Tantalum Cap Size vs. Endurance

[nian28]

Hi guys. A question pop-up in my prof's IM. In his words he asked,

"Does the difference in tantalum size affect the endurance of tantalum cap performance in the long term?"

So basically he is asking which tantalum cap would die out first, the small or the big one? I think the smaller one would give in first as time passes due to the dielectric being heated up much easily. I don't know if there's a study about this, but I was hoping you can give your thoughts on this... Thanks

[999999999]

Re: Tantalum Cap Size vs. Endurance

What you have reworded is not necessarily the same question. Tantalum caps don't usually "die out" quite the same as an electrolytic that dries up (assuming a solid tantalum, not a wet one), they either work within their specs, (don't) drop below their rated specs, or fail totally (explode, usually).

First, the question is not reasonable because "size" isn't specific. Size could mean a different physical construction, a different capacitance, a different voltage, temperature, different purity, or other factors I can't think of at the moment.

Without the specifics of which factors changed along with size, and what the anticipated failure mode is, the generic answer to the question would be no, the difference in size does not effect the endurance, performance if the part is appropriate for the circuit. Since tantalums have lower thresholds for overvoltage and reverse voltage, they simply have to be derated if the circuit could subject them to excessive voltage.

A specific cause of failure could damage either a large or small size within the magnitute related to the spec of the part, but without the cause neither size will substantially change long term.

[PCBONEZ]

Re: Tantalum Cap Size vs. Endurance

You need to be more specific.
There are like 3 types of tantalum caps.
One uses a wet electrolyte.

Other than that about all I know about them is they have low ESR but can't handle much ripple.
And since they can't handle ripple they are useless to me...
.

[999999999]

Re: Tantalum Cap Size vs. Endurance

I should add that if your professor is assuming a faulty implementation which will cause both to fail, IF he was thinking of an overheating condition then the larger capacitor would tend to last longer all else being equal (which it wouldn't be as mentioned previously) because the larger surface area radiates heat better. However, mounting method could make a smaller capacitor absorb less heat if the PCB itself were hotter than the capacitor. There really isn't a clear cut answer if/when a fault is assumed but no mention of cause. Generally they will not fail unless the design is wrong electrically, or does not meet the target use (like a passive enclosure in high ambient temperatures for example).