MAY 2013

A commonly held misconception is that the leakage current

of a Tantalum capacitor can predict the number of failures

which will be seen on a surge screen. This can be disproved

by the results of an experiment carried out at AVX on 47μF

10V surface mount capacitors with different leakage

currents. The results are summarized in the table below.

Leakage Current vs Number of Surge Failures

Again, it must be remembered that these results were

derived from a highly accelerated surge test machine,

and failure rates in the low ppm are more likely with the end

customer.

AVX recommended derating table

For further details on surge in Tantalum capacitors refer

to J.A. Gill’s paper “Surge in Solid Tantalum Capacitors”,

available from AVX offices worldwide.

An added bonus of increasing the derating applied in a

circuit, to improve the ability of the capacitor to withstand

surge conditions, is that the steady-state reliability is

improved by up to an order. Consider the example of a

6.3 volt capacitor being used on a 5 volt rail. The steady-

state reliability of a Tantalum capacitor is affected by three

parameters; temperature, series resistance and voltage

derating. Assuming 40°C operation and 0.1Ω/volt of series

resistance, the scaling factors for temperature and series

resistance will both be 0.05 [see Section 3.1 (page 154)]. The

derating factor will be 0.15. The capacitors reliability will

therefore be

= 0.15 x 0.05 x 1 x 1%/1000 hours

If a 10 volt capacitor was used instead, the new scaling factor

would be 0.017, thus the steady-state reliability would be

= 0.017 x 0.05 x 1 x 1%/1000 hours

So there is an order improvement in the capacitors steady-

state reliability.

3.3 RELIABILITY TESTING

AVX performs extensive life testing on tantalum capacitors.

■ 2,000 hour tests as part of our regular Quality Assurance

Program.

Test conditions:

■ 85°C/rated voltage/circuit impedance of 3Ω max.

■ 125°C/0.67 x rated voltage/circuit impedance of 3Ω max.

3.4 Mode of Failure

This is normally an increase in leakage current which ultimately

becomes a short circuit.

Number tested

Number failed surge

Standard leakage range

10,000

25

0.1 μA to 1μA

Over Catalog limit

10,000

26

5μA to 50μA

Classified Short Circuit

10,000

25

50μA to 500μA

Voltage Rail

Working Cap Voltage

3.3

6.3

510

10

20

12

25

15

35

≥24

Series Combinations (11)

TAP/TEP Technical Summary and

Application Guidelines