I have produced 1000 units of our new developed energy meter. Almost 20 aluminum electrolytic capacitors (2%) have failed short when we test them during the production processes. The Capacitor is a 470uF 35V (UPW1V471MPD) made by Nichicon.
The failure itself varies between total short circuit to small variable resistance. One of the caps spit out its electrolyte.
I have 3 other different aluminum electrolytic caps from the same manufacturer that didn’t fail. A year ago, I have produced 300 units (same design and part no.) and they running perfectly and didn’t find any failed capacitors.
My question has 3 parts:
How this occurred?
Is it normal to have an infant mortality of 2% with short circuit failure for aluminum electrolytic caps?
Or, may be the cap is counterfeited and the con manufacturer didn’t do enough quality testing. (I bought them through a PCB and components supplier in Shenzhen). If they are counterfeit, how to verify that?
What should I do with the rest of the batch?
If I release the batch, would I guarantee that there will be no more short circuit failure? If it didn’t die during the manufacturing, it will not die in the near future! (U shape/bathtub graph).
Or it is better to run my meters for a period of time (24 hours) if didn’t fail it will not fail in the future.
Or I should go the hard way and change them all?
How to avoid this in the future, because I will be going for large quantities > 100K.
I didn’t find very useful notes about electronics parts quality and reliability other than MIL-HDBK-978B. But it is out dated and didn’t have the electrolytic caps.
Voltage = 20V.
Inrush and ripple current = the capacitor is used to store energy to supply a latch/rely only when operate. it operated about 5 times during production. latch/relay impedance 60 ohm. it draw its voltage from a capacitive power supply capable of supplying a 17mA at maximum.
Temperature: about 30C.
there is a guarantee that no cap have been reversed biased.