Crumbling Capacitors - Page 1
Forum section: electronics / projects

author: katzohki
author_rank: Frequent Contributor
timestamp: October 20, 2014, 03:32:33 pm
content: I'm finding some pretty disturbing stuff lately and I was wondering if anyone has any recent or similar experiences. In quite a few of our boards I'm finding what I would describe as "cracked" or "crumbling" capacitors. In the cases of the bad ones, they seem to be extremely brittle and fall apart at a light touch like a stale piece of bread. The good ones can take a pounding more or less.The part is a Xicon 0805 0.01 uF cap:http://www.mouser.com/ProductDetail/Xicon/140-CC501B103K-RC/?qs=6ARB0lp6jlXWqZF4lhG52w%3D%3DThis is some pretty serious shit as we use this capacitor in 90% of what we build and it could shut down our entire production. Does anybody have any opinions on Xicon? Engineering seems to have specified of a Kemet or Murata part, but you know how that goes. I haven't heard anything bad about Xicon. Has anyone had any similar experiences? This doesn't seem like the typical kind of board-flex issue because of the way the fall apart.

author: timb
author_rank: Super Contributor
timestamp: October 20, 2014, 09:58:05 pm
content: Are you doing a board wash post assembly? If so with what?Are you using a suitable heat profile during reflow?Though, a simple ceramic cap should be okay with both of the above extremes.Personally, I'd be on the phone with Xicon right now complaining.Sent from my Smartphone

author: MartinX
author_rank: Regular Contributor
timestamp: October 20, 2014, 09:59:22 pm
content: I have experienced a similar thing, it turned out to be the oldest surface mounting machine that got a bit crazy at random intervals and put a lot of pressure on some parts when they placed them on the board almost crushing them. This machine was due for replacement and maintenance was kept to a minimum, that may not have been the best strategy.

author: katzohki
author_rank: Frequent Contributor
timestamp: October 20, 2014, 10:15:34 pm
content: I have to ask the CM about board wash, but last I looked all their processes were on the up and up including profile. I thought about a pick and place machine maybe crushing the caps onto the board, but this seems to be linked to this specific capacitor. And they crumble, which is the oddest thing. I pushed on it with my tweezers and it flaked apart. Very strange.

author: KJDS
author_rank: Super Contributor
timestamp: October 20, 2014, 10:26:29 pm
content: I've only ever had it once, with a batch of boards, again it was a 10n 0805 X7R cap. No idea who the manufacturer was and it was about 15 years ago. Never did work out what was wrong apart from it must have been a bad reel.

author: calexanian
author_rank: Super Contributor
timestamp: October 21, 2014, 02:06:41 am
content: I have encountered this before. It appeared to have been overheating of substandard materials used in the chip cap. Obviously non ceramic. It felt like some sort of plastic material that separated like crumbling phenolic or polystyrene. Dunlop effect pedals had a run of those things.

author: Neilm
author_rank: Super Contributor
timestamp: October 21, 2014, 05:59:52 pm
content: Is it all the caps or just in one area? I had an issue a few years ago where a particular resistor would be found to be open circuit when it was assembled into the PCB, but it had passed all the tests which did test this area. It turned out that one of the test jigs had a loose clamp that pressed on this particular component and when it was compressed it cracked the resistor.

author: katzohki
author_rank: Frequent Contributor
timestamp: October 21, 2014, 08:40:34 pm
content: It's the same cap on multiple different boards. The only common factor seems to be the cap, even different CMs.

author: matt6ft9
author_rank: Contributor
timestamp: October 24, 2014, 08:49:40 pm
content: This looks like a board flex issue. The cap in the picture seems to be very close to the edge of the PCB which is a red flag. Handling in production or depanelization could cause this. Are there any other ceramic caps as close to the edge of the PCB as the one pictured? Attached is a picture from a few years back I had on a failure near the edge of the board.The solution was to move the 2.2uF cap in further in from the edge. (keep all ceramic caps at least 80 mils from the edge) Check out flex-caps, they are more expensive, but much more forgiving of board flex.

author: TonyStewart
author_rank: Contributor
timestamp: October 25, 2014, 08:06:14 am
content: Sounds like a line stopper to me.Check flux type and compatability with factory. Some no-clean fluxes are quite corrosive with humidity. Apple Air products are the worst I've seen and turns exposed copper in big blue copper sulphate crystals after water exposure, which conveniently is detected by RH colour dots to also void the warranty.You may have to test the design for conformal spray sensitivity to coupling capacitance. But that may be a quick field retrofit in humid climates, if that turns out to be an accelerator with acid & dust..

author: fcb
author_rank: Super Contributor
timestamp: October 25, 2014, 09:08:34 am
content: It's likely to be (as others have stated):1. Faulty parts (I haven't heard if Xicon).2. Board flex (are they near the edge, is the substrate thin, how do you break our the panel,etc).3. Mounted pressure to high (faulty machine, bad programming, etc..)

author: TonyStewart
author_rank: Contributor
timestamp: October 27, 2014, 03:57:18 am
content: It could also be a training issue with excessive twist during manual depanelization on the corner of a board .. ( see rounded PWB corner) ( or simply a bad design to put a brittle ceramic part near the corner of a panelized card.