MIL-PRF-39009 Resistors, Fixed, Wire-Wound \(Power Type, Chassis Mounted\), Nonestablished Reliability, Established Reliability, General SpecificationThis specification covers the general requirements for nonestablished reliability \(non-ER\), and established reliability \(ER\), power type, wire wound, fixed resistors which utilize the principal of heat dissipation through a metal mounting surface. These resistors have initial resistance tolerances of ??1 percent. These resistors are suitable for continuous full load operation at an ambient temperature of +25 degrees C, and when derated up to +250 degrees C \(see figure 1\). These resistors should not be used in circuits where their ac performance is of critical importance in the operation of such circuits. However, provisions have been made in particular styles to minimize inductances \(see 3.1\). These resistors will have life failure rate levels \(FRL\) ranging from 1.0 percent to 0.001 percent per 1,000 hours \(see 1.2.1.4\). These FRL are established at a 60 percent confidence on the basis of the life tests. The FRL, identified by the appropriate symbol, is referred to operation at full rated wattage at +25 degrees C, with a permissible change in resistance of ??2 percent as the criteria for failure.

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MIL-PRF-39009E

4.8.14 High temperature exposure (see 3.20).

a. Mounting: No special mounting required.

b. Initial measurement: DC resistance shall be measured as specified in 4.8.3 at room ambient

conditions.

Procedure: Following initial resistance measurements, resistors shall be placed in a chamber

maintained at +250�C �7�C for a period of 2,000 hours +72 hours, -24 hours with no load applied.

d. Measurement during test: 250 hours +48 hours, -0 hours.

e. Final measurements: After removal from the test chamber, resistors shall be permitted to stabilize

at room ambient temperature and within 6 hours after removal, cleaning of the leads will be

allowed and the dc resistance shall be measured as specified in 4.8.3. Resistors shall be

examined for evidence of mechanical damage.

4.8.15 Solderability (see 3.21). Resistors shall be tested in accordance with method 208 of

MIL-STD-202. The following details shall apply:

a. Both leads shall be tested (spade portion only).

b. Terminals shall be immersed to a depth sufficient to cover test wire and flatted portion of the

terminal.

4.8.16 Low temperature storage (see 3.22).

4.8.16.1 Mounting. Resistors shall be mounted by means other than soldering or may be placed in

trays. When trays are used, they must be designed to present a minimum obstruction to the airstream. In

no case shall the fixture prevent the specified ambient temperature from being achieved within 4 minutes

after resistors are placed in chamber. One chamber may be used for this test.

4.8.16.2 Procedure. DC resistance shall be measured as specified in 4.8.3. Within 1 hour after this

measurement, the resistors shall be placed in a cold chamber at a temperature of -55�C �2�C for a period

of 24 hours �4 hours. The resistors shall then be removed from the chamber and maintained at a

temperature of +25�C �5�C for a period of approximately 2 hours to 8 hours; the dc resistance shall again

be measured as specified in 4.8.3. Resistors shall then be examined for evidence of mechanical damage.

5. PACKAGING

5.1 Packaging. For acquisition purposes, the packaging requirements shall be as specified in the

contract or order (see 6.2). When packaging of materiel is to be performed by DoD or in-house contractor

personnel, these personnel need to contact the responsible packaging activity to ascertain packaging

requirements. Packaging requirements are maintained by the Inventory Control Point's packaging activity

within the Military Department or Defense Agency, or within the military service's system commands.

Packaging data retrieval is available from the managing Military Department's or Defense Agency's

automated packaging files, CD-ROM products, or by contacting the responsible packaging activity.