Lifetime determining technique for a solid electrolytic capacitor and system for the same
A system and method for determining the lifetime of a capacitor element, specifically a capacitor element comprising a solid electrolyte that undergoes oxidation, is provided. The system and method utilize a capacitor element comprising an anode body, a dielectric, and a solid electrolyte, and may also comprise other stages of the production of a capacitor. The system and method provide an estimation of the life of the capacitor while considering the oxidation of the solid electrolyte.
1. A capacitor lifetime determining system comprising:
a capacitor element, wherein the capacitor element comprises a sintered porous anode body, a dielectric that overlies the anode body, and a solid electrolyte that overlies the dielectric;
a capacitance measuring device, the measuring device configured to measure the capacitance of the capacitor element;
a control device, the control device configured to apply thermodynamic temperatures to the system; and
a computing device, wherein the computing device is configured to determine constants A/x and −E/k associated with data obtained at the applied thermodynamic temperatures based on technique (1):
A
x
t
e
[
-
E
k
]
1
T
=
1
(
1
)
wherein x is an amount of oxidized solid electrolyte, t is a time in which the capacitance of the capacitor element is decreased by a specified level, T is a thermodynamic temperature, A is a frequency factor, k is Boltzmann constant, e is Euler constant, and E is an activation energy of the reaction;
wherein the computing device is configured to determine a time to degradation to the specified level at a proposed thermodynamic temperature using the activation energy and frequency factor associated with the applied thermodynamic temperatures based on technique (1); and
wherein the solid electrolyte comprises a conductive polymer.
2. The capacitor lifetime determining circuit of claim 1 , wherein the capacitor element is exposed to an oxygen-containing environment.
3. The capacitor lifetime determining circuit of claim 1 , wherein the conductive polymer comprises poly(3,4-ethylenedioxythiophene).
4. The capacitor lifetime determining circuit of claim 1 , wherein the sintered anode body comprises tantalum.
5. The capacitor lifetime determining circuit of claim 1 , wherein the capacitor element comprises a graphite layer disposed along the solid electrolyte.
6. The capacitor lifetime determining circuit of claim 5 , wherein the capacitor element comprises a silver layer disposed along the graphite layer.
7. The capacitor lifetime determining circuit of claim 1 , wherein the applied thermodynamic temperatures range from 70° C. to 175° C.
8. The capacitor lifetime determining circuit of claim 1 , wherein the proposed thermodynamic temperature ranges from 20° C. to 175° C.
9. A method of determining the lifetime of a capacitor comprising:
controlling a first temperature to which a first capacitor element is exposed,
measuring a capacitance of the first capacitor element after exposure to the first temperature,
determining a time in which the capacitance of the first capacitor element during exposure to the first temperature is decreased by a specified level,
controlling a second temperature to which a second capacitor element is exposed,
measuring a capacitance of the second capacitor element after exposure to the second temperature,
determining a time in which the capacitance of the second capacitor element during exposure to the second temperature is decreased by the specified level,
applying technique (1) to determine constants A/x and −E/k associated with the first and second temperatures:
A
x
t
e
[
-
E
k
]
1
T
=
1
,
(
1
)
wherein x is an amount of oxidized solid electrolyte, t is time, T is thermodynamic temperature, A is a frequency factor, k is Boltzmann constant, e is Euler constant, and E is activation energy of the reaction and applying the constants A/x and −E/k associated with the first and second temperatures to technique (1); and
determining a time to degradation at a third temperature,
wherein the first and second capacitor elements comprise a sintered anode body, a dielectric formed along the sintered anode body, and a solid electrolyte formed along the dielectric; and wherein the solid electrolyte comprises a conductive polymer.
10. The method of claim 9 , further comprising controlling a plurality of temperatures to which a plurality of capacitor elements are exposed, measuring the capacitance of each of the plurality of capacitor elements after temperature exposure, and determining the time for degradation of the capacitance of each of the plurality of capacitor elements to the specified level.
11. The method of claim 9 , further comprising plotting the time for degradation of the capacitance of the first and second capacitor elements at the first and second temperatures.
12. The method of claim 9 , wherein each of the first and second capacitor elements comprise a graphite layer disposed along the solid electrolyte.
13. The method of claim 12 , wherein each of the first and second capacitor elements comprise a silver layer disposed along the graphite layer.
14. The method of claim 10 , wherein each of the capacitor elements of the plurality of capacitor elements comprises one or more of an external layer comprising a conductive polymer, a graphite layer, and a silver layer.
15. The method of claim 9 , wherein the first and second temperatures range from 70° C. to 175° C.
16. The method of claim 9 , wherein the third temperature ranges from 20° C. to 175° C.
17. The method of claim 9 , further comprising contacting the first and second capacitor elements with an atmosphere having a relative humidity of 10% or more.
18. The method of claim 9 , wherein the conductive polymer comprises poly(3,4-ethylenedioxythiophene).
19. The method of claim 9 , wherein the sintered anode body comprises tantalum.
20. The method of claim 9 , further comprising exposing the first and second capacitor elements to an oxygen-containing environment.