Ceramic Capacitor Caused Short Circuit (Formed bridge between its terminals) - Page 1
Forum section: electronics / repair

author: palpurul
author_rank: Regular Contributor
timestamp: March 24, 2022, 06:28:36 am
content: I discovered an unexpected short when I plugged the USB to my board that I developed, there was dead short from 5V to ground. This was totally unexpected because I used this board many times without a single issue.As it turns out short was caused by this 0805 capacitor shown in the pics. Notice the solder bridge between terminals, that was the cause of short circuit.Over time a solder bridge is formed between capacitors terminal causing short between 5V and ground as you see in the first picture. How is that even possible?Has anyone experienced this before?Short between capacitor terminals:The actual place of the capacitor in the board.

author: wraper
author_rank: Unknown
timestamp: March 24, 2022, 06:41:18 am
content: Unless overvolted, MLCC usually fail because of cracking due to mechanical stress. What you likely see is that cap formed a short circuit inside and then started cooking as high current started flowing through it. Often it's not a 0 Ohm short, but something like a few 100 Ohms which then drops over time.

author: palpurul
author_rank: Regular Contributor
timestamp: March 24, 2022, 06:43:27 am
content: Quote from: wraper on March 24, 2022, 06:41:18 amIt was a dead short (was measuring sub 1-ohm) caused by that solder bridge somehow formed over time. The capacitor was fine, after cleaning the solder bridge under it, it measured open circuit.

author: wraper
author_rank: Unknown
timestamp: March 24, 2022, 06:46:44 am
content: Then I guess it was a soldering defect which was on a verge of shorting.

author: palpurul
author_rank: Regular Contributor
timestamp: March 24, 2022, 06:51:28 am
content: Quote from: wraper on March 24, 2022, 06:46:44 amProbably. But what would cause it to complete the bridge? It was just sitting in the shelf

author: wraper
author_rank: Unknown
timestamp: March 24, 2022, 06:52:47 am
content: Might be moisture, or PCB was bent a little bit, just enough to complete the circuit.

author: palpurul
author_rank: Regular Contributor
timestamp: March 24, 2022, 07:42:28 am
content: Well, it makes sense.Probably a small bend or change in temperature caused it finish the solder bridge.

author: whatboy
author_rank: Regular Contributor
timestamp: March 24, 2022, 08:58:43 am
content: Maybe solder whiskers

author: inse
author_rank: Super Contributor
timestamp: March 24, 2022, 11:50:32 am
content: If I remember that NASA report on tin whiskers correctly, the whiskers are too thin to carry a decent amount of current.They are able to compromise signals, but will burn off under load.

author: tooki
author_rank: Super Contributor
timestamp: March 24, 2022, 02:53:16 pm
content: Quote from: whatboy on March 24, 2022, 08:58:43 amA key thing: they’retinwhiskers. (And by “tin”, we mean the element, not “tin” as a synonym for “solder”.) IIRC, practically all tin whiskers form frompuretin plating. It doesn’t take much of something else to prevent whisker formation. Consequently, as best I can tell, tin whiskers forming from lead-free solder has not turned out to be the problem it was predicted to be.

author: SeanB
author_rank: Super Contributor
timestamp: March 24, 2022, 06:20:25 pm
content: Silver also forms whiskers, like tin, just not as common.

author: TimFox
author_rank: Super Contributor
timestamp: March 24, 2022, 06:44:04 pm
content: The photo looks like the solder spattered or dripped, rather than grew as a whisker.Either a manufacturing fault (that took a while to make contact across the cap), or something else failed and spattered the solder which then stuck to the capacitor terminations.

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: March 24, 2022, 08:39:58 pm
content: I watch lots of youtube pc fix video's and capacitor failure is common along with mosfet failures.I havent seen one fail like yours before.Sometimes if the blob was already there and not quite bridging then unleaded solder can whisker over time.

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 24, 2022, 10:27:46 pm
content: I agree with two last posts.

author: thm_w
author_rank: Super Contributor
timestamp: March 24, 2022, 10:48:28 pm
content: Are you sure it looked like thatbeforeyou removed it?Is this board near anywhere where you might be soldering and flicking around hot molten solder?

author: wraper
author_rank: Unknown
timestamp: March 25, 2022, 08:37:55 am
content: Quote from: thm_w on March 24, 2022, 10:48:28 pmActually this could be the case. It could be the solder which dropped from a soldering iron tip while soldering something nearby.

author: MathWizard
author_rank: Super Contributor
timestamp: March 26, 2022, 01:43:39 am
content: I had a stereo with SMD parts, and I guess for ground plane reasons, they had ~0.2mm traces of solder+mask, passing under the middle of all SMD parts. And during soldering/de-soldering for troubleshooting the stereo, and bad flux, I ended up with a bunch of unmasked edges, right under the RC parts and fine pitch quad op-amps. What a nightmare.I wish I had a good way to test SMD caps, in circuit. Or for some stuff, I should pre-heat the PCB in an oven, then use air and just mass decap a few things I have. I don't have anything I suspect bad SMD caps on really, but in general, if WW3 starts, it will be worth the time to check all SMD caps.Probably the most import thing's I've SMD de-capped, was the circuits for the controller chips, of computer SMPS. Then I got all the sizes, to plug into LTspice and try and make ideal models of the controller chips.

author: Hamelec
author_rank: Regular Contributor
timestamp: March 26, 2022, 02:20:29 pm
content: this smd capacitor is already unsoldered from the PCB - so all assumptions are nonsense..

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: August 13, 2022, 12:08:36 pm
content: Quote from: palpurul on March 24, 2022, 06:51:28 amIts possibly a solder splash from manufacture.Unleaded solder can whisker over time.Satellite engineers found to their horror circuits were failing after a few years.

author: palpurul
author_rank: Regular Contributor
timestamp: August 13, 2022, 12:09:53 pm
content: Quote from: nigelwright7557 on August 13, 2022, 12:08:36 pmVery interesting.I use leaded solder, but still an interesting information.

author: abquke
author_rank: Regular Contributor
timestamp: August 13, 2022, 01:59:52 pm
content: Looks like someone put a blob of solder on the cap while removing it. Original board looks like a stock photo. Whatever information that was on the board to diagnose the failure has been destroyed. Put on another cap and hope for the best?

author: coppercone2
author_rank: Super Contributor
timestamp: August 13, 2022, 08:01:14 pm
content: Well I recently fixed a attenuator which had a 1pF ceramic C0G through hole capacitor that was reading 500 ohms DC resistance. Not quite a short but I wonder if it was getting there.. (this had nothing to do with the solder).

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: August 13, 2022, 09:02:16 pm
content: Although I never verified it we had a few failures in one PWM amplifier due to a grouthinside the end caps of a ceramic capacitor which caused the cap to go leaky 500 ohmsto shorted.Resoldering would temporarly fix it.... good for troubleshooting.Jeff

author: tooki
author_rank: Super Contributor
timestamp: August 14, 2022, 06:42:02 pm
content: Quote from: nigelwright7557 on August 13, 2022, 12:08:36 pmNo, it doesn’t. The whiskers come frompure tin platingon component leads. Lead-free solder is never just 100% tin, and even small amounts of alloying eliminates whisker formation.https://www.indium.com/blog/pb-free-solders-are-not-the-cause-of-tin-whiskers.php

author: nigelwright7557
author_rank: Frequent Contributor
timestamp: January 05, 2023, 01:24:13 am
content: I sometimes get solder splashes on my pcb's but I make hundreds.Probably from not wiping solder bit often enough.Once there is a solder splash with unleaded solder it can start to whisker and cause a short.