We have run into these problems from time to time.  In addition to what
Joe wrote you need to be very careful about the handling of the device
and especially the temperature ramp rate during reflow.  Ceramic
multilayer chip capacitors are susceptible to forming hairline cracks if
the ramp rate is to high in your reflow oven.  Check with your component
supplier, usually they have a recommended ramp rate.  You can also
cross-section capacitors out of stock and see if they are cracked
initially.  Run a few parts through the reflow profile you use and check
them for cracks in the same way.

Bill

> ----------
> From:         Joe Reichert[SMTP:[log in to unmask]]
> Reply To:     DesignerCouncil Mail Forum.;Joe Reichert
> Sent:         Thursday, December 04, 1997 10:31 AM
> To:   [log in to unmask]
> Subject:      Re: [DC] SMD Capacitor Cracking
>
> I have had similar problems with cracked capacitors(and other SMT
> ship-style components) on .031" boards that were caused by the board
> being bent or flexed after the components were soldered.  Increasing
> the
> board thickness to .062" solved the problems of cracked components.
> good luck!
>
>
> >----------
> >From:  Pierce Pat[SMTP:[log in to unmask]]
> >Sent:  Thursday, December 04, 1997 9:45 AM
> >To:    [log in to unmask]
> >Subject:       [DC] SMD Capacitor Cracking
> >
> >We are a company new to SMT and are working on a design in which a
> 500V
> >Ceramic capacitor with a 1206 pkg. size has an initial 115VAC input
> >voltage applied to it. On 50% (5 of 10) units tested, the capacitor
> "blew
> >up" (The design works on the 5 that didn't "blow up").  We are no
> where
> >near the limits of the device and believe that the capacitors are
> >cracking at some point in the assembly process. What I am looking for
> is
> >all the possibilities for this occurrence.
> >Some additional info: the board size is .407"x2.075", FR4, .031
> thick,
> >single sided. Assembled in a 7x4 array (28up), scored, panel size
> >3.5"x8.9". Placed in the reflow oven, the capacitor goes in last (at
> end
> >of PCB). Thank You in advance!
> >
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