And it goes without saying the first thing you do is replace all the caps.
never mind that they used the best quality brands in 10-20 years most caps need to be replaced.
The capacitors may be worn out without actually causing failure. It is is not like gradual evaporation of the electrolyte causes sudden failure. A circuit may be completely happy with 5 or 10 times the specified ESR and 1/2 or 1/4 of the capacitance.
In low ripple current applications where self heating is low, small capacitors wear out first through gradual evaporation of their electrolyte, but these applications also tend to be tolerant of increased ESR and lowered capacitance. Large capacitors are more likely to fail in another way, see below.
This got me thinking about my own product. Which uses a lot of caps. And is encased in epoxy.
Does this mean that in 20 years my products are also going to stop working. ?
It is possible to design for an operating and storage life greater than 20 years, but many factors other than aluminum electrolytic capacitors drying up come into play.
How do I address this issue. Some of my customers want to know what if they buy my product and never use it. Will the caps stay ?.
Is there a better cap I can turn to ?. Im already using the best and highest grade caps money can buy.
Use the best capacitors and derate them for greater operating life. Design the circuit to be tolerant of gradual deterioration. In critical circuits where no single capacitor will provide the desired operating life, use multiple capacitors in series and/or parallel.
Should I shift to using Tantalum Caps because they will last longer ?.
Should I use higher voltage caps ?. Im already using 65v when all I need is 5V.
Those are both good options. A higher voltage aluminum electrolytic capacitor has more volume and therefor more electrolyte, which will take longer to evaporate. Tantalum capacitors have no electrolyte to evaporate but are not suitable in all applications. High reliability and long operating life applications may avoid using aluminum electrolytic capacitors at all despite the cost.
One thing I did notice between the caps used in Audio in the 70s vs what you get today is the size. Modern caps seem to have shrunk by a huge margin for the same values and voltages.
And those physically larger capacitors last longer because they start with a greater volume of electrolyte, so it takes longer to finish evaporating. You might have noticed that in applications where ripple current rating is not an issue, huge input capacitors used to filter the 50/60 Hz line last so long that their primary failure mode is water or oxygen getting in through a degraded rubber seal and corroding the connections to the pins until one breaks.
Tantalum caps still may fail as usual caps.
Tantalum caps are good if you like that 'Tantalum' word magic or if you customers may like it. Otherwise, I can't say they are really much-much better in longevity vs price.
The difference is that tantalum capacitors do not have an inherent wear-out mechanism limiting their life, except maybe defect growth in high voltage parts if you believe NASA. Aluminum electrolytic capacitors literally dry out over time, and whether in use or not.