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.

Pages 1 - 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - 11 - 12

MIL-PRF-39015E

APPENDIX A

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 of this appendix A) 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

manufacturers 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 are allowed.

A.5.3 Solder dip/retinning options. The manufacturer (or their authorized category B or category C

distributor) may solder dip/retin as follows:

a. After the 100 percent group A screening tests: Unless otherwise approved (see 4.6.3.2.2) for lots

subjected to this process, electrical measurements are required in accordance with group A,

subgroup 2 (PPM) (NOTE: The manufacturer may solder dip/retin prior to the 100 percent

electrical measurements of the group A, subgroup 1 tests). The percentage defective allowable

(PDA) for the electrical measurements, shall be the subgroup 1 tests.

As a corrective action, if the lot fails the group A solderability test: The lot may be retinned no

more than two times. The lot after retinning shall be 100 percent screened for group A electrical

requirements (total resistance). Any parts failing (lot not exceeding PDA for group A, subgroup 1,

see 4.6.3.2.1) these screens shall not be supplied to this specification. If electrical failures

exceeding 1 percent of the lot are detected after the second retinning operation, the lot shall not

be supplied to this specification.

After the group A inspection has been completed: Following the solder dip/retinning process, the

electrical measurements required in group A, subgroup 1, 100 percent screening test shall be

repeated on 100 percent of the lot. The PDA for the electrical measurements shall be as for the

subgroup 1 tests. Following these tests, the manufacturer shall submit the lot to the group A

solderability test as specified in 4.6.3.2.5.