CSR91B565KB datasheet(80/84 Pages) KEMET

80 / 84 page

Voltage “de-rating” is a common and useful approach

to improved reliability. It can be pursued too far, however,

when it leads to installation of higher voltage capacitors of

much larger size. Inherent failure rate is roughly propor-

tional to CV1.6, where C is capacitance and V is rated volt-

age. The effect becomes particularly noticeable above 50-

volt ratings. It is possible to lose more via higher inherent

failure rate than is gained by voltage derating.

The relationships shown are more useful when the

failure rate has been statistically determined for a given

group of capacitors.

Failure rate is statistically determined for each pro-

duction batch of KEMET High Reliability capacitors, as

described in Specification GR500 Catalog F2956. As

noted above, not all capacitance/voltage rate values are

inherently equal in failure rate. GR500 capacitors are

processed and subjected to 100% reliability testing as a

homogeneous group of one capacitance/voltage value.

Failure rate under standard conditions is available from 1

to 0.001% Khr, depending upon the capacitance/voltage

value.

Several Series are qualified under U.S. military spec-

ification MIL-C-39003. Failure rates as low as 0.001%/Khr

are available for all capacitance/voltage values in given

groups under this test program. The specifications and

their accompanying Qualified Products Lists should be

consulted for details.

For Series not covered by military specifications, and

internal sampling program is operated by KEMET Quality

Assurance. The confidence level chosen for reporting the

data is 60%. However, the cost of sampling each batch

produced is overwhelmingly prohibitive, and no claim is

made concerning knowledge of failure rate for any partic-

ular lot shipped. It is demonstrated that average failure

rate for all commercial Series is between .1 and 1%/Khr at

standard conditions and 60% confidence after 2,000

hours’ testing, +85°C, and rated voltage and

≤ 1 ohm total

series resistance.

17. SURGE CURRENT

All conventional reliability testing is conducted under

steady-state DC voltage. Experience indicates that AC rip-

ple, within the limits prescribed, has little effect on failure

rate. Heavy surge currents are possible in some applica-

tions, however. Circuit impedance may be very low (below

the standard 0.1 ohm/volt) or there may be driving induc-

tance to cause voltage “ringing.” Surge current may

appear during turn-on of equipment, for example.

Failure rate under current-surge conditions may not

be predictable from conventional life test data. A surge cur-

rent test is utilized to ensure against a high frequency of

such failures, and a description is available free of charge.

The test has been adopted for all capacitors under

MIL-C-39003/06/09/10 and KEMET’s GR500 specifica-

tions.

18. ENVIRONMENTAL CONSIDERATION

It is not possible to foresee all the conditions to which

capacitors may be subjected. Following is a list of stan-

dard tests which every Series will survive. Data may be

available (upon request) under more severe stresses for

certain Series.

• LIFE TEST 85°C OR 125°C, 2000 Hours: When sub-

jected to 2000 hours at 85°C at full rated DC voltage, or

125°C at 2/3 of 85°C voltage, the capacitor shall meet

the following requirements when tested at 25°C:

The DCL shall be within 1.25 times the initial DCL

limit.

Capacitance shall be within ±10% of the initial mea-

sured value.

The DF shall not exceed the initial limit.

• SHELF LIFE +85°, 2000 hours. Post test of capacitor

shall meet the following requirements when tested at

25°C:

The DCL shall be within 1.5 times the initial DCL

limit.

Capacitance shall be within ±10% of the initial mea-

sured value.

The DF shall not exceed 1.5 times the initial limit.

• LEAD STRENGTH MIL-STD-202 Method 211: Pull test

will be performed as in MIL-STD-202, Method 211. The

following details and exceptions shall apply.

a. Test condition letter—A

b. The body of the capacitor will be securely clamped

during test.

KEMET

APPLICATION NOTES FOR TANTALUM CAPACITORS

KEMET Electronics Corporation, P.O. Box 5928, Greenville, S.C. 29606 (864) 963-6300

Connect the temperature and

applied voltage ratio of

interest with a straight edge.

The multiplier of failure rate is

given at the intersection of this

line with the model scale.

Given T1 & V1 Read Failure

Rate Multiplier F1

Given T, & F2

Read Reguired Voltage V2

Given F3 & V3

Read Allowable Temp T3

120

125

110

100

°C

Rating

125

°C

Rating

0.67

1.2

1.1

1.0

0.9

0.8

0.7

0.6

0.5

0.4

0.3

0.2

0.1

Figure 12.

Reliability Nomograph

10-1

1.0

102

103

101

10-2

10-3

10-4

10-5

10-6

10-7

10-8

Circuit Impedance

Failure Rate Improvement

(ohms/volt)

(multiplying factors)

0.1

1.0

0.2

0.4

0.6

0.8

1.0

2.0

3 or greater

.07

TABLE 3

Relationship of Failure Rate to Impedance

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