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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