ASTM_F_1263_-_11.pdf

Designation:F126311Standard Guide forAnalysis of Overtest Data in Radiation Testing of ElectronicParts1This standard is issued under the fixed designation F1263;the number immediately following the designation indicates the year oforiginal adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.Asuperscript epsilon()indicates an editorial change since the last revision or reapproval.1.Scope1.1 This guide covers the use of overtesting in order toreduce the required number of parts that must be tested to meeta given quality acceptance standard.Overtesting is testing asample number of parts at a stress level higher than theirspecification stress in order to reduce the amount of necessarydata taking.This guide discusses when and how overtestingmay be applied to forming probabilistic estimates for thesurvival of electronic piece parts subjected to radiation stress.Some knowledge of the probability distribution governing thestress-to-failure of the parts is necessary,although exactknowledge may be replaced by over-conservative estimates ofthis distribution.2.Referenced Documents2.1 Military Standards:MIL-PRF 19500 Semiconductor Devices,General Specifi-cations for2MIL-PRF 38535 Integrated Circuits(Microcircuit Manufac-turing)23.Terminology3.1 Definitions of Terms Specific to This Standard:3.1.1 Confidencethe probability,C,that at least a fraction,P,of the electronic parts from a test lot will survive in actualservice;since radiation testing of electronic parts is generallydestructive,this probability must be calculated from tests onselected specimens from the lot.3.1.2 Rejection Confidencethe probability,R,that a lotwill be rejected based on destructive tests of selected speci-mens if more than a specified fraction,P,of the parts in the lotwill fail in actual service.3.1.3Discussion of Preceding TermsStrictly speaking,most lot acceptance tests(be they testing by attributes orvariables)do not guarantee survivability,but rather that infe-rior lots,where the survival probability of the parts is less thanprobability,P,will be rejected with confidence,C.In order toinfer a true confidence,it would require a Bayes Theoremcalculation.In many cases,the distinction between confidenceand rejection confidence is of little practical importance.However,in other cases(typically when a large number of lotsare rejected)the distinction between these two kinds ofconfidence can be significant.The formulas given in this guideapply whether one is dealing with confidence or rejectionconfidence.4.Summary of Guide4.1 This guide is intended to primarily apply to sampling byattribute plans typified by Lot Tolerance Percent Defective(LTPD)tables given in MIL-PRF 38535 and MIL-PRF 19500,and contains the following:4.1.1 An equation for estimating the effectiveness of over-testing in terms of increased probability of survival,4.1.2 An equation for the required amount of overtestinggiven a necessary survival probability,and4.1.3 Cautions and limitations on the method.5.Significance and Use5.1 Overtesting should be done when(a)testing by vari-ables is impractical because of time and cost considerations orbecause the probability distribution of stress to failure cannotbe estimated with sufficient accuracy,and(b)an unrealisticallylarge number of parts would have to be tested at the specifi-cation stress for the necessary confidence and survival prob-ability.6.Interferences6.1 Probability DistributionsIn overtesting,a knowledgeof the probability distribution governing stress to failure isrequired,though it need not be specified with the sameaccuracy necessary for testing by variables.For bipolar tran-sistors exposed to neutron radiation,the failure mechanism isusually gain degradation and the stress to failure is known to1This guide is under the jurisdiction ofASTM Committee F01 on Electronicsandis the direct responsibility of Subcommittee F01.11 on Nuclear and Space RadiationEffects.Current edition approved June 1,2011.Published July 2011.Originally approvedin 1989.Last previous edition approved in 2005 as F1263 99(2005).DOI:10.1520/F1263-11.2Available from Standardization Documents Order Desk,Bldg.4 Section D,700Robbins Ave.,Philadelphia,PA 19111-5094,Attn:NPODS.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 follow a lognormal distribution.3For bipolar transistors ex-posed to total dose the use of the lognormal distribution is alsofairly accurate.4For more complex electronics and other kindsof radiation stress,the lognormal distribution is widely used inestimating the failure probabilities of electronic piece parts,and therefore this standard governs the use of a lognormaldistribution.However,caution should be exercised when theprobability distribution of stress to failure is not well estab-lished.Nevertheless,even if the lognormal distribution doesnot strictly apply,the equations given in Section 7 will hold aslong as