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Cracked Capacitors - Analysis

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Hey Everyone, we have recently been discovering an increase... - May 16, 2019 by Matt  

#82581

Cracked Capacitors - Analysis | 16 May, 2019

Hey Everyone,

we have recently been discovering an increase of failed MLCC capacitors across various builds and after being in the field for some time. Vendor reports that a "high energy" event occurred but the detail is limited and i'm left looking for root cause.

There is some small potential that handling may lead to these failures but is unproven as of yet and on some assemblies this is much less likely the case.

is anyone familiar with a good 3rd party source for analysis / cross section of MLCC capacitors?

I would like to take the investigation external to the vendor

Any feedback is appreciated.

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#82584

Cracked Capacitors - Analysis | 16 May, 2019

Be sure to consider STI Electronics, Inc.[www.stiusa.com) 256-461-9191], a sponsor of SMTnet:

https://smtnet.com/company/index.cfm?fuseaction=view_company&company_id=52020

Although dated, here is the IPC list of test labs: https://www.ipc.org/4.0_Knowledge/4.1_Standards/test/testing_labs.htm

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#82587

Cracked Capacitors - Analysis | 17 May, 2019

If it happened after a high energy event then maybe the root cause is a lack of TVS diodes in the design of the circuit. Or if they are ceramic diodes then maybe they are too close to the edge and have flex cracks.

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#82596

Cracked Capacitors - Analysis | 21 May, 2019

Matt,

believe it or not, but mechanical stress is cracking these internally and you can't see it with bare eye. Consider de-paneling as a root cause if parts are close to the de-panel V-score edge/router tabs. I can send you more information.

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#82600

Cracked Capacitors - Analysis | 21 May, 2019

Hey,

thanks for your feedback, this was our initial thought however our process engineers don't buy this.

Although they are close to the card edge this product only has de-panel length wise which is perpendicular to these capacitors.

The PCB itself is near 30 layers and is very rigid, it is still possible but no hard evidence pointing to this being the case.

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#82601

Cracked Capacitors - Analysis | 21 May, 2019

There are flex caps that are more tolerant of flexing. I don't think they are a lot more expensive. You might want to try a run with them?

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#82602

Cracked Capacitors - Analysis | 21 May, 2019

Thanks for the feedback,

Do you have a specific vendor for these?

current parts are TDK 0805s, a sample build with this type of part could be interesting to see.

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#82606

Cracked Capacitors - Analysis | 22 May, 2019

hi matt,

we have our customized vision system to check all the chip components, and is specialized for this. Do try understand the system and you will know it. Do email to me i will send some sample and profile to you. itrueriko@gmail.com Thanks

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#82608

Cracked Capacitors - Analysis | 22 May, 2019

Try this link https://www.digikey.ca/products/en/capacitors/ceramic-capacitors/60?k=flex+caps&k=&pkeyword=flex+caps&sv=0&s=50730&s=21887&s=32803&s=5859&sf=0&FV=ffe0003c%2C1f140000&quantity=&ColumnSort=0&page=1&pageSize=25

It should get you started.

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#82609

Cracked Capacitors - Analysis | 22 May, 2019

much appreciated, will dig into this today

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#82612

Cracked Capacitors - Analysis | 22 May, 2019

Matt,

we did the study and YES perpendicular to the V-score is the worst case scenario. We did a cross section and confirmed component is cracked. If you don't have power over PCB design, the easiest way is to change board panelization or even order boards without any rails and process on a pallet.

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#82614

Cracked Capacitors - Analysis | 22 May, 2019

thanks again for the feedback

were your cracks mostly visible in relation to images shown in the document here:

https://www.digikey.ca/en/pdf/t/tdk/guide-flex-cracking-mlcc

most of our cracking has been lengthwise across the body which from what i've seen is more related to thermal cracking than what images of flex cracks are presented as

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#82617

Cracked Capacitors - Analysis | 22 May, 2019

We mostly observed the flex cracks which were not visible.

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#82648

Cracked Capacitors - Analysis | 26 May, 2019

Placement force can cause chip cracking-micro cracks also. As machines are getting faster they tend to not control force other than spring pressures and z displacements. There are some machines that have full closed loop place pressure control , but not many have this, alot claim control but is limited. If PCB 30 layer and quite rigid than maybe not knowing what SMT machine you have forces is too high for given parts ????

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#82655

Cracked Capacitors - Analysis | 28 May, 2019

Back in the day when everyone had turret chipshooters we used to see a lot of cracking due to incorrect z heights, especially where customers swapped between manufacturers.

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#82657

Cracked Capacitors - Analysis | 28 May, 2019

TDK makes the CGA series "soft termination" caps.

The p/n we use is CGA3E3X7S1A225K080AE, which will get you in the ball park for datasheets.

We have moved to this to counter some variability in a heat staking machine (that we have yet to work out with the customer, who owns the machine).

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#82659

Cracked Capacitors - Analysis | 28 May, 2019

Thanks for your suggestion however it looks like AVX may be the only vendor who can supply such a cap in a 0805 package. TDK cannot do anything below 1206 or so i'm being told

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#82660

Cracked Capacitors - Analysis | 28 May, 2019

Not according to the data sheet for the CGA parts, and ours is an 0603, I think.

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#82661

Cracked Capacitors - Analysis | 28 May, 2019

interesting, i will have to check back in with my purchasing department to get the full story here. we are actively getting some samples in from AVX which another user commented on and plan to see how these hold up.

unfortunately most faults occurred after a year or more in use, will need to beat these up.

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#82980

Cracked Capacitors - Analysis | 9 July, 2019

The price increase of electronic components such as MLCC has not stopped. In recent years, driven by the development of electric vehicles, industrial control and other industries, the demand for MLCC products has increased rapidly. However, the overall market supply is limited, resulting in imbalance between supply and demand, which has become one of the reasons for the frequent price increases of electronic components.

In the cooling process after the MLCC is welded, the expansion coefficients of the MLCC and the PCB are different, and stress is also caused to cause cracks. Temperature shock cracking is mainly caused by the temperature shock of the device during soldering, especially wave soldering. The MLCC is unevenly heated during welding, and it is easy to generate cracks from the welded end. Share a capacitor supplier http://www.endezohk.com/list/capacitors.html

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