TABLE OF CONTENTS It is not, for example, generally practical to service an aeroplane in the middle of the sortie, and space systems, for the most part, are non-serviceable during their entire mission life. As such, high reliability is a paramount motivation in aerospace systems, and significant efforts are focused on the qualification of components which must operate in aerospace environments. Reliability and qualification are distinct concepts. Reliability refers to the likelihood of collect operation, which is a function of obvious (e.g. temperature, humidity, mechanical shock) parameters. Reliability is also a function of a great many subtle parameters, including where and when the component was manufactured. For example, it is well known that the radiation tolerance of seemingly identical memory components can fluctuate significantly based on lot code (time) and which facility produced the components. In this case, the sophisticated controls put in place to ensure effective producibility do not consider subtleties that can lead to wide variations in components susceptibility to total ionising dose.
Qualification is a process used to demonstrate that components, subsystems and platforms are capable of operating reliably over a given mission/product life cycle, when the end system is immersed in its intended environment. For packaging and microcircuits used for military aerospace systems, a number of specifications have existed for this purpose. Older specifications emphasised qualification of components and not how the components were actually built. Newer specifications, both military (e.g. MIL-H-38534) and commercial (ISO 9000 series) emphasise process...
