quality aspects_parts_final.ppt

Quality And Reliability OF Electronic Components

C.A. Ignatious DD, VSSC (SR)

Definitions

Reliability - The ability of an item to  perform its required required function under  under  defined conditions for a stated period  of time.

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Failure – The termination of the ability  Failure – of an item to perform its required  function.

Definitions

Reliability - The ability of an item to  perform its required required function under  under  defined conditions for a stated period  of time.

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Failure – The termination of the ability  Failure – of an item to perform its required  function.

Degrees of Failure Failures may be SUDDEN (nonpredictable) or GRADUAL (predictable). They may also be PARTIAL or  COMPLETE.  A Catastrophic failure is both sudden and complete.  A Degradation failure is both gradual and partial.

Causes of Failure failures attributable to the application of stresses beyond the stated capabilities of the item. M i s u s e   –

failures attributable to weakness inherent in the item itself when subjected to stresses within the stated capabilities of the item. In h e r en t W e ak n es s    –

Cost-Reliability Cost-Reliability Functions

MTBF & MTTF Mean Time Between Failures – Applies to

repairable items. Mean Time To Failure – Applies to non-

repairable items. Both of these terms indicate the average time an item is expected to function before failure.

Failure Rate vs Time Early Failures – Failures – substandard

components, manufacturing faults. Random Failures – Failures – this is the

useful lifetime of the item. Reliability is predictable in this region. End-of-Life Failures – Failures – items

reaching the end of their useful life.  Also called the wear-out period.

Because of the characteristic shape, this is commonly known as the “Bathtub Curve”. C urve”.

Useful Lifetime Reliability is predictable.

t  m

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 R

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R = reliability. t = time for which equipment is run. m = MTBF

Note that R has no units. The prediction yields a number