Cracked Capacitors

Check them before the oven for cracks. (after placement) Don't just look at them, take them off the board and check. I"ve seen resisters that were broken by the machine but you couldn't tell untill you took them off. If they are cracked check the component height data in the machine. If that is not it, put some through the oven loose on a board. Maybe they have to much moisture.

Both are long shots but worth checking.

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Describe the location and orientation of the cracks.

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http://www.smtnet.com//forums/index.cfm?fuseaction=view_thread&CFApp=1&Thread_ID=6222&#Message25079

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I just had a "how could I have forgotten" moment. By any chance are these double sided boards and the cracked components are on the fist side? If so support pin placement could be the problem.

In case more info would be good.

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Have experienced this on a few different cap. parts. Agree with other postings. Following are solutions to problems we have had:

1) Cracked cap too close to board edge per IPC spec. Designer replaced part with 3 caps in series to eleviate stress - problem gone. 2) Cracked cap on array with break-out tabs. Stopped breaking out manually and used router in machine shop to depanel. Problem gone. 3) Cracked cap on array with score lines. Stopped manually breaking boards out - used pizza cutter. Problem gone. 4) Cracked cap near PCB edge, single array. Slowed cooling in relow by setting cooling fans at lowest setting. Problem still exists but much less frequency. Check your oven recipe on these PCB's. Too fast ramp or cool-down = breakage of ceramic caps. 5) Warped PCB post reflow inducing stress to leads on caps. Tough to eleviate - usually internal PCB design prob., might need to add caps by hand if low enough volume for this or adjust profile to "normalize" PCB at end of reflow. Might also consider a "pre-stress" oven fixture to get PCB flat post reflow or a carrier if it is sagging too much. Warpage is always a tough one!!! Mucho guess-work.

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