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SMT electronics assembly manufacturing forum.


Cracked Capacitors

Views: 3789

#52242

Cracked Capacitors | 31 October, 2007

Has anyone ever looked into the possibility for laser marking 1812 size X7R ceramic chip capacitors injecting sufficient energy to cause cracking when voltage is applied? If so, what were the findings? We are having failures of caps from one manufacturer which have been part marked, but those from another manufacturer that are not marked are not failing. My thinking is that the instantaneous application of energy from the laser is akin to applying heat from a soldering iron, creating a thermal gradient that leads to failure. These parts are not near the board edge, and we do not believe these to be SMT process related failures.

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#52243

Cracked Capacitors | 31 October, 2007

We wouldn't expect the ceramic of the capacitor to conduct very much heat. [We're surprised how high the thermal conductivity of Al2O3 is: (30W/m-�C).]

Can we assume that you're talking about parts that are defective at incoming inspection?

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#52253

Cracked Capacitors | 1 November, 2007

We've not performed any incoming electrical testing on these caps, as it has always been assumed that new parts would be good. However, after reading a number of messages on this site, I'm starting to have my doubts whether or not that is a good practice. What would you recommend?

Also, has anyone ever done a study on ceramic chip cap reliability versus manufacturer, sort of like Consumer Reports?

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#52261

Cracked Capacitors | 1 November, 2007

Electrically testing components is an age-old practice of the past. True "world class manufacturers" like to minimize, or even eliminate incoming inspection of ANYTHING - the theory being....a world class manufacturer should have such awesome relationships with their suppliers - suppliers who gladly provide Cpk and other quality data - that they're confident enough to do away with incoming inspection altogether, 'cause their suppliers will provide good parts all the time..

Now, that rhetoric is fine and dandy, but that was all written "Pre-China." Now you've got the Chinese providing fake components to the rest of the world. That being said, I think manufacturers SHOULD hire an incoming inspection dept. to test components again.

"Thermal Gradient"... good word. :-)

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#52268

Cracked Capacitors | 1 November, 2007

Glen We do incoming inspection of parts and materials, if we have a reason to do inspection. So, if a catalog part from a supplier has a history of: * Meeting or surpassing expectations => no inspection * Failing to meet expectations => inspection

In asking if you observed the problem at incoming inspection, we should have asked the question differently. Have you observed the problem in stock items, prior to assembly?

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#52280

Cracked Capacitors | 2 November, 2007

> Has anyone ever looked into the possibility for > laser marking 1812 size X7R ceramic chip > capacitors injecting sufficient energy to cause > cracking when voltage is applied? If so, what > were the findings? We are having failures of > caps from one manufacturer which have been part > marked, but those from another manufacturer that > are not marked are not failing. My thinking is > that the instantaneous application of energy from > the laser is akin to applying heat from a > soldering iron, creating a thermal gradient that > leads to failure. These parts are not near the > board edge, and we do not believe these to be SMT > process related failures.

We've seen capacitors crack at during singulation from misaligned wheels on the board cutter. The signature trait of this problem is that the cracked caps are near an edge.

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