MIL-STD-690 Failure Rate Sampling Plans And ProceduresThis standard provides procedures for failure rate FR qualification, sampling plans for establishing and maintaining FR levels at selected confidence levels, and lot conformance inspection procedures associated with FR testing for the purpose of direct reference in appropriate military electronic parts established reliability ER specifications. Figures and tables throughout this standard are based on exponential distribution. Weibull distribution will be acceptable in certain components such as capacitors. Use of Weibull distribution for any component must be approved by the qualifying activity. This standard also provides guidance to specification writers in the use of this standard see appendix A and references material for users of ER parts.

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MIL-STD-690D

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APPENDIX A

A.5.2 Duration of FR test. The ER specification shall indicate the duration for the lot conformance FR inspection test and the extended FR test.

A.5.3 Screening tests. In order to provide the consumer with further assurance of the reliability of the products shipped, ER specifications should include, where applicable, screening tests performed on a 100 percent inspection basis. However, before a screening test is included in an ER specification, there should be sound technical basis for its inclusion and sufficient data to support its effectiveness on all types of product included in the specification. These tests should be specified as a prerequisite for conformance inspection and should include a requirement providing for lot rejection when a specified percentage of the lot exceeds the screening requirements. A burn-in test under conditions of accelerated voltage and temperature or other suitable stresses may be specified as part of the

screening tests. Screening tests should be performed only once and preferably in conjunction with the Government inspector since it should not be repeated for the purpose of reinspection.

A.5.4 Accelerated FR tests and acceleration factors. If engineering considerations permit the use of valid accelerated test procedures and associated acceleration factors, the acceleration factor should be applied primary to reduce the duration of the FR test and not to reduce sample size. Caution must be exercised where large acceleration factors are involved in reducing the duration of the FR test. The test time should not be reduced below some reasonable period applicable to the individual ER specification. In any case, it is recommended that a portion of the FR test data be developed from unaccelerated test conditions. Depending on the acceleration factor, the type of electronic parts and the type of FR test, a requirement that 25 percent of the samples subjected to FR test be tested at unaccelerated (rated) conditions is considered reasonable. The data generated on testing at rated conditions should be evaluated periodically by the qualifying activity to revalidate the acceleration factors used.

A.6. FR QUALIFICATION DATA

A.6.1 Expanding FR sampling plan. Table A-I provides the number of cumulative unit hours for determining the probability of qualification when the true failure rate is 1%/1,000 hours. This table may be used to expand the FR sampling plans specified in section 5 of this standard or to develop additional FR sampling plans.

A.7. APPLICATION INFORMATION

A.7.1 Reliability data. ER specifications or associated military standards should contain as much valid application and use information as is available to the preparing activity. Reference to MIL-HDBK-217 , "Reliability Prediction of Electronic Equipment", should be made when appropriate.