltage is applied by your capacitor meter?
X5R and similar dielectrics actually loose a lot of capacitance when DC voltage is applied. Some manufacturers are more forthcoming than others about this. There should be a capacitance vs DC bias curve in the data sheet or part technical information to help with your design.
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#21 Reply
Posted by
Leo Bodnar
on 16 Oct, 2017 09:06
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Half the expected value is odd, unless it's due to DC bias. Do you know what voltage is applied by your capacitor meter?
I have three meters from various brands and they all show the same value. Don't really have time to look it up but i'd be amazed if there is any DC bias beyond few mV. I trust Agilent not to be complete idiots.
Leo
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#22 Reply
Posted by
BFX
on 16 Oct, 2017 11:49
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@Leo
Capacitors >10uF should be measured at 120Hz +-20%.
I see on your meter 1kHz. That could be problem.
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#23 Reply
Posted by
Ice-Tea
on 16 Oct, 2017 12:02
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I noticed that you never outright say whether you bought them at DK or not... Did you?
Also, I agree: get in touch with Samsung. Failing components off the reel should be in the low ppm region. Or, you know, nothing at all.
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#24 Reply
Posted by
wraper
on 16 Oct, 2017 12:05
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@Leo
Capacitors >10uF should be measured at 120Hz +-20%.
I see on your meter 1kHz. That could be problem.
This, also a significant part of capacitance drops because of ageing. Leo, reheat the capacitor with the hot air or soldering iron, let it cool down for some time and measure again.