MIL-STD-690-SUP 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

5.4.4 Details to be specified. The following details are to be specified in the ER specification when Procedure IV is utilized:

a. Lot conformance plan (the plan letter shall correspond to the qualification maintenance period letter of

FRSP-10) (see 5.4.1 and 5.3.2). b. Duration of lot conformance test. c. Failure criteria (see 4.2).

d. Permissible combination of styles and values that may be represented in an inspection lot (see 5.4).

e. Disposition of samples and inspection lot (ship samples with the lot, ship lot at specified test period, keep samples on test, etc., ) (see 4.7).

5.5 Procedure for truncation of life test data. Truncation shall not be used to avoid a change in the FR level. The truncation point shall occur, with the qualifying activity's approval, either:

a. After life test failure(s) has occurred and an assignable cause has been found and corrective action acceptable to the qualifying activity has been successfully implemented.

b. Following implementation of a new design or process improvement and a failure rate extension is being sought.

An improved FR shall not be granted by the qualifying activity until the first test samples after the truncation point have completed the test. If the truncation procedure is used, no device shall be taken off test even if the data generated by the device on test is not to be used for determination of the "new" FR. FR shall be maintained for the current maintenance period. Random failures are not cause for truncation, and truncation shall not be used to avoid a change in the FR level. Also, truncation shall not be used if the cause of the failure(s) cannot be determined.