Reliability Statistics Glossary Accelerated Life Test: life test
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Reliability Statistics Glossary
Reliability Statistics Glossary
Accelerated Life Test: life test under conditions that more severe than usual operating conditions. helpful, necessary, that relationship between test severity probability distribution life ascertainable. Acceleration Factor: Notation: f(t) time transformation from more severe test conditions usual conditions. acceleration factor f(t)/t. differential acceleration factor df(t)/dt. Acceptance Number: largest numbers defects that occur acceptance sampling plan still have accepted. Acceptance Sampling Plant: accept/reject test purpose which accept reject items material based random samples from lot. Assessment: critical appraisal including qualitative judgments about item, such importance analysis results, design criticality, failure effect. Attribute (Inspection by): term used designate method measurement whereby units examined noting presence absence) some characteristic attribute each units group under consideration counting many units not) possess Inspection attributes kinds: either unit product classified simply defective defective number defects unit product counted with respect given requirement requirements. Attribute Testing: Testing evaluate whether item possesses specified attribute. Auger Electron Spectrometer: instrument, that identifies elements surface sample. excites area interest with electron beam observes resultant emitted Auger electrons. These electrons have specific characteristics near surface elements. usually used identify very thin films, often surface contaminants. Availability (Operational Readiness): probability that point time system either operating satisfactorily ready placed operation demand when used under stated conditions. Average Outgoing Quality (AOQ): average quality outgoing product after inspection rejected lot, with replacement good units defective units found inspection. Bathtub Curve: plot failure rate item (whether repairable not) time. failure rate initially decreases, then stays reasonably constant, then begins rise rather rapidly. shape bathtub. items have this behavior. Bias: difference between s-expected value estimator value true parameter Applied voltage. Burn-in: initial operation item stabilize characteristics minimize infant mortality field. Confidence Interval: interval within which asserted that parameters probability distribution lie. Confidence Level: Equals where risk (%). Corrective Action: documented design, process, procedure, materials change correct true cause failure. Part replacement with like item does constitute appropriate corrective action. Rather, action should make impossible that failure happen again. Cumulative Distribution Function (CDF): probability that random variable takes value less than equal value e.g. Defect: deviation item from some ideal state. ideal state usually given formal specification. Degradation: gradual deterioration performance function time. Derating: intentional reduction stress/strength ratio application item, usually purpose reducing occurrence stress-related failures. Duty Cycle: specified operating time item, followed specified time operation. Early Failure Period: That period life, after final assembly, which failures occur initially high rate because presence defective parts workmanship. This definition applies first part bathtub curve failure rate (infant mortality). Spectrometer: Generally used with scanning electron microscope (SEM) provide elemental analysis X-rays generated region being primary electron beam. Effectiveness: capability system device perform function. Electrical Overstress: electrical stressing electronic components beyond specifications. caused ESD. Electrostatic Discharge: transfer electrostatic charge between bodies different electrostatic potentials caused direct contact induced electrostatic field. Many electronic components sensitive will degraded fail.
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technical questions concerning emitters, contact: emittertechsupport@vishay.com technical questions concerning detectors, contact: detectortechsupport@vishay.com
Document Number: 80088 Rev. 1.3, 27-Aug-08
Reliability Statistics Glossary
Reliability Statistics Glossary
Expected Value: statistical term. random variable CDF, (x), where integration over continuous variables with pdf, this reduces discrete random variables with pfd, this reduces (xn) where over Exponential Distribution: parameter distribution with: lexp (-t); (-t); (-t) failure rate mean time-to-failure This constant failure-rate-distribution. Failure: termination ability item perform required function. Failure Analysis: identification failure mode, failure mechanism, cause (i.e., defective soldering, design weakness, contamination, assembly techniques, etc.). Often includes physical dissection. Failure, Catastrophic: sudden change operating characteristics item resulting complete loss useful performance item. Failure, Degradation: failure that occurs result gradual partial change operating characteristics item. Failure, Initial: first failure occur use. Failure, Latent: malfunction that occurs result previous exposure condition that result immediately detectable failure. Example: Latent failure. Failure Mechanism: mechanical, chemical, other process that results failure. Failure Mode: effect which failure observed. Generally, describes failure occurs tells "how" with respect operation. Failure Rate: conditional probability density that item will fail just after time given item failed time number failures item unit measure life (cycles, time, miles, events, etc.) applicable item. Failure, Wearout: failure which time occurrence governed rapidly increasing failure rate. FIT: Failure Unit; (also, Failures Time) Failures Functional Failure: failure whereby device does perform intended function when inputs controls correct. Gaussian Distribution: parameter distribution with:
Hypothesis, Null: hypothesis stating that there difference between some characteristics parent populations several different samples, i.e., that samples came from similar populations. Infant Mortality: Premature catastrophic failures occurring much greater rate than during period useful life prior onset substantial wear out. Inspection: examination testing supplies services (including when appropriate, materials, components, intermediate assemblies) determine whether they conform specified requirements. Inspection Attributes: Inspection whereby either unit product characteristics thereof classified simply defective defective number defects unit product counted with respect given requirement. Life Test: test, usually several items, made purpose estimating some characteristic(s) probability distribution life. Lot: group units from particular device type submitted each time inspection and/or testing called lot. Reject Rate (LRR): reject rate percentage lots rejected form lots evaluated. Tolerance Percent Defective (LTPD): percent defective, which accepted minimum arbitrary fraction time, that percent defective whose probability rejection designated Mean: arithmetic mean, expected value; specifically modified defined, e.g., harmonic mean (reciprocals), geometric mean product), logarithmic mean (logs). Mean Life: R(t)dt; where R(t) s-reliability item; interval over which mean life desired, usually useful life (longevity). Mean-Life-Between-Failures: concept same mean life except that repaired items mean up-time item. formula same mean life except that R(t) interpreted distribution up-times. Mean-time-between-failures (MTBF): particular interval, total functioning life population item divided total number failures within population during measurement interval. definition holds time, cycles, miles, events, other measure life units. Mean-Time-To-Failure (MTTF): "Mean Life". Mean-Time-To-Repair (MTTR): total corrective maintenance time divided total number corrective maintenance actions during given period time. MTTR: G(t)dt; where G(t) repair time; maximum allowed repair time, i.e., item treated repairable this echelon discarded sent higher echelon repair.
guaf (x). gaufc (x). "Mean value "standard deviation Hazard Rate: Instantaneous failure rate.
Document Number: 80088 Rev. 1.3, 27-Aug-08
technical questions concerning emitters, contact: emittertechsupport@vishay.com technical questions concerning detectors, contact: detectortechsupport@vishay.com
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Reliability Statistics Glossary
Reliability Statistics Glossary
item. scans electron beam over surface sample while held vacuum collects several resultant particles energies. provides depth field resolution significantly exceeding light microscopy used magnifications exceeding times. Screening Test: test combination tests intended remove unsatisfactory items those likely exhibit early failures. Significance: Results that show deviations between hypothesis observations used test hypothesis, greater than explained random variation chance alone, called statistically significant. Significance Level: probability that, hypothesis under test were true, sample test statistic would worse than observed test statistic. SPC: Statistical Process Control. Storage Life (Shelf Life): length time item stored under specified conditions still meet specified requirements. Stress: general ambiguous term used extension meaning mechanics that which could cause failure. does distinguish between those things which cause permanent damage (deterioration) those things which absence failure). Variance: average squares deviations individual measurements from their average. measure dispersion random variable data. Wearout: process attribution which results increase hazard rate with increasing (cycles, time, miles, events, etc.) applicable item.
Operating Characteristic (OC) Curve: curve showing relation between probability acceptance either quality process quality, whichever applicable. Part Million (PPM): arrived multiplying percentage defective 000. Example: 1.000 PPM. Population: totality items, units, measurements, etc., real conceptual that under consideration. Probability Distribution: mathematical function with specific properties, which describes probability that random variable will take value values. random variable continuous well behaved enough, there will pdf. random variable discrete, there will pmf. Qualification: entire process which products obtained from manufacturers distributors, examined tested, then identified Qualified Product List. Quality: property, which refers tendency item made specific specifications customer's express needs. current publications Juran, Deming, Crosby, Quality Assurance: system activities that provides assurance that overall quality control fact, being done effectively. system involves continuing evaluation adequacy effectiveness overall quality control program with view having corrective measures initiated where necessary. specific product service, this involves verifications, audits, evaluation quality factors that affect specification, production inspection, product service. Quality Characteristics: Those properties item process, which measured, reviewed, observed which identified drawings, specifications, contractual requirements. Reliability becomes quality characteristic when defined. Quality Control (QC): overall system activities that provides quality product service, which meets needs users; also, such system. Random Samples: commonly used acceptance sampling theory, process selecting sample units such manner that units under consideration have same probability being selected. Reliability: probability that device will function without failure over specified time period amount usage stated conditions. Reliability Growth: Reliability growth effort, resource commitment, improve design, purchasing, production, inspection procedures improve reliability design. Risk: probability rejecting null hypothesis falsely. Scanning Electron Microscope (SEM): instrument which provides visual image surface features
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ABBREVIATIONS
Acceptable quality level Corrective action report/request Dual in-line package
ECAP Electronic circuit analysis program Electro magnetic compatibility Electro magnetic interference Electrical overstress Electrostatic discharge Failure analysis report/request (Failure time) Failure unit; Failures/109 Fault tree analysis Hazard rate
FMEA Failure mode effects analysis
LTPD tolerance percent defective Metal oxide semiconductor Material review board MTBF Mean-time-between-failures MTTF Mean-time-to-failure
Document Number: 80088 Rev. 1.3, 27-Aug-08
technical questions concerning emitters, contact: emittertechsupport@vishay.com technical questions concerning detectors, contact: detectortechsupport@vishay.com
Reliability Statistics Glossary
Reliability Statistics Glossary
MTTR Mean-time-to-repair Parts million PRST Probability ratio sequential test Quality assurance Quality control Qualified products list Sneak circuit analysis Wearout time Hazard rate Failure rate (Lambda)
Reliability planning management Scanning electron microscope
Document Number: 80088 Rev. 1.3, 27-Aug-08
technical questions concerning emitters, contact: emittertechsupport@vishay.com technical questions concerning detectors, contact: detectortechsupport@vishay.com
www.vishay.com
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