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SMT electronics assembly manufacturing forum.

Film cap losing capacitance?

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Film cap losing capacitance? | 23 September, 2015

We have been experiencing an issue where our Panasonic film caps on a board are losing their rated capacitance. We are well within their recommended reflow specs and no other operation exposes the part to a temp of more than 160°C. The caps will read fine after smt, wave and wash but will not read fine a day or two later. Anyone have experience with this?

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Film cap losing capacitance? | 24 September, 2015

No direct experience with this particular issue....but, I do know that measuring capacitance can be tricky.

How are you arriving at this conclusion? Are you measuring the caps on the bench before assembly, and then on the boards post assembly? Capacitors in circuit nearly always measure differently than caps out of circuit, so, getting accurate readings can be difficult as they are affected by the other components around them.

If you're confident of the measurement methodology, it might be best to involve Panasonic in your investigation. It's probably worth having them do a failure analysis on the components, to help diagnose what the problem is. As long as you bought them from distribution, and not the grey market, you should be able to get a rep involved via your distributor, and get to root cause.

cheers, ..rob

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