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Code: EP113

Description

The video lecture distinguishes between and explains Quality and Reliability. Different aspects and regimes of reliability are explained by reference to the BathTub Curve. Means of minimising infant mortalities and obtaining information on random failures are described.

The lecture then concentrates on wearout reliability (longevity) and the methods of accelerating ageing to obtain acceleration factors of 200 or more. The Arrhenius equation and acceleration of ageing by thermal overstress are explained. The experimental determination of the activation energy is illustrated, together with the use of lognormal distributions and confidence limit calculations. The need to have validation limits is explained and related to other natural phenomena. Damp heat humidity testing equations and relationships are proven. The British Telecom invention of the Non-Saturating Autoclave HAST test is described, and a full tabulation provided between test conditions for non-hermetic packages and the temperate and tropical climatic conditions they represent explained. Other package related failure mechanisms are described.

The evidence and factors for accelerating ageing of thick-film resistors by temperature and humidity are also covered.

Justification is provided of the accelerated testing of hybrid circuits described in the earlier foundation lectures. Illustrations are given of outgassing being accelerated by temperature. Reliability indication by hermeticity testing is critically examined by reference to practical results and by calculation of moisture ingress into a package meeting the "hermeticity" specification. The preferred specification and test method are described.