MIL-PRF-914 Resistor Networks, Fixed, Film, Surface Mount, Nonestablished Reliability, And Established Reliability, General Specification ForThis specification covers the general requirements for nonestablished reliability \(non-ER\) and established reliability \(ER\), hermetically sealed \(see 3.27\) and nonhermetically sealed networks \(see 3.27.1\). These networks consist entirely of fixed, film resistors. They are primarily intended for use in surface mount applications where space is a major concern. ER resistors covered by this specification will have life failure rates \(FR\) ranging from 1 percent to 0.001 percent per 1,000 hours \(see 1.2.1.7\). The ER FR are established at a minimum 60-percent confidence level on the basis of life tests. Designers are CAUTIONED on using these resistors in pulse applications \(see 6.4.4\).

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MIL-PRF-914C

4.8.19 Life (see 3.24). Networks shall be tested in accordance with method 108 of MIL-STD-202. The following

details and exceptions shall apply:

Mounting: As specified in 4.8.1, method B. If forced air circulation is employed, the air velocity shall not

exceed 500 feet per minute and there shall be no direct impingement of the forced-air supply upon the

networks.

Test temperature and tolerance:

(1) Qualification inspection: 70OC �5OC.

FR determination: 70OC �5OC.

(2)

Initial measurements: Measurements shall be made inside or outside the chamber.

(1) Inside of chamber: When measurements are to be made inside the chamber, the initial dc resistance

shall be measured at the applicable test temperature, after temperature stabilization, and within 8 hours

of exposure of the resistor networks to the test temperature. This initial measurement shall be used as

the reference temperature for all subsequent measurements under the same condition.

(2) Outside of chamber: When measurements are to be made outside the chamber, the initial dc

resistance shall be measured at room temperature. This initial measurement shall be used as the

reference temperature for all subsequent measurements under the same condition.

Operating conditions: Rated dc continuous working voltage, filtered or nonfiltered full-wave rectified ac

voltage, shall be simultaneously applied to each resistor in the network intermittently, one and one-half

hours "on" and one-half hour "off", for the specified number of hours and at the test temperature. During the

"on" cycle, the voltage shall be regulated and controlled to maintain the rated continuous working voltage

within �5 percent. In no case shall the network power rating be exceeded.

Test condition: 2,000 hours elapsed time for qualification inspection with all samples continued to 10,000

hours; 10,000 hours for FRL inspection of group C.

Measurements during test:

(1) Qualification inspection: DC resistance shall be measured at the end of the one-half hour "off" periods

after 250 hours +72 hours, -24 hours; 500 hours +72 hours, -24 hours; 1,000 hours +72 hours, -24

hours; 2,000 hours, +96 hours, -0 hours have elapsed.

(2) Extended life testing: DC resistance shall be measured at the end of one-half hour "off" period after 250

hours +72 hours, -24 hours; 500 hours +72 hours, -24 hours; 1,000 hours +72 hours, -24 hours; 2,000

hours +96 hours, -24 hours; and every 2,000 hours +96 hours, -24 hours thereafter until required

10,000 hours +120 hours, -0 hours have elapsed. Measurements shall be made as near as possible to

the specified time but may be adjusted so that measurements need be made only during the normal

workday.

(3) Measurements outside of chamber: When measurements are made outside the chamber, networks

shall be outside of the chamber for a minimum of 45 minutes and stabilized before measurement.

Inspection after test: Networks shall be inspected for evidence of mechanical damage.