Seen that before... You should not use excessive solder (bending
stress)...see tdk...
http://www.component.tdk.com/components/commoncrackingmodes.pdf
                                                               jk

>-----Original Message-----
>From: TechNet [mailto:[log in to unmask]] On Behalf Of FOX, Ian (York Rd)
>Sent: Tuesday, March 25, 2003 11:37 AM
>To: [log in to unmask]
>Subject: [TN] Cracking Capacitors
>
>
>Technetters, have a little problem with capacitors that I'd be
>grateful for comments on. We've been wavesoldering 0805/1206
>chip caps onto the underside of both FR4 and poly/glass PCB's
>for the best part of 15 years and we've been experiencing a
>low failure rate of devices in-house after ESS and burn-in. On
>top of this however we've had some early life in-service
>failures. Process and assembly trials together with FEA
>analysis we've carried out suggests that the thickness of
>solder left on the topside of the device after the soldering
>operation is critical. Too much and the devices nucleate
>cracks relatively quickly, as during the negative part of the
>temperature cycle, the solders modulus increases to the extent
>that the stress imposed on the termination/body interface is
>in excess of that the titanate capacitors can withstand. My
>question to the forum therefore, is has anyone else found
>similar issues? I know we've seen posts before with regard to
>cracking caps, but this failure mode isn't anything to do with
>assembly stresses or thermal shock during the soldering
>operation (we've artificially increased the solder volume on
>convection reflow soldered components using dispensed paste
>and generated exactly the same failure
>mode)
>
>Regards
>Ian Fox
>Goodrich Engine Control Systems
>
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