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

w/ CHANGE 1

3. DEFINITIONS

3.1 Reliability terms. The definitions of all reliability terms used herein are as follows:

*	a.	Burn-in (pre-conditioning). Process of subjecting components to conditions (temperature extreme, power input extremes, etc.) with the intent to either stabilize performance or significantly reduce latent defects.
	b.	Confidence level. This term denotes the probability of disqualifying a product when the true failure rate of the product is at the failure rate specified for qualification.
	c.	Corrective action. A documented design, process, procedure, or materials change implemented and validated to correct the cause of failure or design deficiency.
	d.	Derating. (1) Using an item in such a way that applied stresses are below rated values.

(2) The lowering of the rating of an item in one stress field to allow an increase in another stress field.

e. Established reliability. A quantitative maximum failure rate demonstrated under controlled conditions specified in a Department of Defense specification and usually expressed as percent failures per thousand hours of test.

f. Failure. The event or inoperable state, in which any item, or part of an item does not, or would not, perform as previously specified.

g. Failure analysis. Subsequent to a failure, the logical systematic examination of an item, its construction, application, and documentation to identify the failure made and determine the failure mechanism and its basic course.

h. Failure rate (FR) level. This term denotes the maximum percentage of failures (per 1,000 unit hours) based on a specified confidence level.

i. Failure rate (FR) test. This term denotes the test required to accumulate data from which a failure rate is calculated and is used synonymously with the standard specification term "life test".

j. Higher FR level. This term is a relative description of a FR level associated with a higher number of failures per unit time.

k. Inspection lot. A group of electronic parts offered for inspection at one time and in combinations authorized by the applicable ER specifications.

l. Lower FR level. This term is a relative description of a FR level associated with a fewer number of failures per unit time.

m. Mean time to failure (MTTF). A basic measure of reliability for non-repairable items: the total number of life units of an item divided by the total number of failures within that population, during a particular measurement interval under stated conditions.

n. Predicted. That which is expected at some future time, postulated on analysis of past experience and tests.

o. Qualifying activity. The military activity or its agent delegated to administer the qualification program.