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Cracked MLCC's

Cracked MLCC's

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We are down to the last few unresolved PCBA test failures in... - Aug 14, 2019 by Steve Thomas

Clear pictures of failed MLCC could help investigation. ... - Aug 15, 2019 by sssamw

It could be delamination of the layered material of the MLCC... - Aug 15, 2019 by davef

Please pardon the poor images - it's difficult to focus and ... - Aug 15, 2019 by Steve Thomas

Thanks Dave. I am thinking that this may be a case of knit ... - Aug 15, 2019 by Steve Thomas

Poor knitters get blamed for everything ... - Aug 15, 2019 by davef

True dat...it's the first thing I look for on a molded part ... - Aug 15, 2019 by Steve Thomas

Never automatically rule out that the parts were received de... - Aug 15, 2019 by Stephen

Thanks, Stephen. I'm actually leaning towards that (knit lin... - Aug 15, 2019 by Steve Thomas

I just found this. https://www.avx.com/docs/techinfo/Ceramic... - Aug 15, 2019 by Stephen

I agree that this looks like knit line failure. Here are so... - Aug 15, 2019 by EdHare

Hi Ed, These images contributed to my coming to that conclu... - Aug 16, 2019 by Steve Thomas

Steve, Yes, in my experience clients send in field failures... - Aug 16, 2019 by EdHare

Thanks Ed. I guess about all we can do is hope that the extr... - Aug 16, 2019 by Steve Thomas

At least one of them looks like a handling issue to me - the... - Aug 19, 2019 by Robl

Dave, Perhaps, but my interpretation of that photo is that ... - Aug 19, 2019 by EdHare

Check from the component distributor/manufacturer if they ca... - Aug 22, 2019 by Jandon

I got solution to manufacturer to find out the crack of MLC... - Sep 10, 2019 by itrueriko

CRACKS: THE HIDDEN DEFECT by John Maxwell AVX Corporation - ... - Oct 05, 2019 by davef

Cracked MLCC's | 14 August, 2019

We are down to the last few unresolved PCBA test failures in a work order and scrambling to get them repaired and into a mechanical assembly.

What we have found in quite a few of these cases are cracked 1206 MLCCs. The failed parts are all the same p/n, and there is more than 1 p/n per board with this package. These are all reflowed.

Of the 10 that I've had the chance to look at under magnification, all of them have cracks that appear to be parallel with the basic construction of the stack.

All of my profiles are well under 3°C/sec so unless someone touched them with an iron (no indication) I would not expect thermal shock to be contributing to this.

Aside from just eating a few bad components (so far we've found about 20 out of the 20k or so that we've used), is there anything I should be looking at? Are there any other causes of this mode of failure besides thermal shock?

Cracked MLCC's | 15 August, 2019

Clear pictures of failed MLCC could help investigation.

Cracked MLCC's | 15 August, 2019

It could be delamination of the layered material of the MLCC caused by thermal shock or a component fabrication defect.

For more on MLCC cracks: https://www.avx.com/docs/techinfo/CeramicCapacitors/cracks.pdf

Cracked MLCC's | 15 August, 2019

Please pardon the poor images - it's difficult to focus and stabilize a phone cam through an eyepiece at 40X.

Images 72620 and 72733 are of the same part from opposite sides.

73558 is the only one so far that I've seen crack propagation into the terminal and may be just due to stresses experienced during removal.

For the record, we have seen this on parts still installed as well so we know it's not just a product of removal.

Attachments:

Cracked MLCC's | 15 August, 2019

Thanks Dave.

I am thinking that this may be a case of knit line fracturing.

My concern now is, if this is the case, what is the risk to completed product.

Cracked MLCC's | 15 August, 2019

Poor knitters get blamed for everything

Cracked MLCC's | 15 August, 2019

True dat...it's the first thing I look for on a molded part boss that splits!

Cracked MLCC's | 15 August, 2019

Never automatically rule out that the parts were received defective. Although at 1 in a thousand it would be difficult to rule out.

Cracked MLCC's | 15 August, 2019

Thanks, Stephen. I'm actually leaning towards that (knit line fractures), since it's the only thing I've found that really supports the fractures being planar like they are.

Cracked MLCC's | 15 August, 2019

I just found this. https://www.avx.com/docs/techinfo/CeramicCapacitors/cracks.pdf It is extremely dated but still interesting.

From the conclusion; " but both thermal shock and overstress cracks propagate at angles near 45°. Defective components have voids or cracks that are perpendicular or parallel to interior electrodes"

I think all of us that have been around a while have been bit at least once by bad parts.

Cracked MLCC's | 15 August, 2019

I agree that this looks like knit line failure. Here are some examples of what this looks like in microsections of MLCCs ...

https://www.semlab.com/mlcc-knit-line-failure/

https://www.semlab.com/knit-line-fracture-and-porosity/

https://www.semlab.com/manufacturing-flaws-in-ceramic-capacitor/

Ed

Cracked MLCC's | 16 August, 2019

Hi Ed,

These images contributed to my coming to that conclusion.

Question, in case you have an answer for this.

In your experience, do these kinds of defects exhibit much latency or are they usually found early if they exist at all?

I ask because we've only found a few out of a population of about 20k parts and we're wondering what the risks are to product already delivered.

Cracked MLCC's | 16 August, 2019

Steve,

Yes, in my experience clients send in field failures (so latent failures) that exhibit internal shorts when a secondary fracture propagates from a knit line fracture. These eventually short due to electro-migration from plate-to-plate through the secondary fracture. The fact that you see these on external examination just suggests to me that this is a fairly severe case relative to what I see typically (i.e. no fracture evident externally).

Ed

Cracked MLCC's | 16 August, 2019

Thanks Ed. I guess about all we can do is hope that the extreme nature of the flaw equals a higher degree of early detection.

So far we haven't replaced any of these on RMA's so I guess that's a good sign.

Cracked MLCC's | 19 August, 2019

At least one of them looks like a handling issue to me - the last picture shows the crack going into the termination as a scratch on the right side - as if someone has slid another board into a magazine without leaving enough space. This one looks like a gouge.

Cracked MLCC's | 19 August, 2019

Dave,

Perhaps, but my interpretation of that photo is that it simply shows a knit line fracture that propagated out to the surface. The fact that it shows on the termination is not surprising since the termination wraps around the internal plate structure. Microsection analysis would be helpful to resolve these details.

Ed

Cracked MLCC's | 22 August, 2019

Check from the component distributor/manufacturer if they can verify that the component is genuine or counterfeit component. I know a similar case and the manufacturer could not verify the component as a genuine. They could not find the batch number from their databases.

Cracked MLCC's | 10 September, 2019

I got solution to manufacturer to find out the crack of MLCC if the manufacturer need it.

Cracked MLCC's | 5 October, 2019

CRACKS: THE HIDDEN DEFECT by John Maxwell AVX Corporation - SMTnet Technical Library paper [ https://smtnet.com/library/files/upload/cracks.pdf ]

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