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April 2008

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Subject:
From:
John Maxwell <[log in to unmask]>
Reply To:
TechNet E-Mail Forum <[log in to unmask]>, John Maxwell <[log in to unmask]>
Date:
Mon, 28 Apr 2008 15:03:56 -0700
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Ken,
Boy this take me back to my capacitor cracking days. It will be nice to 
see what the failures look like but from what has been described is 
consistent with assembly flexure cracking. When I wrote my first paper 
on MLCC crack signatures the great majority of cracks were due to 
assembly handling followed closely be excessive solder joint size. 
Things have not changed in the intervening 20+ years. Big wide solder 
joints and a connector right next door, the perfect recipe for cracks.

John Maxwell


>Hi All,
>
>We are experiencing a high failure rate on a ceramic capacitor. I've asked
>Steve to post the pictures to help describe the problem, "Cracked Cap 1, 2
>and 3".
>
>The capacitor that is cracking is used nineteen times on this assembly and
>none of the others ever crack. The assembly process is as follows:
>
>Paste, place SMD, reflow and wash secondary side.
>Paste, place SMD, reflow and wash secondary side.
>Hand place through-hole components, wave solder in selective pallet and
>wash.
>In-circuit test, capacitor fails about 5% of the time.
>Operator removes part and the metalized end cap falls off.
>
>I have looked at the handling of the assembly and don't see anything that
>could contribute to the problem.
>
>I've looked at ICT and nothing appears to be slamming into the part.
>
>The only thing I see different with this part from the others is the
>proximity to the stud from the D-sub connector. It takes a little pressure
>to put the connector stud into the hole but nothing excessive.
>
>I'm wondering if there could be anything happening due to thermal expansion
>of the large solder joint next to the cap.
>
>Picture "Cracked Cap 1" shows the proximity of the capacitor to the
>connector stud, http://stevezeva.homestead.com/files/cracked_cap_1.jpg 
>Picture "Cracked Cap 2" shows a how the connector is installed and soldered,
>http://stevezeva.homestead.com/files/cracked_cap_2.jpg 
>Picture "Cracked Cap 3" shows the unsoldered connector stud,
>http://stevezeva.homestead.com/files/cracked_cap_3.jpg 
>
>Thanks for looking at this,
>
>KennyB
>
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