Electrolytic capacitors and the effect on lifetime of time spent in storeage?

treez said:

So why is it that electrolytics have to be made right before the production run?

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7.3.2 Storage conditions
Capacitors are often stored voltage-free either in original packing or already mounted in a circuit (final application or spare part assembly).

Our aluminum electrolytic capacitors can be stored without damage at ambient temperatures ranging from typical 55 °C up to the upper category temperature. However, it must be taken into account that storage at elevated temperatures will affect leakage current, useful life and solderability. In order to avoid impairing these properties, capacitors should be stored between +5 °C and +35 °C and at a relative humidity of ≤ 75%. Long-term storage at high temperatures and in an environment with high humidity should be avoided. Likewise, one should avoid storing the capacitors in environments that contain halogenated gases (and other hazardous gases), sprinkling water or oil as well as exposure of the capacitors to direct sunlight, ultraviolet rays or other radiation.

If not otherwise specified, our aluminum electrolytic capacitors can be stored voltage-free at above stated conditions (from +5 °C to +35 °C, relative humidity ≤ 75%) for at least two years; capacitors of the SIKOREL series can be stored for as long as 15 years under these conditions. Within these storage periods the capacitors can be operated at their rated voltage directly after being taken out of storage. It is recommended to mount the capacitors in the application within one year of delivery in order to prevent any problems with solderability of capacitors on PCBs.

If the capacitors have been stored at temperatures above +35 °C or for longer than abovementioned periods, it is necessary to consider whether the application circuit is able to tolerate high initial leakage currents. If this is not the case, one should perform the special reforming procedure (see also chapter "General technical information, 3.7.6 Reforming"on page 17) in order to enable normal operation in the application or to continue the storage. Capacitors that have been stored in their original packing should be reformed according to the standards by applying rated voltage via a series resistance of approximately 100 Ω (for VR ≤ 100 V DC) or 1000 Ω (for VR > 100 V DC) for a period of one hour. Finished or semi-finished goods that have been stored with mounted capacitors should be connected to an appropriate input voltage source for one hour. If the circuits contain capacitors connected in series, it should be considered to increase the voltage incrementally.

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