Do some faulty capacitors on PCB's leak

[quasimodo]

Hello,

This is a general question: do some faulty capacitors on PCB's leak?
Usually I see them being outright bad, but I was wondering what others are experiencing and if I should adjust to perform a full capacitor test. I am asking because I recently had a PCB that passed all my standard tests, but in the end I had to replace the PCB. Possible leak was somewhat of an after thought.

Thanks.

[fzabkar]

In the past, smt electrolytic caps were notorious for leaking in all types of consumer equipment. I don't know about HDs though.

The best way to test them in-circuit is with an ESR (equivalent series resistance) meter.

You can build your own from a kit:

http://members.ozemail.com.au/~bobpar/esrmeter.htm

[BlackST]

Solid tantalum do not "leak" as there is no electrolyte. Usually they open or short (they SC if reverse polarity current is applied) .Multilayer ceramic caps do break for mechanical reason or stress.
I don't see many electrolytic caps around in HDDs except some Samsung and some Seagate.
But I have seen many ceramic multilayer caps broken. Oh, BTW... good luck with 0402 case ones

[fzabkar]

I recently saw the following URL in the sci.electronics.repair newsgroup:

"Cracked ceramic capacitors - a problem that never goes away":
http://www.era.co.uk/news/rfa_feature_07b.asp

The article states ...

"It might be thought that most reliability problems in electronics would occur in highly complex semiconductor chips with hundreds of terminals. In fact, the most common electronic component to fail, as seen by the ERA's Reliability and Failure Analysis Service, is the multilayer ceramic chip capacitor."

[BlackST]

There's always a way to avoid it.

[quasimodo]

In the past, smt electrolytic caps were notorious for leaking
http://members.ozemail.com.au/~bobpar/esrmeter.htm

Yep I know, that's why I asked this question. Thanks for the reply.

[quasimodo]

Usually they open or short

That's what I thought and that's what I usually test for. I was just curious if this is always the case on HD PCB, or if it's better to test the capacitors and it's load. I wanted to know if open/short is 100% reliable since it would not be able to find any leaking of the capacitors. Yes, I primarily see MLCC's on modern PCB's, usually they short and of course that's easy to detect, but let me rephrase my question, do MLCC's leak?

Thanks.

[BlackST]

Yes they do.

[fzabkar]

I primarily see MLCC's on modern PCB's, usually they short and of course that's easy to detect, but let me rephrase my question, do MLCC's leak?

See figures 2 & 3 of the article I referenced. It shows how a mechanical crack develops into electrical leakage.