Barring concentrated CTE stresses due to the large amount of solder
around the mounting post, I suspect the cap near the connector is
failing because the capacitor is already soldered in place at the time
the Dsub connector is snapped in place. The arrow-type bifurcated posts
require quite a bit of force to snap them through the holes, applying
stress directly to the pwb. This flexure stress is applied directly to
the ceramic cap nearby, causing the stiff ceramic body to fracture the
bond to the endcap, causing the caps to fail. Some are probably failing
immediately at test, but don't be surprised if some have passed
electrical test and fail later in the field. You may wish to perform
some type of recall/containment action.
-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Ken Bloomquist
Sent: Monday, April 28, 2008 2:38 PM
To: [log in to unmask]
Subject: [TN] Cracking Ceramic Cap
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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