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PCB & Ceramic Cap strain - Specification?

#28511

PCB & Ceramic Cap strain - Specification? | 10 May, 2004

I am looking for a industry specification for the amount of strain that is allowable during a parallel blade shearing operation as related to ceramic capacitors.

Does anyone know of such a specification?

Best regards, Jeff

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#28512

PCB & Ceramic Cap strain - Specification? | 10 May, 2004

There's no such specification. Not should there be. Shear tests [in our opinion] are senseless, because: * Solder joint strength in pull/shear varies with lead geometry, solder volume, lead metal/metallization, and the way the test is done. * Shear stress you measure depends more on the shear rate and on the point where the force is applied than on the grain structure. * When shearing a component, you not only apply shear stress, but also roll the component over. This means that shear stress and normal stress are present, again making the results very dependent on where you apply the load.

Thus, in our opinion, best case, these tests are relative measurements. So, only results with the same measurement parameters can be compared. Additionally, we believe that the variations in the geometry of solder joints and of the measurement itself contribute at least to the same variation in the measurement results as voids, unless your solder joints are reminiscent of Swiss cheese or very poorly wetted.

We think, the best you can do is micro sections in regular intervals and keeping your process under control. If solder joints are metallurgically OK there is no point to concern about their strength

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#28513

PCB & Ceramic Cap strain - Specification? | 10 May, 2004

Sorry, I was not clear. I am interested in the strain on the PCB during depanelization using a parallel blade shear. And the effect on ceramic capacitors on the PCB. I was not shearing the capacitor off of the PCB.

Regards, Jeff

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#28518

PCB & Ceramic Cap strain - Specification? | 10 May, 2004

Oh, OK. There is not specification for that either. Capacitor fabricators [eg, TDK, Kemet, AVX, etc] give good guidelines. For instance: http://www.kemet.com/kemet/web/homepage/kechome.nsf/vapubfiles/F2111/$file/F2111.pdf

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