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signed. These are 1206 22uf 10V ceramic caps, we do not specify a manufactu rer. The caps are on the output of a 3.3V 1amp 2MHz dc to dc converter (5 a mp inductor 2.2uH), there are two in parallel. They become resistive, aroun d 200 ohms. The ripple current is around 0.4 amps total, so I cant see that it is excessive ripple current, they are not near mounting holes so I cant see mechanical issues, and they initially pass test but fail in the field. Heating the cap does not have much effect on the resistance.
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g
ed the cap of flux residue and tried heating and fault stays. It measures 1
86 ohms, another cap reads 400 ohms. Only one of the two parallel caps fail (Both same part) and no other caps fail (Different parts and smaller). I h ave looked for ceramic cracks and cant see any but I am not sure if I would see them even if they were there!er, Rises in 10ms to 3.3V as expected
in parallel, both with very little resistance. The equivalent resistance i s half the resistance of a single cap. With the failure, no matter how high is the resistance of that cap, the equivalent resistance is still less tha n the resistance of the single good cap. Is it not enough? I suppose you us e two caps to double the capacitance not lower the resistance. btw, 47uF/10 V at 1210 (B size) tantalum is quite common. Is it not enough? Too expensiv e? In this case I bet you can find poscap capacitors these days with better resistance (in fact VERY low) and probably less expensive than tantalum. H ard to say though if less expensive than two ceramics of this size.
20uA to 5mA, hence batteries go flat. When I remove the two caps board curr ent returns to 20uA. If I measure the resistance of the caps one is high im pedance, and one around 186 ohms.I would suggest you contact the capacitor manufacturer. They are intimatel y familiar with the various failure modes of the caps and can likely provid e you with some insight.
Rick C.