MIL-PRF-39015 Resistors, Variable, Wirewound, \(Lead Screw Actuated\), Nonestablished Reliability, And Established Reliability, General Specification ForThis specification covers the general requirements for nonestablished reliability \(non-ER\) and established reliability \(ER\), lead screw actuated; wirewound variable resistors with a contact bearing uniformly over the surface of the entire resistive element, wound linearly, when positioned by a multiturn lead screw actuator. These resistors are capable of full load operation \(when the maximum resistance is engaged\), at a maximum temperature of 85OC and are capable for continuous operation, when properly derated, at maximum temperature of 150OC \(see 3.6\), with a resistance tolerance of ??5 percent. The ER resistors have life failure rate \(FR\) levels ranging from 1.0 percent to 0.001 percent per 1,000 hours \(see 1.2.1.4\). These FR levels are established at a 60 percent confidence level on the basis of life tests.

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MIL-PRF-39015E

4.6.3.2.5 Subgroup 4 (solderability). The subgroup 4 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 test 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 the solderability test are available for shipment.

Production lots that fail can be submitted to the solder dip procedure in 4.6.3.2.5.b

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

accordance with the 3.5.8. 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.

TABLE VIII. Solderability sampling plan.

Lot size

Sample size

1 to 3,200

3,201 to 10,000

10,001 to 35,000

35,001 and over

4.6.3.2.5.1 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, verifying that resistors

meet total resistance, and tolerance requirements (i.e., PPM). For ER resistors, this inspection shall

occur after the group A, subgroup 1, 100 percent screens have been completed. In the event of one or

more failures, the lot is rejected.

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 that have

passed PPM assessment. A rejected lot may be rescreened for the quality characteristics 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 this specification.

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

sample. Calculations and exclusion shall be in accordance with EIA-554-1 and qualifying activity

approval. (NOTE: PPM calculations shall not be based on the second sample submission for a rejected

lot as described 4.6.4.2).