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For parts or wires soldered together (e.g., a jumper wire between two parts), the connections model appearing in Section 17 is used. Finally, the effects of connecting circuit boards together is accounted for by adding in a failure rate for each connector (Section 15, Connectors). The wire between connectors is oponmoH tn hooo *E A <.W>V IBIIWIS UIW. VI WW>VWV WW. T>W WWW J procedures described in MIL-STD-756, Reliability Modeling and Prediction, should be used to determine an effective system level failure rate. 3.4.2 Part Quality - The quality of a part has a direct effect on the part failure rate and appears In the part models as a factor, *Q. Many parts are oovered by specifications that have several quality levels. hence, the part models have values of ICQ that are keyed to these quality levels. Such parts with their quality designators are shown m Table 3-1. The detaied requirements for these levels are clearly defined in the applicable specification, except for microcircuits. Microcircuits have quality levels which are -i- I tm rm ooo /uni'ninlAntt 4A uiKioh Ihau oro ei iKlo/vfoH Some parts are covered by older specifications, usually referred to as Nonestablished Reliability (Non-ER), that do not have multi-levels of quality. These part models generally have two quality levels designated as mil eocr i if tka nart ir- nrn^nroH in onmnlato arrnrrlflnrA with thA annlirahlfl i\ntL*t?r tv. , cu IU LVNCI . N ME PAN WMFIVIW MWW.>IW# ...... specification, the nQ value for MIL-SPEC should be used. If any requirements are waived, or if a commercial part is procured, the TCQ value for Lower should be used. The foregoing discussion involves the "as procured" part quality. Poor equipment design, production, and testing facilities can degrade part quality. The use of the higher quality parts requires a total equipment design and quality control process commensurate with the high part quality. It would make little sense to procure high quality parts only to have the equipment production procedures damage the parts or introduce latent defects. Total equipment program descriptions as they might vary with different part quality mixes is beyond the scope of this Handbook. Reliability management and quality control procedures are described in other DoD standards and pubiicaiions. Nevertheless, when a proposed equipment development is pushing the state-of-the-art and has a high reliability requirement necessitating high quality parts, the toial equipment program should be given careful scrutiny and not just

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