No they are not. They are among the best caps when you take in account the low volume/size.
You often hear they are stable, low D and last a long time. But they are not resistant to over voltage. That I why I did a little test using an SMU to see the current leaking and how much over voltage will kill them. I’m not saying there is no risk. If they are used in a rail with lots of transients that go above their voltage rating, all those transients can damage the capacitor a little and that can add up if there are lots of transients. They are not “selfhealing” like some film caps or have a “forming” mechanisme like electrolytes. But used the right way and with enough headroom they will last a very long time. Longer as the average electrolyte. Even filmcaps degrade and people are not tossing them out in big numbers.
Orange 35V 10uF (D= 0,013 op 100Hz)
30V leaks 80 to 200nA,
60V 500-600 nA
65V 700-800 nA,
70V 1,1 tot 1,2 uA
80V >2 uA
90V > 20 uA
100V > 50 uA
110V > 80 uA
120V > 165 uA
130V >355 uA
140V leaks exponential
Capacity after that test 9,846 uF D 0,027
Again testing the same cap starting at 35V, this to check if the damage is permanent.
35V 103 uA
50V 171 uA
60V 290 uA
70V 512 uA
80V 14 mA
90V “shorts” to 50V with current limited to 15mA for safety, I do not want exploding parts.
3rd time, again starting at 35V, now leaking 100 uA
An other thing I noticed, if I heat them they start to leak more.
Blue tantalum, 9,417 uF 35V D=0,014 freshly removed from an old 80’s industrial PCB, so it will have seen a lot of hours.
35V 200 nA
40V 300-400 nA
60V 400-500 nA
70V 600-700 nA
80V 1,9 uA
90V “slaat door naar “shorts” to 22V at CC=15 mA
After some time it drops to 3,2V (it then measures 14 uF and D=0,7)
Second time from 35V:
Now 7 mA, drops to 5,7V, then 2,5V all at 15mA. If I would not limit the current it will probably short.
Now it measures 33,3 uF D1,592. So the worse they leak the higher the capacitance. That is why you use a good LCR meter, D will tell you it is bad
Then at 50mA the short drops to 0,58V
Now it measures a bizar 343mF and a D van 185
DC resistance now below 1 ohm, so it now is really shorted.
Another 10 uF blue one:
90V and now 100mA CC shorts immediately to 5V and gets very hot. Measures 13,15uF D=0,699
Then a test where I connect them wrong, so + to –
Blue 10 uF polarity connected wrong
1V 16 nA
3V 9,x uA
5V 57,x uA
8V 351 uA
10V 870 uA
11V shorts to 5,3V at 100mA CC
After that it measures 9,895 uF D= 0,015