THE USE OF MIL-HDBK-217 WITH THE SCC EEE COMPONENTS

Data for reliability prediction are typically taken from MIL-HDBK-217 which lists failure rates against Military specifications. The practice however for parts procurement for ESA space systems relies amply on the SCC specifications. Test methods, qualification and screening programmes are thus peculiar to this system which utilises a blend of IEC and MIL test methods. Although many similarity exists between the Mil system and the SCC system, a direct correspondence between quality classes and testing levels (i.e. SCC levels B and C) from one system to another cannot in general be claimed. The use of MIL-HDBK-217 data under acquisition systems other than the MIL requires thus some reflection. Additionally, the use of MIL-HDBK-217 for reliability predictions on components with designation other than MIL obliges to adopt the quality factor corresponding to the class ''lower'' (i.e. non-MIL Spec). This implies in general penalising results for components qualified to standard classes like the SCCs, or components upgraded to military screening levels. Being MIL-217 undoubtedly the best source of failure rate information it can be used as reference for deriving quality factors (or more exactly quality factors scale coefficients to be used with parts procured to other systems. In the following the analysis of comparison of the EEE parts specifications is discussed. The scope of the analysis has been essentially to derive scale factors to use with the failure rates of MIL-hdbk 217 when the parts acquisition programme responds to the SCC requirements.