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Cracked Capacitors

Views: 1689

#36412

Cracked Capacitors | 30 August, 2005

We are experiencing cracking of 1206 .1uf/50V capacitors on our boards. Design is keeping the caps away from the board edge 0.200 and perpendicular to the longest edge but still they crack even in the interior of the board. Recommendations? bds are 0.062 thk.

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#36413

Cracked Capacitors | 30 August, 2005

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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#36415

Cracked Capacitors | 30 August, 2005

Describe the location and orientation of the cracks.

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#36433

Cracked Capacitors | 31 August, 2005

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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Rob

#36434

Cracked Capacitors | 31 August, 2005

or damaged on breakout - especially if the V score is non consistant or not deep enough.

What is the manufacturer?

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dougs

#36451

Cracked Capacitors | 1 September, 2005

We had a problem with cracked caps a few months ago,they were near the middle of the board, turns out it was caused when breaking them out of the panel, changed the panel layout and made them v-scored, problem solved. just an option, there's lots more reasons for this fail.

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#36521

Cracked Capacitors | 6 September, 2005

just at 0.200 from both the short and the long edge

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PWH

#36533

Cracked Capacitors | 7 September, 2005

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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Rob

#36535

Cracked Capacitors | 7 September, 2005

or the biggest issue from my days with the worlds largest Chip cap producer..... Incorrect part data or adjustment on a chipshooter (z height).

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#36577

Cracked Capacitors | 9 September, 2005

This pattern indicates flex cracking due to excessive bending of the board or fixture after soldering. Ceramic is strong in compression, but weak in tension.

When bending causes damaged parts, look at: * Board flexes, ceramic is strong in compression, but weak in tension * Solder fillet size affects rending strength. Fillet SB 50-75% of the termination height. Too much solder increases the pulling force during flex. * Uneven solder amounts concentrate stress in the smaller fillet. Proper solder pad dimensions help balance stresses. * Rate of heating and cooling during reflow

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