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

APPENDIX A

A.4 EXTENSION OF QUALIFICATION

A.4.1 Qualification extension of FRL. The extension of qualification or resistance values for each style

shall range between the highest and lowest values qualified. The extension of qualification between the

FR shall be as follows:

Will qualify FRL

FRL

R, P, M, C

P, M, C

M, C

A.4.2 Qualification between styles. Noninductive type styles will qualify corresponding inductive type

styles as specified as follows:

Noninductive style 1/

Will qualify style

RER40

RER60

RER45

RER65

RER50

RER70

RER55

RER75

1/ Qualification of maximum resistance

values in the 40, 45, 50, and 55 series will

also qualify the highest resistance values

in 60, 65, 70, and 75 series.

A.5 SOLDER DIP (RETINNING) LEADS

A.5.1 Solder dip (retinning) leads. The manufacturer (or their authorized category B or category C

distributor) may solder dip/retin the leads of product supplied to this specification provided the solder dip

process (see A.5.2) or an equivalent process has been approved by the qualifying activity.

A.5.2 Qualifying activity approval. Approval of the solder dip process will be based on one of the

following options:

a. When the original lead finish qualified was hot solder dip lead finish 52 of MIL-STD-1276. (NOTE:

The 200 microinch maximum thickness is not applicable.) The manufacturer shall use the same

solder dip process for retinning as is used in the original manufacture of the product.

b. When the lead originally qualified was not hot solder dip lead finish 52 of MIL-STD-1276 as

prescribed in A.5.2a, approval for the process to be used for solder dip shall be based on the

following test procedure:

(1)

Thirty samples of any resistance value for each style and lead finish are subjected to the

manufacturer's solder dip process. Following the solder dip process, the resistors are

subjected to the dc resistance test (and other group A electricals). No defects are allowed.

(2)

Ten of the 30 samples are then subjected to the solderability test. No defects are allowed.

(3)

The remaining 20 samples are subjected to the resistance to solder heat test followed by

the moisture resistance test. No defects allowed.