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

4.6.3.2.4 Subgroup 3 (solderability). The subgroup 3 test shall be performed on an inspection lot basis

for ER parts. A sample shall be selected from each lot in accordance with table VIII. As an option, the

manufacturer may use electrical rejects from the subgroup 1 tests for all or part of the sample. If there are

one or more defects, the lot is rejected. The manufacturer may use one of the following options for

corrective action:

a. Each production lot that was used to form the failed inspection lot shall be individually submitted to

the solderability test. Production lots that pass are available for shipment. Production lots that fail

can be submitted to the solder dip procedure of 4.6.3.2.4b.

TABLE VIII. Solderability sample plan.

Lot size

Sample size

1 to 3,200

3,201 to 10,000

10,001 to 35,000

35,001 and over

b. The failed lot is submitted to a 100 percent hot solder dip using an approved solder dip process in

accordance with 3.5.4. A subsequent solderability test shall then be performed. If the lot passes, it

is available for shipment; if the lot fails, the manufacturer may perform the hot solder dip one

additional time. If the lot fails to pass, the lot is considered rejected and shall not be supplied to

this specification.

4.6.3.2.4.1 Disposition of samples. The solderability test is considered a destructive test and samples

submitted to the solderability test shall not be supplied on the contract.

4.6.4 PPM assessment (non-ER and ER). The manufacturer shall establish and maintain a system for

assessing the average outgoing quality in PPM of lots supplied to this specification. This PPM

assessment should be based on inspections performed on each inspection lot to verify that resistors meet

dc resistance and tolerance requirements. For ER resistors, this inspection shall occur after the group A,

subgroup 1, 100 percent screens have been completed.

4.6.4.1 Sampling plan. Minimum sample sizes for inspection lots shall be selected in accordance with

table VII. For non-ER resistors, the sampling system and plan used for the group A inspection (see

4.6.3.1) may be the basis for assessing PPM.

4.6.4.2 Rejected lots. Any rejected lot shall be segregated from new lots and those lots which have

passed the PPM assessment. A rejected lot may be rescreened for the quality characteristic found

defective in the sample and any defects removed. A new second sample shall be randomly selected. If

one or more defects are found, this lot is rejected and shall not be supplied to the specification.

4.6.4.3 PPM calculations. PPM calculations shall be based on the accumulated results of the initial

sample. Calculations and exclusions shall be in accordance with EIA-554-1. (NOTE: PPM calculations

shall not be based on the second sample submission for a rejected lot as described in 4.6.4.2).