Nemco Electronics Performance Info - Manual (Page 8)

General Technical Information
z Reliability Tantalum capacitors have no known wear-out mechanism and in certain circumstances are capable of
self-healing. Random failures can still occur in operation. The failure rate will decrease with time and not
increase as with other capacitor types and other electronic components. The reliability of solid tantalum
capacitors is dependent upon three key factors which affect the working environment and operating conditions:
Operating voltage
Operating temperature
Circuit impedance
Operational reliability generally increases with reduction of applied voltage and temperature and with an increase
of series resistance.
PCT, LSR, MCT and TB series:
1% per 1,000 hours at 85°C, Vr with 0.1Ω / V series impedance, 60% confidence level.
CGT series:
.2% per 1,000 hours at 85°C, 0.5xVr with 0.1Ω / V series impedance, 60% confidence level.
z Base Failure Rate Standard tantalum product conforms to Level M reliability (i.e. 1%/1000 hours) at rated voltage, rated
temperature (+85°C) and 0.1 Ω/volt circuit impedance. This is known as the base failure rate, F
B
, which
is used for calculating operating reliability. The effect of varying the operating conditions on failure rate
are shown.
z Reliability Assessment
Operational reliability F in any circuit condition can be deduced from the three previous graphs by multiplying the base failure
rate, F
B
, for the series by the correction factors, F
U
, F
T
, and F
R
.
Worked example of reliability calculation. For a capacitor with a 16v rating, being operated on a 10v line with 0.8 Ω per volt
circuit impedance, at a temperature of 50°C, the correction factors given by the previous F
U
= 0.04
graphs are as follows: F
T
= 0.1
F
R
= 0.2
For a series with F
B
= 1%/1000 hours, the failure rate F will be F = F
U
x F
T
x F
R
x F
B
= (0.04 x 0.1 x 0.2 x 1)%/1000 hours
= 0.0008% per 1000 hours at 60% confidence level
It should be noted that the above analysis refers to steady state operating conditions. The failure rate will also be affected by
the presence of surges.