There can be many possibilties. Check the vendor recommendations for oven
profiles and land pattern. Are you breaking the board out of the panels
by hand or using a post assembly score finishing machine (after-score)?
Try testing the boards before you break them out. The part is being
stressed, but where?

Scott

 ----------
From:  DesignerCouncil Mail Forum.
Sent:  Thursday, December 04, 1997 10:21 AM
To:  DesignerCouncil
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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